How to set ulimit values

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux (RHEL) 5, 6, 7

Issue

  • How to set ulimit values

Resolution

  • Settings in /etc/security/limits.conf take the following form:

    # vi /etc/security/limits.conf
    #<domain>        <type>  <item>  <value>
    
    *               -       core             <value>
    *               -       data             <value>
    *               -       priority         <value>
    *               -       fsize            <value>
    *               soft    sigpending       <value> eg:57344
    *               hard    sigpending       <value> eg:57444
    *               -       memlock          <value>
    *               -       nofile           <value> eg:1024
    *               -       msgqueue         <value> eg:819200
    *               -       locks            <value>
    *               soft    core             <value>
    *               hard    nofile           <value>
    @<group>        hard    nproc            <value>
    <user>          soft    nproc            <value>
    %<group>        hard    nproc            <value>
    <user>          hard    nproc            <value>
    @<group>        -       maxlogins        <value>
    <user>          hard    cpu              <value>
    <user>          soft    cpu              <value>
    <user>          hard    locks            <value>
    
    • <domain> can be:

      • a user name
      • a group name, with @group syntax
      • the wildcard *, for default entry
      • the wildcard %, can be also used with %group syntax, for maxlogin limit
    • <type> can have two values:

      • soft for enforcing the soft limits
      • hard for enforcing hard limits
    • <item> can be one of the following:

      • core - limits the core file size (KB)
      • data - max data size (KB)
      • fsize - maximum filesize (KB)
      • memlock - max locked-in-memory address space (KB)
      • nofile - max number of open files
      • rss - max resident set size (KB)
      • stack - max stack size (KB)
      • cpu - max CPU time (MIN)
      • nproc - max number of processes
      • as - address space limit (KB)
      • maxlogins - max number of logins for this user
      • maxsyslogins - max number of logins on the system
      • priority - the priority to run user process with
      • locks - max number of file locks the user can hold
      • sigpending - max number of pending signals
      • msgqueue - max memory used by POSIX message queues (bytes)
      • nice - max nice priority allowed to raise to values: [-20, 19]
      • rtprio - max realtime priority
  • Exit and re-login from the terminal for the change to take effect.

  • More details can be found from below command:

# man limits.conf

Diagnostic Steps

To improve performance, we can safely set the limit of processes for the super-user root to be unlimited. Edit the .bashrc file and add the following line:

# vi /root/.bashrc
ulimit -u unlimited

Exit and re-login from the terminal for the change to take effect.

Can also run ulimit -u unlimited at the command prompt instead of adding it to the /root/.bashrc file.

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14 Comments

the example isn't helpful or referral to the man page wasn't either. Why don't you show them putting in the "oracle" user not the wildcard since that was the question.

This is just confusing!

Just give simple steps, not theory

Also useless as it doesn't say what the keyword is in the .conf file for ulimit. Also the value field doesn't tell you how to set it to unlimited. As per previous reviewer, the man page is useless also.

From limits.conf(5) on RHEL7.1: " All items support the values -1, unlimited or infinity indicating no limit, except for priority and nice."

ulimits are controlled in three places, as I understand it. The kernel, PAM, and your shell. You covered the shell part. You only half covered the PAM part: as well as the limits.conf file you have to make sure /etc/pam.d/login has a line that says "session required pam_limits.so". And this article doesn't cover the kernel part at all. You have to add a file in /etc/sysctl.d/ with "fs.file-max = 20000" (or whatever you want the number to be), then do "sysctl --system".

I think command corresponding to ulimit should be listed here. This copy pate of limits.conf file

Hello, Values set by Ulimt command wont be persistent across reboot so it is always recommended to use the limits.conf. For example:

ulimit -l 128 ulimit -l

128

After Reboot:

ulimit -l 64

A big piece that was missing is that a reboot is not necessary for the changes to the file to take place if you're concerned about a particular user or application. But if it affects root processes, you're most likely going to want to reboot.

Further, if it's a change for just an application or user, then all their processes must stop and they must login again, and the processes restart.

RHEL-7-specific version is here: https://access.redhat.com/solutions/1257953. I don't think RHEL7 should be mentionned in this article.

Thanks for the link, Ugo. I didn't know about the per-service overrides. But don't forget that the above stuff still applies in RHEL7 to the non-systemd parts of the operating system (like per-user limits).

if you set oracle maxsyslogins 2 , only 2 putty session allowed on Linux for any user. Likewise oracle maxlogins 2 , only 2 session able to open as oracle user. 3 session will get closed.

oracle hard nproc 10000

oracle soft nproc 10000

If It's too simple most people can't understand it.

It's not described what is meant by 'hard' and 'soft' here.