The role of /etc/profile, /etc/bashrc, ~/.bash_profile, ~/.bashrc files

/etc/profile: This file sets the environment information for each user of the system. When the user logs in for the first time, this file is executed.And collect the shell settings from the configuration files in the /etc/profile.d directory.Think of system environment variables.

/etc/bashrc: Execute this file for every user running the bash shell, which is read when the bash shell is opened.

~/.bash_profile: Each user can use this file to enter shell information dedicated to their own use. When the user logs in, this file is executed only once! By default, he sets some environment variables and executes the user's.bashrc file.

~/.bashrc: This file contains bash information specific to your bash shell and is read when logging in and every time a new shell is opened.

~/.bash_logout: This file is executed every time you exit the system (exit the bash shell).

In addition, the variables (global) set in /etc/profile can act on any user, while the variables (local) set in ~/.bashrc can only inherit the variables in /etc/profile, theyIt's a "father-son" relationship.

~/.bash_profile is the interactive, login mode to enter the bash operation
~/.bashrc is the interactive non-login mode to enter the bash operation
Usually the two settings are roughly the same, so usually the former will callthe latter.
Several initialization files of bash - [Ubuntu]
(1) /etc/profile
Global (public) configuration, no matter which user is, the file will be read when logging in.
(2) /ect/bashrc
Ubuntu does not have this file, the corresponding one is /ect/bash.bashrc
It is also a global (public)
When bash is executed, no matter what it ismode, will read this file.
(3) ~/.profile
If bash is executed in login mode, read /.bash_profile, if it does not exist, read /.bash_login, if the first two do not exist, read ~/.profile.
Also, when logging in graphical mode, this file will be read even if /.bash_profile and /.bash_login exist.
(4) ~/.bash_login
If bash is executed in login mode, read /.bash_profile, if it does not exist, read /.bash_login, if the first two do not exist, read ~/.profile.
(5) ~/.bash_profile
Unbutu does not have this file by default, you can create a new one.
This file is read only when bash is executed as login.Usually this configuration file is also configured to read ~/.bashrc.
(6) ~/.bashrc
When bash is executed in non-login form, read this file.If executed in login form, this file will not be read.
(7) ~/.bash_logout
This file will only be read when it is logged out and in the form of longin.That is, when logging out in text mode, this file will be read, and when logging out in graphics mode, this file will not be read.

Here are a few examples on this machine:

When logging in in graphical mode, read sequentially: /etc/profile and ~/.profile
After logging in in graphical mode, when opening a terminal, read in sequence: /etc/bash.bashrc and ~/.bashrc
When logging in in text mode, read in sequence: /etc/bash.bashrc, /etc/profile and ~/.bash_profile
From other users su to this user, there are two cases:
(1) IfWith -l parameter (or - parameter, --login parameter), such as: su -l username, then bash is logged in, it will sequentially read the following configuration files: /etc/bash.bashrc, /etc/profile and ~/.bash_profile.
(2) If there is no -l parameter, then bash is non-login, it will read sequentially: /etc/bash.bashrc and ~/.bashrc
When logging out, or logging out of su user, if it is the longin method, then bash will read: ~/.bash_logout
When executing a custom shell file, if the "bash -l a.sh" method is used, bash will read the line: /etc/profile and ~/.bash_profile, if you use other methods, such as: bash a.sh, ./a.sh, sh a.sh (this does not belong to the bash shell), it will not read any of the above files.
The above example always reads /.bash_profile, if the file does not exist, then reads /.bash_login, if the first two do not exist, reads ~/.profile.