How Do Ulimit Settings Impact Linux Server Faul

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How do ulimit settings impact Linux?

Asked 8 years, 11 months ago

Viewed 38k times

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',
  spawnargs: 
   [ '--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

linux
ulimit

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edited Jul 7, 2016 at 20:51

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asked Apr 28, 2016 at 14:38

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2 Answers

Sorted by:

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!

core file size (blocks, -c)

The maximum size of core files created. Core dump is a system snapshot (RAM + context switch + processor registers).

https://en.wikipedia.org/wiki/Core_dump

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 initialised static variables.

https://en.wikipedia.org/wiki/Data_segment

scheduling priority (-e)

The maximum scheduling priority (“nice”) a process can be given.

https://en.wikipedia.org/wiki/Scheduling_%28computing%29

file size (blocks, -f)

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

pending signals (-i)

Set of signals that are pending for delivery to the calling thread.

https://unix.stackexchange.com/questions/197600/what-are-pending-signals

max locked memory (kbytes, -l)

The maximum size that may be locked into memory. Memory locking ensures the memory is always in RAM and never moved to the swap disk.

https://stackoverflow.com/questions/9818755/why-would-we-need-to-lock-a-processs-address-space-in-ram

max memory size (kbytes, -m)

How much memory a process currently has in main memory (RAM), opposed to how much virtual memory the process has in total.

https://en.wikipedia.org/wiki/Resident_set_size

open files (-n)

The maximum number of open file descriptors. A file descriptor is an abstract indicator used to access a file or other input/output resource, such as a pipe or network socket.

https://en.wikipedia.org/wiki/File_descriptor

List file descriptors: http://www.cyberciti.biz/tips/linux-procfs-file-descriptors.html

pipe size (512 bytes, -p)

Pipe’s internal buffer size. See “pipe capacity” section in http://man7.org/linux/man-pages/man7/pipe.7.html

POSIX message queues (bytes, -q)

The maximum number of bytes in POSIX message queues. POSIX message queues allow processes to exchange data in the form of messages.

http://linux.die.net/man/7/mq_overview

Message queues in general https://en.wikipedia.org/wiki/Message_queue

real-time priority (-r)

The maximum real-time scheduling priority. A realtime priority thread can never be pre-empted by timer interrupts and runs at a higher priority than any other thread in the system.

https://stackoverflow.com/questions/1663993/what-is-the-realtime-setting-for-for-process-priority

stack size (kbytes, -s)

The maximum stack size. The stack size is a reserved region of memory that is used to store the location of function calls in order to allow return statements to return to the correct location.

https://en.wikipedia.org/wiki/Stack-based_memory_allocation

cpu time (seconds, -t)

The maximum amount of cpu time in seconds.

https://en.wikipedia.org/wiki/CPU_time

max user processes (-u)

The maximum number of processes a user can start or fork.

https://en.wikipedia.org/wiki/Process_%28computing%29

This command shows how much processes each user is currently using:

ps h -Led -o user | sort | uniq -c | sort -n

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.

https://en.wikipedia.org/wiki/Virtual_memory

file locks (-x)

File locking is a mechanism that restricts access to a computer file by allowing only one user or process access at any specific time.

https://en.wikipedia.org/wiki/File_locking

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edited Aug 30, 2019 at 20:41

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answered Apr 28, 2016 at 21:42

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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.

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answered Apr 28, 2016 at 14:44

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Ali Ghasempour

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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

Commented Apr 28, 2016 at 15:09
Unlimited didn’t fix your problem ?

– Ali Ghasempour

Commented Apr 28, 2016 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

Commented Apr 28, 2016 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

Commented Apr 28, 2016 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

Commented Apr 28, 2016 at 16:10