# /etc/security/limits.conf
#
#This file sets the resource limits for the users logged in via PAM.
該文件為通過PAM登錄的用戶設置資源限制。
#It does not affect resource limits of the system services.
#它不影響系統(tǒng)服務的資源限制。
#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.
請注意/etc/security/limits.d下按照字母順序排列的配置文件會覆蓋 /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.
這意味著，例如使用通配符的domain會被子目錄中相同的通配符配置所覆蓋，但是某一用戶的特定配置
只能被字母路中用戶的配置所覆蓋。其實就是某一用戶A如果在/etc/security/limits.conf有配置，當
/etc/security/limits.d子目錄下配置文件也有用戶A的配置時，那么A中某些配置會被覆蓋。最終取的值是 /etc/security/limits.d 下的配置文件的配置。

#
#Each line describes a limit for a user in the form:
#每一行描述一個用戶配置
#<domain> <type> <item> <value>

#Where:
#<domain> can be:
# - a user name    一個用戶名
# - a group name, with @group syntax    用戶組格式為@GROUP_NAME
# - the wildcard *, for default entry    默認配置為*，代表所有用戶
# - 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指的是當前系統(tǒng)生效的設置值，軟限制也可以理解為警告值。
hard表名系統(tǒng)中所能設定的最大值。soft的限制不能比hard限制高，用-表名同時設置了soft和hard的值。
#<item> can be one of the following:    <item>可以使以下選項中的一個
# - core - limits the core file size (KB)    限制內(nèi)核文件的大小。
# - data - max data size (KB)    最大數(shù)據(jù)大小
# - fsize - maximum filesize (KB)    最大文件大小
# - memlock - max locked-in-memory address space (KB)    最大鎖定內(nèi)存地址空間
# - nofile - max number of open file descriptors 最大打開的文件數(shù)(以文件描敘符，file descripter計數(shù)) 
# - rss - max resident set size (KB) 最大持久設置大小
# - stack - max stack size (KB) 最大棧大小
# - cpu - max CPU time (MIN)    最多CPU占用時間，單位為MIN分鐘
# - nproc - max number of processes 進程的最大數(shù)目
# - as - address space limit (KB) 地址空間限制 
# - maxlogins - max number of logins for this user    此用戶允許登錄的最大數(shù)目
# - maxsyslogins - max number of logins on the system    系統(tǒng)最大同時在線用戶數(shù)
# - priority - the priority to run user process with    運行用戶進程的優(yōu)先級
# - locks - max number of file locks the user can hold    用戶可以持有的文件鎖的最大數(shù)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優(yōu)先級允許提升到值
# - 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 # 所有的用戶默認可以打開最大的進程數(shù)為 4096
root soft    nproc     unlimited # root 用戶默認可以打開最大的進程數(shù) 無限制的。

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 # 設置軟限制
      -H	use the `hard` resource limit # 設置硬限制
      -a	all current limits are reported# 顯示所有的配置。
      -b	the socket buffer size # 設置socket buffer 的最大值。
      -c	the maximum size of core files created # 設置core文件的最大值.
      -d	the maximum size of a process's data segment  # 設置線程數(shù)據(jù)段的最大值
      -e	the maximum scheduling priority (`nice') # 設置最大調(diào)度優(yōu)先級
      -f	the maximum size of files written by the shell and its children # 創(chuàng)建文件的最大值。
      -i	the maximum number of pending signals # 設置最大的等待信號
      -l	the maximum size a process may lock into memory #設置在內(nèi)存中鎖定進程的最大值
      -m	the maximum resident set size 
      -n	the maximum number of open file descriptors # 設置最大可以的打開文件描述符。
      -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  # 設置用戶可以創(chuàng)建的最大進程數(shù)。
      -v	the size of virtual memory  # 設置虛擬內(nèi)存的最大值
      -x	the maximum number of file locks

ulimit  -a

ulimit  -n

ulimit  -SHn  65536