collectd exec plugin fork freeze

collectd_exec_example

#!/bin/bash

HOSTNAME="${COLLECTD_HOSTNAME:-localhost}"
INTERVAL="${COLLECTD_INTERVAL:-10}"
 
while sleep "$INTERVAL"; do
  VALUE=1.23
  echo "PUTVAL \"$HOSTNAME/exec-magic/gauge-magic_level\" interval=$INTERVAL N:$VALUE"
done

running test_collectd_exec to reproduce the issue

root@jesse-precise-desktop:~# bin/test_collectd_exec.sh 
Wed Jun  6 09:39:24 CST 2012: starting collectd
Starting statistics collection and monitoring daemon: collectd,,.
Wed Jun  6 09:39:24 CST 2012: exec started?
 2461 pts/2    S+     0:00              \_ /bin/bash bin/test_collectd_exec.sh
 2470 pts/2    S+     0:00                  \_ grep collect
 2466 ?        Ss     0:00 /usr/sbin/collectdmon -P /var/run/collectdmon.pid -- -C /etc/collectd/collectd.conf
 2468 ?        SLl    0:00  \_ collectd -C /etc/collectd/collectd.conf -f
Wed Jun  6 09:39:26 CST 2012: stopping collectd
Stopping statistics collection and monitoring daemon: collectd.
collectd is stopped.
collectd is stopped.
collectd is stopped.
collectd is stopped.
Wed Jun  6 09:39:30 CST 2012: killing any remaining processes
collectd: no process found
Wed Jun  6 09:39:31 CST 2012: starting collectd
Starting statistics collection and monitoring daemon: collectd,,.
Wed Jun  6 09:39:31 CST 2012: exec started?
 2461 pts/2    S+     0:00              \_ /bin/bash bin/test_collectd_exec.sh
 2520 pts/2    S+     0:00                  \_ grep collect
 2516 ?        Ss     0:00 /usr/sbin/collectdmon -P /var/run/collectdmon.pid -- -C /etc/collectd/collectd.conf
 2518 ?        RLl    0:00  \_ collectd -C /etc/collectd/collectd.conf -f
Wed Jun  6 09:39:33 CST 2012: stopping collectd
Stopping statistics collection and monitoring daemon: collectd.
collectd (2531) is running.
collectd (2531) is running.
^C
root@jesse-precise-desktop:~# ps afx | grep collectd
 2531 ?        S      0:00 collectd -C /etc/collectd/collectd.conf -f
root@jesse-precise-desktop:~# strace -p 2531
Process 2531 attached - interrupt to quit
futex(0x7fa983a9edb0, FUTEX_WAIT_PRIVATE, 2, NULL^C <unfinished ...>
Process 2531 detached

test_collectd_exec.sh

#!/bin/bash

# this starts and stops collectd and looks to see if any collectd processes remain

while true ; do

  echo "`date`: starting collectd"
  /etc/init.d/collectd start

  echo "`date`: exec started?"
  ps afx | grep collect
  sleep 2

  echo "`date`: stopping collectd"
  /etc/init.d/collectd stop
  /etc/init.d/collectd status
  sleep 1
  /etc/init.d/collectd status
  sleep 1
  /etc/init.d/collectd status
  sleep 1
  /etc/init.d/collectd status

  echo "`date`: killing any remaining processes"
  killall -9 collectd
  sleep 1

done

I've managed to reproduce this on a lucid vm (ubuntu 10.04.3, 32 bit) with collectd 4.8.2 but only the once, out of about fifty attempts:

Wed Jun 6 22:24:14 CST 2012: starting collectd
Starting statistics collection and monitoring daemon: collectd.
Wed Jun 6 22:24:15 CST 2012: exec started?
1518 pts/0 S+ 0:00 _ /bin/bash ./test_collectd_exec.sh
2065 pts/0 S+ 0:00 _ grep collect
2052 ? Ss 0:00 /usr/sbin/collectdmon -P /var/run/collectdmon.pid -- -C /etc/collectd/collectd.conf
2054 ? Sl 0:00 _ collectd -C /etc/collectd/collectd.conf -f
2062 ? S 0:00 _ collectd -C /etc/collectd/collectd.conf -f
Wed Jun 6 22:24:17 CST 2012: stopping collectd
Stopping statistics collection and monitoring daemon: collectd.
collectd (2062) is running.
collectd (2062) is running.
collectd (2062) is running.
collectd (2062) is running.
Wed Jun 6 22:24:21 CST 2012: killing any remaining processes

Linux lucid32 2.6.32-33-generic #70-Ubuntu SMP Thu Jul 7 21:09:46 UTC 2011 i686 GNU/Linux

On a slackware-ish linux running collectd 4.10.7 I get this error about one in ten times (roughly) - but it seems to go away when I comment out the ping plugin...

[/var/log/collectd.log] 2012-06-06 16:06:24 UTC exec plugin: exec_read_one: Waiting for `/usr/bin/diskmonitor' to exit.
[/var/log/collectd.log] 2012-06-06 16:06:24 UTC exec plugin: Child 7067 exited with status 15.
[/var/log/collectd.log] 2012-06-06 16:06:24 UTC exec plugin: Sent SIGTERM to 0
[/var/log/syslog] [2012-06-06 16:06:24 UTC] [INFO] daemon 127.0.0.1 collectd[7055]: exec plugin: Sent SIGTERM to 0

WIth collectd 5 this happens much more often, and again commenting out the ping plugin makes the problem go away.

I've raised a bug report here: collectd/collectd#89