Lately, I had a EAGAIN error with some async code that made me take a closer look at ulimit settings. While I clearly understand certain limits, such as nofile, others are still quite confused to me.

It's quite easy to find resources on how to set those, but I couldn't find any article explaining precisely what each setting is about and how that could impact the system.

Definition taken from /etc/security/limits.conf is not really self-explanatory:

- 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
- chroot - change root to directory (Debian-specific)

So I'd be glad if someone could enlighten me on those rather important Linux settings!

The error I face is actually:

{ [Error: spawn mediainfo EAGAIN]
  code: 'EAGAIN',
  errno: 'EAGAIN',
  syscall: 'spawn mediainfo',
  path: 'mediainfo',
   [ '--Output=XML',
     '/home/buzut/testMedia' ],
  cmd: 'mediainfo --Output=XML /home/buzut/testMedia' }

As per the definition on gnu.org:

An operation that would block was attempted on an object that has non-blocking mode selected. Trying the same operation again will block until some external condition makes it possible to read, write, or connect (whatever the operation).

I understand that EAGAIN error refers to a resource that is temporarily not available. It wouldn't be wise to set all parameters to unlimited. Thus I would understand the implication of which params to identify the one blocking and adjust – ulimit settings, my code or both – accordingly.

Here are my current limits:

core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 127698
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 64000
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 127698
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

I have made my homework and (almost) found what each option does. Also, I've noted that there is more options in /etc/security/limits.conf than it appears with ulimit -a. Therefore, I've only documented the latter here. Of course, everyone is invited to enrich this answer!

  • data seg size (kbytes, -d)

    The maximum size of a process's data segment. a data segment is a portion of an object file or the corresponding virtual address space of a program that contains initialized static variables.


  • file size (blocks, -f)

    The maximum size of files written by the shell and its children.

  • pipe size (512 bytes, -p)


  • virtual memory (kbytes, -v)

    The maximum amount of virtual memory available to the shell. Virtual memory maps memory addresses used by a program, called virtual addresses, into physical addresses in computer memory.



As you didn't mention what's your exact problem with limitation in Linux so it would be hard to fix it. You use ulimit -a for check all of you limitation in OS. Also you can change every limitation you have ( you can decrease it not increase except root can do anything ) Try to look at man ulimit to find out which option you need to change.

  • I edited my question to make my problem clearer. But beside that, I'd be glad to know which param does what (like nofile is the number of files a given user can have open simultaneously)! – Buzut Apr 28 '16 at 15:09
  • Unlimited didn't fix your problem ? – Ali Ghasempour Apr 28 '16 at 15:33
  • I didn't try unlimited so far. I changed nofiles from 1024 to 64000, but it didn't solve my problem. And I'd rather not change what I don't understand. And clearly, I don't know what others do… – Buzut Apr 28 '16 at 15:39
  • 1
    Only option you shouldn't change is core !!! Core is env + bug log of applications. Put it on default (zero ) if you don't your disk will be full soon. First check your limitation ulimit -a then try unlimited – Ali Ghasempour Apr 28 '16 at 15:42
  • 1
    I don't know what kind of resource you mean but options cpu ( how much user take CPU for its process ) and nproc ( max number of process user can make or fork ) . Hope these will help you. Have fun ;) – Ali Ghasempour Apr 28 '16 at 16:10

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