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This is an odd one and I know that the answer will be something simple that I have over looked... I have inherited responsibility for a Linux server running an old version of Ubuntu 10.04, it has a backup scrip running every hour but I can't find out where it's running from.

In the auth logs I see an entry every hour corresponding exactly to the time the backup is fired suggesting that this is a cron job:

"pam_unix(cron:session): session opened for user root"

It is not a remote command over SSH as there is no SSH session entry preceding it.

I have run the following command to list all user's cron jobs, which produces no results for anyone:

"for user in $(cut -f1 -d: /etc/passwd); do crontab -u $user -l; done"

It's not anacron either... What else is there? Any suggestions on where I might look next? I am thinking potentially there is a GUI app and the auth log entry is misleading.

Thanks in advance

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Try also /etc/cron.d/*, /etc/cron.hourly, /etc/crontab. –  MadHatter Dec 19 '13 at 9:20
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1 Answer

The message comes from PAM which is consulted every time a shell is spawned. See contents of /etc/pam.d, especially files /etc/pam.d/common-session and /etc/pam.d/cron.

This message means that there is indeed a cronjob somewhere which is run by the root user. That does not mean the job is doing anything (it might, for example, just check if a certain logfile is big enough to be rotated and exit without rotating it).

Definitions of cronjobs are spread over several directories and files. For the root user you should take a look into file /etc/crontab, output of crontab -l -u root and contents of directories /etc/cron.hourly, /etc/cron.daily, /etc/cron.weekly, /etc/cron.monthly and /etc/cron.d. The last one contains traditional cronjob definition tables whereas all the other directories contain executable scripts or binaries which are run by the cron with a period mentioned in the directory name (for more information see man run-parts).

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