/etc/security/Detailed explanation and configuration process

# /etc/security/
#
#This file sets the resource limits for the users logged in via PAM.
The file is passedPAMLogin user settings resource limits。
#It does not affect resource limits of the system services.
#It does not affect the resource limitations of system services.#Also note that configuration files in /etc/security/ directory,
#which are read in alphabetical order, override the settings in this
#file in case the domain is the same or more specific.
Please note/etc/security/The configuration files arranged in alphabetical order will be overwritten /etc/security/In-house
domainSame configuration
#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.
This means，For example, using wildcard charactersdomainWill be overwritten by the same wildcard configuration in the subdirectory，But a specific configuration of a user
Can only be overridden by the user's configuration in the alphabetical path。Actually, it's a userAIf/etc/security/Configure，when
/etc/security/There are also users in the configuration file in the subdirectoryAWhen the configuration，SoASome configurations will be overwritten。The final value is /etc/security/ Configuration of configuration files under。

#
#Each line describes a limit for a user in the form:
#Each line describes a user configuration#<domain> <type> <item> <value>

#Where:
#<domain> can be:
# - a user name A user name# - a group name, with @group syntax The user group format is @GROUP_NAME# - the wildcard *, for default entry is configured as *, representing all users# - 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
havesoft，hardand-，soft指的是when前系统生效的设置值，Soft limits can also be understood as warning values。
hardThe maximum value that can be set in the table name system。softThe limitations cannot be compared withhardHigh limit，use-The table name is set at the same timesoftandhardValue of。
#<item> can be one of the following: <item># - core - limits the core file size (KB) Limits the size of the kernel file.# - data - max data size (KB) Maximum data size# - fsize - maximum filesize (KB) Maximum file size# - memlock - max locked-in-memory address space (KB) Maximum locked memory address space# - nofile - max number of open file descriptors Maximum number of open file descriptors (counted with file descriptors, file descriptors)# - rss - max resident set size (KB) Maximum persistent setting size# - stack - max stack size (KB) Maximum stack size# - cpu - max CPU time (MIN) Maximum CPU usage time in MIN minutes# - nproc - max number of processes# - as - address space limit (KB) Address space limit# - maxlogins - max number of logins for this user# - maxsyslogins - max number of logins on the system Maximum number of simultaneous online users# - priority - the priority to run user process with priority to run user process# - 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] max nice priority allowed to raise to values: [-20, 19]# - rtprio - max realtime pr iority
#
#&lt;domain&gt; &lt;type&gt; &lt;item&gt; &lt;value&gt;
#

#* 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 # All users can open the maximum number of processes by default: 4096root soft    nproc     unlimited # root The maximum number of processes can be opened by default by users Unlimited。

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 # Set soft limits      -H	use the `hard` resource limit # Set hard limits      -a	all current limits are reported# Show all configurations.      -b	the socket buffer size # Set the maximum value of socket buffer.      -c	the maximum size of core files created # Set the maximum value of the core file.      -d	the maximum size of a process's data segment  # Set the maximum value of thread data segment      -e	the maximum scheduling priority (`nice') # Set maximum scheduling priority      -f	the maximum size of files written by the shell and its children # Create maximum value of the file.      -i	the maximum number of pending signals # Set the maximum waiting signal      -l	the maximum size a process may lock into memory #Set the maximum value of locking process in memory      -m	the maximum resident set size 
      -n	the maximum number of open file descriptors # Set the maximum open file descriptor.      -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  # Set the maximum number of processes that the user can create.      -v	the size of virtual memory  # Set the maximum value of virtual memory      -x	the maximum number of file locks

ulimit  -a

ulimit  -n

ulimit  -SHn  65536