password required pam_unix.so shadow nullok use_authtok
This line specifies that if the program changes the user's password, it should use the
password
component of the
pam_unix.so
module to do so. This only happens if the
auth
portion of the
pam_unix.so
module has determined that the password needs to be changed.
The argument
shadow
tells the module to create shadow passwords when updating a user's
password.
The argument
nullok
instructs the module to allow the user to change their password from a
blank password, otherwise a null password is treated as an account lock.
The final argument on this line,
use_authtok
, provides a good example of the importance of
order when stacking PAM modules. This argument tells the module not to prompt the user for a
new password. Instead, it accepts any password that was recorded by a previous password
module. In this way, all new passwords must pass the
pam_cracklib.so
test for secure
passwords before being accepted.
session required pam_unix.so
The final line specifies that the session component of the
pam_unix.so
module manages the
session. This module logs the username and the service type to
/var/log/messages
at the
beginning and end of each session. It can be supplemented by stacking it with other session
modules for more functionality.
The next sample configuration file illustrates
auth
module stacking for the
rlogin
program.
#%PAM-1.0 auth required pam_nologin.so auth required pam_securetty.so auth
required pam_env.so auth sufficient pam_rhosts_auth.so auth required
pam_stack.so service=system-auth
First,
pam_nologin.so
checks to see if
/etc/nologin
exists. If it does, no one can log in
except for root.
auth required pam_securetty.so
The
pam_securetty.so
module prevents the root user from logging in on insecure terminals.
This effectively disallows all root
rlogin
attempts due to the application's limited security
safeguards.
Tip
To log in remotely as the root user, use OpenSSH instead. For more information,
Chapter 16. Pluggable Authent...
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