How to set environment variable for everyone under my linux system?

Question

Can I have certain settings that are universal for all my users?

Answer 1

Amazingly, Unix and Linux do not actually have a place to set global environment variables. The best you can do is arrange for any specific shell to have a site-specific initialization.

If you put it in /etc/profile, that will take care of things for most posix-compatible shell users. This is probably "good enough" for non-critical purposes.

But anyone with a csh or tcsh shell won't see it, and I don't believe csh has a global initialization file.

Answer 2

Some interesting excerpts from the bash manpage:

When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.
...
When an interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and ~/.bashrc, if these files exist. This may be inhibited by using the --norc option. The --rcfile file option will force bash to read and execute commands from file instead of /etc/bash.bashrc and ~/.bashrc.

So have a look at /etc/profile or /etc/bash.bashrc, these files are the right places for global settings. Put something like this in them to set up an environement variable:

export MY_VAR=xxx

Answer 3

Every process running under the Linux kernel receives its own, unique environment that it inherits from its parent. In this case, the parent will be either a shell itself (spawning a sub shell), or the 'login' program (on a typical system).

As each process' environment is protected, there is no way to 'inject' an environmental variable to every running process, so even if you modify the default shell .rc / profile, it won't go into effect until each process exits and reloads its start up settings.

Look in /etc/ to modify the default start up variables for any particular shell. Just realize that users can (and often do) change them in their individual settings.

Unix is designed to obey the user, within limits.

NB: Bash is not the only shell on your system. Pay careful attention to what the /bin/sh symbolic link actually points to. On many systems, this could actually be dash which is (by default, with no special invocation) POSIXLY correct. Therefore, you should take care to modify both defaults, or scripts that start with /bin/sh will not inherit your global defaults. Similarly, take care to avoid syntax that only bash understands when editing both, aka avoiding bashisms.

Answer 4

As well as /etc/profile which others have mentioned, some Linux systems now use a directory /etc/profile.d/; any .sh files in there will be sourced by /etc/profile. It's slightly neater to keep your custom environment stuff in these files than to just edit /etc/profile.