Ulimit

lastmod 2024-05-27created 2016-06-083 edits

Limits system resource usage for processes

Used because, when running a web service such as Apache with many concurrent users, the number of running Apache processes and the number of files those processes handle also increase, so the system needs a way to adjust the corresponding settings

There are two kinds of process resource limits: soft and hard

The ulimit command affects the performance and functions of the kernel, so use it with care

The configuration method differs between sysvinit environments and systemd environments

Limits

• soft - the limit applied by default when a new program is created
• hard - the maximum to which the soft limit can be raised

Setting list

• nofile
  • Maximum number of files the domain (user, group) can open
  • Limits the maximum number of file descriptors (FD) that can be opened
• nproc
  • Maximum number of processes for the domain (user, group)
  • Limits the maximum number of processes (user processes) allowed for one user
• core
  • Limits the core file size
  • Limits the maximum size when a core file is created
• data
  • Maximum data size
  • Limits the maximum size of the process data segment
• fsize
  • Maximum file size
  • Limits the maximum size of files that can be created by the shell
• memlock
  • Maximum locked-in-memory address space
  • Limits the maximum amount of virtual memory allowed for the shell
• rss
  • Maximum resident memory size
  • Limits the maximum size that can be resident in memory (resident set size)
• stack
  • Maximum stack size
  • Limits the maximum stack size
• cpu
  • Maximum CPU time
  • Limits the maximum allowed CPU time per second
• as
  • Address space limit
  • Sets the pipe size in 512-byte blocks
• maxlogins
  • Maximum number of logins for this user
• maxsyslogins
  • Maximum number of logins on the system
• priority
  • Priority at which user processes run
• locks
  • Maximum number of file locks the user can hold
• sigpending
  • Maximum number of pending signals
• msgqueue
  • Maximum memory used by POSIX message queues
• nice
  • Maximum nice priority that can be raised to [-20 ~ 19]
• rtprio
  • Maximum real-time priority
• chroot
  • Change root to directory (Debian-specific)

Options

• -a - Print all limit values
• -b - Limit the maximum socket buffer size
• -d - Limit the maximum size of a process's data segment
• -e - Maximum scheduling priority
• -f - Limit the maximum size of files created by the shell
• -i - Limit the maximum number of pending signals
• -l - Limit the maximum size that can be locked in memory
• -s - Limit the maximum stack size
• -t - Limit CPU usage time per second
• -m - Limit the maximum size that can be resident in memory
• -c - Limit the maximum size when a core file is created
• -u - Limit the maximum number of processes available to a given user
• -v - Limit the maximum size of virtual memory the shell can use
• -p - Set the pipe size in 512-byte blocks
• -q - Limit the maximum number of bytes in POSIX message queues
• -r - Maximum real-time scheduling priority
• -n - Limit the number of FDs that can be opened (errors such as too many open file can be solved by changing this value)
• -x - Limit the maximum number of file locks
• -S - Set the soft limit for the given resource
• -H - Set the hard limit for the given resource
• -T - Limit the maximum number of threads

Checking values

• core file size - maximum size of a core file (-c option)
• data seg size - maximum size of a process's data segment (-d option)
• scheduling priority - maximum size of files created by the shell (-e option)
• file size - maximum file size (-f option)
• pending signals - pending signal limit (-i option)
• max locked memory - maximum size that can be locked in memory (-l option)
• max memory size - maximum resident set size (maximum memory size, -m option)
• open files - maximum number of open file descriptors per process (maximum number of files that can be opened, -n option)
• pipe size - pipe size in 512-byte blocks (-p option)
• POSIX message queues - maximum number of bytes in POSIX message queues (-q option)
• real-time priority - maximum real-time scheduling priority (-r option)
• stack size - maximum stack size (-s option)
• cpu time - total accumulated CPU time [seconds] (-t option)
• max user processes - maximum number of processes available to a single user (-u option)
• virtual memory - maximum amount of virtual memory available to the shell (-v option)
• file locks - maximum number of file locks (-x option)

Configuration

Edit the /etc/security/limit.conf file:

<Domain> <Type> <Item> <Value>

• Domain : the target to limit (*, user name, group name) - prefix with @ to apply to a group
• Type : whether to limit strictly or with some leeway (Soft, Hard)
• Item : the item to limit; there are many, such as core, data, seg, file size (stack, nproc, nofile, etc.)
• Value : the value to set as the limit

ulimit settings in systemd

systemd completely ignores /etc/security/limits*. Therefore, limits in systemd must be configured differently from the traditional method.

Order of precedence:

1. Service Daemon
2. Global

File paths:

• System - /etc/systemd/system.conf
• User - /etc/systemd/user.conf

Options

See also

• Core dump
• apport (Ubuntu)
• abrt (RHEL)
• Breakpad

Favorite site

• [Recommended] Core dump settings ¹
• Linux ulimit :: Las notepad
• (Linux) ulimit explanation and configuration

References