LD_LIBRARY_PATH unset by screen

Question

Running screen in bash wipes the variable LD_LIBRARY_PATH. I've done some reading and it seems that this is expected behaviour, but I need to get around it.

The workaround is adding the LD_LIBRARY_PATH declaration to ~/.bashrc. In my case, LD_LIBRARY_PATH gets changed a lot between the launch of the shell and when I invoke screen, so I need to get the current value of LD_LIBRARY_PATH into the screen session.

Answer 1

screen doesn't unset the environment variable; it is removed by Linux itself.

On most systems, the /usr/bin/screen executable is installed with the setgid bit for utmp group, in order to be able to modify the utmp database. It also uses setgid to control access to the socket directory (/var/run/screen/).

On Linux, when a setuid (or setgid) program is ran, it does not receive certain environment variables (including LD_LIBRARY_PATH, several other LD_* variables, and HOSTALIASES), in order to reduce the possible attack points: Otherwise you could write a small library and trick su or sudo into calling your "improved" functions that way.

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You can remove the setgid bit from screen, but you will have to make the socket directory fully accessible by everyone (mode 0777). It shouldn't be a security risk, though, as screen also checks the attacher's UID itself.

However, you should not make the utmp database world-writable.

Answer 2

Try exporting the environment variable you are interested in.

export LD_LIBRARY_PATH