Do changes in /etc/security/limits.conf require a reboot before taking effect?

For example, if I have a script that sets the following limits in /etc/security/limits.conf, does this require a system reboot before those limits will take effect?

* hard nofile 94000
* soft nofile 94000
* hard nproc 64000
* soft nproc 64000
  • 7
    logout should be enough
    – UVV
    Commented Jan 9, 2014 at 18:59
  • Edit the file /etc/security/limits.d/90-nproc.conf and reboot you system
    – user80746
    Commented Aug 13, 2014 at 17:48

5 Answers 5


No but you should close all active sessions windows. They still remember the old values. In other words, log out and back in. Every remote new session or a local secure shell take effect of the limits changes.

  • 25
    What if I want to set the limits for a user that doesn't have a login, like if I want to set the nofile limit to 94000 for the mongodb user? How'd I do that without a reboot? Would I just need to restart the mongodb service? Commented Jan 9, 2014 at 19:35
  • 4
    @AlexejMagura You can modify the the rlimits of running processes with the prlimit command.
    – Bratchley
    Commented Jan 9, 2014 at 23:46
  • 8
    @Gilles, thanks for the precisions, I edited my answer to to avoid ambiguity. However Starting a new service using sudo service mongodb restart is enough to let the service running with the new limit values.
    – Slyx
    Commented Jan 10, 2014 at 15:01
  • 9
    if you are using Ubuntu, and mongodb is started by upstart, then changing these limits will not affect mongodb. As upstart does not read /etc/security config bugs.launchpad.net/ubuntu/+source/upstart/+bug/938669 you must set limit stanza in its upstart config file. Commented Jan 19, 2015 at 3:22
  • 6
    It's another issue. upstart by design ignores the limits set in /etc/security/limits.conf.
    – Slyx
    Commented Jan 20, 2015 at 11:00

Apply the changes directly to a running process if you have prlimit installed (comes with util-linux-2.21)

prlimit --pid <pid> --<limit>=<soft>:<hard>

for example

prlimit --pid 12345 --nofile=1024:2048

Refer here

  • If you aren't root, you are still bound by the settings in limits.conf, so the original question still comes into play (if you are relying on a modification to the hard limit, for example). Commented May 18, 2023 at 17:34

To temporarily set the open files limit for the user you are currently logged in under (e.g. 'root'):You can also use the ulimit command to change the values in your current shell. However, hard limits can only be adjusted downwards unless you're root.


# ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 62449
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 1024
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

To change the nofile to 94000 you can do:

ulimit -n 94000
  • 1
    I was successfully able to change nofile limit for root with this command, but what if I want to do so from the root for a regular user? What would be my approach then? Commented Nov 30, 2021 at 16:08

Limits are inherited from a parent process to its child processes. Processes running as root can change limits arbitrarily; other processes cannot increase hard limits. Thus the hard limits set by the login process affect all the processes in a session.

If you change /etc/security/limits.conf, this will affect all new sessions, and processes in these new sessions. It won't affect processes that are already running, nor processes started by processes that are already running.

So if you need to increase some limits, you'll have to either log out and back in, or start another session (e.g. with ssh localhost, or on another console).


To quote @Tombart's answer

These limits will be applied after reboot.

If you want to apply changes without reboot, modify /etc/pam.d/common-session by adding this line at the end of file:

session required pam_limits.so
  • This answer is incorrect. New limits configurations are applied for new sessions, by default. See also e.g. Gilles answer. Commented Mar 27, 2021 at 21:56

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