Centos – Increasing nproc on CentOS/RHEL

centosMySQLredhatulimit

I have a problem where mysqld runs out of threads and throws errors when under heavy load. I have traced this back to a problem where the pid seems to be limited a soft limit of 1024 processes (have removed other limits for readability):

[root@db1 limits.d]# cat /proc/`pidof mysqld`/limits
Limit                     Soft Limit           Hard Limit           Units
Max processes             1024                 191967               processes

I have a file in /etc/security/limits.d/ called 99-mysql.conf which contains:

mysql soft nofile 20000
mysql hard nofile 20000
mysql soft nproc 20000
mysql hard nproc 20000

As far as I can see the problem comes from MySQL being started by a user. I haven't tested this, but I assume that if MySQL is started by the system at boot time, then it should have the correct limits.

Is there a way to increase the soft limit for nproc for this pid and for future mysqld processes?

Best Answer

It seems you can set the limits of a running pid by using:

echo -n "Max processes=20000:191967" > /proc/`pidof mysqld`/limits

This solves the immediate problem, but if I restart MySQL again I would need to reset the limits (unless I add this to the startup script), which seems like a pain.

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