Unfortunately, the solution with .xsession file doesn't work.
I resorted to something very simplistic:
<begin-of-the-file>
exec /usr/bin/marco
<EOF>
Note: I use mate desktop with marco wm.
They also use some other stuff, I'm not sure if I need any of these lines:
xsetroot -solid gray
xmodmap -e "keysym Super_L = Multi_key"
xset s off; xset dpms 0 1800 0
exec fvwm
...and my session doesn't start at all - login popup disappears and nothing else happens on the screen.
I see that marco is started and ssh-agent is the only process under it.
I have no idea why my .xsession file name appears in the command line where ssh-agent is started but it looks suspicious. Another x-session is started?
root 17474 0.0 0.1 165776 9604 ? Sl 21:23 0:00 \_ lightdm --session-child 12 21
arek 17484 0.0 0.3 274164 27188 ? Ssl 21:23 0:00 \_ /usr/bin/marco
arek 17572 0.0 0.0 5964 468 ? Ss 21:23 0:00 \_ /usr/bin/ssh-agent env TMPDIR=/tmp/0_arek /usr/bin/im-launch /bin/bash /home/arek/.xsession
What could happen here?