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'''<code>ulimit</code>''' is a built-in [[Linux]] shell command that allows '''viewing or limiting system resource amounts''' that individual users consume. Limiting resource usage is valuable in environments with multiple users and system performance issues.  
{{Status
|status=Draft
|owner=Knowledge Agent
|last_update=2026-07-16
|review=Pending
}}
 
{{TOC}}
 
== Overview ==
 
Ulimit에 대한 기술 문서입니다.
 
=== Summary ===
 
* 무엇인가? - Ulimit
* 왜 필요한가? - HPC 및 서버 환경에서 필수 개념
* 언제 사용하는가? - 서버 구성, 성능 튜닝, 문제 해결 시
 
 
== Purpose ==
 
이 문서가 존재하는 이유


* Goal: Ulimit에 대한 기술 정보 제공
* Scope: Ulimit의 개념, 사용법, 설정
* Non-goals: 다른 주제로의 확장




== Key Concepts ==
{| class="wikitable"
! Concept
! Description
! Related
|-
| Ulimit
| HPC/서버 환경에서 중요한 기술 개념
| [[Linux]], [[Server]]
|}


''/etc/security/limits.conf'' file is a configuration file that defines the system resource allocation settings '''<code>ulimit</code>''' uses.  Changing the values in the file persist after system reboot.


== Detailed Explanation ==


'''<code>ulimit</code>''' is a built-in [[Linux]] shell command that allows '''viewing or limiting system resource amounts''' that individual users consume. Limiting resource usage is valuable in environments with multiple users and system performance issues.
''/etc/security/limits.conf'' file is a configuration file that defines the system resource allocation settings '''<code>ulimit</code>''' uses.  Changing the values in the file persist after system reboot.
'''To specify the ''type'' with ''ulimit'', we use ''-H'' (hard) and ''-S'' (soft), where''' ''-H'' sets hard limits, while ''-S'' sets soft limits. By default, without either flag, ''-S'' is presumed<ref>https://linuxhint.com/linux_ulimit_command/</ref>
'''To specify the ''type'' with ''ulimit'', we use ''-H'' (hard) and ''-S'' (soft), where''' ''-H'' sets hard limits, while ''-S'' sets soft limits. By default, without either flag, ''-S'' is presumed<ref>https://linuxhint.com/linux_ulimit_command/</ref>
== Soft limit ==
The soft limit is manageable by any user, and its maximum value cannot exceed the hard limit. The hard limit acts as a ceiling for the soft limit.
The soft limit is manageable by any user, and its maximum value cannot exceed the hard limit. The hard limit acts as a ceiling for the soft limit.
<code>ulimit -Sa</code>
<code>ulimit -Sa</code>
== Hard Limit ==
The hard resource limit defines physical resource limit for a user. At the same time, the hard limit is the maximum value for soft limit. '''Only root users are allowed to change the hard limit'''.
The hard resource limit defines physical resource limit for a user. At the same time, the hard limit is the maximum value for soft limit. '''Only root users are allowed to change the hard limit'''.
<code>ulimit -Ha</code>
<code>ulimit -Ha</code>
== Flag ==
The '''<code>ulimit</code>''' command takes the following general syntax
The '''<code>ulimit</code>''' command takes the following general syntax
<code>ulimit [flags][limit]</code>
<code>ulimit [flags][limit]</code>
{| class="wikitable sortable"
{| class="wikitable sortable"
Line 34: Line 63:
|'''<code>-S</code>'''
|'''<code>-S</code>'''
|
|
|The '''soft limit''' for the given resource. Any process can change the soft limit.
|-
|'''<code>-a</code>'''
|
|Lists all current resource limits.
|-
|'''<code>-b</code>'''
|socket
|The maximum socket buffer size.
|-
|'''<code>-c</code>'''
|core dump
|The core dump size, expressed in the number of 512-byte blocks.
|-
|'''<code>-d</code>'''
|file
|The data area size, in kilobytes.
|-
|'''<code>-e</code>'''
|process
|The highest process scheduling priority (nice).
|-
|'''<code>-f</code>'''
|file
|The file size limit in blocks when using the '''<code>[limit]</code>''' parameter. Not specifying a '''<code>[limit]</code>''' instructs the command to report the file size limit.
|-
|'''<code>-i</code>'''
|signal
|The pending signal number limit.
|-
|'''<code>-k</code>'''
|socket
|The queue allocation number limit.
|-
|'''<code>-l</code>'''
|memory
|The maximum size allowed for locking in memory.
|-
|'''<code>-m</code>'''
|memory
|The physical memory size, in kilobytes.
|-
|'''<code>-n</code>'''
|process
|The maximum number of file descriptors that a process can have.
|-
|'''<code>-p</code>'''
|pipe
|The pipe buffer size.
|-
|'''<code>-P</code>'''
|terminals
|The maximum number of pseudo terminals.
|-
|'''<code>-q</code>'''
|message queues
|The maximum number of bytes in POSIX message queues.
|-
|'''<code>-r</code>'''
|thread
|The maximum number of threads a process can have.
|-
|'''<code>-R</code>'''
|process
|The maximum process running time, expressed in microseconds.
|-
|'''<code>-s</code>'''
|memory
|The stack size, in kilobytes.
|-
|'''<code>-t</code>'''
|process
|Specifies a process' maximum running time, in seconds.
|-
|'''<code>-T</code>'''
|thread
|The thread number limit.
|-
|'''<code>-u</code>'''
|process
|Specifies how many processes a user can create.
|-
|'''<code>-v</code>'''
|memory
|The maximum virtual memory available for processes.
|-
|'''<code>-x</code>'''
|file
|The maximum number of file locks.
|}
== Example ==
Resource limits set with ulimit are not system-wide and only apply to processes started in the same shell session and their descendants.<syntaxhighlight lang="bash">
#limit the process number to 10
ulimit -u 10
#limits the file size to 50KB
ulimit -f 50
#limits the virtual memory available for a process to 1000KB
ulimit -v 1000
#limits the number of open files to five
ulimit -n 5
</syntaxhighlight>
== limit keywords ==
* 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)
== Tuning ulimit ==
=== File descriptor limit ===
On Ubuntu, the default file descriptor limit is 1024 which can be checked by $ulimit -n.
To increase this value if you are running an application server which receive thousands or millions of request each second <syntaxhighlight lang="bash">
Add those lines to file /etc/security/limits.conf


*    - nofile 1048576


then relogin and check $ulimit -n
== Best Practices ==
</syntaxhighlight>system wide file descriptor limit can be done through fs.file-max<ref>https://www.cyberciti.biz/faq/linux-increase-the-maximum-number-of-open-files/</ref> <syntaxhighlight lang="bash">
Use the following command command to display maximum number of open file descriptors:


cat /proc/sys/fs/file-max
* 최신 버전 사용 권장
* 공식 문서 참고
* 테스트 환경에서 먼저 검증


The number of concurrently open file descriptors throughout the system can be changed
via /etc/sysctl.conf file under Linux operating systems.


for temperary change,
== References ==
# sysctl -w fs.file-max=100000


for permenant change, add following line in /etc/sysctl.conf
* [https://wiki.hpcmate.com Ulimit]
fs.file-max = 100000


to changes take effect just type and check /proc/sys/fs/file-max
# sysctl -p


</syntaxhighlight>
== Related Pages ==


=== In order to allow allocation of large amount of pinned memory ===
* [[Linux]]
<syntaxhighlight lang="bash">
* [[Server]]
#ulimit -v unlimited
* [[Hardware]]
#ulimit -m unlimited
* [[Network]]
#ulimit -l unlimited


</syntaxhighlight>


[[Category:Linux]]
== Knowledge Graph ==


RHEL/CentOS/Fedora/Scientific Linux users need additional configuration to edit /etc/pam.d/common-session file and add/modify the following line
Related
session required pam_limits.so


== Reference ==
→ [[Linux]]
<references />
→ [[Linux Kernel Tuning]]
→ [[THP (Transparent Huge Pages)]]
→ [[Sar]]
→ [[Vmstat]]


[[Category: Terminology]]
[[Category:Configuration]]
[[Category: Tuning]]

Latest revision as of 11:31, 17 July 2026

Template:Status

Template:TOC

Overview

Ulimit에 대한 기술 문서입니다.

Summary

  • 무엇인가? - Ulimit
  • 왜 필요한가? - HPC 및 서버 환경에서 필수 개념
  • 언제 사용하는가? - 서버 구성, 성능 튜닝, 문제 해결 시


Purpose

이 문서가 존재하는 이유

  • Goal: Ulimit에 대한 기술 정보 제공
  • Scope: Ulimit의 개념, 사용법, 설정
  • Non-goals: 다른 주제로의 확장


Key Concepts

Concept Description Related
Ulimit HPC/서버 환경에서 중요한 기술 개념 Linux, Server


Detailed Explanation

ulimit is a built-in Linux shell command that allows viewing or limiting system resource amounts that individual users consume. Limiting resource usage is valuable in environments with multiple users and system performance issues. /etc/security/limits.conf file is a configuration file that defines the system resource allocation settings ulimit uses. Changing the values in the file persist after system reboot. To specify the type with ulimit, we use -H (hard) and -S (soft), where -H sets hard limits, while -S sets soft limits. By default, without either flag, -S is presumed[1] The soft limit is manageable by any user, and its maximum value cannot exceed the hard limit. The hard limit acts as a ceiling for the soft limit. ulimit -Sa The hard resource limit defines physical resource limit for a user. At the same time, the hard limit is the maximum value for soft limit. Only root users are allowed to change the hard limit. ulimit -Ha The ulimit command takes the following general syntax ulimit [flags][limit]

Flag Effect to Description
-H The hard limit for the given resource. Only root users can raise the hard limit, and any process can lower it.
-S


Best Practices

  • 최신 버전 사용 권장
  • 공식 문서 참고
  • 테스트 환경에서 먼저 검증


References


Related Pages

Knowledge Graph

Related

→ Linux → Linux Kernel Tuning → THP (Transparent Huge Pages) → Sar → Vmstat

  1. ↑ https://linuxhint.com/linux_ulimit_command/
Retrieved from "http://wiki.hpcmate.com/index.php?title=Ulimit&oldid=3479"