pam.conf(4)
NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | ATTRIBUTES | SEE ALSO | NOTES
NAME
- pam.conf- configuration file for
pluggable authentication modules
SYNOPSIS
/etc/pam.conf
DESCRIPTION
-
<service_name> <module_type> <control_flag> <module_path> <options>
- /usr/lib/security/pam_<module_name>.so.x
-
Implements various function of specific authentication services.
- /etc/pam.conf
-
Configuration file.
- /usr/lib/libpam.so.1
-
Implements the PAM framework library.
pam.conf is the configuration file for the Pluggable Authentication Module architecture, or PAM. A PAM module provides functionality for one or more of four possible services: authentication, account management, session management, and password management. An authentication service module provides functionality to authenticate a user and set up user credentials. A account management module provides functionality to determine if the current user's account is valid. This includes checking for password and account expiration, as well as verifying access hour restrictions. A session management module provides functionality to set up and terminate login sessions. A password management module provides functionality to change a user's authentication token or password. Each of the four service modules can be implemented as a shared library object which can be referenced in the pam.conf configuration file.
Simplified PAM.CONF configuration file
The pam.conf file contains a listing of services. Each service is paired with a corresponding service module. When a service is requested, its associated module is invoked. Each entry has the following format:
Below is an example of the pam.conf configuration file with support for authentication, account management, and session management modules.
| login | auth | required | /usr/lib/security/pam_unix.so.1 | debug |
| login | session | required | /usr/lib/security/pam_unix.so.1 | |
| login | account | required | /usr/lib/security/pam_unix.so.1 | |
| telnet | session | required | /usr/lib/security/pam_unix.so.1 | |
| other | auth | required | /usr/lib/security/pam_unix.so.1 | |
| other | passwd | required | /usr/lib/security/pam_unix.so.1 |
The service_name denotes the service (for example, login, dtlogin, or rlogin). The keyword, other, indicates the module all other applications which have not been specified should use. The other keyword can also be used if all services of the same module_type have the same requirements. In the example above, since all of the services use the same session module, they could have been replace by a single other line.
module_type denotes the service module type: authentication (auth), account management (account), session management (session), or password management (password).
The control_flag field determines the behavior of stacking, and will be discussed in more detail below.
The module_path field specifies the pathname to a shared library object which implements the service functionality. If the pathname is not absolute, it is assumed to be relative to /usr/lib/security.
The options field is used by the PAM framework layer to pass module specific options to the modules. It is up to the module to parse and interpret the options. This field can be used by the modules to turn on debugging or to pass any module specific parameters such as a TIMEOUT value. It can also be used to support unified login. The options supported by the modules are documented in their respective manual pages. For example, pam_unix(5) lists the options accepted by the UNIX module.
Integrating Multiple Authentication Services With Stacking
When a service_name of the same module_type is defined more than once, the service is said to be stacked. Each module referenced in the module_path for that service is then processed in the order that it occurs in the configuration file. The control_flag field specifies the continuation and failure semantics of the modules, and may be requisite, required, optional, or sufficient.
The PAM framework processes each service module in the stack. If all requisite and required modules in the stack succeed, then success is returned, and optional and sufficient error values are ignored. If one or more requisite or required modules fail, then the error value from the first requisite or required module that failed is returned.
If none of the service modules in the stack are designated as requisite or required, then the PAM framework requires that at least one optional or sufficient module succeed. If all fail then the error value from the first service module in the stack is returned.
The requisite and sufficient flags cause two exceptions to the above semantics. If a service module that is designated as requisite fails, then the PAM framework immediately returns an error to the application, and all subsequent service modules in the stack are ignored. If a prior required service module has failed, then that error is returned. If no prior required service module failed, then the error from the failed requisite service module is returned.
If a service module that is designated as sufficient succeeds, then the PAM framework immediately returns success to the application, and all subsequent services modules in the stack, even requisite and required ones, are ignored, given that all prior requisite and required modules have also succeeded. If a prior required module has failed, then the error value from that module is returned.
If any entry in pam.conf is incorrect, or if a module does not exist or cannot be opened, then all PAM services will fail and users will not be permitted access to the system. An error will be logged through syslog(3) at the LOG_CRIT level. To fix incorrect entries in pam.conf, a system administrator may boot the system in maintenance mode (single user) to edit the file. Below is a sample configuration file that stacks the su, login, and rlogin services.
| su | auth | requisite | /usr/lib/security/pam_inhouse.so.1 | |
| su | auth | required | /usr/lib/security/pam_unix.so.1 | debug |
| login | auth | required | /usr/lib/security/pam_unix.so.1 | debug |
| login | auth | optional | /usr/lib/security/pam_inhouse.so.1 | |
| rlogin | auth | sufficient | /usr/lib/security/pam_rhosts_auth.so.1 | |
| rlogin | auth | required | /usr/lib/security/pam_unix.so.1 |
In the case of su, the user is authenticated by the Inhouse and UNIX authentication modules. Because the Inhouse and UNIX authentication modules are requisite and required, respectively, an error is returned back to the application if either module fails. In addition, if the requisite authentication (Inhouse authentication) fails, the UNIX authentication module is never invoked, and the error is returned immediately back to the application.
In the case of login, the required keyword for control_flag requires that the user be allowed to login only if the user is authenticated by the UNIX service module. If UNIX authentication fails, control continues to proceed down the stack, and the Inhouse authentication module is invoked. Inhouse authentication is optional by virtue of the optional keyword in the control_flag field. The user can still log in even if Inhouse authentication fails, assuming the UNIX authentication succeeded.
In the case of rlogin, the sufficient keyword for control_flag specifies that if the rhosts authentication check succeeds, then PAM should return success to rlogin and rlogin should not prompt the user for a password. The UNIX authentication module, which is the next module in the stack, will only be invoked if the rhosts check fails. This gives the system administrator the flexibility to determine if rhosts alone is sufficient enough to authenticate a remote user.
Some modules may return PAM_IGNORE in certain situations. In these cases the PAM framework ignores the entire entry in pam.conf regardless of whether or not it is requisite, required, optional or sufficient.
Utilities and Files
A following is a list of the utilities that are known to use PAM: include: login, passwd, su, rlogind, rshd, telnetd, ftpd, rpc.rexd, uucpd, init, sac, and ttymon.
The utility dtlogin also uses PAM. Note however that dtlogin is the login service utility for the Common Desktop Environment (CDE).
The PAM configuration file does not dictate either the name or the location of the service specific modules. The convention, however, is the following:
EXAMPLES
Example 1 A sample pam.conf configuration file.
The following is a sample pam.conf configuration file. Lines that begin with the # symbol are treated as comments, and therefore ignored.
# # PAM configuration # # Authentication management for login service is stacked. # Both UNIX and inhouse authentication functions are invoked. |
| login | auth | required | /usr/lib/security/pam_unix.so.1 | |
| login | auth | required | /usr/lib/security/pam_inhouse.so.1 | try_first_pass |
| dtlogin | auth | required | /usr/lib/security/pam_unix.so.1 | |
| dtlogin | auth | required | /usr/lib/security/pam_inhouse.so.1 | try_first_pass |
# # Authentication management for rlogin service is stacked. # If the rhost check succeeds, do not continue |
| rlogin | auth | sufficient | /usr/lib/security/pam_rhosts_auth.so.1 |
| rlogin | auth | required | /usr/lib/security/pam_unix.so.1 |
# # Other services use UNIX authentication other auth required /usr/lib/security/pam_unix.so.1 # # Account management for login service is stacked. # UNIX account management is required # Inhouse account management is optional login account required /usr/lib/security/pam_unix.so.1 login account optional /usr/lib/security/pam_inhouse.so.1 dtlogin account required /usr/lib/security/pam_unix.so.1 dtlogin account optional /usr/lib/security/pam_inhouse.so.1 other account required /usr/lib/security/pam_unix.so.1 # # Session management other session required /usr/lib/security/pam_unix.so.1 # # Password management other password required /usr/lib/security/pam_unix.so.1 |
ATTRIBUTES
See attributes(5) for description of the following attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|---|---|
| MT Level | MT-Safe with exceptions |
SEE ALSO
login(1), passwd(1), in.ftpd(1M), in.rlogind(1M), in.rshd(1M), in.telnetd(1M), in.uucpd(1M), init(1M), rpc.rexd(1M), sac(1M), su(1M), ttymon(1M), pam(3), syslog(3), libpam(4), attributes(5), pam_unix(5)
NOTES
The interfaces in libpam() are MT-Safe only if each thread within the multi-threaded application uses its own PAM handle.
NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | ATTRIBUTES | SEE ALSO | NOTES
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