# Linux命令ulimit

## ulimit命令简介

ulimit [-HSTabcdefilmnpqrstuvx [limit]]

Provides control over the resources available to the shell and to processes started by it, on systems that allow such control. The -H and -S options specify that the hard or soft limit is set for the given resource. A hard limit cannot be increased by a non-root user once it is set; a soft limit may be increased up to the value of the hard limit. If neither -H nor -S is specified, both the soft and hard limits are set. The value of limit can be a number in the unit specified for the resource or one of the special values hard, soft, or unlimited, which stand for the current hard limit, the current soft limit, and no limit, respectively. If limit is omitted, the current value of the soft limit of the resource is printed, unless the -H option is given. When more than one resource is specified, the limit name and unit are printed before the value. Other options are interpreted as follows:

• -a : All current limits are reported
• -b : The maximum socket buffer size
• -c : The maximum size of core files created
• -d : The maximum size of a process’s data segment
• -e : The maximum scheduling priority (“nice”)
• -f : The maximum size of files written by the shell and its children
• -i : The maximum number of pending signals
• -l : The maximum size that may be locked into memory
• -m : The maximum resident set size (many systems do not honor this limit)
• -n : The maximum number of open file descriptors (most systems do not allow this value to be set)
• -p : The pipe size in 512-byte blocks (this may not be set)
• -q : The maximum number of bytes in POSIX message queues
• -r : The maximum real-time scheduling priority
• -s : The maximum stack size
• -t : The maximum amount of cpu time in seconds
• -u : The maximum number of processes available to a single user
• -v : The maximum amount of virtual memory available to the shell
• -x : The maximum number of file locks
• -T : The maximum number of threads

If limit is given, it is the new value of the specified resource (the -a option is display only). If no option is given, then -f is assumed. Values are in 1024-byte increments, except for -t, which is in seconds, -p, which is in units of 512-byte blocks, and -T, -b, -n, and -u, which are unscaled values. The return status is 0 unless an invalid option or argument is supplied, or an error occurs while setting a new limit.

• 进行资源控制的对象？当前的shell以及其下启动的process；
• 什么时候生效？ulimit -n 1024设置之后，当前shell就生效了，重启即失效；

[dev@cib69 elasticsearch-1.4.4]\$ ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 514940
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 2048
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 1024
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited


## limits.conf文件

# /etc/security/limits.conf
#
#Each line describes a limit for a user in the form:
#
#<domain>        <type>  <item>  <value>
#
#Where:
#<domain> can be:
#        - an user name
#        - a group name, with @group syntax
#        - the wildcard *, for default entry
#        - the wildcard %, can be also used with %group syntax,
#
#<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)
#        - 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
#
#<domain>      <type>  <item>         <value>
#

#*               soft    core            0
#@student        hard    nproc           20
#@faculty        soft    nproc           20
#@faculty        hard    nproc           50
#ftp             hard    nproc           0

# End of file


dev		soft	nofile	64000
dev		hard	nofile	64000


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