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Still unknown problems with CRON and PAM (How does pam determine its state?)



Since nobody came up with an answer to my pam problems, I dug a little deeper today. The problem seems to be only with cron jobs in some vservers.

The interesting lines in are in the cron job's do_command.c
     148: fork
     165: write crontab invocation log message
     117: setsid ?? open new tty,
     xxx   stdin/out manipulation
204: do_univ (should not apply to standard ubuntu linux, calls universe function if any)
     213: setuid
     222: debugmessage
230: execle (stack destruction - nothing remains from cron app, only guest app runs)

Which lines would interact with pam? And how is the handshake between pam and the cron job done (syscall)?

Would I need to debug into the kernel to see the cause?

The problem is reproducible on some vservers after reboot but not on all.


My old message:

I'm trying to find out which files, commands can change the state and
behavior of the pam modules. This is because I have two servers which
should be identical in regard to login/pam configuration but they behave
different.

hosta: A linux vserver instance, with pam, cron
hostb: A clone of hostb

After cloning of hosta I installed logcheck, which runs without problems
on hosta, but produces pam error messages in auth.log on hostb. The
error messages are triggered via the logcheck cronjob, but a much
simpler cronjob is also sufficient:

* *     * * *   nobody  date > /tmp/pamtest

On hosta  I get every minute:

Aug 23 13:05:01 hosta CRON[16877]: (pam_unix) session opened for user
nobody by (uid=0)
Aug 23 13:05:01 hosta CRON[16877]: (pam_unix) session closed for user nobody

On hostb:

Aug 23 13:08:01 hostb CRON[16908]: (pam_unix) session opened for user
nobody by (uid=0)
Aug 23 13:08:01 hostb pam_limits[16908]: setrlimit limit #6 to soft=-1,
hard=-1 failed: Operation not permitted; uid=0 euid=0
Aug 23 13:08:01 hostb pam_limits[16908]: setrlimit limit #8 to soft=-1,
hard=-1 failed: Operation not permitted; uid=0 euid=0
Aug 23 13:08:01 hostb pam_limits[16908]: setrlimit limit #11 to soft=-1,
hard=-1 failed: Operation not permitted; uid=0 euid=0
Aug 23 13:08:01 hostb pam_limits[16908]: setrlimit limit #12 to soft=-1,
hard=-1 failed: Operation not permitted; uid=0 euid=0
Aug 23 13:08:01 hostb pam_limits[16908]: setrlimit limit #13 to soft=20,
hard=20 failed: Operation not permitted; uid=0 euid=0
Aug 23 13:08:01 hostb pam_limits[16908]: setrlimit limit #14 to soft=-1,
hard=-1 failed: Operation not permitted; uid=0 euid=0
Aug 23 13:08:01 hostb CRON[16908]: (pam_unix) session closed for user nobody

There are no differences in /etc/pam.conf, /etc/pam.d, the passwd/shadow files are identical. None of the instances was rebootet since installing logcheck.

What could cause the different behavior?



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