linux-system boot process, execution of configuration files

Note: Settings for environment variables are set by export.

For export use see: http://www.cnblogs.com/DengGao/p/6341443.html

Environment variables are closely related to the shell, and the user logs on to the system and launches a shell. It's usually bash for Linux, but it can be reset or switched to another Shell. For UNIX, it could be cshelll. Environment variables are set by shell commands, and set environment variables can be used by all current users running programs. For bash, the shell program can use variable names to access the appropriate environment variables, and export to set environment variables. This is illustrated by a few examples below.

1) Etc/profile: This file sets the environment information for each user of the system, and the file is executed when the user logs on for the first time.
and collect the shell settings from the configuration file of the/ETC/PROFILE.D directory.
Note: Here we set the global variables that are available to all users.

2)/ETC/BASHRC: Executes this file for each user running the bash shell. When the bash shell is opened, the file is read.

3) ~/.bash_profile: Each user can use the file to enter the shell information dedicated to their own use, when the user log on, the file is only executed once! By default, he sets some environment variables to execute the user's. bashrc file.
Note: ~ Under Linux is the variable representing the home.
In addition to different Linux operating systems, this file may be different, may be ~/.bash_profile, ~/.bash_login or ~/.profile one or several, if there are several, then the order of execution is: ~/.bash_ Profile, ~/.bash_login, ~/.profile. For example, I use Ubuntu, my User folder, the default is only the ~/.profile file.

4) ~/.BASHRC: This file contains bash information dedicated to your bash shell, which is read when you log in and every time you open a new shell.
(Note: This file is. Beginning, so it is hidden in the folder)
So how do we add our own defined environment variables?
Open the file with Notepad, and then write it in the last:
Xiaokang=kangkang
And then save it so that each time we open a new terminal, we have this variable in effect. Remember, if you have opened a terminal, and then you modify the file, then this terminal will not be effective. In general, the user is best to make changes here, but sometimes it will overwrite the parent variables, such as path is root set, but if you write in this file path=xx, then all of the future path is XX, so we should write in this file:
Path= $PATH: XX
This adds the original and your own. And note that the Linux system uses: Split to represent side by side, not windo;
3 and 4 are all in the user directory, their only difference is:. Bash_profile can only be started once when logging in. This 3 file does not seem to be in my Ubuntu.

5) ~/.bash_logout: Executes the file each time it exits the system (exiting the bash shell).
In addition, the variables set in/etc/profile (global) can be applied to any user, while the variables set in ~/.BASHRC, etc. (local) only inherit variables from/etc/profile, they are "parent-child \" relationships.

~/.bash_profile is interactive, login way into bash run
~/.BASHRC is an interactive non-login way into bash run
Usually the two settings are roughly the same, so the former usually calls the latter.

OK, let's summarize how they do it:
When you log in and the shell is bash, bash first executes the command in the/etc/profile file (if the file exists), and then it looks for the ~/.bash_profile,~/.bash_login or ~/.profile file sequentially, and executes the command found in the first readable file. When login bash exits, it executes the commands in the ~/.bash_logout file.
When you start an interactive bash, it executes the commands in the ~/.BASHRC file (if the file exists and is readable). When you start non-interactively to run a shell script, bash looks for the BASH_ENV environment variable to determine the name of the execution file.

The second piece of information
--------------------------------------------------------------------------------

The procedure to execute a file when logging on to Linux is as follows:
When you first log in to Linux, start the/etc/profile file, and then start the ~/.bash_profile in the user directory, ~/.bash_login or ~/. One of the profiles (depending on the different Linux operating systems, the naming is different!!!!!!!!!! In my Ubuntu only ~/.profile),

The order of execution is: ~/.bash_profile, ~/.bash_login, ~/.profile.
If the ~/.bash_profile file exists, the ~/.BASHRC file is typically executed.

Because the following code is commonly found in the ~/.bash_profile file:
If [-f ~/.BASHRC]; Then
. ./BASHRC
Fi
In ~/.BASHRC, the following code is generally available:
if [-F/ETC/BASHRC]; Then
. /bashrc
Fi
Therefore, ~/.BASHRC will call the/ETC/BASHRC file. Finally, when you exit the shell, the ~/.bash_logout file is also executed.
Order of execution:/etc/profile---(~/.bash_profile | ~/.bash_login | ~/.profile), ~/.BASHRC,/ETC/BASHRC, ~/.bash_lo Gout
For the scope of each file, the following instructions were found on the Web:
(1)/etc/profile: This file sets the environment information for each user of the system, and the file is executed when the user logs on for the first time. and collect the shell settings from the configuration file of the/ETC/PROFILE.D directory.
(2)/ETC/BASHRC: Executes this file for each user running the bash shell. When the bash shell is opened, the file is read.
(3) ~/.bash_profile: Each user can use this file to enter the shell information dedicated to their own use, when the user log on, the file is only executed once! By default, he sets some environment variables to execute the user's. bashrc file.
(4) ~/.BASHRC: This file contains bash information dedicated to your bash shell, which is read when you log in and every time you open a new shell.
(5)
~/.bash_logout: Executes the file each time it exits the system (exiting the bash shell).
In addition, the variables set in/etc/profile (global) can be applied to any user, while the variables set in the ~/.BASHRC (local) only inherit
Variables in/etc/profile, they are "parent-child" relationships.
(6) ~/.bash_profile is the interactive, login way into bash run ~/.BASHRC is the interactive non-login way into bash normally the two settings are roughly the same, so the former usually calls the latter.
The use of various environment variable settings files such as/etc/profile and/etc/environment
First add the export LANG=ZH_CN to/etc/profile, exit the system to log in again, login prompt display in English.
Delete the export lang=zh_cn in/etc/profile, add LNAG=ZH_CN to/etc/environment, exit the system to log in again, sign in prompt to display Chinese.
The user environment is established by always executing/etc/profile and then reading the/etc/environment. Why is it as different as the above?
The/etc/environment should be executed first and then executed/etc/profile.
/etc/environment is the environment that sets up the entire system, and/etc/profile is the environment for setting up all users, regardless of the logged-on user, which is related to the logged-on user.
The execution of the system application can be irrelevant to the user environment, but it is related to the system environment, so when you log in, you see the prompt information, such as date, time information display format is related to the system environment Lang, default Lang=en_us, if the system environment LANG=ZH_CN, The message is in Chinese, otherwise it is in English.
For a user's shell initialization, the/etc/profile is executed first, and then the file/etc/environment is read. The/etc/environment is performed first for the entire system. Do you understand that correctly?
/etc/enviroment--/etc/profile-$HOME/.profile--$HOME/.env (if present)
/etc/profile is the environment variable for all users
/etc/enviroment is the environment variable of the system
The order in which the shell reads the system when logging in should be
/etc/profile->/etc/enviroment-$HOME/.profile-$HOME/.env
The reason should be the difference between the user environment and the system environment described by JTW.
If the same variable has different values in the user environment (/etc/profile) and the system environment (/etc/environment), then the user environment should prevail.

linux-system boot process, execution of configuration files