Persistent environment variables
So far we've only discussed ways set an environment variable value temporarily until the shell session in which it was set is closed. One may wonder if there is a way to somehow permanently set an environment variable to a certain value.
Note: The shell config files mentioned below are only meant to be read by particular shells and desktop environments and should not be used.
Session-wide environment variables
Environment variable settings that should affect just a particular user (rather than the system as a whole) should be set into:
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~/.pam_environment - This file is specifically meant for setting a user's environment. It is not a script file, but rather consists of assignment expressions, one per line.
PATH DEFAULT=${PATH}:${HOME}/MyPrograms
Note: Using .pam_environment requires a re-login in order to initialize the variables. Restarting just the terminal is not sufficient to be able to use the variables.
If you are using KDE, see the KDE User-base page on this topic.
Not recommended anymore:
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~/.profile - In this file you can also place environment variable assignments, since it gets executed automatically by the DisplayManager during the start-up process desktop session as well as by the login shell when one logs-in from the textual console.
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~/.bash_profile or ~/.bash_login - If one of these file exist, bash executes it rather than "~/.profile" when it is started as a login shell. (Bash will prefer "~/.bash_profile" to "~/.bash_login"). However, these files won't influence a graphical session by default.
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~/.bashrc - Because of the way Ubuntu currently sets up the various script files by default, this may be the easiest place to set variables in. The default configuration nearly guarantees that this file will be executed in each and every invocation of bash as well as while logging in to the graphical environment. The performance cost of this will be negligible; the overhead of forking and execing bash will massively dominate the small cost of setting a handful of variables.
System-wide environment variables
Environment variable settings that affect the system as a whole (rather than just a particular user) should not be placed in any of the many system-level scripts that get executed when the system or the desktop session are loaded, but into
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/etc/environment - This file is specifically meant for system-wide environment variable settings. It is not a script file, but rather consists of assignment expressions, one per line. Specifically, this file stores the system-wide locale and path settings.
Not recommended:
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/etc/profile - This file gets executed whenever a bash login shell is entered (e.g. when logging in from the console or over ssh), as well as by the DisplayManager when the desktop session loads. This is probably the file you will get referred to when asking veteran UNIX system administrators about environment variables. In Ubuntu, however, this file does little more than invoke the /etc/bash.bashrc file.
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/etc/bash.bashrc - This is the system-wide version of the ~/.bashrc file. Ubuntu is configured by default to execute this file whenever a user enters a shell or the desktop environment.
Note: Any variables added to these locations will not be reflected when invoking them with a sudo command, as sudo has a default policy of resetting the Environment and setting a secure path (this behavior is defined in /etc/sudoers). As a workaround, you can use "sudo su" that will provide a shell with root privileges but retaining any modified PATH variables.
Note: When dealing with end-user/home desktop systems may be appropriate to place settings in the user's ~/.pam_environment files discussed above rather than the system-wide ones, since those files do not require one to utilize root privileges in order to edit and are easily moved between systems.
Note: Some systems now use an envvar.sh placed in the /etc/profile.d/ directory to set system wide environment strings.