Why does my $LD_LIBRARY_PATH get unset when using screen with bash?

Question

This is related to Why does my LD_LIBRARY_PATH get unset launching terminal?, but a different set of symptoms.

First, /usr/bin/screen is setuid as per the other question. Second, the default shell on this system is /bin/tcsh for various historical reasons, and we're not allowed to chsh to /bin/bash, so I typically run bash manually immediately after login. Third, I almost always use screen, but I want ctrl-a ctrl-c in screen to create a new bash "tab", so I always invoke bash first.

That is:

{~} $ echo $SHELL
/bin/tcsh
{~} $ bash
[~] echo $SHELL
/bin/bash
[~] screen -U
[~]

...and when reconnecting:

{~} $ echo $SHELL
/bin/tcsh
{~} $ screen -dUr
[~] echo $SHELL
/bin/bash
[~] 

However, my $LD_LIBRARY_PATH is there in tcsh, there in bash, but empty once I run screen; it is still present if I just run screen from tcsh, but then I get new tcsh "tabs" when I use ctrl-a ctrl-c in screen.

Any ideas?

Solution

Because screen is setuid, it unsets LD_LIBRARY_PATH. When your shell is tcsh, tcsh initialisation (from .tcshrc I suppose, since screen doesn't default to creating login shells) sets LD_LIBRARY_PATH again. If you want LD_LIBRARY_PATH to be set in your bash screen windows, set it from .bashrc.

Comments

[Admin]

As in my comment to that other question you linked: LD_LIBRARY_PATH is good for debugging / short-term patching binaries, but as a constant addition to your environment, it's a mistake. So I'd recommend that, once you understood why it isn't set in your case, you remove the need for setting it wholesale...

[UltraNurd]

I'm pretty sure this isn't a problem with my bash config, since $LD_LIBRARY_PATH is still inherited from tcsh properly when running bash directly; it's only a problem in the interaction between bash and screen.

[jamesbtate]

@SetJMP fixed --more characters--

[moodboom]

THANK you I just combed half the internet and wrote a bunch of bash scripts to figure this out, before getting it confirmed here. I like to set LD_LIBRARY_PATH and LDFLAGS based on the software I'm developing, not globally. At least now I know where things are going wrong for me now.