Linux command ulimit

ulimit

說明：顯示/設定使用者、群組等級的shell、process使用的資源限制

使用概念

• 針對本session shell或session shell中的process做設置
• 直接顯示或設定資源限制
• 設定分為soft and hard
• 使用ulimit做的設定，都是暫時性的(只針對本session)
• 全系統的永久性修改，須改 /etc/security/limits.conf

Options

  
ulimit [-HSTabcdefilmnpqrstuvx [limit]]

-H: hard limit 執行緒不能在執行中改變數值(除非有root權限)
-S: soft limit 執行緒可在執行中改變數值

不加 -H,-S，默认兩者都设置。

LIMIT 的值，除了可以是数字，也可以是 
    hard， soft， unlimited

    hard: 当前 hard 限制值
    soft: 当前 soft 限制值
    unlimited: 无限制

不加 LIMIT，表示打印对应选项的资源（有多个选项时，会显示资源名和单位）：

#ulimit -f
unlimited

#ulimit -c
0

#ulimit -c -f
core file size          (blocks, -c) 0
file size               (blocks, -f) unlimited

             
    -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 and, on some systems, to its children
    -x     The maximum number of file locks
    -T     The maximum number of threads

    If limit is given, and the -a option is not used, limit  is  the
    new  value  of  the  specified resource.  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 sup‐
    plied, or an error occurs while setting a new limit.

Example

顯示當前user 的open files(n)的hard設定

ulimit -Hn
1024

顯示當前user 所有設定

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) 31204
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024         (file descriptor)
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) 31204
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

把當前user的file descriptor數量暫時修改為10240

#ulimit -n 10240