Set environment variable for all of tmux shells when gnome-sessions gets restarted

environment-variableshooktmux

To solve this problem, I need to set the environment variable DBUS_SESSION_BUS_ADDRESS for all shells inside tmux every time I restart gnome without restarting tmux (this is often). How can I best solve this?

I cannot cleanly change another processes' environment.
I cannot send a command to every pane
I could set the environment variable in my PROMPT_COMMAND. It means I need to press Enter before I can run gnome applications. It's ugly and overkill.
I could set the environment variable by executing a command before every command, but that's a bit overkill.

Is there another way to fix this in a cleaner way?

Best Answer

In this specific case, instead of letting Gnome run dbus-launch to create a random D-Bus address, start dbus-daemon explicitly early in your X session startup and give it a fixed address like unix:path=~/.dbus-$HOSTNAME-$DISPLAY.

Given the information in the bug report, you may even be able to get away with unset DBUS_SESSION_BUS_ADDRESS and let applications find out the bus address from the root window properties.

In the general case, your assessment is correct: all you have is unreliable methods such as ptrace (which may crash the program, or not work due to a security framework such as Apparmor or SELinux) or injecting a shell command (which only works in panes that are currently at a shell prompt). Running a command at each shell prompt (with zsh's preexec or bash's PROMPT_COMMAND) at least doesn't risk breaking stuff.

Another solution would be an LD_PRELOAD library that intercepts getenv calls. This also feels like overkill.

Your best bet is to let the application do the job by creating a level of indirection: arrange for the value of the environment variable to remain valid, and for the application to interpret it in a situation-aware manner. Letting the application look up the D-Bus bus address in the root window properties is an example of this approach.

Related Solutions

Set the language for a single program execution

In ksh, bash, and similar shells,

LANG=es_MX.utf8 ./hellogt

will set LANG=es_MX.utf8 only for the invocation of ./hellogt.

More portably, there is a program called env

env LANG=es_MX.utf8 ./hellogt

which will set environment variables and run the program specified. This works in all shells, including csh and traditional sh (which do not support the first method).

Shell – Environment variable for command called via nice

JIM=x
JIM=20 nice -n 10 echo $JIM

does pass the JIM=20 environment variable to nice, but it's not nice nor echo that expands $JIM, that's the shell.

The shell forks a process and executes:

execve("/usr/bin/nice", ["nice", "-n", "10", "echo", "x"], ["JIM=20", other vars])

nice sets the niceness and then executes in the same process:

execve("/bin/echo", ["echo", "x"], ["JIM=20", other vars])

So echo does receive JIM=20 in its environment, but echo doesn't do anything with its environment.

Had you run:

JIM=20 nice -n 10 sh -c 'echo $JIM'

Then sh would have done something with that environment variable. Shells map the environment variables they receive to shell variables. So above, that sh would have set its $JIM variable to 20 and called its echo builtin with 20 as argument.

Best Answer

Related Solutions

Set the language for a single program execution

Shell – Environment variable for command called via nice

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