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Here are log entries I found in auth.log. What does + ??? mean? And was there an unauthorized access?

Feb 11 07:48:32 tts-server su[31265]: Successful su for www-data by root
Feb 11 07:48:32 tts-server su[31265]: + ??? root:www-data
Feb 11 07:48:32 tts-server su[31265]: pam_unix(su:session): session opened for user www-data by (uid=0)
Feb 11 07:48:32 tts-server su[31265]: pam_unix(su:session): session closed for user www-data
Feb 11 07:48:32 tts-server su[31275]: Successful su for www-data by root
Feb 11 07:48:32 tts-server su[31275]: + ??? root:www-data
Feb 11 07:48:32 tts-server su[31275]: pam_unix(su:session): session opened for user www-data by (uid=0)
Feb 11 07:48:32 tts-server su[31275]: pam_unix(su:session): session closed for user www-data
Feb 12 09:46:27 tts-server su[11208]: Successful su for www-data by root
Feb 12 09:46:27 tts-server su[11208]: + ??? root:www-data
Feb 12 09:46:27 tts-server su[11208]: pam_unix(su:session): session opened for user www-data by (uid=0)
Feb 12 09:46:27 tts-server su[11208]: pam_unix(su:session): session closed for user www-data
Feb 12 09:46:27 tts-server su[11222]: Successful su for www-data by root
Feb 12 09:46:27 tts-server su[11222]: + ??? root:www-data
Feb 12 09:46:27 tts-server su[11222]: pam_unix(su:session): session opened for user www-data by (uid=0)
Feb 12 09:46:27 tts-server su[11222]: pam_unix(su:session): session closed for user www-data
Feb 13 12:25:41 tts-server su[22032]: Successful su for www-data by root
Feb 13 12:25:41 tts-server su[22032]: + ??? root:www-data
Feb 13 12:25:41 tts-server su[22032]: pam_unix(su:session): session opened for user www-data by (uid=0)
Feb 13 12:25:41 tts-server su[22032]: pam_unix(su:session): session closed for user www-data
Feb 13 12:25:41 tts-server su[22043]: Successful su for www-data by root
Feb 13 12:25:41 tts-server su[22043]: + ??? root:www-data
Feb 13 12:25:41 tts-server su[22043]: pam_unix(su:session): session opened for user www-data by (uid=0)
Feb 13 12:25:41 tts-server su[22043]: pam_unix(su:session): session closed for user www-data
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1 Answer

up vote 5 down vote accepted

Those are probably from a cron job. From Securing Debian Manual. Chapter 11 - Frequently asked Questions (FAQ)

11.2.3 I found users doing 'su' in my logs: Am I compromised?

You might find lines in your logs like:

 Apr  1 09:25:01 server su[30315]: + ??? root-nobody
 Apr  1 09:25:01 server PAM_unix[30315]: (su) 
   session opened for user nobody by (uid=0)

Don't worry too much, check out if this is due to a job running through the cron (usually /etc/cron.daily/find or logrotate):

$ grep 25 /etc/crontab
25 6    * * *   root    test -e /usr/sbin/anacron || run-parts --report
/etc/cron.daily
$ grep nobody /etc/cron.daily/*
find:cd / && updatedb --localuser=nobody 2>/dev/null
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Thank you sooo much for the explanation and for the link!! I found these lines: ~ > grep www-data /etc/cron.daily/* /etc/cron.daily/lighttpd: su -s /bin/sh -c "find $cache/compress -type f -atime +30 -print0 | xargs -0 -r rm" www-data /etc/cron.daily/lighttpd: su -s /bin/sh -c "find $cache/uploads -type f -atime +1 -print0 | xargs -0 -r rm" www-data –  zuba Feb 13 '13 at 16:12
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