memcached: Failed To Set rlimit For Open Files Error and Solution

I'm using RHEL 6 / CentOS 6.x and install the memcached server. However, whey I try to start the server using service memcached start command, I get the following error:

Starting memcached: failed to set rlimit for open files. Try running as root or requesting smaller maxconns value. [FAILED]

How do I fix this problem?

Linux comes with per-process file and system-wide file system descriptor limits. Each user has per-process file descriptor limits. The default is set to 1024 including the hard limit, which is also set to 1024. Only root user can increase the hard limit. In my experience you need to to increase this when starting the memcached server.

More About Memcached

The memcached server is run as memcached user. You can verify this by visiting the /etc/passwd file, enter:
$ less /etc/passwd
$ grep -i memcached /etc/passwd
The default config file is located at /etc/sysconfig/memcached:
$ cat /etc/sysconfig/memcached
Sample outputs:

PORT="11211"
USER="memcached"
MAXCONN="4096"
CACHESIZE="256"
OPTIONS="-l 192.168.1.100"

Set Per-process File Descriptor Limits For Memcached

Edit /etc/security/limits.conf file, enter:
# vi /etc/security/limits.conf
Set max number of open files for memcached user as follows:

 
#"soft" for enforcing the soft limits
#"hard" for enforcing hard limits
# "nofile" max open file
# *********************************************************************
# * Note soft limit must be >= MAXCONN value (defined in /etc/sysconfig/memcached *
# *********************************************************************
# Username      type    item           value
memcached       soft    nofile          5000
memcached       hard    nofile         6144
 

Save and close the file. You need to logout and login again. Now type the following command to start the memcached server:
# /sbin/service memcached start
Please note that you can set global limit for all process by replacing the memcached with * as follows:

 
# Username      type    item           value
*       soft    nofile          5000
*       hard    nofile         6144