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How Is The Environment Established?
When we log on to the system, the bash program starts, and reads a series of configura- tion scripts called startup files, which define the default environment shared by all users. This is followed by more startup files in our home directory that define our personal envi- ronment. The exact sequence depends on the type of shell session being started. There are two kinds: a login shell session and a non-login shell session.
A login shell session is one in which we are prompted for our username and password; when we start a virtual console session, for example. A non-login shell session typically occurs when we launch a terminal session in the GUI.
Login shells read one or more startup files as shown in Table 11-2:
Table 11-2: Startup Files For Login Shell Sessions
File Contents
File Contents
/etc/profile A global configuration script that applies to all users.
~/.bash_profile A user's personal startup file. Can be used to extend or
override settings in the global configuration script.
~/.bash_login If ~/.bash_profile is not found, bash attempts to
read this script.
~/.profile If neither ~/.bash_profile nor ~/.bash_login
is found, bash attempts to read this file. This is the default in Debian-based distributions, such as Ubuntu.
Non-login shell sessions read the following startup files:
Table 11-3: Startup Files For Non-Login Shell Sessions
File Contents
File Contents
/etc/bash.bashrc A global configuration script that applies to all users.
~/.bashrc A user's personal startup file. Can be used to extend or
override settings in the global configuration script.
In addition to reading the startup files above, non-login shells also inherit the environ- ment from their parent process, usually a login shell.
Take a look and see which of these startup files are installed. Remember — since most of the filenames listed above start with a period (meaning that they are hidden), we will need to use the “-a” option when using ls.
The ~/.bashrc file is probably the most important startup file from the ordinary user’s point of view, since it is almost always read. Non-login shells read it by default and most startup files for login shells are written in such a way as to read the ~/.bashrc file as well.