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.
How long should pam_timestamp treat timestamp as valid after their last modification date (in seconds). Default is 300 seconds.
Attempt to inform the user when access is granted.
Turns on debugging messages sent to syslog(3).
The module was not able to retrieve the user name or no valid timestamp file was found.
Everything was successful.
Timestamp file could not be created or updated.
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.
auth sufficient pam_timestamp.so verbose auth required pam_unix.so session required pam_unix.so session optional pam_timestamp.so