On Sun, 2003-09-14 at 06:22, Wouter DeBacker wrote:
> Can Linux/LTSP be configured to prevent a user to login more 
> than once? If so, how is it done?
> 
> Regards,
> Wouter DeBacker

Wouter,
the answer depends on the distribution you use on your server, but most
likely the answer is yes.  If your system uses pam, see
/usr/share/doc/pam-0.75/txts/README.pam_limits.

In a nutshell, your login program uses /etc/pam.d/system-auth to
determine if you are allowed to sign in.  The following line requires
all successful sign-ins to call pam_limits.so:
session     required      /lib/security/$ISA/pam_limits.so

pam_limits.so enforces the limits given in /etc/security/limits.conf. 
For example, the following two lines will limit members of the "student"
group to a single session, except for the student named "wouter", who
gets 50:
@student        -       maxlogins       1
wouter          -       maxlogins       50

Note that pam_limits.so is a "session" service, not an "auth" service. 
If a user signs in a second time, the signin is *successful* but will
end a few seconds later, before any of the usual session startup scripts
start. 

There are three side effects you will see.
- users will not get the usual "jiggly window" warning that they
mistyped their password.  Instead, they will get "Authentication Denied"
in a popup.
-limits won't increment the failed-login counts, so you won't have to
reset passwords of stubborn users
-you will see entries like the following in your system log:
Sep 17 17:36:26 server gdm(pam_unix)[19302]: session opened for user
testuser by (uid=0)
Sep 17 17:36:26 server gdm-binary[19302]: Couldn't open session for
testuser
Sep 17 17:36:31 server pam_limits[19302]: Too many logins (max 1) for
testuser


Regards,
David



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