pam.conf − configuration file for pluggable authentication modules
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.
authentication service module
Provides functionality to authenticate a user and set up user credentials.
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.
session management module
Provides functionality to set up and terminate login sessions.
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.
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:
service_name module_type control_flag module_path options
The following is an example of the pam.conf configuration file with support for authentication, account management, and session management modules.
login auth requisite pam_authtok_get.so.1 login auth required pam_dhkeys.so.1 login auth required pam_unix_auth.so.1 login auth required pam_dial_auth.so.1 other session required pam_unix_session.so.1
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In the example, since all of the services use the same session module, they could have been replaced by a single other line.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.
The module_path field specifies the relative 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/$ISA/.
The ISA token is replaced by an implementation defined directory name which defines the path relative to the calling program’s instruction set architecture.
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.
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 can 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 fail and users are not be permitted access to the system. An error is logged through syslog(3C) at the LOG_CRIT level. To fix incorrect entries in pam.conf, a system administrator can boot the system in maintenance mode (single user) to edit the file.
The following is a sample configuration file that stacks the su, login, and rlogin services.
su auth requisite pam_inhouse.so.1 su auth requisite pam_authtok_get.so.1 su auth required pam_dhkeys.so.1 su auth required pam_unix_auth.so.1 login auth requisite pam_authtok_get.so.1 login auth required pam_dhkeys.so.1 login auth required pam_unix_auth.so.1 login auth required pam_dial_auth.so.1 login auth optional pam_inhouse.so.1 rlogin auth sufficient pam_rhosts_auth.so.1 rlogin auth requisite pam_authtok_get.so.1 rlogin auth required pam_dhkeys.so.1 rlogin auth required pam_unix_auth.so.1
In the case of su, the user is authenticated by the inhouseand authtok_get, dhkesys and unix_auth authentication modules. Because the inhouse and the other authentication modules are requisite and required, respectively, an error is returned back to the application if any module fails. In addition, if the requisite authentication (inhouse authentication) fails, the other authentication modules 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 all the service modules. If authtok_get 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 modules stacked above 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 other authentication modules, which are 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 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.
The following is a list of the utilities that use PAM: login, passwd, su, rlogind, rshd, telnetd, ftpd, rpc.rexd, uucpd, init, sac, cron, ppp, dtsession, ssh and ttymon.
The utility dtlogin also uses PAM. dtlogin is the login service utility for the Common Desktop Environment (CDE).
configuration file does not dictate either the name or the
location of the service specific modules. The convention,
however, is the following:
File that implements various function of specific authentication services. As the relative pathname specified, /usr/lib/security/$ISA is prepended to it.
File that implements the PAM framework library.
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 # # Unless explicitly defined, all services use the modules # defined in the "other" section. # # Modules are defined with relative pathnames, i.e., they are # relative to /usr/lib/security/$ISA. Absolute path names, as # present in this file in previous releases are still acceptable. # # Authentication management # # login service (explicit because of pam_dial_auth) # login auth requisite pam_authtok_get.so.1 login auth required pam_dhkeys.so.1 login auth required pam_unix_auth.so.1 login auth required pam_dial_auth.so.1 # # rlogin service (explicit because of pam_rhost_auth) # rlogin auth sufficient pam_rhosts_auth.so.1 rlogin auth requisite pam_authtok_get.so.1 rlogin auth required pam_dhkeys.so.1 rlogin auth required pam_unix_auth.so.1 # # rsh service (explicit because of pam_rhost_auth) # and pam_unix_auth for meaningful pam_setcred) # rsh auth sufficient pam_rhosts_auth.so.1 rsh auth required pam_authtok_get.so.1 # # ppp service (explicit because of pam_dial_auth) # ppp auth requisite pam_authtok_get.so.1 ppp auth required pam_dhkeys.so.1 ppp auth required pam_unix_auth.so.1 ppp auth required pam_dial_auth.so.1 # # Default definitions for Authentication management # Used when service name is not explicitly mentioned for authenctication # other auth requisite pam_authtok_get.so.1 other auth required pam_dhkeys.so.1 other auth required pam_unix_auth.so.1 # # passwd command (explicit because of a different authentication module) # passwd auth required pam_passwd_auth.so.1 # # cron service (explicit because of non-usage of pam_roles.so.1) # cron account required pam_projects.so.1 cron account required pam_unix_account.so.1 # # Default definition for Account management # Used when service name is not explicitly mentioned for account management # other account requisite pam_roles.so.1 other account required pam_projects.so.1 other account required pam_unix_account.so.1 # # Default definition for Session management # Used when service name is not explicitly mentioned for session management # other session required pam_unix_session.so.1 # # Default definition for Password management # Used when service name is not explicitly mentioned for password management # other password required pam_dhkeys.so.1 other password requisite pam_authtok_get.so.1 other password requisite pam_authtok_check.so.1 other password required pam_authtok_store.so.1 # # Support for Kerberos V5 authentication (uncomment to use Kerberos) # #rlogin auth optional pam_krb5.so.1 try_first_pass #login auth optional pam_krb5.so.1 try_first_pass #other auth optional pam_krb5.so.1 try_first_pass #cron account optional pam_krb5.so.1 #other account optional pam_krb5.so.1 #other session optional pam_krb5.so.1 #other password optional pam_krb5.so.1 try_first_pass
See attributes(5) for descriptions of the following attributes:
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), ttymon(1M), su(1M), pam(3PAM), syslog(3C), libpam(3LIB), attributes(5), environ(5), pam_authtok_check(5), pam_authtok_get(5), pam_authtok_store(5), pam_dhkeys(5), pam_passwd_auth(5), pam_unix(5), pam_unix_account(5), pam_unix_auth(5), pam_unix_session(5)
The pam_unix(5) module might not be supported in a future release. Similar functionality is provided by pam_authtok_check(5), pam_authtok_get(5), pam_authtok_store(5), pam_dhkeys(5), pam_passwd_auth(5), pam_unix_account(5), pam_unix_auth(5), and pam_unix_session(5).