xflock4 fails to lock, if light-locker (and xscreensaver) is not running, but still exits with 0

[Jarno Suni]

xflock4 fails to lock, but still exits with 0, if xscreensaver is not running and light-locker is not running, but is installed. Related to Bug #1536238. Could be fixed by examining the output of "light-locker-command -q" to check, if light-locker is available for locking or by fixing `light-locker-command -l` to exit with nonzero in such case. (Besides, e.g. `i3lock -d -c 000000` or `xtrlock -b` could be used as backup locker in case light-locker fails for some reason.)

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: xfce4-session 4.12.1-3ubuntu1
ProcVersionSignature: Ubuntu 4.2.0-25.30-generic 4.2.6
Uname: Linux 4.2.0-25-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CurrentDesktop: XFCE
Date: Sun Jan 24 17:53:54 2016
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-11-21 (63 days ago)
InstallationMedia: Xubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
SourcePackage: xfce4-session
UpgradeStatus: No upgrade log present (probably fresh install)

[Jarno Suni (jarnos)]

Besides fixing this bug, the patch works around Bug #1536237, and adds support for i3lock and xtrlock.

[Jarno Suni (jarnos)]

Does this security fix have to work in 12.04? Note that the script does not work there with xtrlock; `xtrlock -b`does not work there, for the option -b is implemented since xtrlock version 2.4 only. I can work this out, though. On the other hand, xlock is not provided after 12.04, propably for a reason, so it might be a good idea to remove the xlock option from the script.

[Jarno Suni (jarnos)]

Now xtrlock -b should not be a problem even in 12.04. I did not install mate-screensaver or cinnamon-screensaver it, but according to manual pages, mate-screensaver-command and cinnamon-screensaver-command support the same command-line options that are used in the script for light-locker-command and gnome-screensaver-command. (It is easy to remove the support for Mate and Cinnamon.)

[Jarno Suni (jarnos)]

Note, that the former attachments do not work by 14.04, because the old light-locker-command does not have --query option. See https://bugzilla.xfce.org/show_bug.cgi?id=10217 and espceially attachment http://bug-attachment.xfce.org/attachment.cgi?id=6595, especially comments 41 and 43 for more backwards compatible implementation; see also comment 40, but note that its attachment is not backwards compatible.

[Jarno Suni (jarnos)]

This bug is a regression. In 14.04 `light-locker-command -l` works as expected (i.e. returns non-zero, if the daemon is not running).

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "patch against Wily's xflock4" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Jarno Suni (jarnos)]

A remaining attachment contains a fix for Wily:
https://bugs.launchpad.net/ubuntu/+source/xfce4-session/+bug/1537507/+attachment/4558529/+files/xflock4-new

However, I have attached a better version in Xfce Bugzilla; the version that works with older light-locker could be backported to an older release of Xubuntu. Maybe most importantly, it restores DPMS state after using a regular (daemonless) locker, so Xfce4-power-manager's presentation mode is not disturbed (https://bugzilla.xfce.org/show_bug.cgi?id=9574). (That backwards compatible version of xflock4 contains line "set -o xtrace", so it displays debug information. Change it to "set +o xtrace" or delete the line to disable debug information.)

[Theo Linkspfeifer (lastonestanding)]

It looks like this was fixed. Tested in 18.04:

xubuntu@xubuntu:~$ which light-locker xscreensaver
/usr/bin/light-locker
/usr/bin/xscreensaver
xubuntu@xubuntu:~$ killall light-locker xscreensaver
light-locker: no process found
xscreensaver: no process found
xubuntu@xubuntu:~$ xflock4
xubuntu@xubuntu:~$ echo $?
1
xubuntu@xubuntu:~$

[Jarno Suni (jarnos)]

It still fails to work corrently, if additionally gnome-screensaver is installed, but not running IIRC. Please confirm.

[Theo Linkspfeifer (lastonestanding)]

Yes, I can confirm that.

xubuntu@xubuntu:~$ killall gnome-screensaver
gnome-screensaver: no process found
xubuntu@xubuntu:~$ gnome-screensaver-command --lock
xubuntu@xubuntu:~$ echo $?
0
xubuntu@xubuntu:~$

The command starts a gnome-screensaver process, but --lock does not seem to work at all (--activate shows the unlock screen without login form).

[Jarno Suni (jarnos)]

So the fix would be to modify the xflock4 script. I have done such a fix and I have developed the script further; See my attachment (and recent comments) at https://bugzilla.xfce.org/show_bug.cgi?id=10217

Note that later version of xfce4-session puts primary burden of determining which locker to use to new xfce-screensaver.c (but still uses xflock4 as one possible option).

[Theo Linkspfeifer (lastonestanding)]

How would that fix the broken gnome-screensaver(-command)? I assume that removing it from xflock4 is the only fix.

[Jarno Suni (jarnos)]

By using --query option like I do in https://bugzilla.xfce.org/attachment.cgi?id=7254 I referred to in previous comment (or in the attachment I uploaded in comment #4 about two and half years ago).

[Theo Linkspfeifer (lastonestanding)]

Again, why even keep supporting gnome-screensaver if it is deprecated and not working properly anymore..

[Jarno Suni (jarnos)]

I do not know. It is still in the repos and seems to be supported by the latest xfce4-session in git.

[Jarno Suni (jarnos)]

Do you know other issues with gnome-screensaver?

[Theo Linkspfeifer (lastonestanding)]

The only one I know about and encountered is that gnome-screensaver-command --lock exits with 0 after spawning a gnome-screensaver process (bug 1536237) while the screen remains not locked.

[Jarno Suni (jarnos)]

Oh, in my experience it does not spwan gnome-screensaver anymore in 18.04, but please tell about that in the bug report. It is still unconfirmed bug there.