What does var mean in linux

In Linux, var means "changeable" and is the abbreviation of variable. It is a directory used to store data that needs to be changed when the system is running. The files stored in this directory often change and are often used for deployment. Project program files; usually the size of the directory where these data are located changes or expands frequently.

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

What does var mean in Linux

variable variable, volatile

The files stored in this directory often change (increase, Modify, delete)

Often used to deploy project programs (php) files

/var includes data to be changed when the system is running. These include directories that are specific to each system, that is, cannot be shared with other computers, such as /var/log, /var/lock, /var/run. Some directories can still be shared with other systems, such as /var/mail, /var/cache/man, /var/cache/fonts,/var/spool/news. The purpose of the var directory is to extract files that need to be changed or temporarily generated files and directories in the usr directory during operation, so that the usr directory can be mounted in a read-only manner. It is implicitly required that the var directory must be mounted in a readable and writable manner.

/var File system: /var contains data that needs to be changed during normal system operation. Usually the size of the directory where these data are located is frequently changed or expanded. It turns out that some contents in the /var directory are in /usr, but in order to maintain the relative stability of the /usr directory, directories that need to be changed frequently are placed in /var.

Through the analysis of this directory, pay attention to the following needs

1) The purpose and function of each directory.

2) What information can be obtained through the information in the directory, and how to access this information.

3) Is it safe to operate files in the directory?

Extended knowledge:

/var/account/pact

Purpose: This directory saves the process records used in the system . When a process terminates, each process writes a record to the statistics file (pacct or acct). The purpose of process statistics is to provide command usage statistics for basic services in the system. The file can be analyzed by data tools (sa, ac).

Usage: The process statistics subsystem is not activated by default, it must be started. To start process statistics in a Linux system, use the accton command, which must be run as root. The form of accton command is accton file, file must exist first. If it does not exist, first use the touch command to create the pacct file: touch /var/log/pacct, and then run accton: accton /var/account/pacct. Once accton is activated, you can use the lastcomm command to monitor the commands executed at any time in the system. To turn off statistics, use the accton command without any parameters.

pact files cannot be read directly with cat.

Note: This file will grow a lot and needs to be maintained (delete, dump)

/var/crash

Purpose: When the system crashes The dumped file can be used to analyze the reasons for machine down.

Use: crash tool to analyze the files in this directory. Reference document linux-2.6.20.6/Documentation/kdump/kdump.txt

crash -S /boot/System.map-2.6.18-53.el5PAE /boot/vmlinuz-2.6.18-53.el5PAE /var/crash/xxxx

/var/cache

Purpose: To store the cache data of the application. The data saved in this directory can be regenerated by the application. Therefore, the loss of data in this directory will not affect the system.

/var/lib

This directory saves status information during the running of the system or an application. Users are not allowed to change files in this directory.

/var/mail

The directory where mail storage files are linked to /var/spool/mail in CGS. In the fhs document, it is clearly stated that it should be extracted from /var/spool/mail so that it can be used by multiple applications on multiple hosts.

/var/opt

add-on application stores variables in this directory and static variables in /opt.

/var/tmp

Temporary files generated by the application can be sorted regularly. /usr/tmp -> ../var/tmp.

/var/lock

Many programs follow the convention of creating a lock file in /var/lock to support the specific device or file they are using. . Other programs are aware of this locked file and will not attempt to use this device or file. Note that this directory cannot be changed at will.

Related recommendations: "Linux Video Tutorial"

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