What's the best distro/shell-agnostic way to set environment variables?
There is unfortunately no fully portable location to set environment variables. The two files that come closest are ~/.profile
, which is the traditional location and works out of the box on many setups, and ~/.pam_environment
, a modern, commonplace but limited alternative.
What to put in ~/.pam_environment
The file ~/.pam_environment
is read by all login methods that use PAM and that have this file enabled. This covers most Linux systems nowadays.
The major advantage of ~/.pam_environment
is that (when enabled) it is read before the user's shell starts, so it works regardless of the session type, login shell and other complexities. It even works for non-interactive logins such as su -c somecommand
and ssh somecommand
.
The major limitation of ~/.pam_environment
is that you can only put simple assignments there, not complex shell syntax. The syntax of this file is as follows.
- Files are parsed line by line.
- Each line must have the form
VAR=VALUE
where VAR consists of letters, digits and underscores. The alternative formVAR DEFAULT=value
allows expansions of environment variables using${VAR}
syntax and the special variables@{HOME}
and@{SHELL}
. #
starts a comment, it cannot appear in a value.- If VALUE is surrounded by
"
, then VAR is set to the string between the quotes. \$
or\@
insert a literal$
or@
and long lines can be split by escaping the newline with a\
.- If there is a syntax error such as no
=
or unquoted whitespace, the variable is removed from the environment.
So on the upside, ~/.pam_environment
works in a large array of circumstances. On the downside, you cannot use the output of a command (e.g. test if a directory or program is present), and some characters (#"
, newline) are impossible or troublesome to put in the value.
What to put in ~/.profile
This file should have portable (POSIX) sh syntax. Only use ksh or bash extensions (arrays, [[ … ]]
, etc.) if you know that your system has these shells as /bin/sh
.
This file may be read by scripts in automated applications, so it should not call programs that produce any output or call exec
. If you want to do that on text-mode logins, do it only for interactive shells. Example:
case $- in *i*)
# Display a message if I have new mail
if mail -e; then echo 'You have new mail'; fi
# If zsh is available, and this looks like a text-mode login, run zsh
case "`ps $PPID` " in
*" login "*)
if type zsh >/dev/null 2>/dev/null; then exec zsh; fi;;
esac
esac
This is an example of using /bin/sh
as your login shell and switching to your favorite shell. See also how can I use bash as my login shell when my sysadmin refuses to let me change it
When is ~/.profile
not read on non-graphical login?
Different login shells read different files.
If your login shell is bash
Bash reads ~/.bash_login
or ~/.bash_profile
if they exist instead of ~/.profile
. Also bash does not read ~/.bashrc
in a login shell even if it is interactive. To never have to remember these quirks again, create a ~/.bash_profile
with the following two lines:
. ~/.profile
case $- in *i*) . ~/.bashrc;; esac
See also Which setup files should be used for setting up environment variables with bash?
If your login shell is zsh
Zsh reads ~/.zprofile
and ~/.zlogin
, but not ~/.profile
. Zsh has a different syntax from sh, but can read ~/.profile
in sh emulation mode. You can use this for your ~/.zprofile
:
emulate sh -c '. ~/.profile'
See also Zsh not hitting ~/.profile
If your login shell is some other shell
There's not much you can do there, short of using /bin/sh
as your login shell and your favorite shell (such as fish) as an interactive shell only. That's what I do with zsh. See above for an example of invoking another shell from ~/.profile
.
Remote commands
When invoking a remote command without going through an interactive shell, not all shells read a startup file.
Ksh reads the file specified by the ENV
variable, if you manage to pass it.
Bash reads ~/.bashrc
if it is not interactive (!) and its parent process is called rshd
or sshd
. So you can start your ~/.bashrc
with
if [[ $- != *i* ]]; then
. ~/.profile
return
fi
Zsh always reads ~/.zshenv
when it starts. Use with caution, since this is read by every single instance of zsh, even when it is a subshell where you've set other variables. If zsh is your login shell and you want to use it to set variables only for remote commands, use a guard: set some variable in ~/.profile
, such as MY_ENVIRONMENT_HAS_BEEN_SET=yes
, and check this guard before reading ~/.profile
.
if [[ -z $MY_ENVIRONMENT_HAS_BEEN_SET ]]; then emulate sh -c '~/.profile'; fi
The case of graphical logins
Many distributions, display managers and desktop environments arrange to run ~/.profile
, either by explicitly sourcing it from the startup scripts or by running a login shell.
Unfortunately, there is no general method to handle distro/DM/DE combinations where ~/.profile
is not read.
If you use a traditional session started by ~/.xsession
, this is the place where you should set your environment variables; do it by sourcing ~/.profile
(i.e. . ~/.profile
). Note that in some setups, the desktop environment startup scripts will source ~/.profile
again.
As far as I know there exists no distro and shell agnostic standard how to set environment variables.
The most common and de facto standard seems to be /etc/profile
and ~/.profile
. The second most common seems to be /etc/environment
and ~/.pam_environment
.
It seems to me that all documentation that I found you also already found. I list them here anyway for the other readers.
- Debian recommends
/etc/profile
and~/.profile
(link). - Ubuntu recommends
/etc/environment
and~/.pam_environment
(link). - Arch Linux mentions, among others,
/etc/profile
and/etc/environment
(link).
Bonus: a text questioning the use and/or misuse of /etc/environment
in debian (link, last update 2008).