How can I find out the startup files read and environment variables created when Ubuntu was started with graphical interface

Question

In Ubuntu 16.04 with LXDE or Gnome,

• how can I find out the environment variables created when Ubuntu was started with graphical interface?

• when Ubuntu was started with graphical interface, which startup files are read and executed, /etc/profile, /etc/profile.d/*, ~/.profile, ~/.bash_profile, /etc/environment, /etc/bash.bashrc, ~/.bashrc?

Thanks.

Answer 1

This is quite complex.

Pam also can add environment variables, as well as other things (login program, getty, whatever...).

What I used to do is to add lines of the style (see this)

export CALLED_IN_ETC_PROFILE=$(date date +%s.%N) 

in all suspicious files, and then look at the result for example using https://askubuntu.com/a/356973/16395.

To find which program/file could be responsible of the setting of a variable, you can try to look at the process tree of a shell into a terminal emulator:

[romano:/etc/X11/Xsession.d] % pstree -a -s -l -p -u $$
systemd,1 splash
  └─gdm3,1926
      └─gdm-session-wor,3752
          └─gdm-x-session,3807,romano --run-script gnome-session --session=gnome
              └─upstart,3824 --user
                  └─gnome-terminal-,5027
                      └─zsh,11224
                          └─pstree,11831 -a -s -l -p -u 11224

...I think that to start the graphic session, gdm-x-session is started from a user shell (note the UID change in the chain) in non-interactive mode, so that .profile is read (but not .bashrc, which is read by the shell in terminal emulator).

The tree is somewhat different if called from the gnome-shell:

bash-4.3$ pstree -a -s -l -p -u $$
systemd,1 splash
  └─gdm3,1926
      └─gdm-session-wor,3752
          └─gdm-x-session,3807,romano --run-script gnome-session --session=gnome
              └─upstart,3824 --user
                  └─gnome-session-b,4162 --session=gnome
                      └─gnome-shell,4278
                          └─xterm,11882 -e bash --noprofile --norc
                              └─bash,11884 --noprofile --norc
                                  └─pstree,11885 -a -s -l -p -u 11884

but this is expected.

BTW, a lot of environment variables could also be set before the UID change to the user; there are a lot of scripts in /etc/X11/Xsession.d and around that the X server, gdm (or whichever display manager you use), that can set environment variables.