How to determine which lightdm greeter is in use?

Question

For those who don't know, greeter is basically the login screen. In case of Lightdm specifically, there are several versions of it:

• unity-greeter
• kylin-greeter
• lightdm-gtk-greeter
• lightdm-kde-greeter
• lightdm-webkit-greeter
• razorqt-lightdm-greeter

The goal:

I need to know how to obtain the greeter version currently in use. Scripting solutions are most welcome ( preferably python, shell scripts, perl ) but also open to C code. Ideally , the solution would work like so:

$ ./get_greeter
kylin-greeter

Issues and failed approaches:

• Checking process listing doesn't work. I have kylin-greeter in use right now, but pgrep -f lightdm | xargs -L 1 ps -o args --no-header -p or pgrep -f kylin | xargs -L 1 ps -o args --no-header -p return nothing that points to /usr/sbin/kylin-greeter
• lsof -p <LIGHTDM_PID> also provides no insights - no /usr/sbin/kylin-greeter among the listing.
• Parsing /etc/lightdm/lightdm.conf is a potential, but not ideal solution, since some flavors of Ubuntu ( such as Kylin ) won't explicitly state greeter session in that file. I would prefer something more reliable.
• gsettings doesn't provide a reliable means of determining greeter in use either - presence of schemas for unity-greeter doesn't mean I am currently using that.
• examining paths and methods on org.freedesktop.DisplayManager service for system bus provided no insights into what greeter is in use either.

Solution

From a couple of quick tests, it seems the only way is to ask LightDM itself:

$ lightdm --show-config |& awk -F= '/greeter-session=/{print $2}'
kylin-greeter

I started testing with default Ubuntu, then installed lightdm-gtk-greeter and the installed kylin-greeter. In each case, it returned the correct option. For example, after editing /etc/lightdm/lightdm.conf to add greeter-session=unity, the output changed:

$ lightdm --show-config |& awk -F= '/greeter-session=/{print $2}'
unity

$ lightdm --show-config
   [LightDM]
A  backup-logs=false

   [Seat:*]
B  greeter-wrapper=/usr/lib/lightdm/lightdm-greeter-session
C  guest-wrapper=/usr/lib/lightdm/lightdm-guest-session
D  user-session=ubuntu
I  greeter-session=unity
F  xserver-command=X -core
I  autologin-guest=false
I  autologin-user=muru
I  autologin-user-timeout=0

Sources:
A  /usr/share/lightdm/lightdm.conf.d/50-disable-log-backup.conf
B  /usr/share/lightdm/lightdm.conf.d/50-greeter-wrapper.conf
C  /usr/share/lightdm/lightdm.conf.d/50-guest-wrapper.conf
D  /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf
E  /usr/share/lightdm/lightdm.conf.d/50-unity-greeter.conf
F  /usr/share/lightdm/lightdm.conf.d/50-xserver-command.conf
G  /usr/share/lightdm/lightdm.conf.d/60-lightdm-gtk-greeter.conf
H  /usr/share/lightdm/lightdm.conf.d/95-kylin-greeter.conf
I  /etc/lightdm/lightdm.conf

Note the source of the configuration.

Comments

[WinEunuuchs2Unix]

There are lots of answers here: wiki.archlinux.org/index.php/LightDM#Greeter

[Sergiy Kolodyazhnyy]

@WinEunuuchs2Unix those all tell me what is available, but not what is being used currently

[Terrance]

Does this help? grep -i exec= /etc/alternatives/lightdm-greeter

[Sergiy Kolodyazhnyy]

@Terrance nope, that also doesn't do it. It gives Exec=lightdm-gtk-greeter , even though I'm using kylin-greeter. I switched to lightdm-webkit-greeter to test, but it still shows the same line

[Terrance]

OK, I tried. Good luck! I hope you find the answer my friend!

[Sergiy Kolodyazhnyy]

@Terrance thank you for the efforts , I do appreciate any help. I'll probably put bounty on the question in 2 days, so keep an eye on it. If you find something, feel free to post

[Terrance]

Nice find there! It is interesting that there are so many configuration files. I didn't even stop to look there. +1