What is starting i3 when I run startx?

Question

I'm trying to find the configuration file that startx uses to start the i3 window manager.

The weird part is, grep -r i3 returns no relevant results in ~ and /etc/X11/.

I have checked every file I can think of. My ~ directory does not have any .x* files in it. No .x* file in the /etc/X11 sub dirs has any reference to i3. I checked .xinitrc, .Xsession, etc.

But.. when I login, I can run startx and i3 magically starts. I am utterly perplexed.

Running Ubuntu on an odroid, but that shouldn't make a difference.

If it makes a difference, I installed i3 as root before creating my user.

cat /etc/issue
Ubuntu 16.04.1 LTS \n \l
uname -a
Linux odroid 3.10.96-113 #1 SMP PREEMPT Wed Jul 6 22:19:28 UTC 2016 armv7l armv7l armv7l GNU/Linux

As you can see below, there are no places left to hide:

[email protected]:/home/matt# find / -name *xinit*
/var/lib/dpkg/info/xinit.conffiles
/var/lib/dpkg/info/xinit.list
/var/lib/dpkg/info/xinit.md5sums
/var/lib/dpkg/info/xinit.postinst
/etc/X11/xinit
/etc/X11/xinit/xinitrc.d
/etc/X11/xinit/xinitrc
/usr/share/doc/xinit
/usr/share/man/man1/xinit.1.gz
/usr/bin/xinit
[email protected]:/home/matt# 
[email protected]:/home# grep -r 'exec i3'
matt/.config/i3/config_bak:bindsym $mod+Return exec i3-sensible-terminal
matt/.config/i3/config:bindsym $mod+Return exec i3-sensible-terminal
[email protected]:/home# cd /etc/
[email protected]:/etc# grep -r 'exec i3'
i3/config:bindsym Mod1+Return exec i3-sensible-terminal
i3/config:exec i3-config-wizard
i3/config.keycodes:bindcode $mod+36 exec i3-sensible-terminal
[email protected]:/etc# 

What is starting i3 when I run startx?

Solution

i3 seems to be a X Window Manager. If it's your system's default window manager, it's registered with the 'alternatives' system - which you can check with update-alternatives --display x-window-manager. This means that /usr/bin/x-window-manager is a symlink to /etc/alternatives/x-window-manager; this in turn is set by the 'alternatives' system to point to i3.

If you want to change the system default window manager, root can update-alternatives --config x-window-manager.

If Xsession finds a window manager, it will make this the default program to start in the session. In Debian, this is done in /etc/X11/Xsession.d/50x11-common_determine-startup.

If a users want to run a different program in their X session, then they can write a ~/.xsession that starts (or execs) the desired program.