[Linux] using Linux ulimit

1. What is ulimit?

Ulimit is a command that can set or report the current user resource limit. The ulimit command requires administrator privileges and can only be used on systems that allow shell control. In other words, it has been embedded into the shell.

2. Basic use

➜  ~ ulimit
unlimited

As shown in the output, unlimited, the current user has unlimited resources to access. This means that the current user can consume all the resources supported by the current system.

➜  ~ ulimit -a
-t: cpu time (seconds)              unlimited
-f: file size (blocks)              unlimited
-d: data seg size (kbytes)          unlimited
-s: stack size (kbytes)             8192
-c: core file size (blocks)         0
-m: resident set size (kbytes)      unlimited
-u: processes                       7823
-n: file descriptors                1024
-l: locked-in-memory size (kbytes)  64
-v: address space (kbytes)          unlimited
-x: file locks                      unlimited
-i: pending signals                 7823
-q: bytes in POSIX msg queues       819200
-e: max nice                        0
-r: max rt priority                 0
-N 15:                              unlimited

-a parameter can show detailed parameters, that is, what resources we can limit. There are two types of restrictions here: Soft & hard. Hard resource limitation means physical limitation; Soft resource limits are managed by users, and the maximum value of soft is limited by hard.

System resources are defined in the * / etc/security/limits.conf * file. When we use ulimit, we are using the values defined in this file.

#*               soft    core            0
 *
#root            hard    core            100000
 *root           soft    stack           86400
 *root           hard    stack           86400
#*               hard    rss             10000
#@student        hard    nproc           20
#@faculty        soft    nproc           20
#@faculty        hard    nproc           50
#ftp             hard    nproc           0
#ftp             -       chroot          /ftp
#@student        -       maxlogins       4

3. View other resource constraints

ulimit -c # View the maximum value of the core file

ulimit -d # View the maximum value of the data segment

ulimit -e # View the maximum scheduling priority of the current user

ulimit -s # The maximum stack size of the current user

ulimit -u # Maximum number of processes for the current user

ulimit -v # View the size of virtual memory

ulimit -b # View the size of socket buffer

ulimit -t # View the time allowed for each process to run

ulimit -n # View the maximum number of file descriptors a process can have

Other commands can be viewed through – help

4. Set resource limits

Through the above content, we learned how to view some resource limit values in the current system. Now let's see how to modify them.

Note: for hard restriction, we need root permission pip

First enter the limits.conf file

vim /etc/security/limits.conf

Edit the file in the following format:

<domain> <type> <item> <value>

Can be the following values:

#Where:
#<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
#        - NOTE: group and wildcard limits are not applied to root.
#          To apply a limit to the root user, <domain> must be
#          the literal username root.
#
#<type> can have the 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
#        - chroot - change root to directory (Debian-specific)
#
#<domain>      <type>  <item>         <value>

Of which:

• Core: core file size (KB)
• Data: maximum data size (KB)
• fsize: maximum file size (KB)
• memlock: maximum locked in memory address space (KB)
• nofile: the maximum number of open files
• rss: maximum resident set size (KB)
• Stack: maximum stack size (KB)
• cpu: maximum cpu time (minutes)
• nproc: maximum number of processes
• as: limit of address space (KB)
• maxlogins: the maximum number of logins of the current user
• maxsyslogins: the maximum number of logins in the current system
• Priority: the priority of the running user process
• Locks: the number of file locks that a user can hold
• sigpending: the maximum number of pending signals