ulimit: ulimit [-SHabcdefilmnpqrstuvxT] [limit]
    Modify shell resource limits.

    Provides control over the resources available to the shell and processes
    it creates, on systems that allow such control.

    Options:
      -S    use the `soft' resource limit
      -H    use the `hard' resource limit
      -a    all current limits are reported
      -b    the 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 a process may lock into memory
      -m    the maximum resident set size
      -n    the maximum number of open file descriptors
      -p    the pipe buffer size
      -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 user processes
      -v    the size of virtual memory
      -x    the maximum number of file locks
      -T    the maximum number of threads

    Not all options are available on all platforms.

    If LIMIT is given, it is the new value of the specified resource; the
    special LIMIT values `soft', `hard', and `unlimited' stand for the
    current soft limit, the current hard limit, and no limit, respectively.
    Otherwise, the current value of the specified resource is printed.  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 increments of 512 bytes, and -u, which is an unscaled
    number of processes.

    Exit Status:
    Returns success unless an invalid option is supplied or an error occurs.

ulimit命令参数及用法

功能说明：控制shell程序的资源。

补充说明：ulimit为shell内建指令，可用来控制shell执行程序的资源。

参 数：

-a 显示目前资源限制的设定。

-c 设定core文件的最大值，单位为区块。

-d <数据节区大小> 程序数据节区的最大值，单位为KB。

-f <文件大小> shell所能建立的最大文件，单位为区块。

-H 设定资源的硬性限制，也就是管理员所设下的限制。

-m <内存大小> 指定可使用内存的上限，单位为KB。

-n <文件数目> 指定同一时间最多可开启的文件数。

-p <缓冲区大小> 指定管道缓冲区的大小，单位512字节。

-s <堆叠大小> 指定堆叠的上限，单位为KB。

-S 设定资源的弹性限制。

-t 指定CPU使用时间的上限，单位为秒。

-u <程序数目> 用户最多可开启的程序数目。

-v <虚拟内存大小> 指定可使用的虚拟内存上限，单位为KB。