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How do I set ulimits for the mongod process/user on CentOS?

I've read the official documentation but it doesn't provide OS-specific instructions.

  • I need to set ulimit -u 64000 and need this to persist after reboot.

  • I'm running CentOS 5.5 although will be upgrading to 6.5 soon.

  • I'd prefer not to modify any scripts installed by the package manager

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up vote 6 down vote accepted

Modify /etc/security/limits.conf with what you need. Example:

user soft nproc 64000

This line will set the number of processors (-u) to 64000 for "user". Soft/hard limits can be the same (soft allows spikes while hard prevents spawning).

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Thanks, but after doing this and restarting mongod cat /proc/{pid}/limits shows no change. Does something additional need to be done to ensure the conf is read? – Tim Apr 28 '14 at 17:07
Yes, reboot the server. It's set by the kernel. – Nathan C Apr 28 '14 at 17:49
Ah, many thanks! – Tim Apr 29 '14 at 11:25

The newer version of the CentOS mongod startup script (/etc/init.d/mongod) has the default settings built into the start option:

  # Recommended ulimit values for mongod or mongos
  # See
  ulimit -f unlimited
  ulimit -t unlimited
  ulimit -v unlimited
  ulimit -n 64000
  ulimit -m unlimited
  ulimit -u 32000

  echo -n $"Starting mongod: "
  daemon --user "$MONGO_USER" "$NUMACTL $mongod $OPTIONS >/dev/null 2>&1"
  [ $RETVAL -eq 0 ] && touch /var/lock/subsys/mongod

If you want to change the values and not modify the script, copy the script to /etc/init.d/mongod-custom, then edit the custom init script, set your values and change chkconfig to use mongod-custom instead of mongod.

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Make this change in the /etc/security/limits.conf file. Set the hard and soft limits, and you should be good.

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To add to thaspius's answer, the limits seem to be set as he describes in the init script, but I was still getting the warning

[initandlisten] ** WARNING: soft rlimits too low. rlimits set to 1024 processes, 64000 files. Number of processes should be at least 32000 : 0.5 times number of files.

This seems to suggest that files limit defined in the init script had taken effect, but not the processes limit. Also following Nathan C's answer and adding

mongod soft nproc 64000

to /etc/security/limits.d/90-nproc.conf and restarting the system solved the issue.

If anyone is able to shed light on why that was necessary despite having the values in the mongodb init script I'm all ears!

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