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The Linux-PAM System Administrators' Guide
Andrew G. Morgan
<morgan@kernel.org>
Thorsten Kukuk
<kukuk@thkukuk.de>
Version 1.1.1, 16. December 2009
Abstract
This manual documents what a system-administrator needs to know about the
Linux-PAM library. It covers the correct syntax of the PAM configuration file
and discusses strategies for maintaining a secure system.
-------------------------------------------------------------------------------
1. Introduction
2. Some comments on the text
3. Overview
4. The Linux-PAM configuration file
4.1. Configuration file syntax
4.2. Directory based configuration
4.3. Example configuration file entries
5. Security issues
5.1. If something goes wrong
5.2. Avoid having a weak `other' configuration
6. A reference guide for available modules
6.1. pam_access - logdaemon style login access control
6.2. pam_cracklib - checks the password against dictionary words
6.3. pam_debug - debug the PAM stack
6.4. pam_deny - locking-out PAM module
6.5. pam_echo - print text messages
6.6. pam_env - set/unset environment variables
6.7. pam_exec - call an external command
6.8. pam_faildelay - change the delay on failure per-application
6.9. pam_filter - filter module
6.10. pam_ftp - module for anonymous access
6.11. pam_group - module to modify group access
6.12. pam_issue - add issue file to user prompt
6.13. pam_keyinit - display the keyinit file
6.14. pam_lastlog - display date of last login
6.15. pam_limits - limit resources
6.16. pam_listfile - deny or allow services based on an arbitrary file
6.17. pam_localuser - require users to be listed in /etc/passwd
6.18. pam_loginuid - record user's login uid to the process attribute
6.19. pam_mail - inform about available mail
6.20. pam_mkhomedir - create users home directory
6.21. pam_motd - display the motd file
6.22. pam_namespace - setup a private namespace
6.23. pam_nologin - prevent non-root users from login
6.24. pam_permit - the promiscuous module
6.25. pam_pwhistory - grant access using .pwhistory file
6.26. pam_rhosts - grant access using .rhosts file
6.27. pam_rootok - gain only root access
6.28. pam_securetty - limit root login to special devices
6.29. pam_selinux - set the default security context
6.30. pam_shells - check for valid login shell
6.31. pam_succeed_if - test account characteristics
6.32. pam_tally - login counter (tallying) module
6.33. pam_tally2 - login counter (tallying) module
6.34. pam_time - time controled access
6.35. pam_timestamp - authenticate using cached successful authentication
attempts
6.36. pam_umask - set the file mode creation mask
6.37. pam_unix - traditional password authentication
6.38. pam_userdb - authenticate against a db database
6.39. pam_warn - logs all PAM items
6.40. pam_wheel - only permit root access to members of group wheel
6.41. pam_xauth - forward xauth keys between users
7. See also
8. Author/acknowledgments
9. Copyright information for this document
Chapter 1. Introduction
Linux-PAM (Pluggable Authentication Modules for Linux) is a suite of shared
libraries that enable the local system administrator to choose how applications
authenticate users.
In other words, without (rewriting and) recompiling a PAM-aware application, it
is possible to switch between the authentication mechanism(s) it uses. Indeed,
one may entirely upgrade the local authentication system without touching the
applications themselves.
Historically an application that has required a given user to be authenticated,
has had to be compiled to use a specific authentication mechanism. For example,
in the case of traditional UN*X systems, the identity of the user is verified
by the user entering a correct password. This password, after being prefixed by
a two character ``salt'', is encrypted (with crypt(3)). The user is then
authenticated if this encrypted password is identical to the second field of
the user's entry in the system password database (the /etc/passwd file). On
such systems, most if not all forms of privileges are granted based on this
single authentication scheme. Privilege comes in the form of a personal
user-identifier (UID) and membership of various groups. Services and
applications are available based on the personal and group identity of the
user. Traditionally, group membership has been assigned based on entries in the
/etc/group file.
It is the purpose of the Linux-PAM project to separate the development of
privilege granting software from the development of secure and appropriate
authentication schemes. This is accomplished by providing a library of
functions that an application may use to request that a user be authenticated.
This PAM library is configured locally with a system file, /etc/pam.conf (or a
series of configuration files located in /etc/pam.d/) to authenticate a user
request via the locally available authentication modules. The modules
themselves will usually be located in the directory /lib/security or /lib64/
security and take the form of dynamically loadable object files (see dlopen
(3)).
Chapter 2. Some comments on the text
Before proceeding to read the rest of this document, it should be noted that
the text assumes that certain files are placed in certain directories. Where
they have been specified, the conventions we adopt here for locating these
files are those of the relevant RFC (RFC-86.0, see bibliography"). If you are
using a distribution of Linux (or some other operating system) that supports
PAM but chooses to distribute these files in a different way you should be
careful when copying examples directly from the text.
As an example of the above, where it is explicit, the text assumes that PAM
loadable object files (the modules) are to be located in the following
directory: /lib/security/ or /lib64/security depending on the architecture.
This is generally the location that seems to be compatible with the Filesystem
Hierarchy Standard (FHS). On Solaris, which has its own licensed version of
PAM, and some other implementations of UN*X, these files can be found in /usr/
lib/security. Please be careful to perform the necessary transcription when
using the examples from the text.
Chapter 3. Overview
For the uninitiated, we begin by considering an example. We take an application
that grants some service to users; login is one such program. Login does two
things, it first establishes that the requesting user is whom they claim to be
and second provides them with the requested service: in the case of login the
service is a command shell (bash, tcsh, zsh, etc.) running with the identity of
the user.
Traditionally, the former step is achieved by the login application prompting
the user for a password and then verifying that it agrees with that located on
the system; hence verifying that as far as the system is concerned the user is
who they claim to be. This is the task that is delegated to Linux-PAM.
From the perspective of the application programmer (in this case the person
that wrote the login application), Linux-PAM takes care of this authentication
task -- verifying the identity of the user.
The flexibility of Linux-PAM is that you, the system administrator, have the
freedom to stipulate which authentication scheme is to be used. You have the
freedom to set the scheme for any/all PAM-aware applications on your Linux
system. That is, you can authenticate from anything as naive as simple trust (
pam_permit) to something as paranoid as a combination of a retinal scan, a
voice print and a one-time password!
To illustrate the flexibility you face, consider the following situation: a
system administrator (parent) wishes to improve the mathematical ability of her
users (children). She can configure their favorite ``Shoot 'em up game''
(PAM-aware of course) to authenticate them with a request for the product of a
couple of random numbers less than 12. It is clear that if the game is any good
they will soon learn their multiplication tables. As they mature, the
authentication can be upgraded to include (long) division!
Linux-PAM deals with four separate types of (management) task. These are:
authentication management; account management; session management; and password
management. The association of the preferred management scheme with the
behavior of an application is made with entries in the relevant Linux-PAM
configuration file. The management functions are performed by modules specified
in the configuration file. The syntax for this file is discussed in the section
below.
Here is a figure that describes the overall organization of Linux-PAM:
+----------------+
| application: X |
+----------------+ / +----------+ +================+
| authentication-[---->--\--] Linux- |--<--| PAM config file|
| + [----<--/--] PAM | |================|
|[conversation()][--+ \ | | | X auth .. a.so |
+----------------+ | / +-n--n-----+ | X auth .. b.so |
| | | __| | | _____/
| service user | A | | |____,-----'
| | | V A
+----------------+ +------|-----|---------+ -----+------+
+---u-----u----+ | | |
| auth.... |--[ a ]--[ b ]--[ c ]
+--------------+
| acct.... |--[ b ]--[ d ]
+--------------+
| password |--[ b ]--[ c ]
+--------------+
| session |--[ e ]--[ c ]
+--------------+
By way of explanation, the left of the figure represents the application;
application X. Such an application interfaces with the Linux-PAM library and
knows none of the specifics of its configured authentication method. The
Linux-PAM library (in the center) consults the contents of the PAM
configuration file and loads the modules that are appropriate for
application-X. These modules fall into one of four management groups
(lower-center) and are stacked in the order they appear in the configuration
file. These modules, when called by Linux-PAM, perform the various
authentication tasks for the application. Textual information, required from/or
offered to the user, can be exchanged through the use of the
application-supplied conversation function.
If a program is going to use PAM, then it has to have PAM functions explicitly
coded into the program. If you have access to the source code you can add the
appropriate PAM functions. If you do not have access to the source code, and
the binary does not have the PAM functions included, then it is not possible to
use PAM.
Chapter 4. The Linux-PAM configuration file
When a PAM aware privilege granting application is started, it activates its
attachment to the PAM-API. This activation performs a number of tasks, the most
important being the reading of the configuration file(s): /etc/pam.conf.
Alternatively, this may be the contents of the /etc/pam.d/ directory. The
presence of this directory will cause Linux-PAM to ignore /etc/pam.conf.
These files list the PAMs that will do the authentication tasks required by
this service, and the appropriate behavior of the PAM-API in the event that
individual PAMs fail.
4.1. Configuration file syntax
The syntax of the /etc/pam.conf configuration file is as follows. The file is
made up of a list of rules, each rule is typically placed on a single line, but
may be extended with an escaped end of line: `\<LF>'. Comments are preceded
with `#' marks and extend to the next end of line.
The format of each rule is a space separated collection of tokens, the first
three being case-insensitive:
service type control module-path module-arguments
The syntax of files contained in the /etc/pam.d/ directory, are identical
except for the absence of any service field. In this case, the service is the
name of the file in the /etc/pam.d/ directory. This filename must be in lower
case.
An important feature of PAM, is that a number of rules may be stacked to
combine the services of a number of PAMs for a given authentication task.
The service is typically the familiar name of the corresponding application:
login and su are good examples. The service-name, other, is reserved for giving
default rules. Only lines that mention the current service (or in the absence
of such, the other entries) will be associated with the given
service-application.
The type is the management group that the rule corresponds to. It is used to
specify which of the management groups the subsequent module is to be
associated with. Valid entries are:
account
this module type performs non-authentication based account management. It
is typically used to restrict/permit access to a service based on the time
of day, currently available system resources (maximum number of users) or
perhaps the location of the applicant user -- 'root' login only on the
console.
auth
this module type provides two aspects of authenticating the user. Firstly,
it establishes that the user is who they claim to be, by instructing the
application to prompt the user for a password or other means of
identification. Secondly, the module can grant group membership or other
privileges through its credential granting properties.
password
this module type is required for updating the authentication token
associated with the user. Typically, there is one module for each
'challenge/response' based authentication (auth) type.
session
this module type is associated with doing things that need to be done for
the user before/after they can be given service. Such things include the
logging of information concerning the opening/closing of some data exchange
with a user, mounting directories, etc.
If the type value from the list above is prepended with a - character the PAM
library will not log to the system log if it is not possible to load the module
because it is missing in the system. This can be useful especially for modules
which are not always installed on the system and are not required for correct
authentication and authorization of the login session.
The third field, control, indicates the behavior of the PAM-API should the
module fail to succeed in its authentication task. There are two types of
syntax for this control field: the simple one has a single simple keyword; the
more complicated one involves a square-bracketed selection of value=action
pairs.
For the simple (historical) syntax valid control values are:
required
failure of such a PAM will ultimately lead to the PAM-API returning failure
but only after the remaining stacked modules (for this service and type)
have been invoked.
requisite
like required, however, in the case that such a module returns a failure,
control is directly returned to the application. The return value is that
associated with the first required or requisite module to fail. Note, this
flag can be used to protect against the possibility of a user getting the
opportunity to enter a password over an unsafe medium. It is conceivable
that such behavior might inform an attacker of valid accounts on a system.
This possibility should be weighed against the not insignificant concerns
of exposing a sensitive password in a hostile environment.
sufficient
success of such a module is enough to satisfy the authentication
requirements of the stack of modules (if a prior required module has failed
the success of this one is ignored). A failure of this module is not deemed
as fatal to satisfying the application that this type has succeeded. If the
module succeeds the PAM framework returns success to the application
immediately without trying any other modules.
optional
the success or failure of this module is only important if it is the only
module in the stack associated with this service+type.
include
include all lines of given type from the configuration file specified as an
argument to this control.
substack
include all lines of given type from the configuration file specified as an
argument to this control. This differs from include in that evaluation of
the done and die actions in a substack does not cause skipping the rest of
the complete module stack, but only of the substack. Jumps in a substack
also can not make evaluation jump out of it, and the whole substack is
counted as one module when the jump is done in a parent stack. The reset
action will reset the state of a module stack to the state it was in as of
beginning of the substack evaluation.
For the more complicated syntax valid control values have the following form:
[value1=action1 value2=action2 ...]
Where valueN corresponds to the return code from the function invoked in the
module for which the line is defined. It is selected from one of these: success
, open_err, symbol_err, service_err, system_err, buf_err, perm_denied, auth_err
, cred_insufficient, authinfo_unavail, user_unknown, maxtries, new_authtok_reqd
, acct_expired, session_err, cred_unavail, cred_expired, cred_err,
no_module_data, conv_err, authtok_err, authtok_recover_err, authtok_lock_busy,
authtok_disable_aging, try_again, ignore, abort, authtok_expired,
module_unknown, bad_item, conv_again, incomplete, and default.
The last of these, default, implies 'all valueN's not mentioned explicitly.
Note, the full list of PAM errors is available in /usr/include/security/
_pam_types.h. The actionN can be: an unsigned integer, n, signifying an action
of 'jump over the next n modules in the stack'; or take one of the following
forms:
ignore
when used with a stack of modules, the module's return status will not
contribute to the return code the application obtains.
bad
this action indicates that the return code should be thought of as
indicative of the module failing. If this module is the first in the stack
to fail, its status value will be used for that of the whole stack.
die
equivalent to bad with the side effect of terminating the module stack and
PAM immediately returning to the application.
ok
this tells PAM that the administrator thinks this return code should
contribute directly to the return code of the full stack of modules. In
other words, if the former state of the stack would lead to a return of
PAM_SUCCESS, the module's return code will override this value. Note, if
the former state of the stack holds some value that is indicative of a
modules failure, this 'ok' value will not be used to override that value.
done
equivalent to ok with the side effect of terminating the module stack and
PAM immediately returning to the application.
reset
clear all memory of the state of the module stack and start again with the
next stacked module.
Each of the four keywords: required; requisite; sufficient; and optional, have
an equivalent expression in terms of the [...] syntax. They are as follows:
required
[success=ok new_authtok_reqd=ok ignore=ignore default=bad]
requisite
[success=ok new_authtok_reqd=ok ignore=ignore default=die]
sufficient
[success=done new_authtok_reqd=done default=ignore]
optional
[success=ok new_authtok_reqd=ok default=ignore]
module-path is either the full filename of the PAM to be used by the
application (it begins with a '/'), or a relative pathname from the default
module location: /lib/security/ or /lib64/security/, depending on the
architecture.
module-arguments are a space separated list of tokens that can be used to
modify the specific behavior of the given PAM. Such arguments will be
documented for each individual module. Note, if you wish to include spaces in
an argument, you should surround that argument with square brackets.
squid auth required pam_mysql.so user=passwd_query passwd=mada \
db=eminence [query=select user_name from internet_service \
where user_name='%u' and password=PASSWORD('%p') and \
service='web_proxy']
When using this convention, you can include `[' characters inside the string,
and if you wish to include a `]' character inside the string that will survive
the argument parsing, you should use `\]'. In other words:
[..[..\]..] --> ..[..]..
Any line in (one of) the configuration file(s), that is not formatted
correctly, will generally tend (erring on the side of caution) to make the
authentication process fail. A corresponding error is written to the system log
files with a call to syslog(3).
4.2. Directory based configuration
More flexible than the single configuration file is it to configure libpam via
the contents of the /etc/pam.d/ directory. In this case the directory is filled
with files each of which has a filename equal to a service-name (in
lower-case): it is the personal configuration file for the named service.
The syntax of each file in /etc/pam.d/ is similar to that of the /etc/pam.conf
file and is made up of lines of the following form:
type control module-path module-arguments
The only difference being that the service-name is not present. The
service-name is of course the name of the given configuration file. For
example, /etc/pam.d/login contains the configuration for the login service.
4.3. Example configuration file entries
In this section, we give some examples of entries that can be present in the
Linux-PAM configuration file. As a first attempt at configuring your system you
could do worse than to implement these.
If a system is to be considered secure, it had better have a reasonably secure
'other entry. The following is a paranoid setting (which is not a bad place to
start!):
#
# default; deny access
#
other auth required pam_deny.so
other account required pam_deny.so
other password required pam_deny.so
other session required pam_deny.so
Whilst fundamentally a secure default, this is not very sympathetic to a
misconfigured system. For example, such a system is vulnerable to locking
everyone out should the rest of the file become badly written.
The module pam_deny (documented in a later section) is not very sophisticated.
For example, it logs no information when it is invoked so unless the users of a
system contact the administrator when failing to execute a service application,
the administrator may go for a long while in ignorance of the fact that his
system is misconfigured.
The addition of the following line before those in the above example would
provide a suitable warning to the administrator.
#
# default; wake up! This application is not configured
#
other auth required pam_warn.so
other password required pam_warn.so
Having two 'other auth' lines is an example of stacking.
On a system that uses the /etc/pam.d/ configuration, the corresponding default
setup would be achieved with the following file:
#
# default configuration: /etc/pam.d/other
#
auth required pam_warn.so
auth required pam_deny.so
account required pam_deny.so
password required pam_warn.so
password required pam_deny.so
session required pam_deny.so
This is the only explicit example we give for an /etc/pam.d/ file. In general,
it should be clear how to transpose the remaining examples to this
configuration scheme.
On a less sensitive computer, one on which the system administrator wishes to
remain ignorant of much of the power of Linux-PAM, the following selection of
lines (in /etc/pam.d/other) is likely to mimic the historically familiar Linux
setup.
#
# default; standard UN*X access
#
auth required pam_unix.so
account required pam_unix.so
password required pam_unix.so
session required pam_unix.so
In general this will provide a starting place for most applications.
Chapter 5. Security issues
5.1. If something goes wrong
Linux-PAM has the potential to seriously change the security of your system.
You can choose to have no security or absolute security (no access permitted).
In general, Linux-PAM errs towards the latter. Any number of configuration
errors can disable access to your system partially, or completely.
The most dramatic problem that is likely to be encountered when configuring
Linux-PAM is that of deleting the configuration file(s): /etc/pam.d/* and/or /
etc/pam.conf. This will lock you out of your own system!
To recover, your best bet is to restore the system from a backup or boot the
system into a rescue system and correct things from there.
5.2. Avoid having a weak `other' configuration
It is not a good thing to have a weak default (other) entry. This service is
the default configuration for all PAM aware applications and if it is weak,
your system is likely to be vulnerable to attack.
Here is a sample "other" configuration file. The pam_deny module will deny
access and the pam_warn module will send a syslog message to auth.notice:
#
# The PAM configuration file for the `other' service
#
auth required pam_deny.so
auth required pam_warn.so
account required pam_deny.so
account required pam_warn.so
password required pam_deny.so
password required pam_warn.so
session required pam_deny.so
session required pam_warn.so
Chapter 6. A reference guide for available modules
Here, we collect together the descriptions of the various modules coming with
Linux-PAM.
6.1. pam_access - logdaemon style login access control
pam_access.so [ debug ] [ nodefgroup ] [ noaudit ] [ accessfile=file ] [
fieldsep=sep ] [ listsep=sep ]
6.1.1. DESCRIPTION
The pam_access PAM module is mainly for access management. It provides
logdaemon style login access control based on login names, host or domain
names, internet addresses or network numbers, or on terminal line names in case
of non-networked logins.
By default rules for access management are taken from config file /etc/security
/access.conf if you don't specify another file.
If Linux PAM is compiled with audit support the module will report when it
denies access based on origin (host or tty).
6.1.2. DESCRIPTION
The /etc/security/access.conf file specifies (user/group, host), (user/group,
network/netmask) or (user/group, tty) combinations for which a login will be
either accepted or refused.
When someone logs in, the file access.conf is scanned for the first entry that
matches the (user/group, host) or (user/group, network/netmask) combination,
or, in case of non-networked logins, the first entry that matches the (user/
group, tty) combination. The permissions field of that table entry determines
whether the login will be accepted or refused.
Each line of the login access control table has three fields separated by a ":"
character (colon):
permission:users/groups:origins
The first field, the permission field, can be either a "+" character (plus) for
access granted or a "-" character (minus) for access denied.
The second field, the users/group field, should be a list of one or more login
names, group names, or ALL (which always matches). To differentiate user
entries from group entries, group entries should be written with brackets, e.g.
(group).
The third field, the origins field, should be a list of one or more tty names
(for non-networked logins), host names, domain names (begin with "."), host
addresses, internet network numbers (end with "."), internet network addresses
with network mask (where network mask can be a decimal number or an internet
address also), ALL (which always matches) or LOCAL. LOCAL keyword matches if
and only if the PAM_RHOST is not set and <origin> field is thus set from
PAM_TTY or PAM_SERVICE". If supported by the system you can use @netgroupname
in host or user patterns. The @@netgroupname syntax is supported in the user
pattern only and it makes the local system hostname to be passed to the
netgroup match call in addition to the user name. This might not work correctly
on some libc implementations causing the match to always fail.
The EXCEPT operator makes it possible to write very compact rules.
If the nodefgroup is not set, the group file is searched when a name does not
match that of the logged-in user. Only groups are matched in which users are
explicitly listed. However the PAM module does not look at the primary group id
of a user.
The "#" character at start of line (no space at front) can be used to mark this
line as a comment line.
6.1.3. OPTIONS
accessfile=/path/to/access.conf
Indicate an alternative access.conf style configuration file to override
the default. This can be useful when different services need different
access lists.
debug
A lot of debug information is printed with syslog(3).
noaudit
Do not report logins from disallowed hosts and ttys to the audit subsystem.
fieldsep=separators
This option modifies the field separator character that pam_access will
recognize when parsing the access configuration file. For example: fieldsep
=| will cause the default `:' character to be treated as part of a field
value and `|' becomes the field separator. Doing this may be useful in
conjunction with a system that wants to use pam_access with X based
applications, since the PAM_TTY item is likely to be of the form
"hostname:0" which includes a `:' character in its value. But you should
not need this.
listsep=separators
This option modifies the list separator character that pam_access will
recognize when parsing the access configuration file. For example: listsep
=, will cause the default ` ' (space) and `\t' (tab) characters to be
treated as part of a list element value and `,' becomes the only list
element separator. Doing this may be useful on a system with group
information obtained from a Windows domain, where the default built-in
groups "Domain Users", "Domain Admins" contain a space.
nodefgroup
User tokens which are not enclosed in parentheses will not be matched
against the group database. The backwards compatible default is to try the
group database match even for tokens not enclosed in parentheses.
6.1.4. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.1.5. RETURN VALUES
PAM_SUCCESS
Access was granted.
PAM_PERM_DENIED
Access was not granted.
PAM_IGNORE
pam_setcred was called which does nothing.
PAM_ABORT
Not all relevant data or options could be gotten.
PAM_USER_UNKNOWN
The user is not known to the system.
6.1.6. FILES
/etc/security/access.conf
Default configuration file
6.1.7. EXAMPLES
These are some example lines which might be specified in /etc/security/
access.conf.
User root should be allowed to get access via cron, X11 terminal :0, tty1, ...,
tty5, tty6.
+ : root : crond :0 tty1 tty2 tty3 tty4 tty5 tty6
User root should be allowed to get access from hosts which own the IPv4
addresses. This does not mean that the connection have to be a IPv4 one, a IPv6
connection from a host with one of this IPv4 addresses does work, too.
+ : root : 192.168.200.1 192.168.200.4 192.168.200.9
+ : root : 127.0.0.1
User root should get access from network 192.168.201. where the term will be
evaluated by string matching. But it might be better to use network/netmask
instead. The same meaning of 192.168.201. is 192.168.201.0/24 or 192.168.201.0/
255.255.255.0.
+ : root : 192.168.201.
User root should be able to have access from hosts foo1.bar.org and
foo2.bar.org (uses string matching also).
+ : root : foo1.bar.org foo2.bar.org
User root should be able to have access from domain foo.bar.org (uses string
matching also).
+ : root : .foo.bar.org
User root should be denied to get access from all other sources.
- : root : ALL
User foo and members of netgroup admins should be allowed to get access from
all sources. This will only work if netgroup service is available.
+ : @admins foo : ALL
User john and foo should get access from IPv6 host address.
+ : john foo : 2001:db8:0:101::1
User john should get access from IPv6 net/mask.
+ : john : 2001:db8:0:101::/64
Disallow console logins to all but the shutdown, sync and all other accounts,
which are a member of the wheel group.
-:ALL EXCEPT (wheel) shutdown sync:LOCAL
All other users should be denied to get access from all sources.
- : ALL : ALL
6.1.8. AUTHORS
The logdaemon style login access control scheme was designed and implemented by
Wietse Venema. The pam_access PAM module was developed by Alexei Nogin
<alexei@nogin.dnttm.ru>. The IPv6 support and the network(address) / netmask
feature was developed and provided by Mike Becher
<mike.becher@lrz-muenchen.de>.
6.2. pam_cracklib - checks the password against dictionary words
pam_cracklib.so [ ... ]
6.2.1. DESCRIPTION
This module can be plugged into the password stack of a given application to
provide some plug-in strength-checking for passwords.
The action of this module is to prompt the user for a password and check its
strength against a system dictionary and a set of rules for identifying poor
choices.
The first action is to prompt for a single password, check its strength and
then, if it is considered strong, prompt for the password a second time (to
verify that it was typed correctly on the first occasion). All being well, the
password is passed on to subsequent modules to be installed as the new
authentication token.
The strength checks works in the following manner: at first the Cracklib
routine is called to check if the password is part of a dictionary; if this is
not the case an additional set of strength checks is done. These checks are:
Palindrome
Is the new password a palindrome?
Case Change Only
Is the new password the the old one with only a change of case?
Similar
Is the new password too much like the old one? This is primarily controlled
by one argument, difok which is a number of character changes (inserts,
removals, or replacements) between the old and new password that are enough
to accept the new password. This defaults to 5 changes.
Simple
Is the new password too small? This is controlled by 6 arguments minlen,
maxclassrepeat, dcredit, ucredit, lcredit, and ocredit. See the section on
the arguments for the details of how these work and there defaults.
Rotated
Is the new password a rotated version of the old password?
Same consecutive characters
Optional check for same consecutive characters.
Too long monotonic character sequence
Optional check for too long monotonic character sequence.
Contains user name
Optional check whether the password contains the user's name in some form.
This module with no arguments will work well for standard unix password
encryption. With md5 encryption, passwords can be longer than 8 characters and
the default settings for this module can make it hard for the user to choose a
satisfactory new password. Notably, the requirement that the new password
contain no more than 1/2 of the characters in the old password becomes a
non-trivial constraint. For example, an old password of the form "the quick
brown fox jumped over the lazy dogs" would be difficult to change... In
addition, the default action is to allow passwords as small as 5 characters in
length. For a md5 systems it can be a good idea to increase the required
minimum size of a password. One can then allow more credit for different kinds
of characters but accept that the new password may share most of these
characters with the old password.
6.2.2. OPTIONS
debug
This option makes the module write information to syslog(3) indicating the
behavior of the module (this option does not write password information to
the log file).
authtok_type=XXX
The default action is for the module to use the following prompts when
requesting passwords: "New UNIX password: " and "Retype UNIX password: ".
The example word UNIX can be replaced with this option, by default it is
empty.
type=XXX
Alias for authtok_type kept for backwards compatibility.
retry=N
Prompt user at most N times before returning with error. The default is 1.
difok=N
This argument will change the default of 5 for the number of character
changes in the new password that differentiate it from the old password.
minlen=N
The minimum acceptable size for the new password (plus one if credits are
not disabled which is the default). In addition to the number of characters
in the new password, credit (of +1 in length) is given for each different
kind of character (other, upper, lower and digit). The default for this
parameter is 9 which is good for a old style UNIX password all of the same
type of character but may be too low to exploit the added security of a md5
system. Note that there is a pair of length limits in Cracklib itself, a
"way too short" limit of 4 which is hard coded in and a defined limit (6)
that will be checked without reference to minlen. If you want to allow
passwords as short as 5 characters you should not use this module.
dcredit=N
(N >= 0) This is the maximum credit for having digits in the new password.
If you have less than or N digits, each digit will count +1 towards meeting
the current minlen value. The default for dcredit is 1 which is the
recommended value for minlen less than 10.
(N < 0) This is the minimum number of digits that must be met for a new
password.
ucredit=N
(N >= 0) This is the maximum credit for having upper case letters in the
new password. If you have less than or N upper case letters each letter
will count +1 towards meeting the current minlen value. The default for
ucredit is 1 which is the recommended value for minlen less than 10.
(N < 0) This is the minimum number of upper case letters that must be met
for a new password.
lcredit=N
(N >= 0) This is the maximum credit for having lower case letters in the
new password. If you have less than or N lower case letters, each letter
will count +1 towards meeting the current minlen value. The default for
lcredit is 1 which is the recommended value for minlen less than 10.
(N < 0) This is the minimum number of lower case letters that must be met
for a new password.
ocredit=N
(N >= 0) This is the maximum credit for having other characters in the new
password. If you have less than or N other characters, each character will
count +1 towards meeting the current minlen value. The default for ocredit
is 1 which is the recommended value for minlen less than 10.
(N < 0) This is the minimum number of other characters that must be met for
a new password.
minclass=N
The minimum number of required classes of characters for the new password.
The default number is zero. The four classes are digits, upper and lower
letters and other characters. The difference to the credit check is that a
specific class if of characters is not required. Instead N out of four of
the classes are required.
maxrepeat=N
Reject passwords which contain more than N same consecutive characters. The
default is 0 which means that this check is disabled.
maxsequence=N
Reject passwords which contain monotonic character sequences longer than N.
The default is 0 which means that this check is disabled. Examples of such
sequence are '12345' or 'fedcb'. Note that most such passwords will not
pass the simplicity check unless the sequence is only a minor part of the
password.
maxclassrepeat=N
Reject passwords which contain more than N consecutive characters of the
same class. The default is 0 which means that this check is disabled.
reject_username
Check whether the name of the user in straight or reversed form is
contained in the new password. If it is found the new password is rejected.
gecoscheck
Check whether the words from the GECOS field (usualy full name of the user)
longer than 3 characters in straight or reversed form are contained in the
new password. If any such word is found the new password is rejected.
enforce_for_root
The module will return error on failed check also if the user changing the
password is root. This option is off by default which means that just the
message about the failed check is printed but root can change the password
anyway. Note that root is not asked for an old password so the checks that
compare the old and new password are not performed.
use_authtok
This argument is used to force the module to not prompt the user for a new
password but use the one provided by the previously stacked password
module.
dictpath=/path/to/dict
Path to the cracklib dictionaries.
6.2.3. MODULE TYPES PROVIDED
Only the password module type is provided.
6.2.4. RETURN VALUES
PAM_SUCCESS
The new password passes all checks.
PAM_AUTHTOK_ERR
No new password was entered, the username could not be determined or the
new password fails the strength checks.
PAM_AUTHTOK_RECOVERY_ERR
The old password was not supplied by a previous stacked module or got not
requested from the user. The first error can happen if use_authtok is
specified.
PAM_SERVICE_ERR
A internal error occurred.
6.2.5. EXAMPLES
For an example of the use of this module, we show how it may be stacked with
the password component of pam_unix(8)
#
# These lines stack two password type modules. In this example the
# user is given 3 opportunities to enter a strong password. The
# "use_authtok" argument ensures that the pam_unix module does not
# prompt for a password, but instead uses the one provided by
# pam_cracklib.
#
passwd password required pam_cracklib.so retry=3
passwd password required pam_unix.so use_authtok
Another example (in the /etc/pam.d/passwd format) is for the case that you want
to use md5 password encryption:
#%PAM-1.0
#
# These lines allow a md5 systems to support passwords of at least 14
# bytes with extra credit of 2 for digits and 2 for others the new
# password must have at least three bytes that are not present in the
# old password
#
password required pam_cracklib.so \
difok=3 minlen=15 dcredit= 2 ocredit=2
password required pam_unix.so use_authtok nullok md5
And here is another example in case you don't want to use credits:
#%PAM-1.0
#
# These lines require the user to select a password with a minimum
# length of 8 and with at least 1 digit number, 1 upper case letter,
# and 1 other character
#
password required pam_cracklib.so \
dcredit=-1 ucredit=-1 ocredit=-1 lcredit=0 minlen=8
password required pam_unix.so use_authtok nullok md5
6.2.6. AUTHOR
pam_cracklib was written by Cristian Gafton <gafton@redhat.com>
6.3. pam_debug - debug the PAM stack
pam_debug.so [ auth=value ] [ cred=value ] [ acct=value ] [ prechauthtok=value
] [ chauthtok=value ] [ auth=value ] [ open_session=value ] [ close_session=
value ]
6.3.1. DESCRIPTION
The pam_debug PAM module is intended as a debugging aide for determining how
the PAM stack is operating. This module returns what its module arguments tell
it to return.
6.3.2. OPTIONS
auth=value
The pam_sm_authenticate(3) function will return value.
cred=value
The pam_sm_setcred(3) function will return value.
acct=value
The pam_sm_acct_mgmt(3) function will return value.
prechauthtok=value
The pam_sm_chauthtok(3) function will return value if the PAM_PRELIM_CHECK
flag is set.
chauthtok=value
The pam_sm_chauthtok(3) function will return value if the PAM_PRELIM_CHECK
flag is not set.
open_session=value
The pam_sm_open_session(3) function will return value.
close_session=value
The pam_sm_close_session(3) function will return value.
Where value can be one of: success, open_err, symbol_err, service_err,
system_err, buf_err, perm_denied, auth_err, cred_insufficient,
authinfo_unavail, user_unknown, maxtries, new_authtok_reqd, acct_expired,
session_err, cred_unavail, cred_expired, cred_err, no_module_data, conv_err,
authtok_err, authtok_recover_err, authtok_lock_busy, authtok_disable_aging,
try_again, ignore, abort, authtok_expired, module_unknown, bad_item,
conv_again, incomplete.
6.3.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.3.4. RETURN VALUES
PAM_SUCCESS
Default return code if no other value was specified, else specified return
value.
6.3.5. EXAMPLES
auth requisite pam_permit.so
auth [success=2 default=ok] pam_debug.so auth=perm_denied cred=success
auth [default=reset] pam_debug.so auth=success cred=perm_denied
auth [success=done default=die] pam_debug.so
auth optional pam_debug.so auth=perm_denied cred=perm_denied
auth sufficient pam_debug.so auth=success cred=success
6.3.6. AUTHOR
pam_debug was written by Andrew G. Morgan <morgan@kernel.org>.
6.4. pam_deny - locking-out PAM module
pam_deny.so
6.4.1. DESCRIPTION
This module can be used to deny access. It always indicates a failure to the
application through the PAM framework. It might be suitable for using for
default (the OTHER) entries.
6.4.2. OPTIONS
This module does not recognise any options.
6.4.3. MODULE TYPES PROVIDED
All module types (account, auth, password and session) are provided.
6.4.4. RETURN VALUES
PAM_AUTH_ERR
This is returned by the account and auth services.
PAM_CRED_ERR
This is returned by the setcred function.
PAM_AUTHTOK_ERR
This is returned by the password service.
PAM_SESSION_ERR
This is returned by the session service.
6.4.5. EXAMPLES
#%PAM-1.0
#
# If we don't have config entries for a service, the
# OTHER entries are used. To be secure, warn and deny
# access to everything.
other auth required pam_warn.so
other auth required pam_deny.so
other account required pam_warn.so
other account required pam_deny.so
other password required pam_warn.so
other password required pam_deny.so
other session required pam_warn.so
other session required pam_deny.so
6.4.6. AUTHOR
pam_deny was written by Andrew G. Morgan <morgan@kernel.org>
6.5. pam_echo - print text messages
pam_echo.so [ file=/path/message ]
6.5.1. DESCRIPTION
The pam_echo PAM module is for printing text messages to inform user about
special things. Sequences starting with the % character are interpreted in the
following way:
%H
The name of the remote host (PAM_RHOST).
%h
The name of the local host.
%s
The service name (PAM_SERVICE).
%t
The name of the controlling terminal (PAM_TTY).
%U
The remote user name (PAM_RUSER).
%u
The local user name (PAM_USER).
All other sequences beginning with % expands to the characters following the %
character.
6.5.2. OPTIONS
file=/path/message
The content of the file /path/message will be printed with the PAM
conversion function as PAM_TEXT_INFO.
6.5.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.5.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_SUCCESS
Message was successful printed.
PAM_IGNORE
PAM_SILENT flag was given or message file does not exist, no message
printed.
6.5.5. EXAMPLES
For an example of the use of this module, we show how it may be used to print
information about good passwords:
password optional pam_echo.so file=/usr/share/doc/good-password.txt
password required pam_unix.so
6.5.6. AUTHOR
Thorsten Kukuk <kukuk@thkukuk.de>
6.6. pam_env - set/unset environment variables
pam_env.so [ debug ] [ conffile=conf-file ] [ envfile=env-file ] [ readenv=0|1
] [ user_envfile=env-file ] [ user_readenv=0|1 ]
6.6.1. DESCRIPTION
The pam_env PAM module allows the (un)setting of environment variables.
Supported is the use of previously set environment variables as well as
PAM_ITEMs such as PAM_RHOST.
By default rules for (un)setting of variables is taken from the config file /
etc/security/pam_env.conf if no other file is specified.
This module can also parse a file with simple KEY=VAL pairs on separate lines
(/etc/environment by default). You can change the default file to parse, with
the envfile flag and turn it on or off by setting the readenv flag to 1 or 0
respectively.
6.6.2. DESCRIPTION
The /etc/security/pam_env.conf file specifies the environment variables to be
set, unset or modified by pam_env(8). When someone logs in, this file is read
and the environment variables are set according.
Each line starts with the variable name, there are then two possible options
for each variable DEFAULT and OVERRIDE. DEFAULT allows and administrator to set
the value of the variable to some default value, if none is supplied then the
empty string is assumed. The OVERRIDE option tells pam_env that it should enter
in its value (overriding the default value) if there is one to use. OVERRIDE is
not used, "" is assumed and no override will be done.
VARIABLE [DEFAULT=[value]] [OVERRIDE=[value]]
(Possibly non-existent) environment variables may be used in values using the $
{string} syntax and (possibly non-existent) PAM_ITEMs may be used in values
using the @{string} syntax. Both the $ and @ characters can be backslash
escaped to be used as literal values values can be delimited with "", escaped "
not supported. Note that many environment variables that you would like to use
may not be set by the time the module is called. For example, HOME is used
below several times, but many PAM applications don't make it available by the
time you need it.
The "#" character at start of line (no space at front) can be used to mark this
line as a comment line.
6.6.3. OPTIONS
conffile=/path/to/pam_env.conf
Indicate an alternative pam_env.conf style configuration file to override
the default. This can be useful when different services need different
environments.
debug
A lot of debug information is printed with syslog(3).
envfile=/path/to/environment
Indicate an alternative environment file to override the default. This can
be useful when different services need different environments.
readenv=0|1
Turns on or off the reading of the file specified by envfile (0 is off, 1
is on). By default this option is on.
user_envfile=filename
Indicate an alternative .pam_environment file to override the default. This
can be useful when different services need different environments. The
filename is relative to the user home directory.
user_readenv=0|1
Turns on or off the reading of the user specific environment file. 0 is
off, 1 is on. By default this option is off as user supplied environment
variables in the PAM environment could affect behavior of subsequent
modules in the stack without the consent of the system administrator.
6.6.4. MODULE TYPES PROVIDED
The auth and session module types are provided.
6.6.5. RETURN VALUES
PAM_ABORT
Not all relevant data or options could be gotten.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
No pam_env.conf and environment file was found.
PAM_SUCCESS
Environment variables were set.
6.6.6. FILES
/etc/security/pam_env.conf
Default configuration file
/etc/environment
Default environment file
$HOME/.pam_environment
User specific environment file
6.6.7. EXAMPLES
These are some example lines which might be specified in /etc/security/
pam_env.conf.
Set the REMOTEHOST variable for any hosts that are remote, default to
"localhost" rather than not being set at all
REMOTEHOST DEFAULT=localhost OVERRIDE=@{PAM_RHOST}
Set the DISPLAY variable if it seems reasonable
DISPLAY DEFAULT=${REMOTEHOST}:0.0 OVERRIDE=${DISPLAY}
Now some simple variables
PAGER DEFAULT=less
MANPAGER DEFAULT=less
LESS DEFAULT="M q e h15 z23 b80"
NNTPSERVER DEFAULT=localhost
PATH DEFAULT=${HOME}/bin:/usr/local/bin:/bin\
:/usr/bin:/usr/local/bin/X11:/usr/bin/X11
Silly examples of escaped variables, just to show how they work.
DOLLAR DEFAULT=\$
DOLLARDOLLAR DEFAULT= OVERRIDE=\$${DOLLAR}
DOLLARPLUS DEFAULT=\${REMOTEHOST}${REMOTEHOST}
ATSIGN DEFAULT="" OVERRIDE=\@
6.6.8. AUTHOR
pam_env was written by Dave Kinchlea <kinch@kinch.ark.com>.
6.7. pam_exec - call an external command
pam_exec.so [ debug ] [ expose_authtok ] [ seteuid ] [ quiet ] [ log=file ]
command [ ... ]
6.7.1. DESCRIPTION
pam_exec is a PAM module that can be used to run an external command.
The child's environment is set to the current PAM environment list, as returned
by pam_getenvlist(3) In addition, the following PAM items are exported as
environment variables: PAM_RHOST, PAM_RUSER, PAM_SERVICE, PAM_TTY, PAM_USER and
PAM_TYPE, which contains one of the module types: account, auth, password,
open_session and close_session.
6.7.2. OPTIONS
debug
Print debug information.
expose_authtok
During authentication the calling command can read the password from stdin
(3). Only first PAM_MAX_RESP_SIZE bytes of a password are provided to the
command.
log=file
The output of the command is appended to file
quiet
Per default pam_exec.so will echo the exit status of the external command
if it fails. Specifying this option will suppress the message.
seteuid
Per default pam_exec.so will execute the external command with the real
user ID of the calling process. Specifying this option means the command is
run with the effective user ID.
6.7.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.7.4. RETURN VALUES
PAM_SUCCESS
The external command was run successfully.
PAM_SERVICE_ERR
No argument or a wrong number of arguments were given.
PAM_SYSTEM_ERR
A system error occurred or the command to execute failed.
PAM_IGNORE
pam_setcred was called, which does not execute the command.
6.7.5. EXAMPLES
Add the following line to /etc/pam.d/passwd to rebuild the NIS database after
each local password change:
passwd optional pam_exec.so seteuid make -C /var/yp
This will execute the command
make -C /var/yp
with effective user ID.
6.7.6. AUTHOR
pam_exec was written by Thorsten Kukuk <kukuk@thkukuk.de>.
6.8. pam_faildelay - change the delay on failure per-application
pam_faildelay.so [ debug ] [ delay=microseconds ]
6.8.1. DESCRIPTION
pam_faildelay is a PAM module that can be used to set the delay on failure
per-application.
If no delay is given, pam_faildelay will use the value of FAIL_DELAY from /etc/
login.defs.
6.8.2. OPTIONS
debug
Turns on debugging messages sent to syslog.
delay=N
Set the delay on failure to N microseconds.
6.8.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.8.4. RETURN VALUES
PAM_IGNORE
Delay was successful adjusted.
PAM_SYSTEM_ERR
The specified delay was not valid.
6.8.5. EXAMPLES
The following example will set the delay on failure to 10 seconds:
auth optional pam_faildelay.so delay=10000000
6.8.6. AUTHOR
pam_faildelay was written by Darren Tucker <dtucker@zip.com.au>.
6.9. pam_filter - filter module
pam_filter.so [ debug ] [ new_term ] [ non_term ] run1|run2 filter [ ... ]
6.9.1. DESCRIPTION
This module is intended to be a platform for providing access to all of the
input/output that passes between the user and the application. It is only
suitable for tty-based and (stdin/stdout) applications.
To function this module requires filters to be installed on the system. The
single filter provided with the module simply transposes upper and lower case
letters in the input and output streams. (This can be very annoying and is not
kind to termcap based editors).
Each component of the module has the potential to invoke the desired filter.
The filter is always execv(2) with the privilege of the calling application and
not that of the user. For this reason it cannot usually be killed by the user
without closing their session.
6.9.2. OPTIONS
debug
Print debug information.
new_term
The default action of the filter is to set the PAM_TTY item to indicate the
terminal that the user is using to connect to the application. This
argument indicates that the filter should set PAM_TTY to the filtered
pseudo-terminal.
non_term
don't try to set the PAM_TTY item.
runX
In order that the module can invoke a filter it should know when to invoke
it. This argument is required to tell the filter when to do this.
Permitted values for X are 1 and 2. These indicate the precise time that
the filter is to be run. To understand this concept it will be useful to
have read the pam(3) manual page. Basically, for each management group
there are up to two ways of calling the module's functions. In the case of
the authentication and session components there are actually two separate
functions. For the case of authentication, these functions are
pam_authenticate(3) and pam_setcred(3), here run1 means run the filter from
the pam_authenticate function and run2 means run the filter from
pam_setcred. In the case of the session modules, run1 implies that the
filter is invoked at the pam_open_session(3) stage, and run2 for
pam_close_session(3).
For the case of the account component. Either run1 or run2 may be used.
For the case of the password component, run1 is used to indicate that the
filter is run on the first occasion of pam_chauthtok(3) (the
PAM_PRELIM_CHECK phase) and run2 is used to indicate that the filter is run
on the second occasion (the PAM_UPDATE_AUTHTOK phase).
filter
The full pathname of the filter to be run and any command line arguments
that the filter might expect.
6.9.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.9.4. RETURN VALUES
PAM_SUCCESS
The new filter was set successfully.
PAM_ABORT
Critical error, immediate abort.
6.9.5. EXAMPLES
Add the following line to /etc/pam.d/login to see how to configure login to
transpose upper and lower case letters once the user has logged in:
session required pam_filter.so run1 /lib/security/pam_filter/upperLOWER
6.9.6. AUTHOR
pam_filter was written by Andrew G. Morgan <morgan@kernel.org>.
6.10. pam_ftp - module for anonymous access
pam_ftp.so [ debug ] [ ignore ] [ users=XXX,YYY, ...]
6.10.1. DESCRIPTION
pam_ftp is a PAM module which provides a pluggable anonymous ftp mode of
access.
This module intercepts the user's name and password. If the name is ftp or
anonymous, the user's password is broken up at the @ delimiter into a PAM_RUSER
and a PAM_RHOST part; these pam-items being set accordingly. The username (
PAM_USER) is set to ftp. In this case the module succeeds. Alternatively, the
module sets the PAM_AUTHTOK item with the entered password and fails.
This module is not safe and easily spoofable.
6.10.2. OPTIONS
debug
Print debug information.
ignore
Pay no attention to the email address of the user (if supplied).
ftp=XXX,YYY,...
Instead of ftp or anonymous, provide anonymous login to the comma separated
list of users: XXX,YYY,.... Should the applicant enter one of these
usernames the returned username is set to the first in the list: XXX.
6.10.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.10.4. RETURN VALUES
PAM_SUCCESS
The authentication was successful.
PAM_USER_UNKNOWN
User not known.
6.10.5. EXAMPLES
Add the following line to /etc/pam.d/ftpd to handle ftp style anonymous login:
#
# ftpd; add ftp-specifics. These lines enable anonymous ftp over
# standard UN*X access (the listfile entry blocks access to
# users listed in /etc/ftpusers)
#
auth sufficient pam_ftp.so
auth required pam_unix.so use_first_pass
auth required pam_listfile.so \
onerr=succeed item=user sense=deny file=/etc/ftpusers
6.10.6. AUTHOR
pam_ftp was written by Andrew G. Morgan <morgan@kernel.org>.
6.11. pam_group - module to modify group access
pam_group.so
6.11.1. DESCRIPTION
The pam_group PAM module does not authenticate the user, but instead it grants
group memberships (in the credential setting phase of the authentication
module) to the user. Such memberships are based on the service they are
applying for.
By default rules for group memberships are taken from config file /etc/security
/group.conf.
This module's usefulness relies on the file-systems accessible to the user. The
point being that once granted the membership of a group, the user may attempt
to create a setgid binary with a restricted group ownership. Later, when the
user is not given membership to this group, they can recover group membership
with the precompiled binary. The reason that the file-systems that the user has
access to are so significant, is the fact that when a system is mounted nosuid
the user is unable to create or execute such a binary file. For this module to
provide any level of security, all file-systems that the user has write access
to should be mounted nosuid.
The pam_group module functions in parallel with the /etc/group file. If the
user is granted any groups based on the behavior of this module, they are
granted in addition to those entries /etc/group (or equivalent).
6.11.2. DESCRIPTION
The pam_group PAM module does not authenticate the user, but instead it grants
group memberships (in the credential setting phase of the authentication
module) to the user. Such memberships are based on the service they are
applying for.
For this module to function correctly there must be a correctly formatted /etc/
security/group.conf file present. White spaces are ignored and lines maybe
extended with '\' (escaped newlines). Text following a '#' is ignored to the
end of the line.
The syntax of the lines is as follows:
services;ttys;users;times;groups
The first field, the services field, is a logic list of PAM service names that
the rule applies to.
The second field, the tty field, is a logic list of terminal names that this
rule applies to.
The third field, the users field, is a logic list of users, or a UNIX group, or
a netgroup of users to whom this rule applies. Group names are preceded by a
'%' symbol, while netgroup names are preceded by a '@' symbol.
For these items the simple wildcard '*' may be used only once. With UNIX groups
or netgroups no wildcards or logic operators are allowed.
The times field is used to indicate "when" these groups are to be given to the
user. The format here is a logic list of day/time-range entries. The days are
specified by a sequence of two character entries, MoTuSa for example is Monday
Tuesday and Saturday. Note that repeated days are unset MoMo = no day, and MoWk
= all weekdays bar Monday. The two character combinations accepted are Mo Tu We
Th Fr Sa Su Wk Wd Al, the last two being week-end days and all 7 days of the
week respectively. As a final example, AlFr means all days except Friday.
Each day/time-range can be prefixed with a '!' to indicate "anything but". The
time-range part is two 24-hour times HHMM, separated by a hyphen, indicating
the start and finish time (if the finish time is smaller than the start time it
is deemed to apply on the following day).
The groups field is a comma or space separated list of groups that the user
inherits membership of. These groups are added if the previous fields are
satisfied by the user's request.
For a rule to be active, ALL of service+ttys+users must be satisfied by the
applying process.
6.11.3. OPTIONS
This module does not recognise any options.
6.11.4. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.11.5. RETURN VALUES
PAM_SUCCESS
group membership was granted.
PAM_ABORT
Not all relevant data could be gotten.
PAM_BUF_ERR
Memory buffer error.
PAM_CRED_ERR
Group membership was not granted.
PAM_IGNORE
pam_sm_authenticate was called which does nothing.
PAM_USER_UNKNOWN
The user is not known to the system.
6.11.6. FILES
/etc/security/group.conf
Default configuration file
6.11.7. EXAMPLES
These are some example lines which might be specified in /etc/security/
group.conf.
Running 'xsh' on tty* (any ttyXXX device), the user 'us' is given access to the
floppy (through membership of the floppy group)
xsh;tty*&!ttyp*;us;Al0000-2400;floppy
Running 'xsh' on tty* (any ttyXXX device), the user 'sword' is given access to
games (through membership of the floppy group) after work hours.
xsh; tty* ;sword;!Wk0900-1800;games, sound
xsh; tty* ;*;Al0900-1800;floppy
Any member of the group 'admin' running 'xsh' on tty*, is granted access (at
any time) to the group 'plugdev'
xsh; tty* ;%admin;Al0000-2400;plugdev
6.11.8. AUTHORS
pam_group was written by Andrew G. Morgan <morgan@kernel.org>.
6.12. pam_issue - add issue file to user prompt
pam_issue.so [ noesc ] [ issue=issue-file-name ]
6.12.1. DESCRIPTION
pam_issue is a PAM module to prepend an issue file to the username prompt. It
also by default parses escape codes in the issue file similar to some common
getty's (using \x format).
Recognized escapes:
\d
current day
\l
name of this tty
\m
machine architecture (uname -m)
\n
machine's network node hostname (uname -n)
\o
domain name of this system
\r
release number of operating system (uname -r)
\t
current time
\s
operating system name (uname -s)
\u
number of users currently logged in
\U
same as \u except it is suffixed with "user" or "users" (eg. "1 user" or
"10 users")
\v
operating system version and build date (uname -v)
6.12.2. OPTIONS
noesc
Turns off escape code parsing.
issue=issue-file-name
The file to output if not using the default.
6.12.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.12.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The prompt was already changed.
PAM_SERVICE_ERR
A service module error occurred.
PAM_SUCCESS
The new prompt was set successfully.
6.12.5. EXAMPLES
Add the following line to /etc/pam.d/login to set the user specific issue at
login:
auth optional pam_issue.so issue=/etc/issue
6.12.6. AUTHOR
pam_issue was written by Ben Collins <bcollins@debian.org>.
6.13. pam_keyinit - display the keyinit file
pam_keyinit.so [ debug ] [ force ] [ revoke ]
6.13.1. DESCRIPTION
The pam_keyinit PAM module ensures that the invoking process has a session
keyring other than the user default session keyring.
The session component of the module checks to see if the process's session
keyring is the user default, and, if it is, creates a new anonymous session
keyring with which to replace it.
If a new session keyring is created, it will install a link to the user common
keyring in the session keyring so that keys common to the user will be
automatically accessible through it.
The session keyring of the invoking process will thenceforth be inherited by
all its children unless they override it.
This module is intended primarily for use by login processes. Be aware that
after the session keyring has been replaced, the old session keyring and the
keys it contains will no longer be accessible.
This module should not, generally, be invoked by programs like su, since it is
usually desirable for the key set to percolate through to the alternate
context. The keys have their own permissions system to manage this.
This module should be included as early as possible in a PAM configuration, so
that other PAM modules can attach tokens to the keyring.
The keyutils package is used to manipulate keys more directly. This can be
obtained from:
Keyutils
6.13.2. OPTIONS
debug
Log debug information with syslog(3).
force
Causes the session keyring of the invoking process to be replaced
unconditionally.
revoke
Causes the session keyring of the invoking process to be revoked when the
invoking process exits if the session keyring was created for this process
in the first place.
6.13.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.13.4. RETURN VALUES
PAM_SUCCESS
This module will usually return this value
PAM_AUTH_ERR
Authentication failure.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The return value should be ignored by PAM dispatch.
PAM_SERVICE_ERR
Cannot determine the user name.
PAM_SESSION_ERR
This module will return this value if its arguments are invalid or if a
system error such as ENOMEM occurs.
PAM_USER_UNKNOWN
User not known.
6.13.5. EXAMPLES
Add this line to your login entries to start each login session with its own
session keyring:
session required pam_keyinit.so
This will prevent keys from one session leaking into another session for the
same user.
6.13.6. AUTHOR
pam_keyinit was written by David Howells, <dhowells@redhat.com>.
6.14. pam_lastlog - display date of last login
pam_lastlog.so [ debug ] [ silent ] [ never ] [ nodate ] [ nohost ] [ noterm ]
[ nowtmp ] [ noupdate ] [ showfailed ] [ inactive=<days> ]
6.14.1. DESCRIPTION
pam_lastlog is a PAM module to display a line of information about the last
login of the user. In addition, the module maintains the /var/log/lastlog file.
Some applications may perform this function themselves. In such cases, this
module is not necessary.
If the module is called in the auth or account phase, the accounts that were
not used recently enough will be disallowed to log in. The check is not
performed for the root account so the root is never locked out.
6.14.2. OPTIONS
debug
Print debug information.
silent
Don't inform the user about any previous login, just update the /var/log/
lastlog file.
never
If the /var/log/lastlog file does not contain any old entries for the user,
indicate that the user has never previously logged in with a welcome
message.
nodate
Don't display the date of the last login.
noterm
Don't display the terminal name on which the last login was attempted.
nohost
Don't indicate from which host the last login was attempted.
nowtmp
Don't update the wtmp entry.
noupdate
Don't update any file.
showfailed
Display number of failed login attempts and the date of the last failed
attempt from btmp. The date is not displayed when nodate is specified.
inactive=<days>
This option is specific for the auth or account phase. It specifies the
number of days after the last login of the user when the user will be
locked out by the module. The default value is 90.
6.14.3. MODULE TYPES PROVIDED
The auth and account module type allows to lock out users which did not login
recently enough. The session module type is provided for displaying the
information about the last login and/or updating the lastlog and wtmp files.
6.14.4. RETURN VALUES
PAM_SUCCESS
Everything was successful.
PAM_SERVICE_ERR
Internal service module error.
PAM_USER_UNKNOWN
User not known.
PAM_AUTH_ERR
User locked out in the auth or account phase due to inactivity.
PAM_IGNORE
There was an error during reading the lastlog file in the auth or account
phase and thus inactivity of the user cannot be determined.
6.14.5. EXAMPLES
Add the following line to /etc/pam.d/login to display the last login time of an
user:
session required pam_lastlog.so nowtmp
To reject the user if he did not login during the previous 50 days the
following line can be used:
auth required pam_lastlog.so inactive=50
6.14.6. AUTHOR
pam_lastlog was written by Andrew G. Morgan <morgan@kernel.org>.
Inactive account lock out added by Tom?? Mr?z <tm@t8m.info>.
6.15. pam_limits - limit resources
pam_limits.so [ change_uid ] [ conf=/path/to/limits.conf ] [ debug ] [
utmp_early ] [ noaudit ]
6.15.1. DESCRIPTION
The pam_limits PAM module sets limits on the system resources that can be
obtained in a user-session. Users of uid=0 are affected by this limits, too.
By default limits are taken from the /etc/security/limits.conf config file.
Then individual *.conf files from the /etc/security/limits.d/ directory are
read. The files are parsed one after another in the order of "C" locale. The
effect of the individual files is the same as if all the files were
concatenated together in the order of parsing. If a config file is explicitly
specified with a module option then the files in the above directory are not
parsed.
The module must not be called by a multithreaded application.
If Linux PAM is compiled with audit support the module will report when it
denies access based on limit of maximum number of concurrent login sessions.
6.15.2. DESCRIPTION
The pam_limits.so module applies ulimit limits, nice priority and number of
simultaneous login sessions limit to user login sessions. This description of
the configuration file syntax applies to the /etc/security/limits.conf file and
*.conf files in the /etc/security/limits.d directory.
The syntax of the lines is as follows:
<domain> <type> <item> <value>
The fields listed above should be filled as follows:
<domain>
* a username
* a groupname, with @group syntax. This should not be confused with
netgroups.
* the wildcard *, for default entry.
* the wildcard %, for maxlogins limit only, can also be used with %group
syntax. If the % wildcard is used alone it is identical to using * with
maxsyslogins limit. With a group specified after % it limits the total
number of logins of all users that are member of the group.
* an uid range specified as <min_uid>:<max_uid>. If min_uid is omitted,
the match is exact for the max_uid. If max_uid is omitted, all uids
greater than or equal min_uid match.
* a gid range specified as @<min_gid>:<max_gid>. If min_gid is omitted,
the match is exact for the max_gid. If max_gid is omitted, all gids
greater than or equal min_gid match. For the exact match all groups
including the user's supplementary groups are examined. For the range
matches only the user's primary group is examined.
* a gid specified as %:<gid> applicable to maxlogins limit only. It
limits the total number of logins of all users that are member of the
group with the specified gid.
<type>
hard
for enforcing hard resource limits. These limits are set by the
superuser and enforced by the Kernel. The user cannot raise his
requirement of system resources above such values.
soft
for enforcing soft resource limits. These limits are ones that the user
can move up or down within the permitted range by any pre-existing hard
limits. The values specified with this token can be thought of as
default values, for normal system usage.
-
for enforcing both soft and hard resource limits together.
Note, if you specify a type of '-' but neglect to supply the item and
value fields then the module will never enforce any limits on the
specified user/group etc. .
<item>
core
limits the core file size (KB)
data
maximum data size (KB)
fsize
maximum filesize (KB)
memlock
maximum locked-in-memory address space (KB)
nofile
maximum number of open file descriptors
rss
maximum resident set size (KB) (Ignored in Linux 2.4.30 and higher)
stack
maximum stack size (KB)
cpu
maximum CPU time (minutes)
nproc
maximum number of processes
as
address space limit (KB)
maxlogins
maximum number of logins for this user (this limit does not apply to
user with uid=0)
maxsyslogins
maximum number of all logins on system; user is not allowed to log-in
if total number of all users' logins is greater than specified number
(this limit does not apply to user with uid=0)
priority
the priority to run user process with (negative values boost process
priority)
locks
maximum locked files (Linux 2.4 and higher)
sigpending
maximum number of pending signals (Linux 2.6 and higher)
msgqueue
maximum memory used by POSIX message queues (bytes) (Linux 2.6 and
higher)
nice
maximum nice priority allowed to raise to (Linux 2.6.12 and higher)
values: [-20,19]
rtprio
maximum realtime priority allowed for non-privileged processes (Linux
2.6.12 and higher)
All items support the values -1, unlimited or infinity indicating no limit,
except for priority and nice.
If a hard limit or soft limit of a resource is set to a valid value, but
outside of the supported range of the local system, the system may reject the
new limit or unexpected behavior may occur. If the control value required is
used, the module will reject the login if a limit could not be set.
In general, individual limits have priority over group limits, so if you impose
no limits for admin group, but one of the members in this group have a limits
line, the user will have its limits set according to this line.
Also, please note that all limit settings are set per login. They are not
global, nor are they permanent; existing only for the duration of the session.
In the limits configuration file, the '#' character introduces a comment -
after which the rest of the line is ignored.
The pam_limits module does report configuration problems found in its
configuration file and errors via syslog(3).
6.15.3. OPTIONS
change_uid
Change real uid to the user for who the limits are set up. Use this option
if you have problems like login not forking a shell for user who has no
processes. Be warned that something else may break when you do this.
conf=/path/to/limits.conf
Indicate an alternative limits.conf style configuration file to override
the default.
debug
Print debug information.
utmp_early
Some broken applications actually allocate a utmp entry for the user before
the user is admitted to the system. If some of the services you are
configuring PAM for do this, you can selectively use this module argument
to compensate for this behavior and at the same time maintain system-wide
consistency with a single limits.conf file.
noaudit
Do not report exceeded maximum logins count to the audit subsystem.
6.15.4. MODULE TYPES PROVIDED
Only the session module type is provided.
6.15.5. RETURN VALUES
PAM_ABORT
Cannot get current limits.
PAM_IGNORE
No limits found for this user.
PAM_PERM_DENIED
New limits could not be set.
PAM_SERVICE_ERR
Cannot read config file.
PAM_SESSION_ERR
Error recovering account name.
PAM_SUCCESS
Limits were changed.
PAM_USER_UNKNOWN
The user is not known to the system.
6.15.6. FILES
/etc/security/limits.conf
Default configuration file
6.15.7. EXAMPLES
These are some example lines which might be specified in /etc/security/
limits.conf.
* soft core 0
* hard nofile 512
@student hard nproc 20
@faculty soft nproc 20
@faculty hard nproc 50
ftp hard nproc 0
@student - maxlogins 4
:123 hard cpu 5000
@500: soft cpu 10000
600:700 hard locks 10
6.15.8. AUTHORS
pam_limits was initially written by Cristian Gafton <gafton@redhat.com>
6.16. pam_listfile - deny or allow services based on an arbitrary file
pam_listfile.so item=[tty|user|rhost|ruser|group|shell] sense=[allow|deny] file
=/path/filename onerr=[succeed|fail] [ apply=[user|@group] ] [ quiet ]
6.16.1. DESCRIPTION
pam_listfile is a PAM module which provides a way to deny or allow services
based on an arbitrary file.
The module gets the item of the type specified -- user specifies the username,
PAM_USER; tty specifies the name of the terminal over which the request has
been made, PAM_TTY; rhost specifies the name of the remote host (if any) from
which the request was made, PAM_RHOST; and ruser specifies the name of the
remote user (if available) who made the request, PAM_RUSER -- and looks for an
instance of that item in the file=filename. filename contains one line per item
listed. If the item is found, then if sense=allow, PAM_SUCCESS is returned,
causing the authorization request to succeed; else if sense=deny, PAM_AUTH_ERR
is returned, causing the authorization request to fail.
If an error is encountered (for instance, if filename does not exist, or a
poorly-constructed argument is encountered), then if onerr=succeed, PAM_SUCCESS
is returned, otherwise if onerr=fail, PAM_AUTH_ERR or PAM_SERVICE_ERR (as
appropriate) will be returned.
An additional argument, apply=, can be used to restrict the application of the
above to a specific user (apply=username) or a given group (apply=@groupname).
This added restriction is only meaningful when used with the tty, rhost and
shell items.
Besides this last one, all arguments should be specified; do not count on any
default behavior.
No credentials are awarded by this module.
6.16.2. OPTIONS
item=[tty|user|rhost|ruser|group|shell]
What is listed in the file and should be checked for.
sense=[allow|deny]
Action to take if found in file, if the item is NOT found in the file, then
the opposite action is requested.
file=/path/filename
File containing one item per line. The file needs to be a plain file and
not world writable.
onerr=[succeed|fail]
What to do if something weird happens like being unable to open the file.
apply=[user|@group]
Restrict the user class for which the restriction apply. Note that with
item=[user|ruser|group] this does not make sense, but for item=[tty|rhost|
shell] it have a meaning.
quiet
Do not treat service refusals or missing list files as errors that need to
be logged.
6.16.3. MODULE TYPES PROVIDED
All module types (auth, account, password and session) are provided.
6.16.4. RETURN VALUES
PAM_AUTH_ERR
Authentication failure.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The rule does not apply to the apply option.
PAM_SERVICE_ERR
Error in service module.
PAM_SUCCESS
Success.
6.16.5. EXAMPLES
Classic 'ftpusers' authentication can be implemented with this entry in /etc/
pam.d/ftpd:
#
# deny ftp-access to users listed in the /etc/ftpusers file
#
auth required pam_listfile.so \
onerr=succeed item=user sense=deny file=/etc/ftpusers
Note, users listed in /etc/ftpusers file are (counterintuitively) not allowed
access to the ftp service.
To allow login access only for certain users, you can use a /etc/pam.d/login
entry like this:
#
# permit login to users listed in /etc/loginusers
#
auth required pam_listfile.so \
onerr=fail item=user sense=allow file=/etc/loginusers
For this example to work, all users who are allowed to use the login service
should be listed in the file /etc/loginusers. Unless you are explicitly trying
to lock out root, make sure that when you do this, you leave a way for root to
log in, either by listing root in /etc/loginusers, or by listing a user who is
able to su to the root account.
6.16.6. AUTHOR
pam_listfile was written by Michael K. Johnson <johnsonm@redhat.com> and Elliot
Lee <sopwith@cuc.edu>.
6.17. pam_localuser - require users to be listed in /etc/passwd
pam_localuser.so [ debug ] [ file=/path/passwd ]
6.17.1. DESCRIPTION
pam_localuser is a PAM module to help implementing site-wide login policies,
where they typically include a subset of the network's users and a few accounts
that are local to a particular workstation. Using pam_localuser and pam_wheel
or pam_listfile is an effective way to restrict access to either local users
and/or a subset of the network's users.
This could also be implemented using pam_listfile.so and a very short awk
script invoked by cron, but it's common enough to have been separated out.
6.17.2. OPTIONS
debug
Print debug information.
file=/path/passwd
Use a file other than /etc/passwd.
6.17.3. MODULE TYPES PROVIDED
All module types (account, auth, password and session) are provided.
6.17.4. RETURN VALUES
PAM_SUCCESS
The new localuser was set successfully.
PAM_SERVICE_ERR
No username was given.
PAM_USER_UNKNOWN
User not known.
6.17.5. EXAMPLES
Add the following line to /etc/pam.d/su to allow only local users in group
wheel to use su.
account sufficient pam_localuser.so
account required pam_wheel.so
6.17.6. AUTHOR
pam_localuser was written by Nalin Dahyabhai <nalin@redhat.com>.
6.18. pam_loginuid - record user's login uid to the process attribute
pam_loginuid.so [ require_auditd ]
6.18.1. DESCRIPTION
The pam_loginuid module sets the loginuid process attribute for the process
that was authenticated. This is necessary for applications to be correctly
audited. This PAM module should only be used for entry point applications like:
login, sshd, gdm, vsftpd, crond and atd. There are probably other entry point
applications besides these. You should not use it for applications like sudo or
su as that defeats the purpose by changing the loginuid to the account they
just switched to.
6.18.2. OPTIONS
require_auditd
This option, when given, will cause this module to query the audit daemon
status and deny logins if it is not running.
6.18.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.18.4. RETURN VALUES
PAM_SESSION_ERR
An error occurred during session management.
6.18.5. EXAMPLES
#%PAM-1.0
auth required pam_unix.so
auth required pam_nologin.so
account required pam_unix.so
password required pam_unix.so
session required pam_unix.so
session required pam_loginuid.so
6.18.6. AUTHOR
pam_loginuid was written by Steve Grubb <sgrubb@redhat.com>
6.19. pam_mail - inform about available mail
pam_mail.so [ close ] [ debug ] [ dir=maildir ] [ empty ] [ hash=count ] [
noenv ] [ nopen ] [ quiet ] [ standard ]
6.19.1. DESCRIPTION
The pam_mail PAM module provides the "you have new mail" service to the user.
It can be plugged into any application that has credential or session hooks. It
gives a single message indicating the newness of any mail it finds in the
user's mail folder. This module also sets the PAM environment variable, MAIL,
to the user's mail directory.
If the mail spool file (be it /var/mail/$USER or a pathname given with the dir=
parameter) is a directory then pam_mail assumes it is in the Maildir format.
6.19.2. OPTIONS
close
Indicate if the user has any mail also on logout.
debug
Print debug information.
dir=maildir
Look for the users' mail in an alternative location defined by maildir/
<login>. The default location for mail is /var/mail/<login>. Note, if the
supplied maildir is prefixed by a '~', the directory is interpreted as
indicating a file in the user's home directory.
empty
Also print message if user has no mail.
hash=count
Mail directory hash depth. For example, a hashcount of 2 would make the
mail file be /var/spool/mail/u/s/user.
noenv
Do not set the MAIL environment variable.
nopen
Don't print any mail information on login. This flag is useful to get the
MAIL environment variable set, but to not display any information about it.
quiet
Only report when there is new mail.
standard
Old style "You have..." format which doesn't show the mail spool being
used. This also implies "empty".
6.19.3. MODULE TYPES PROVIDED
The session and auth (on establishment and deletion of credentials) module
types are provided.
6.19.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_SERVICE_ERR
Badly formed arguments.
PAM_SUCCESS
Success.
PAM_USER_UNKNOWN
User not known.
6.19.5. EXAMPLES
Add the following line to /etc/pam.d/login to indicate that the user has new
mail when they login to the system.
session optional pam_mail.so standard
6.19.6. AUTHOR
pam_mail was written by Andrew G. Morgan <morgan@kernel.org>.
6.20. pam_mkhomedir - create users home directory
pam_mkhomedir.so [ silent ] [ umask=mode ] [ skel=skeldir ]
6.20.1. DESCRIPTION
The pam_mkhomedir PAM module will create a users home directory if it does not
exist when the session begins. This allows users to be present in central
database (such as NIS, kerberos or LDAP) without using a distributed file
system or pre-creating a large number of directories. The skeleton directory
(usually /etc/skel/) is used to copy default files and also sets a umask for
the creation.
The new users home directory will not be removed after logout of the user.
6.20.2. OPTIONS
silent
Don't print informative messages.
umask=mask
The user file-creation mask is set to mask. The default value of mask is
0022.
skel=/path/to/skel/directory
Indicate an alternative skel directory to override the default /etc/skel.
6.20.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.20.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_CRED_INSUFFICIENT
Insufficient credentials to access authentication data.
PAM_PERM_DENIED
Not enough permissions to create the new directory or read the skel
directory.
PAM_USER_UNKNOWN
User not known to the underlying authentication module.
PAM_SUCCESS
Environment variables were set.
6.20.5. EXAMPLES
A sample /etc/pam.d/login file:
auth requisite pam_securetty.so
auth sufficient pam_ldap.so
auth required pam_unix.so
auth required pam_nologin.so
account sufficient pam_ldap.so
account required pam_unix.so
password required pam_unix.so
session required pam_mkhomedir.so skel=/etc/skel/ umask=0022
session required pam_unix.so
session optional pam_lastlog.so
session optional pam_mail.so standard
6.20.6. AUTHOR
pam_mkhomedir was written by Jason Gunthorpe <jgg@debian.org>.
6.21. pam_motd - display the motd file
pam_motd.so [ motd=/path/filename ]
6.21.1. DESCRIPTION
pam_motd is a PAM module that can be used to display arbitrary motd (message of
the day) files after a successful login. By default the /etc/motd file is
shown. The message size is limited to 64KB.
6.21.2. OPTIONS
motd=/path/filename
The /path/filename file is displayed as message of the day.
6.21.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.21.4. RETURN VALUES
PAM_IGNORE
This is the only return value of this module.
6.21.5. EXAMPLES
The suggested usage for /etc/pam.d/login is:
session optional pam_motd.so motd=/etc/motd
6.21.6. AUTHOR
pam_motd was written by Ben Collins <bcollins@debian.org>.
6.22. pam_namespace - setup a private namespace
pam_namespace.so [ debug ] [ unmnt_remnt ] [ unmnt_only ] [ require_selinux ] [
gen_hash ] [ ignore_config_error ] [ ignore_instance_parent_mode ] [
no_unmount_on_close ] [ use_current_context ] [ use_default_context ]
6.22.1. DESCRIPTION
The pam_namespace PAM module sets up a private namespace for a session with
polyinstantiated directories. A polyinstantiated directory provides a different
instance of itself based on user name, or when using SELinux, user name,
security context or both. If an executable script /etc/security/namespace.init
exists, it is used to initialize the instance directory after it is set up and
mounted on the polyinstantiated directory. The script receives the
polyinstantiated directory path, the instance directory path, flag whether the
instance directory was newly created (0 for no, 1 for yes), and the user name
as its arguments.
The pam_namespace module disassociates the session namespace from the parent
namespace. Any mounts/unmounts performed in the parent namespace, such as
mounting of devices, are not reflected in the session namespace. To propagate
selected mount/unmount events from the parent namespace into the disassociated
session namespace, an administrator may use the special shared-subtree feature.
For additional information on shared-subtree feature, please refer to the mount
(8) man page and the shared-subtree description at http://lwn.net/Articles/
159077 and http://lwn.net/Articles/159092.
6.22.2. DESCRIPTION
The pam_namespace.so module allows setup of private namespaces with
polyinstantiated directories. Directories can be polyinstantiated based on user
name or, in the case of SELinux, user name, sensitivity level or complete
security context. If an executable script /etc/security/namespace.init exists,
it is used to initialize the namespace every time an instance directory is set
up and mounted. The script receives the polyinstantiated directory path and the
instance directory path as its arguments.
The /etc/security/namespace.conf file specifies which directories are
polyinstantiated, how they are polyinstantiated, how instance directories would
be named, and any users for whom polyinstantiation would not be performed.
When someone logs in, the file namespace.conf is scanned. Comments are marked
by # characters. Each non comment line represents one polyinstantiated
directory. The fields are separated by spaces but can be quoted by " characters
also escape sequences \b, \n, and \t are recognized. The fields are as follows:
polydir instance_prefix method list_of_uids
The first field, polydir, is the absolute pathname of the directory to
polyinstantiate. The special string $HOME is replaced with the user's home
directory, and $USER with the username. This field cannot be blank.
The second field, instance_prefix is the string prefix used to build the
pathname for the instantiation of <polydir>. Depending on the polyinstantiation
method it is then appended with "instance differentiation string" to generate
the final instance directory path. This directory is created if it did not
exist already, and is then bind mounted on the <polydir> to provide an instance
of <polydir> based on the <method> column. The special string $HOME is replaced
with the user's home directory, and $USER with the username. This field cannot
be blank.
The third field, method, is the method used for polyinstantiation. It can take
these values; "user" for polyinstantiation based on user name, "level" for
polyinstantiation based on process MLS level and user name, "context" for
polyinstantiation based on process security context and user name, "tmpfs" for
mounting tmpfs filesystem as an instance dir, and "tmpdir" for creating
temporary directory as an instance dir which is removed when the user's session
is closed. Methods "context" and "level" are only available with SELinux. This
field cannot be blank.
The fourth field, list_of_uids, is a comma separated list of user names for
whom the polyinstantiation is not performed. If left blank, polyinstantiation
will be performed for all users. If the list is preceded with a single "~"
character, polyinstantiation is performed only for users in the list.
The method field can contain also following optional flags separated by :
characters.
create=mode,owner,group - create the polyinstantiated directory. The mode,
owner and group parameters are optional. The default for mode is determined by
umask, the default owner is the user whose session is opened, the default group
is the primary group of the user.
iscript=path - path to the instance directory init script. The base directory
for relative paths is /etc/security/namespace.d.
noinit - instance directory init script will not be executed.
shared - the instance directories for "context" and "level" methods will not
contain the user name and will be shared among all users.
mntopts=value - value of this flag is passed to the mount call when the tmpfs
mount is done. It allows for example the specification of the maximum size of
the tmpfs instance that is created by the mount call. See mount(8) for details.
The directory where polyinstantiated instances are to be created, must exist
and must have, by default, the mode of 0000. The requirement that the instance
parent be of mode 0000 can be overridden with the command line option
ignore_instance_parent_mode
In case of context or level polyinstantiation the SELinux context which is used
for polyinstantiation is the context used for executing a new process as
obtained by getexeccon. This context must be set by the calling application or
pam_selinux.so module. If this context is not set the polyinstatiation will be
based just on user name.
The "instance differentiation string" is <user name> for "user" method and
<user name>_<raw directory context> for "context" and "level" methods. If the
whole string is too long the end of it is replaced with md5sum of itself. Also
when command line option gen_hash is used the whole string is replaced with
md5sum of itself.
6.22.3. OPTIONS
debug
A lot of debug information is logged using syslog
unmnt_remnt
For programs such as su and newrole, the login session has already setup a
polyinstantiated namespace. For these programs, polyinstantiation is
performed based on new user id or security context, however the command
first needs to undo the polyinstantiation performed by login. This argument
instructs the command to first undo previous polyinstantiation before
proceeding with new polyinstantiation based on new id/context
unmnt_only
For trusted programs that want to undo any existing bind mounts and process
instance directories on their own, this argument allows them to unmount
currently mounted instance directories
require_selinux
If selinux is not enabled, return failure
gen_hash
Instead of using the security context string for the instance name,
generate and use its md5 hash.
ignore_config_error
If a line in the configuration file corresponding to a polyinstantiated
directory contains format error, skip that line process the next line.
Without this option, pam will return an error to the calling program
resulting in termination of the session.
ignore_instance_parent_mode
Instance parent directories by default are expected to have the restrictive
mode of 000. Using this option, an administrator can choose to ignore the
mode of the instance parent. This option should be used with caution as it
will reduce security and isolation goals of the polyinstantiation
mechanism.
no_unmount_on_close
For certain trusted programs such as newrole, open session is called from a
child process while the parent performs close session and pam end
functions. For these commands use this option to instruct pam_close_session
to not unmount the bind mounted polyinstantiated directory in the parent.
use_current_context
Useful for services which do not change the SELinux context with setexeccon
call. The module will use the current SELinux context of the calling
process for the level and context polyinstantiation.
use_default_context
Useful for services which do not use pam_selinux for changing the SELinux
context with setexeccon call. The module will use the default SELinux
context of the user for the level and context polyinstantiation.
6.22.4. MODULE TYPES PROVIDED
Only the session module type is provided. The module must not be called from
multithreaded processes.
6.22.5. RETURN VALUES
PAM_SUCCESS
Namespace setup was successful.
PAM_SERVICE_ERR
Unexpected system error occurred while setting up namespace.
PAM_SESSION_ERR
Unexpected namespace configuration error occurred.
6.22.6. FILES
/etc/security/namespace.conf
Main configuration file
/etc/security/namespace.d
Directory for additional configuration files
/etc/security/namespace.init
Init script for instance directories
6.22.7. EXAMPLES
These are some example lines which might be specified in /etc/security/
namespace.conf.
# The following three lines will polyinstantiate /tmp,
# /var/tmp and user's home directories. /tmp and /var/tmp
# will be polyinstantiated based on the security level
# as well as user name, whereas home directory will be
# polyinstantiated based on the full security context and user name.
# Polyinstantiation will not be performed for user root
# and adm for directories /tmp and /var/tmp, whereas home
# directories will be polyinstantiated for all users.
#
# Note that instance directories do not have to reside inside
# the polyinstantiated directory. In the examples below,
# instances of /tmp will be created in /tmp-inst directory,
# where as instances of /var/tmp and users home directories
# will reside within the directories that are being
# polyinstantiated.
#
/tmp /tmp-inst/ level root,adm
/var/tmp /var/tmp/tmp-inst/ level root,adm
$HOME $HOME/$USER.inst/inst- context
For the <service>s you need polyinstantiation (login for example) put the
following line in /etc/pam.d/<service> as the last line for session group:
session required pam_namespace.so [arguments]
This module also depends on pam_selinux.so setting the context.
6.22.8. AUTHORS
The namespace setup scheme was designed by Stephen Smalley, Janak Desai and
Chad Sellers. The pam_namespace PAM module was developed by Janak Desai
<janak@us.ibm.com>, Chad Sellers <csellers@tresys.com> and Steve Grubb
<sgrubb@redhat.com>. Additional improvements by Xavier Toth <txtoth@gmail.com>
and Tomas Mraz <tmraz@redhat.com>.
6.23. pam_nologin - prevent non-root users from login
pam_nologin.so [ file=/path/nologin ] [ successok ]
6.23.1. DESCRIPTION
pam_nologin is a PAM module that prevents users from logging into the system
when /etc/nologin exists. The contents of the /etc/nologin file are displayed
to the user. The pam_nologin module has no effect on the root user's ability to
log in.
6.23.2. OPTIONS
file=/path/nologin
Use this file instead the default /etc/nologin.
successok
Return PAM_SUCCESS if no file exists, the default is PAM_IGNORE.
6.23.3. MODULE TYPES PROVIDED
The auth and acct module types are provided.
6.23.4. RETURN VALUES
PAM_AUTH_ERR
The user is not root and /etc/nologin exists, so the user is not permitted
to log in.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
This is the default return value.
PAM_SUCCESS
Success: either the user is root or the /etc/nologin file does not exist.
PAM_USER_UNKNOWN
User not known to the underlying authentication module.
6.23.5. EXAMPLES
The suggested usage for /etc/pam.d/login is:
auth required pam_nologin.so
6.23.6. AUTHOR
pam_nologin was written by Michael K. Johnson <johnsonm@redhat.com>.
6.24. pam_permit - the promiscuous module
pam_permit.so
6.24.1. DESCRIPTION
pam_permit is a PAM module that always permit access. It does nothing else.
In the case of authentication, the user's name will be set to nobody if the
application didn't set one. Many applications and PAM modules become confused
if this name is unknown.
This module is very dangerous. It should be used with extreme caution.
6.24.2. OPTIONS
This module does not recognise any options.
6.24.3. MODULE TYPES PROVIDED
The auth, account, password and session module types are provided.
6.24.4. RETURN VALUES
PAM_SUCCESS
This module always returns this value.
6.24.5. EXAMPLES
Add this line to your other login entries to disable account management, but
continue to permit users to log in.
account required pam_permit.so
6.24.6. AUTHOR
pam_permit was written by Andrew G. Morgan, <morgan@kernel.org>.
6.25. pam_pwhistory - grant access using .pwhistory file
pam_pwhistory.so [ debug ] [ use_authtok ] [ enforce_for_root ] [ remember=N ]
[ retry=N ] [ authtok_type=STRING ]
6.25.1. DESCRIPTION
This module saves the last passwords for each user in order to force password
change history and keep the user from alternating between the same password too
frequently.
This module does not work together with kerberos. In general, it does not make
much sense to use this module in conjunction with NIS or LDAP, since the old
passwords are stored on the local machine and are not available on another
machine for password history checking.
6.25.2. OPTIONS
debug
Turns on debugging via syslog(3).
use_authtok
When password changing enforce the module to use the new password provided
by a previously stacked password module (this is used in the example of the
stacking of the pam_cracklib module documented below).
enforce_for_root
If this option is set, the check is enforced for root, too.
remember=N
The last N passwords for each user are saved in /etc/security/opasswd. The
default is 10.
retry=N
Prompt user at most N times before returning with error. The default is 1.
authtok_type=STRING
See pam_get_authtok(3) for more details.
6.25.3. MODULE TYPES PROVIDED
Only the password module type is provided.
6.25.4. RETURN VALUES
PAM_AUTHTOK_ERR
No new password was entered, the user aborted password change or new
password couldn't be set.
PAM_IGNORE
Password history was disabled.
PAM_MAXTRIES
Password was rejected too often.
PAM_USER_UNKNOWN
User is not known to system.
6.25.5. FILES
/etc/security/opasswd
File with password history
6.25.6. EXAMPLES
An example password section would be:
#%PAM-1.0
password required pam_pwhistory.so
password required pam_unix.so use_authtok
In combination with pam_cracklib:
#%PAM-1.0
password required pam_cracklib.so retry=3
password required pam_pwhistory.so use_authtok
password required pam_unix.so use_authtok
6.25.7. AUTHOR
pam_pwhistory was written by Thorsten Kukuk <kukuk@thkukuk.de>
6.26. pam_rhosts - grant access using .rhosts file
pam_rhosts.so
6.26.1. DESCRIPTION
This module performs the standard network authentication for services, as used
by traditional implementations of rlogin and rsh etc.
The authentication mechanism of this module is based on the contents of two
files; /etc/hosts.equiv (or and ~/.rhosts. Firstly, hosts listed in the former
file are treated as equivalent to the localhost. Secondly, entries in the
user's own copy of the latter file is used to map "remote-host remote-user"
pairs to that user's account on the current host. Access is granted to the user
if their host is present in /etc/hosts.equiv and their remote account is
identical to their local one, or if their remote account has an entry in their
personal configuration file.
The module authenticates a remote user (internally specified by the item
PAM_RUSER connecting from the remote host (internally specified by the item
PAM_RHOST). Accordingly, for applications to be compatible this authentication
module they must set these items prior to calling pam_authenticate(). The
module is not capable of independently probing the network connection for such
information.
6.26.2. OPTIONS
debug
Print debug information.
silent
Don't print informative messages.
superuser=account
Handle account as root.
6.26.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.26.4. RETURN VALUES
PAM_AUTH_ERR
The remote host, remote user name or the local user name couldn't be
determined or access was denied by .rhosts file.
PAM_USER_UNKNOWN
User is not known to system.
6.26.5. EXAMPLES
To grant a remote user access by /etc/hosts.equiv or .rhosts for rsh add the
following lines to /etc/pam.d/rsh:
#%PAM-1.0
#
auth required pam_rhosts.so
auth required pam_nologin.so
auth required pam_env.so
auth required pam_unix.so
6.26.6. AUTHOR
pam_rhosts was written by Thorsten Kukuk <kukuk@thkukuk.de>
6.27. pam_rootok - gain only root access
pam_rootok.so [ debug ]
6.27.1. DESCRIPTION
pam_rootok is a PAM module that authenticates the user if their UID is 0.
Applications that are created setuid-root generally retain the UID of the user
but run with the authority of an enhanced effective-UID. It is the real UID
that is checked.
6.27.2. OPTIONS
debug
Print debug information.
6.27.3. MODULE TYPES PROVIDED
Only the auth type is provided.
6.27.4. RETURN VALUES
PAM_SUCCESS
The UID is 0.
PAM_AUTH_ERR
The UID is not 0.
6.27.5. EXAMPLES
In the case of the su(1) application the historical usage is to permit the
superuser to adopt the identity of a lesser user without the use of a password.
To obtain this behavior with PAM the following pair of lines are needed for the
corresponding entry in the /etc/pam.d/su configuration file:
# su authentication. Root is granted access by default.
auth sufficient pam_rootok.so
auth required pam_unix.so
6.27.6. AUTHOR
pam_rootok was written by Andrew G. Morgan, <morgan@kernel.org>.
6.28. pam_securetty - limit root login to special devices
pam_securetty.so [ debug ]
6.28.1. DESCRIPTION
pam_securetty is a PAM module that allows root logins only if the user is
logging in on a "secure" tty, as defined by the listing in /etc/securetty.
pam_securetty also checks to make sure that /etc/securetty is a plain file and
not world writable.
This module has no effect on non-root users and requires that the application
fills in the PAM_TTY item correctly.
For canonical usage, should be listed as a required authentication method
before any sufficient authentication methods.
6.28.2. OPTIONS
debug
Print debug information.
6.28.3. MODULE TYPES PROVIDED
Only the auth module type is provided.
6.28.4. RETURN VALUES
PAM_SUCCESS
The user is allowed to continue authentication. Either the user is not
root, or the root user is trying to log in on an acceptable device.
PAM_AUTH_ERR
Authentication is rejected. Either root is attempting to log in via an
unacceptable device, or the /etc/securetty file is world writable or not a
normal file.
PAM_INCOMPLETE
An application error occurred. pam_securetty was not able to get
information it required from the application that called it.
PAM_SERVICE_ERR
An error occurred while the module was determining the user's name or tty,
or the module could not open /etc/securetty.
PAM_USER_UNKNOWN
The module could not find the user name in the /etc/passwd file to verify
whether the user had a UID of 0. Therefore, the results of running this
module are ignored.
6.28.5. EXAMPLES
auth required pam_securetty.so
auth required pam_unix.so
6.28.6. AUTHOR
pam_securetty was written by Elliot Lee <sopwith@cuc.edu>.
6.29. pam_selinux - set the default security context
pam_selinux.so [ close ] [ debug ] [ open ] [ nottys ] [ verbose ] [
select_context ] [ env_params ] [ use_current_range ]
6.29.1. DESCRIPTION
In a nutshell, pam_selinux sets up the default security context for the next
execed shell.
When an application opens a session using pam_selinux, the shell that gets
executed will be run in the default security context, or if the user chooses
and the pam file allows the selected security context. Also the controlling tty
will have it's security context modified to match the users.
Adding pam_selinux into a pam file could cause other pam modules to change
their behavior if the exec another application. The close and open option help
mitigate this problem. close option will only cause the close portion of the
pam_selinux to execute, and open will only cause the open portion to run. You
can add pam_selinux to the config file twice. Add the pam_selinux close as the
executes the open pass through the modules, pam_selinux open_session will
happen last. When PAM executes the close pass through the modules pam_selinux
close_session will happen first.
6.29.2. OPTIONS
close
Only execute the close_session portion of the module.
debug
Turns on debugging via syslog(3).
open
Only execute the open_session portion of the module.
nottys
Do not try to setup the ttys security context.
verbose
attempt to inform the user when security context is set.
select_context
Attempt to ask the user for a custom security context role. If MLS is on
ask also for sensitivity level.
env_params
Attempt to obtain a custom security context role from PAM environment. If
MLS is on obtain also sensitivity level. This option and the select_context
option are mutually exclusive. The respective PAM environment variables are
SELINUX_ROLE_REQUESTED, SELINUX_LEVEL_REQUESTED, and
SELINUX_USE_CURRENT_RANGE. The first two variables are self describing and
the last one if set to 1 makes the PAM module behave as if the
use_current_range was specified on the command line of the module.
use_current_range
Use the sensitivity level of the current process for the user context
instead of the default level. Also suppresses asking of the sensitivity
level from the user or obtaining it from PAM environment.
6.29.3. MODULE TYPES PROVIDED
Only the session module type is provided.
6.29.4. RETURN VALUES
PAM_AUTH_ERR
Unable to get or set a valid context.
PAM_SUCCESS
The security context was set successfully.
PAM_USER_UNKNOWN
The user is not known to the system.
6.29.5. EXAMPLES
auth required pam_unix.so
session required pam_permit.so
session optional pam_selinux.so
6.29.6. AUTHOR
pam_selinux was written by Dan Walsh <dwalsh@redhat.com>.
6.30. pam_shells - check for valid login shell
pam_shells.so
6.30.1. DESCRIPTION
pam_shells is a PAM module that only allows access to the system if the users
shell is listed in /etc/shells.
It also checks if /etc/shells is a plain file and not world writable.
6.30.2. OPTIONS
This module does not recognise any options.
6.30.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.30.4. RETURN VALUES
PAM_AUTH_ERR
Access to the system was denied.
PAM_SUCCESS
The users login shell was listed as valid shell in /etc/shells.
PAM_SERVICE_ERR
The module was not able to get the name of the user.
6.30.5. EXAMPLES
auth required pam_shells.so
6.30.6. AUTHOR
pam_shells was written by Erik Troan <ewt@redhat.com>.
6.31. pam_succeed_if - test account characteristics
pam_succeed_if.so [flag...] [condition...]
6.31.1. DESCRIPTION
pam_succeed_if.so is designed to succeed or fail authentication based on
characteristics of the account belonging to the user being authenticated. One
use is to select whether to load other modules based on this test.
The module should be given one or more conditions as module arguments, and
authentication will succeed only if all of the conditions are met.
6.31.2. OPTIONS
The following flags are supported:
debug
Turns on debugging messages sent to syslog.
use_uid
Evaluate conditions using the account of the user whose UID the application
is running under instead of the user being authenticated.
quiet
Don't log failure or success to the system log.
quiet_fail
Don't log failure to the system log.
quiet_success
Don't log success to the system log.
Conditions are three words: a field, a test, and a value to test for.
Available fields are user, uid, gid, shell, home and service:
field < number
Field has a value numerically less than number.
field <= number
Field has a value numerically less than or equal to number.
field eq number
Field has a value numerically equal to number.
field >= number
Field has a value numerically greater than or equal to number.
field > number
Field has a value numerically greater than number.
field ne number
Field has a value numerically different from number.
field = string
Field exactly matches the given string.
field != string
Field does not match the given string.
field =~ glob
Field matches the given glob.
field !~ glob
Field does not match the given glob.
field in item:item:...
Field is contained in the list of items separated by colons.
field notin item:item:...
Field is not contained in the list of items separated by colons.
user ingroup group
User is in given group.
user notingroup group
User is not in given group.
user innetgr netgroup
(user,host) is in given netgroup.
user notinnetgr group
(user,host) is not in given netgroup.
6.31.3. MODULE TYPES PROVIDED
All module types (account, auth, password and session) are provided.
6.31.4. RETURN VALUES
PAM_SUCCESS
The condition was true.
PAM_AUTH_ERR
The condition was false.
PAM_SERVICE_ERR
A service error occurred or the arguments can't be parsed correctly.
6.31.5. EXAMPLES
To emulate the behaviour of pam_wheel, except there is no fallback to group 0:
auth required pam_succeed_if.so quiet user ingroup wheel
Given that the type matches, only loads the othermodule rule if the UID is over
500. Adjust the number after default to skip several rules.
type [default=1 success=ignore] pam_succeed_if.so quiet uid > 500
type required othermodule.so arguments...
6.31.6. AUTHOR
Nalin Dahyabhai <nalin@redhat.com>
6.32. pam_tally - login counter (tallying) module
pam_tally.so [ file=/path/to/counter ] [ onerr=[fail|succeed] ] [ magic_root ]
[ even_deny_root_account ] [ deny=n ] [ lock_time=n ] [ unlock_time=n ] [
per_user ] [ no_lock_time ] [ no_reset ] [ audit ] [ silent ] [ no_log_info ]
pam_tally [ --file /path/to/counter ] [ --user username ] [ --reset[=n] ] [
--quiet ]
6.32.1. DESCRIPTION
This module maintains a count of attempted accesses, can reset count on
success, can deny access if too many attempts fail.
pam_tally comes in two parts: pam_tally.so and pam_tally. The former is the PAM
module and the latter, a stand-alone program. pam_tally is an (optional)
application which can be used to interrogate and manipulate the counter file.
It can display users' counts, set individual counts, or clear all counts.
Setting artificially high counts may be useful for blocking users without
changing their passwords. For example, one might find it useful to clear all
counts every midnight from a cron job. The faillog(8) command can be used
instead of pam_tally to to maintain the counter file.
Normally, failed attempts to access root will not cause the root account to
become blocked, to prevent denial-of-service: if your users aren't given shell
accounts and root may only login via su or at the machine console (not telnet/
rsh, etc), this is safe.
6.32.2. OPTIONS
GLOBAL OPTIONS
This can be used for auth and account module types.
onerr=[fail|succeed]
If something weird happens (like unable to open the file), return with
PAM_SUCCESS if onerr=succeed is given, else with the corresponding PAM
error code.
file=/path/to/counter
File where to keep counts. Default is /var/log/faillog.
audit
Will log the user name into the system log if the user is not found.
silent
Don't print informative messages.
no_log_info
Don't log informative messages via syslog(3).
AUTH OPTIONS
Authentication phase first checks if user should be denied access and if
not it increments attempted login counter. Then on call to pam_setcred(3)
it resets the attempts counter.
deny=n
Deny access if tally for this user exceeds n.
lock_time=n
Always deny for n seconds after failed attempt.
unlock_time=n
Allow access after n seconds after failed attempt. If this option is
used the user will be locked out for the specified amount of time after
he exceeded his maximum allowed attempts. Otherwise the account is
locked until the lock is removed by a manual intervention of the system
administrator.
magic_root
If the module is invoked by a user with uid=0 the counter is not
incremented. The sysadmin should use this for user launched services,
like su, otherwise this argument should be omitted.
no_lock_time
Do not use the .fail_locktime field in /var/log/faillog for this user.
no_reset
Don't reset count on successful entry, only decrement.
even_deny_root_account
Root account can become unavailable.
per_user
If /var/log/faillog contains a non-zero .fail_max/.fail_locktime field
for this user then use it instead of deny=n/ lock_time=n parameter.
no_lock_time
Don't use .fail_locktime filed in /var/log/faillog for this user.
ACCOUNT OPTIONS
Account phase resets attempts counter if the user is not magic root. This
phase can be used optionally for services which don't call pam_setcred(3)
correctly or if the reset should be done regardless of the failure of the
account phase of other modules.
magic_root
If the module is invoked by a user with uid=0 the counter is not
incremented. The sysadmin should use this for user launched services,
like su, otherwise this argument should be omitted.
no_reset
Don't reset count on successful entry, only decrement.
6.32.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.32.4. RETURN VALUES
PAM_AUTH_ERR
A invalid option was given, the module was not able to retrieve the user
name, no valid counter file was found, or too many failed logins.
PAM_SUCCESS
Everything was successful.
PAM_USER_UNKNOWN
User not known.
6.32.5. EXAMPLES
Add the following line to /etc/pam.d/login to lock the account after too many
failed logins. The number of allowed fails is specified by /var/log/faillog and
needs to be set with pam_tally or faillog(8) before.
auth required pam_securetty.so
auth required pam_tally.so per_user
auth required pam_env.so
auth required pam_unix.so
auth required pam_nologin.so
account required pam_unix.so
password required pam_unix.so
session required pam_limits.so
session required pam_unix.so
session required pam_lastlog.so nowtmp
session optional pam_mail.so standard
6.32.6. AUTHOR
pam_tally was written by Tim Baverstock and Tomas Mraz.
6.33. pam_tally2 - login counter (tallying) module
pam_tally2.so [ file=/path/to/counter ] [ onerr=[fail|succeed] ] [ magic_root ]
[ even_deny_root ] [ deny=n ] [ lock_time=n ] [ unlock_time=n ] [
root_unlock_time=n ] [ serialize ] [ audit ] [ silent ] [ no_log_info ] [ debug
]
pam_tally2 [ --file /path/to/counter ] [ --user username ] [ --reset[=n] ] [
--quiet ]
6.33.1. DESCRIPTION
This module maintains a count of attempted accesses, can reset count on
success, can deny access if too many attempts fail.
pam_tally2 comes in two parts: pam_tally2.so and pam_tally2. The former is the
PAM module and the latter, a stand-alone program. pam_tally2 is an (optional)
application which can be used to interrogate and manipulate the counter file.
It can display users' counts, set individual counts, or clear all counts.
Setting artificially high counts may be useful for blocking users without
changing their passwords. For example, one might find it useful to clear all
counts every midnight from a cron job.
Normally, failed attempts to access root will not cause the root account to
become blocked, to prevent denial-of-service: if your users aren't given shell
accounts and root may only login via su or at the machine console (not telnet/
rsh, etc), this is safe.
6.33.2. OPTIONS
GLOBAL OPTIONS
This can be used for auth and account module types.
onerr=[fail|succeed]
If something weird happens (like unable to open the file), return with
PAM_SUCCESS if onerr=succeed is given, else with the corresponding PAM
error code.
file=/path/to/counter
File where to keep counts. Default is /var/log/tallylog.
audit
Will log the user name into the system log if the user is not found.
silent
Don't print informative messages.
no_log_info
Don't log informative messages via syslog(3).
debug
Always log tally count when it is incremented as a debug level message
to the system log.
AUTH OPTIONS
Authentication phase first increments attempted login counter and checks if
user should be denied access. If the user is authenticated and the login
process continues on call to pam_setcred(3) it resets the attempts counter.
deny=n
Deny access if tally for this user exceeds n.
lock_time=n
Always deny for n seconds after failed attempt.
unlock_time=n
Allow access after n seconds after failed attempt. If this option is
used the user will be locked out for the specified amount of time after
he exceeded his maximum allowed attempts. Otherwise the account is
locked until the lock is removed by a manual intervention of the system
administrator.
magic_root
If the module is invoked by a user with uid=0 the counter is not
incremented. The sysadmin should use this for user launched services,
like su, otherwise this argument should be omitted.
no_lock_time
Do not use the .fail_locktime field in /var/log/faillog for this user.
even_deny_root
Root account can become unavailable.
root_unlock_time=n
This option implies even_deny_root option. Allow access after n seconds
to root account after failed attempt. If this option is used the root
user will be locked out for the specified amount of time after he
exceeded his maximum allowed attempts.
serialize
Serialize access to the tally file using locks. This option might be
used only for non-multithreaded services because it depends on the
fcntl locking of the tally file. Also it is a good idea to use this
option only in such configurations where the time between auth phase
and account or setcred phase is not dependent on the authenticating
client. Otherwise the authenticating client will be able to prevent
simultaneous authentications by the same user by simply artificially
prolonging the time the file record lock is held.
ACCOUNT OPTIONS
Account phase resets attempts counter if the user is not magic root. This
phase can be used optionally for services which don't call pam_setcred(3)
correctly or if the reset should be done regardless of the failure of the
account phase of other modules.
magic_root
If the module is invoked by a user with uid=0 the counter is not
changed. The sysadmin should use this for user launched services, like
su, otherwise this argument should be omitted.
6.33.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.33.4. RETURN VALUES
PAM_AUTH_ERR
A invalid option was given, the module was not able to retrieve the user
name, no valid counter file was found, or too many failed logins.
PAM_SUCCESS
Everything was successful.
PAM_USER_UNKNOWN
User not known.
6.33.5. NOTES
pam_tally2 is not compatible with the old pam_tally faillog file format. This
is caused by requirement of compatibility of the tallylog file format between
32bit and 64bit architectures on multiarch systems.
There is no setuid wrapper for access to the data file such as when the
pam_tally2.so module is called from xscreensaver. As this would make it
impossible to share PAM configuration with such services the following
workaround is used: If the data file cannot be opened because of insufficient
permissions (EACCES) the module returns PAM_IGNORE.
6.33.6. EXAMPLES
Add the following line to /etc/pam.d/login to lock the account after 4 failed
logins. Root account will be locked as well. The accounts will be automatically
unlocked after 20 minutes. The module does not have to be called in the account
phase because the login calls pam_setcred(3) correctly.
auth required pam_securetty.so
auth required pam_tally2.so deny=4 even_deny_root unlock_time=1200
auth required pam_env.so
auth required pam_unix.so
auth required pam_nologin.so
account required pam_unix.so
password required pam_unix.so
session required pam_limits.so
session required pam_unix.so
session required pam_lastlog.so nowtmp
session optional pam_mail.so standard
6.33.7. FILES
/var/log/tallylog
failure count logging file
6.33.8. AUTHOR
pam_tally2 was written by Tim Baverstock and Tomas Mraz.
6.34. pam_time - time controled access
pam_time.so [ debug ] [ noaudit ]
6.34.1. DESCRIPTION
The pam_time PAM module does not authenticate the user, but instead it
restricts access to a system and or specific applications at various times of
the day and on specific days or over various terminal lines. This module can be
configured to deny access to (individual) users based on their name, the time
of day, the day of week, the service they are applying for and their terminal
from which they are making their request.
By default rules for time/port access are taken from config file /etc/security/
time.conf.
If Linux PAM is compiled with audit support the module will report when it
denies access.
6.34.2. DESCRIPTION
The pam_time PAM module does not authenticate the user, but instead it
restricts access to a system and or specific applications at various times of
the day and on specific days or over various terminal lines. This module can be
configured to deny access to (individual) users based on their name, the time
of day, the day of week, the service they are applying for and their terminal
from which they are making their request.
For this module to function correctly there must be a correctly formatted /etc/
security/time.conf file present. White spaces are ignored and lines maybe
extended with '\' (escaped newlines). Text following a '#' is ignored to the
end of the line.
The syntax of the lines is as follows:
services;ttys;users;times
In words, each rule occupies a line, terminated with a newline or the beginning
of a comment; a '#'. It contains four fields separated with semicolons, ';'.
The first field, the services field, is a logic list of PAM service names that
the rule applies to.
The second field, the tty field, is a logic list of terminal names that this
rule applies to.
The third field, the users field, is a logic list of users or a netgroup of
users to whom this rule applies.
For these items the simple wildcard '*' may be used only once. With netgroups
no wildcards or logic operators are allowed.
The times field is used to indicate the times at which this rule applies. The
format here is a logic list of day/time-range entries. The days are specified
by a sequence of two character entries, MoTuSa for example is Monday Tuesday
and Saturday. Note that repeated days are unset MoMo = no day, and MoWk = all
weekdays bar Monday. The two character combinations accepted are Mo Tu We Th Fr
Sa Su Wk Wd Al, the last two being week-end days and all 7 days of the week
respectively. As a final example, AlFr means all days except Friday.
Each day/time-range can be prefixed with a '!' to indicate "anything but". The
time-range part is two 24-hour times HHMM, separated by a hyphen, indicating
the start and finish time (if the finish time is smaller than the start time it
is deemed to apply on the following day).
For a rule to be active, ALL of service+ttys+users must be satisfied by the
applying process.
Note, currently there is no daemon enforcing the end of a session. This needs
to be remedied.
Poorly formatted rules are logged as errors using syslog(3).
6.34.3. OPTIONS
debug
Some debug information is printed with syslog(3).
noaudit
Do not report logins at disallowed time to the audit subsystem.
6.34.4. MODULE TYPES PROVIDED
Only the account type is provided.
6.34.5. RETURN VALUES
PAM_SUCCESS
Access was granted.
PAM_ABORT
Not all relevant data could be gotten.
PAM_BUF_ERR
Memory buffer error.
PAM_PERM_DENIED
Access was not granted.
PAM_USER_UNKNOWN
The user is not known to the system.
6.34.6. FILES
/etc/security/time.conf
Default configuration file
6.34.7. EXAMPLES
These are some example lines which might be specified in /etc/security/
time.conf.
All users except for root are denied access to console-login at all times:
login ; tty* & !ttyp* ; !root ; !Al0000-2400
Games (configured to use PAM) are only to be accessed out of working hours.
This rule does not apply to the user waster:
games ; * ; !waster ; Wd0000-2400 | Wk1800-0800
6.34.8. AUTHOR
pam_time was written by Andrew G. Morgan <morgan@kernel.org>.
6.35. pam_timestamp - authenticate using cached successful authentication
attempts
pam_timestamp.so [ timestamp_timeout=number ] [ verbose ] [ debug ]
6.35.1. DESCRIPTION
In a nutshell, pam_timestamp caches successful authentication attempts, and
allows you to use a recent successful attempt as the basis for authentication.
This is similar mechanism which is used in sudo.
When an application opens a session using pam_timestamp, a timestamp file is
created in the timestampdir directory for the user. When an application
attempts to authenticate the user, a pam_timestamp will treat a sufficiently
recent timestamp file as grounds for succeeding.
6.35.2. OPTIONS
timestamp_timeout=number
How long should pam_timestamp treat timestamp as valid after their last
modification date (in seconds). Default is 300 seconds.
verbose
Attempt to inform the user when access is granted.
debug
Turns on debugging messages sent to syslog(3).
6.35.3. MODULE TYPES PROVIDED
The auth and session module types are provided.
6.35.4. RETURN VALUES
PAM_AUTH_ERR
The module was not able to retrieve the user name or no valid timestamp
file was found.
PAM_SUCCESS
Everything was successful.
PAM_SESSION_ERR
Timestamp file could not be created or updated.
6.35.5. NOTES
Users can get confused when they are not always asked for passwords when
running a given program. Some users reflexively begin typing information before
noticing that it is not being asked for.
6.35.6. EXAMPLES
auth sufficient pam_timestamp.so verbose
auth required pam_unix.so
session required pam_unix.so
session optional pam_timestamp.so
6.35.7. FILES
/var/run/sudo/...
timestamp files and directories
6.35.8. AUTHOR
pam_tally was written by Nalin Dahyabhai.
6.36. pam_umask - set the file mode creation mask
pam_umask.so [ debug ] [ silent ] [ usergroups ] [ umask=mask ]
6.36.1. DESCRIPTION
pam_umask is a PAM module to set the file mode creation mask of the current
environment. The umask affects the default permissions assigned to newly
created files.
The PAM module tries to get the umask value from the following places in the
following order:
* umask= argument
* umask= entry of the users GECOS field
* pri= entry of the users GECOS field
* ulimit= entry of the users GECOS field
* UMASK= entry from /etc/default/login
* UMASK entry from /etc/login.defs
6.36.2. OPTIONS
debug
Print debug information.
silent
Don't print informative messages.
usergroups
If the user is not root, and the user ID is equal to the group ID, and the
username is the same as primary group name, the umask group bits are set to
be the same as owner bits (examples: 022 -> 002, 077 -> 007).
umask=mask
Sets the calling process's file mode creation mask (umask) to mask & 0777.
The value is interpreted as Octal.
6.36.3. MODULE TYPES PROVIDED
Only the session type is provided.
6.36.4. RETURN VALUES
PAM_SUCCESS
The new umask was set successfully.
PAM_SERVICE_ERR
No username was given.
PAM_USER_UNKNOWN
User not known.
6.36.5. EXAMPLES
Add the following line to /etc/pam.d/login to set the user specific umask at
login:
session optional pam_umask.so umask=0022
6.36.6. AUTHOR
pam_umask was written by Thorsten Kukuk <kukuk@thkukuk.de>.
6.37. pam_unix - traditional password authentication
pam_unix.so [ ... ]
6.37.1. DESCRIPTION
This is the standard Unix authentication module. It uses standard calls from
the system's libraries to retrieve and set account information as well as
authentication. Usually this is obtained from the /etc/passwd and the /etc/
shadow file as well if shadow is enabled.
The account component performs the task of establishing the status of the
user's account and password based on the following shadow elements: expire,
last_change, max_change, min_change, warn_change. In the case of the latter, it
may offer advice to the user on changing their password or, through the
PAM_AUTHTOKEN_REQD return, delay giving service to the user until they have
established a new password. The entries listed above are documented in the
shadow(5) manual page. Should the user's record not contain one or more of
these entries, the corresponding shadow check is not performed.
The authentication component performs the task of checking the users
credentials (password). The default action of this module is to not permit the
user access to a service if their official password is blank.
A helper binary, unix_chkpwd(8), is provided to check the user's password when
it is stored in a read protected database. This binary is very simple and will
only check the password of the user invoking it. It is called transparently on
behalf of the user by the authenticating component of this module. In this way
it is possible for applications like xlock(1) to work without being
setuid-root. The module, by default, will temporarily turn off SIGCHLD handling
for the duration of execution of the helper binary. This is generally the right
thing to do, as many applications are not prepared to handle this signal from a
child they didn't know was fork()d. The noreap module argument can be used to
suppress this temporary shielding and may be needed for use with certain
applications.
The maximum length of a password supported by the pam_unix module via the
helper binary is PAM_MAX_RESP_SIZE - currently 512 bytes. The rest of the
password provided by the conversation function to the module will be ignored.
The password component of this module performs the task of updating the user's
password.
The session component of this module logs when a user logins or leave the
system.
Remaining arguments, supported by others functions of this module, are silently
ignored. Other arguments are logged as errors through syslog(3).
6.37.2. OPTIONS
debug
Turns on debugging via syslog(3).
audit
A little more extreme than debug.
nullok
The default action of this module is to not permit the user access to a
service if their official password is blank. The nullok argument overrides
this default.
try_first_pass
Before prompting the user for their password, the module first tries the
previous stacked module's password in case that satisfies this module as
well.
use_first_pass
The argument use_first_pass forces the module to use a previous stacked
modules password and will never prompt the user - if no password is
available or the password is not appropriate, the user will be denied
access.
nodelay
This argument can be used to discourage the authentication component from
requesting a delay should the authentication as a whole fail. The default
action is for the module to request a delay-on-failure of the order of two
second.
use_authtok
When password changing enforce the module to set the new password to the
one provided by a previously stacked password module (this is used in the
example of the stacking of the pam_cracklib module documented below).
not_set_pass
This argument is used to inform the module that it is not to pay attention
to/make available the old or new passwords from/to other (stacked) password
modules.
nis
NIS RPC is used for setting new passwords.
remember=n
The last n passwords for each user are saved in /etc/security/opasswd in
order to force password change history and keep the user from alternating
between the same password too frequently.
shadow
Try to maintain a shadow based system.
md5
When a user changes their password next, encrypt it with the MD5 algorithm.
bigcrypt
When a user changes their password next, encrypt it with the DEC C2
algorithm.
sha256
When a user changes their password next, encrypt it with the SHA256
algorithm. If the SHA256 algorithm is not known to the crypt(3) function,
fall back to MD5.
sha512
When a user changes their password next, encrypt it with the SHA512
algorithm. If the SHA512 algorithm is not known to the crypt(3) function,
fall back to MD5.
blowfish
When a user changes their password next, encrypt it with the blowfish
algorithm. If the blowfish algorithm is not known to the crypt(3) function,
fall back to MD5.
rounds=n
Set the optional number of rounds of the SHA256, SHA512 and blowfish
password hashing algorithms to n.
broken_shadow
Ignore errors reading shadow information for users in the account
management module.
no_pass_expiry
When set ignore password expiration as defined by the shadow entry of the
user. The option has an effect only in case pam_unix was not used for the
authentication or it returned authentication failure meaning that other
authentication source or method succeeded. The example can be public key
authentication in sshd. The module will return PAM_SUCCESS instead of
eventual PAM_NEW_AUTHTOK_REQD or PAM_AUTHTOK_EXPIRED.
Invalid arguments are logged with syslog(3).
6.37.3. MODULE TYPES PROVIDED
All module types (account, auth, password and session) are provided.
6.37.4. RETURN VALUES
PAM_IGNORE
Ignore this module.
6.37.5. EXAMPLES
An example usage for /etc/pam.d/login would be:
# Authenticate the user
auth required pam_unix.so
# Ensure users account and password are still active
account required pam_unix.so
# Change the users password, but at first check the strength
# with pam_cracklib(8)
password required pam_cracklib.so retry=3 minlen=6 difok=3
password required pam_unix.so use_authtok nullok md5
session required pam_unix.so
6.37.6. AUTHOR
pam_unix was written by various people.
6.38. pam_userdb - authenticate against a db database
pam_userdb.so db=/path/database [ debug ] [ crypt=[crypt|none] ] [ icase ] [
dump ] [ try_first_pass ] [ use_first_pass ] [ unknown_ok ] [ key_only ]
6.38.1. DESCRIPTION
The pam_userdb module is used to verify a username/password pair against values
stored in a Berkeley DB database. The database is indexed by the username, and
the data fields corresponding to the username keys are the passwords.
6.38.2. OPTIONS
crypt=[crypt|none]
Indicates whether encrypted or plaintext passwords are stored in the
database. If it is crypt, passwords should be stored in the database in
crypt(3) form. If none is selected, passwords should be stored in the
database as plaintext.
db=/path/database
Use the /path/database database for performing lookup. There is no default;
the module will return PAM_IGNORE if no database is provided. Note that the
path to the database file should be specified without the .db suffix.
debug
Print debug information.
dump
Dump all the entries in the database to the log. Don't do this by default!
icase
Make the password verification to be case insensitive (ie when working with
registration numbers and such). Only works with plaintext password storage.
try_first_pass
Use the authentication token previously obtained by another module that did
the conversation with the application. If this token can not be obtained
then the module will try to converse. This option can be used for stacking
different modules that need to deal with the authentication tokens.
use_first_pass
Use the authentication token previously obtained by another module that did
the conversation with the application. If this token can not be obtained
then the module will fail. This option can be used for stacking different
modules that need to deal with the authentication tokens.
unknown_ok
Do not return error when checking for a user that is not in the database.
This can be used to stack more than one pam_userdb module that will check a
username/password pair in more than a database.
key_only
The username and password are concatenated together in the database hash as
'username-password' with a random value. if the concatenation of the
username and password with a dash in the middle returns any result, the
user is valid. this is useful in cases where the username may not be unique
but the username and password pair are.
6.38.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.38.4. RETURN VALUES
PAM_AUTH_ERR
Authentication failure.
PAM_AUTHTOK_RECOVERY_ERR
Authentication information cannot be recovered.
PAM_BUF_ERR
Memory buffer error.
PAM_CONV_ERR
Conversation failure.
PAM_SERVICE_ERR
Error in service module.
PAM_SUCCESS
Success.
PAM_USER_UNKNOWN
User not known to the underlying authentication module.
6.38.5. EXAMPLES
auth sufficient pam_userdb.so icase db=/etc/dbtest
6.38.6. AUTHOR
pam_userdb was written by Cristian Gafton >gafton@redhat.com<.
6.39. pam_warn - logs all PAM items
pam_warn.so
6.39.1. DESCRIPTION
pam_warn is a PAM module that logs the service, terminal, user, remote user and
remote host to syslog(3). The items are not probed for, but instead obtained
from the standard PAM items. The module always returns PAM_IGNORE, indicating
that it does not want to affect the authentication process.
6.39.2. OPTIONS
This module does not recognise any options.
6.39.3. MODULE TYPES PROVIDED
The auth, account, password and session module types are provided.
6.39.4. RETURN VALUES
PAM_IGNORE
This module always returns PAM_IGNORE.
6.39.5. EXAMPLES
#%PAM-1.0
#
# If we don't have config entries for a service, the
# OTHER entries are used. To be secure, warn and deny
# access to everything.
other auth required pam_warn.so
other auth required pam_deny.so
other account required pam_warn.so
other account required pam_deny.so
other password required pam_warn.so
other password required pam_deny.so
other session required pam_warn.so
other session required pam_deny.so
6.39.6. AUTHOR
pam_warn was written by Andrew G. Morgan <morgan@kernel.org>.
6.40. pam_wheel - only permit root access to members of group wheel
pam_wheel.so [ debug ] [ deny ] [ group=name ] [ root_only ] [ trust ] [
use_uid ]
6.40.1. DESCRIPTION
The pam_wheel PAM module is used to enforce the so-called wheel group. By
default it permits root access to the system if the applicant user is a member
of the wheel group. If no group with this name exist, the module is using the
group with the group-ID 0.
6.40.2. OPTIONS
debug
Print debug information.
deny
Reverse the sense of the auth operation: if the user is trying to get UID 0
access and is a member of the wheel group (or the group of the group
option), deny access. Conversely, if the user is not in the group, return
PAM_IGNORE (unless trust was also specified, in which case we return
PAM_SUCCESS).
group=name
Instead of checking the wheel or GID 0 groups, use the name group to
perform the authentication.
root_only
The check for wheel membership is done only.
trust
The pam_wheel module will return PAM_SUCCESS instead of PAM_IGNORE if the
user is a member of the wheel group (thus with a little play stacking the
modules the wheel members may be able to su to root without being prompted
for a passwd).
use_uid
The check for wheel membership will be done against the current uid instead
of the original one (useful when jumping with su from one account to
another for example).
6.40.3. MODULE TYPES PROVIDED
The auth and account module types are provided.
6.40.4. RETURN VALUES
PAM_AUTH_ERR
Authentication failure.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The return value should be ignored by PAM dispatch.
PAM_PERM_DENY
Permission denied.
PAM_SERVICE_ERR
Cannot determine the user name.
PAM_SUCCESS
Success.
PAM_USER_UNKNOWN
User not known.
6.40.5. EXAMPLES
The root account gains access by default (rootok), only wheel members can
become root (wheel) but Unix authenticate non-root applicants.
su auth sufficient pam_rootok.so
su auth required pam_wheel.so
su auth required pam_unix.so
6.40.6. AUTHOR
pam_wheel was written by Cristian Gafton <gafton@redhat.com>.
6.41. pam_xauth - forward xauth keys between users
pam_xauth.so [ debug ] [ xauthpath=/path/to/xauth ] [ systemuser=UID ] [
targetuser=UID ]
6.41.1. DESCRIPTION
The pam_xauth PAM module is designed to forward xauth keys (sometimes referred
to as "cookies") between users.
Without pam_xauth, when xauth is enabled and a user uses the su(1) command to
assume another user's privileges, that user is no longer able to access the
original user's X display because the new user does not have the key needed to
access the display. pam_xauth solves the problem by forwarding the key from the
user running su (the source user) to the user whose identity the source user is
assuming (the target user) when the session is created, and destroying the key
when the session is torn down.
This means, for example, that when you run su(1) from an xterm session, you
will be able to run X programs without explicitly dealing with the xauth(1)
xauth command or ~/.Xauthority files.
pam_xauth will only forward keys if xauth can list a key connected to the
$DISPLAY environment variable.
Primitive access control is provided by ~/.xauth/export in the invoking user's
home directory and ~/.xauth/import in the target user's home directory.
If a user has a ~/.xauth/import file, the user will only receive cookies from
users listed in the file. If there is no ~/.xauth/import file, the user will
accept cookies from any other user.
If a user has a .xauth/export file, the user will only forward cookies to users
listed in the file. If there is no ~/.xauth/export file, and the invoking user
is not root, the user will forward cookies to any other user. If there is no ~
/.xauth/export file, and the invoking user is root, the user will not forward
cookies to other users.
Both the import and export files support wildcards (such as *). Both the import
and export files can be empty, signifying that no users are allowed.
6.41.2. OPTIONS
debug
Print debug information.
xauthpath=/path/to/xauth
Specify the path the xauth program (it is expected in /usr/X11R6/bin/xauth,
/usr/bin/xauth, or /usr/bin/X11/xauth by default).
systemuser=UID
Specify the highest UID which will be assumed to belong to a "system" user.
pam_xauth will refuse to forward credentials to users with UID less than or
equal to this number, except for root and the "targetuser", if specified.
targetuser=UID
Specify a single target UID which is exempt from the systemuser check.
6.41.3. MODULE TYPES PROVIDED
Only the session type is provided.
6.41.4. RETURN VALUES
PAM_BUF_ERR
Memory buffer error.
PAM_PERM_DENIED
Permission denied by import/export file.
PAM_SESSION_ERR
Cannot determine user name, UID or access users home directory.
PAM_SUCCESS
Success.
PAM_USER_UNKNOWN
User not known.
6.41.5. EXAMPLES
Add the following line to /etc/pam.d/su to forward xauth keys between users
when calling su:
session optional pam_xauth.so
6.41.6. AUTHOR
pam_xauth was written by Nalin Dahyabhai <nalin@redhat.com>, based on original
version by Michael K. Johnson <johnsonm@redhat.com>.
Chapter 7. See also
* The Linux-PAM Application Writers' Guide.
* The Linux-PAM Module Writers' Guide.
* The V. Samar and R. Schemers (SunSoft), ``UNIFIED LOGIN WITH PLUGGABLE
AUTHENTICATION MODULES'', Open Software Foundation Request For Comments
86.0, October 1995.
Chapter 8. Author/acknowledgments
This document was written by Andrew G. Morgan (morgan@kernel.org) with many
contributions from Chris Adams, Peter Allgeyer, Tim Baverstock, Tim Berger,
Craig S. Bell, Derrick J. Brashear, Ben Buxton, Seth Chaiklin, Oliver Crow,
Chris Dent, Marc Ewing, Cristian Gafton, Emmanuel Galanos, Brad M. Garcia, Eric
Hester, Michel D'Hooge, Roger Hu, Eric Jacksch, Michael K. Johnson, David
Kinchlea, Olaf Kirch, Marcin Korzonek, Thorsten Kukuk, Stephen Langasek,
Nicolai Langfeldt, Elliot Lee, Luke Kenneth Casson Leighton, Al Longyear, Ingo
Luetkebohle, Marek Michalkiewicz, Robert Milkowski, Aleph One, Martin Pool,
Sean Reifschneider, Jan Rekorajski, Erik Troan, Theodore Ts'o, Jeff Uphoff,
Myles Uyema, Savochkin Andrey Vladimirovich, Ronald Wahl, David Wood, John
Wilmes, Joseph S. D. Yao and Alex O. Yuriev.
Thanks are also due to Sun Microsystems, especially to Vipin Samar and Charlie
Lai for their advice. At an early stage in the development of Linux-PAM, Sun
graciously made the documentation for their implementation of PAM available.
This act greatly accelerated the development of Linux-PAM.
Chapter 9. Copyright information for this document
Copyright (c) 2006 Thorsten Kukuk <kukuk@thkukuk.de>
Copyright (c) 1996-2002 Andrew G. Morgan <morgan@kernel.org>
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright
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2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. The name of the author may not be used to endorse or promote
products derived from this software without specific prior
written permission.
Alternatively, this product may be distributed under the terms of the GNU
General Public License (GPL), in which case the provisions of the GNU GPL are
required instead of the above restrictions. (This clause is necessary due to a
potential bad interaction between the GNU GPL and the restrictions contained in
a BSD-style copyright.)
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