We have a CentOS box that I'm trying to increase the max number of files that a user can have open. Currently when I run ulimit -Sn I get 1024 and ulimit -Hn gives 4096. I need that number up around 6000.

In /etc/sysctl.conf I've set fs.file-max = 100000. In /etc/security/limits.conf I have the following set:

username soft nofile 6000
username hard nofile 65535

I've logged out and logged back in as username but am still not seeing my changes. What do I need to get this value changed?

All I have in /etc/security/limits.d is 90-nproc.conf. I've also ensured that ulimit is not being called in my .bash_profile or .bashrc.

When I run sysctl -p it spits out the settings I want and it shows the value for fs.file-max that I want. But when I run ulimit -Sn, I get 1048. If I try to run sysctl --system I get error: Unknown parameter "--system".

  • Did you try to reboot? As far as I know those settings are read during system boot.
    – Kamil
    Oct 15, 2014 at 16:21
  • You don't need a reboot for that. Oct 15, 2014 at 17:52

2 Answers 2


To force /etc/sysctl.conf to be read again run sysctl -p.

File /etc/security/limits.conf is read by login shells and you should close active sessions windows if in GUI. For remote logins, it takes effect on relog.

  • 1
    Ran that, still not seeing changes after a relog.
    – nwalke
    Oct 15, 2014 at 19:55
  • @tubaguy50035 fs.file-max is the max number of open file on the system. It's a hard limit and it won't be reflected by ulimit calls in your case. Oct 15, 2014 at 20:00
  • Oh, okay. Should I not be running into too many files open anymore then?
    – nwalke
    Oct 15, 2014 at 20:08
  • @tubaguy50035 Not related. It's the system hard limit that will override any number above in limits.conf. But limits.conf is still what's applied. Could you try to set the hard & soft limits with ulimit directly in a new session and see if you get same maximums? Something seems to override your configuration. Oct 15, 2014 at 20:10
  • It says operation is not permitted. Do I need to give the user access to something? I'd rather the web user not have root privileges.
    – nwalke
    Oct 15, 2014 at 20:19

As another poster has said, you need to have sysctl set the value in the running kernel. There are several ways you can set the value without rebooting:

sysctl -p /etc/sysctl.conf
sysctl -w fs.file-max=100000
sysctl --system

IMHO the last method is the best, as it replicates the order that the settings would be applied during boot (and thus if you have a conflict it will become apparent).

Note: I'm not sure which version of CentOS you're using, but on 7 at least I have run into a problem where if dracut rebuilds the initramfs for any reason (such as when installing a new kernel module) it will copy over the contents of /etc/sysctl.* into the initramfs, which will then be executed by systemd-sysctl during that phase, even if you later delete those entries out of /etc/sysctl.conf.

In my environment I've edited the systemd dracut module to exclude /etc/sysctl.* from that environment (as those settings will get set once the rootfs is mounted and systemd-sysctl runs again). It's just a gotcha that you might run into.

  • I'm on CentOS 6.5. Also updated my question with results of some of that.
    – nwalke
    Oct 15, 2014 at 19:57

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