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Oct 18 2009

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logrotate weirdness in debian etch

I have two VPSs, both running debian. One runs lenny, the other runs etch. The older etch install runs fine, and is much as the supplier delivered it. Until now I have not had cause to consider the need to upgrade the etch install to lenny because it “just worked”. But today I noticed for the first time a very odd difference between the two machines. A difference which had me scratching my head, and reading too many man entries, for some long time before I found the answer.

For reasons I don’t need to go into, I log all policy drops in my iptables config to a file called “/var/log/firewall”. This file is (supposedly) rotated weekly. The logrotate and cron entries on both machines are identical.. The entry in “/etc/logrotate.d/firewall” looks like this:

/var/log/firewall {
rotate 6
weekly
mail logger@baldric.net
compress
missingok
notifempty
}

The (standard) file “/etc/logrotate.conf” simply calls the firewall logrotate file out of the included directory “/etc/logrotate.d”. The “/etc/cron.daily/logrotate” file (which calls the logrotate script) is also standard and simply says:

#!/bin/sh

test -x /usr/sbin/logrotate || exit 0
/usr/sbin/logrotate /etc/logrotate.conf

and the (again standard) crontab file says:

# /etc/crontab: system-wide crontab
# Unlike any other crontab you don’t have to run the `crontab’
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# m h dom mon dow user command
54 * * * * root cd / && run-parts –report /etc/cron.hourly
55 4 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts –report /etc/cron.daily )
36 5 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts –report /etc/cron.weekly )
3 3 5 * * root test -x /usr/sbin/anacron || ( cd / && run-parts –report /etc/cron.monthly )
#

So far so simple, and you would expect the file “/var/log/firewall” to be rotated once a week at 04.55 on a sunday morning. Wouldn’t you.

Well, on lenny, you’d be right. But on the etch machine the file was rotated daily at a time completely unrelated to the crontab entry. It turns out that there is a bug in the way etch handles logrotation because syslog doesn’t use logrotate and overrides the logrotation entries run out of cron. I found this after much searching (and swearing).

See the bug report at bugs.debian.org and this entry which pointed me there.

I love standards.

Permanent link to this article: http://baldric.net/2009/10/18/logrotate-weirdness-in-debian-etch/