fuser forks and never reaps its children

[Volodymyr Kolesnykov]

$ lsb_release -rd
Description: Ubuntu 11.10
Release: 11.10

# cat /etc/cron.d/php5
# /etc/cron.d/php5: crontab fragment for php5
# This purges session files older than X, where X is defined in seconds
# as the largest value of session.gc_maxlifetime from all your php.ini
# files, or 24 minutes if not defined. See /usr/lib/php5/maxlifetime

# Look for and purge old sessions every 30 minutes
09,39 * * * * root [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) ! -execdir fuser -s {} 2>/dev/null \; -delete

When

find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) ! -execdir fuser -s {} 2>/dev/null \; -delete

is run either from cron or manually, fuser forks itself until the system is unable to fork any new processes (which affects the whole system).

# ps -C fuser | wc -l
22634

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: psmisc 22.14-1
ProcVersionSignature: Ubuntu 3.0.0-12.20-server 3.0.4
Uname: Linux 3.0.0-12-server x86_64
ApportVersion: 1.23-0ubuntu3
Architecture: amd64
Date: Wed Oct 19 04:36:08 2011
ExecutablePath: /bin/fuser
InstallationMedia: Ubuntu-Server 10.04.2 LTS "Lucid Lynx" - Release amd64 (20110211.1)
ProcEnviron:
 SHELL=/bin/bash
 LANG=en_US.UTF-8
SourcePackage: psmisc
UpgradeStatus: Upgraded to oneiric on 2011-10-19 (0 days ago)

[Volodymyr Kolesnykov (sjinks)]

Output of ps -faux when the problem occurs

[Volodymyr Kolesnykov (sjinks)]

ls -la /var/lib/php5

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Graham Poulter (grahampo)]

We also found this problem: the PHP cron launches one fuser for each PHP session file, and the process is never reaped (remains in <defunct> state)

Workaround for PHP is to remove the fuser check, which was only added 11.10 anyway.

This is the 11.10 cron job:

09,39 * * * * root [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) ! -execdir fuser -s {} 2>/dev/null \; -delete

And this is the 11.04 cron job:

09,39 * * * * root [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[klemens_u (klemens)]

I've got the same problem. Reverted to the Ubuntu 10.04 setting as suggested above.

[Simon Hirscher (codethief)]

I can confirm the bug on Ubuntu 11.10 with php5-fpm.
Found this Debian bug via Google: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=633100 . Maybe it provides anybody with more information on how to hunt this bug down.