There are files in /tmp created on each user login that look like .xsession-errors or some other log. Current name for example is /tmp/filercrEUk. I don't see them getiting erased after logout and I don't need them.
Example head content
Xsession: X session started for user at п'ятниця, 5 липня 2019 14:34:41 +0300
localuser:user being added to access control list
dbus-update-activation-environment: warning: error sending to systemd: org.freedesktop.DBus.Error.Spawn.ChildExited: Process org.freedesktop.systemd1 exited with status 1
startkde: Starting up...
dbus-update-activation-environment: warning: error sending to systemd: org.freedesktop.DBus.Error.Spawn.ChildExited: Process org.freedesktop.systemd1 exited with status 1
kdeinit5: preparing to launch '/usr/lib/x86_64-linux-gnu/libexec/kf5/klauncher'
kdeinit5: Launched KLauncher, pid = 498, result = 0
kdeinit5: opened connection to :0
kdeinit5: preparing to launch 'libkdeinit5_kded5'
kdeinit5: Launched KDED, pid = 503 result = 0