/etc/security/limits.conf详解与配置过程

# /etc/security/limits.conf
#
#This file sets the resource limits for the users logged in via PAM.
该文件为通过PAM登录的用户设置资源限制。
#It does not affect resource limits of the system services.
#它不影响系统服务的资源限制。
#Also note that configuration files in /etc/security/limits.d directory,
#which are read in alphabetical order, override the settings in this
#file in case the domain is the same or more specific.
请注意/etc/security/limits.d下按照字母顺序排列的配置文件会覆盖 /etc/security/limits.conf中的
domain相同的的配置
#That means for example that setting a limit for wildcard domain here
#can be overriden with a wildcard setting in a config file in the
#subdirectory, but a user specific setting here can be overriden only
#with a user specific setting in the subdirectory.
这意味着，例如使用通配符的domain会被子目录中相同的通配符配置所覆盖，但是某一用户的特定配置
只能被字母路中用户的配置所覆盖。其实就是某一用户A如果在/etc/security/limits.conf有配置，当
/etc/security/limits.d子目录下配置文件也有用户A的配置时，那么A中某些配置会被覆盖。最终取的值是 /etc/security/limits.d 下的配置文件的配置。

#
#Each line describes a limit for a user in the form:
#每一行描述一个用户配置
#<domain> <type> <item> <value>

#Where:
#<domain> can be:
# - a user name    一个用户名
# - a group name, with @group syntax    用户组格式为@GROUP_NAME
# - the wildcard *, for default entry    默认配置为*，代表所有用户
# - the wildcard %, can be also used with %group syntax,
# for maxlogin limit 
#
#<type> can have the two values:
# - "soft" for enforcing the soft limits 
# - "hard" for enforcing hard limits
有soft，hard和-，soft指的是当前系统生效的设置值，软限制也可以理解为警告值。
hard表名系统中所能设定的最大值。soft的限制不能比hard限制高，用-表名同时设置了soft和hard的值。
#<item> can be one of the following:    <item>可以使以下选项中的一个
# - core - limits the core file size (KB)    限制内核文件的大小。
# - data - max data size (KB)    最大数据大小
# - fsize - maximum filesize (KB)    最大文件大小
# - memlock - max locked-in-memory address space (KB)    最大锁定内存地址空间
# - nofile - max number of open file descriptors 最大打开的文件数(以文件描叙符，file descripter计数) 
# - rss - max resident set size (KB) 最大持久设置大小
# - stack - max stack size (KB) 最大栈大小
# - cpu - max CPU time (MIN)    最多CPU占用时间，单位为MIN分钟
# - nproc - max number of processes 进程的最大数目
# - as - address space limit (KB) 地址空间限制 
# - maxlogins - max number of logins for this user    此用户允许登录的最大数目
# - maxsyslogins - max number of logins on the system    系统最大同时在线用户数
# - priority - the priority to run user process with    运行用户进程的优先级
# - locks - max number of file locks the user can hold    用户可以持有的文件锁的最大数量
# - 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] max nice优先级允许提升到值
# - rtprio - max realtime pr iority
#
#<domain> <type> <item> <value>
#

#* soft core 0
#* hard rss 10000
#@student hard nproc 20
#@faculty soft nproc 20
#@faculty hard nproc 50
#ftp hard nproc 0
#@st

# Default limit for number of user's processes to prevent
# accidental fork bombs.
# See rhbz #432903 for reasoning.
*    soft    nproc     4096 # 所有的用户默认可以打开最大的进程数为 4096
root soft    nproc     unlimited # root 用户默认可以打开最大的进程数 无限制的。

root soft nofile 65535
root hard nofile 65535
* soft nofile 65535
* hard nofile 65535

*    -     nproc   65535
root soft  nproc  unlimited
root hard  nproc  unlimited

root soft nofile 65538
root hard nofile 65538
* soft nofile 65539
* hard nofile 65539

root soft nofile 65538
root hard nofile 65538
* soft nofile 65539
* hard nofile 65539
root soft nofile 65539

root soft nofile 65538
root hard nofile 65538
* soft nofile 65539
* hard nofile 65539

root soft nofile 65536
root hard nofile 65536
* soft nofile 65540
* hard nofile 65540

ulimit  -SHn  65536

      -S	use the `soft` resource limit # 设置软限制
      -H	use the `hard` resource limit # 设置硬限制
      -a	all current limits are reported# 显示所有的配置。
      -b	the socket buffer size # 设置socket buffer 的最大值。
      -c	the maximum size of core files created # 设置core文件的最大值.
      -d	the maximum size of a process's data segment  # 设置线程数据段的最大值
      -e	the maximum scheduling priority (`nice') # 设置最大调度优先级
      -f	the maximum size of files written by the shell and its children # 创建文件的最大值。
      -i	the maximum number of pending signals # 设置最大的等待信号
      -l	the maximum size a process may lock into memory #设置在内存中锁定进程的最大值
      -m	the maximum resident set size 
      -n	the maximum number of open file descriptors # 设置最大可以的打开文件描述符。
      -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  # 设置用户可以创建的最大进程数。
      -v	the size of virtual memory  # 设置虚拟内存的最大值
      -x	the maximum number of file locks

ulimit  -a

ulimit  -n

ulimit  -SHn  65536