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I've just installed Mir and I'm wondering if I'm actually running it or if it fell back to X. How can I tell if Mir is running?

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up vote 11 down vote accepted

You can also simply check if the system compositor process is running:

 ps afx | grep unity-system-compositor

On my system running Mir it returns something like this:

jorge@jillociraptor:~$ ps afx | grep unity-system-compositor
 4260 pts/0    S+     0:00          |   |               \_ grep --color=auto unity-system-compositor
 1606 ?        S      0:00 /usr/sbin/unity-system-compositor --from-dm-fd 9 --to-dm-fd 13 --vt 7

Machines NOT running Mir will not show unity-system-compositor running.


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You can also use ps -e | grep unity-system-compositor to avoid matching grep itself. With this, no output will be shown if Mir is not running. – minerz029 Jan 2 '14 at 5:42
@minerz029 Running Jorge's Command, I get 4868 pts/4 S+ 0:00 _ grep --color=auto unity-system-compositor Running your command, I get nothing. So I am confused. – Akiva Jul 26 '14 at 23:23
ps -e | grep unity-system-co

Will return one response if Mir is running, nothing if it is not. This is because 'ps -e' actually truncates the process names to 15 characters (known upstream bug/limitation). I found the suggestion from minerz029 always returned nothing even if Mir was running.

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Why would anyone use ps | grep when the command pgrep exists? Try pgrep -fa unity-system-compositor. – muru Sep 12 '14 at 0:38

It's going to depend on what you mean by "I just installed Mir". Mir is really just a set of libraries. There are client libraries and server libraries. There are also several different packages that provide actual Mir server binaries.

There is a demo Mir server, but if you were running it you would know, because you'd have switched to a VT and typed in the command to run it. That server is found in the mir-demos package.

There's the Unity 8 Mir server. It runs as a part of Unity 8 (package unity8). You'd know you were running that because your desktop would look like a Unity 8 desktop.

Finally, there is the unity-system-compositor Mir server, which is generally started by LightDM. Unless you wrote your own LightDM integration scripts, you either need to install the Unity 8 desktop session (package unity8-desktop-session-mir), in which case the only way to run the Mir server is to log in to the Unity 8 desktop, or you installed the ubuntu-desktop-mir package, in which case the other answers are correct: a ps will show the unity-system-compositor running underneath the X server.

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