Ubuntu – How to lock the screen in XUbuntu 16.04

16.04lock-screenxubuntu

I've been trying to figure out how to lock the screen in XUbuntu 16.04 and I can't seem to make anything work. Various posts suggest using the settings under 'Power Manager' and 'Light Locker Settings', which have selectors to enable and disable the screensaver, and I've tried all possible combinations of them, but none of them do anything.

Other places suggest running xflock4 or hitting ctrl-alt-del (which on the keyboard shortcuts runs xflock4), but that also does nothing. There's also no documentation for xflock4 (man xflock4 says "No manual entry" and xflock4 --help does nothing.)

Update

After poking around things for awhile, I fould dm-tool which has a lock option. Running dm-tool lock from a terminal successfully locks the screen. I can also set the keyboard shortcuts to make ctrl-alt-del run dm-tool lock, so I can now lock the screen with a key combo.

However, I still can't figure out how to get it to lock the screen after a timeout…

Best Answer

Here's the default Xubuntu setup:

light-locker is set to autostart because it must be running in the background to work
Keyboard shortcuts for Ctrl+Alt+Del and Ctrl+Alt+L are configured that call xflock4
xflock4 calls light-locker to lock the screen

If you run xflock4 in a terminal and nothing happens, odds are light-locker isn't running. The solution more or less is to restore the default settings:

Remove light-locker-settings package. It's not necessary because screen lock settings are handled by Xfce Power Manager (as you can see in the screenshot you posted)
```
sudo apt remove light-locker-settings
```

Make sure essential packages are installed (just to be safe)

sudo apt install light-locker xfce4-power-manager xfce4-session

Reset light-locker settings
```
sudo dpkg-reconfigure light-locker
```
Remove any autostart overrides
```
rm ~/.config/autostart/light-locker.desktop
```
(This can be removed because the light-locker package installs a default autostart file here: /etc/xdg/autostart/light-locker.desktop)
Reset the LockCommand setting in case it's been overrriden
```
xfconf-query -c xfce4-session -p /general/LockCommand -r
```
(xflock4 is just a shell script that will first look at LockCommand to see what command to run, falling back to light-locker if it isn't set)

Reset keyboard shortcuts

If you're not worried about losing any other custom keyboard shortcuts, you can just reset them all to default:
```
xfconf-query -c xfce4-keyboard-shortcuts -p / -rR
```

Otherwise, these are the specific keyboard shortcuts Xubuntu sets by default for screen locking:

xfconf-query -c xfce4-keyboard-shortcuts -p "/commands/custom/<Primary><Alt>Delete" -s "xflock4" -n -t string
xfconf-query -c xfce4-keyboard-shortcuts -p "/commands/custom/<Primary><Alt>l" -s "xflock4" -n -t string
xfconf-query -c xfce4-keyboard-shortcuts -p "/commands/default/<Primary><Alt>Delete" -s "xflock4" -n -t string
xfconf-query -c xfce4-keyboard-shortcuts -p "/commands/default/<Primary><Alt>l" -s "xflock4" -n -t string

Log out and log back in. This will make sure light-locker autostart is working and also may be necessary for the keyboard shortcuts to refresh.

Make sure light-locker is running

$ ps -e | grep light-locker
 1869 ?        00:00:00 light-locker

Make sure xflock4 locks the screen
```
xflock4
```
Make sure the keyboard shortcuts to lock the screen work
- Ctrl+Alt+Del
- Ctrl+Alt+L
Lastly, if you want the screen to automatically lock after a certain time
1. Open the menu > Settings > Power Manager > Security
2. Automatically lock the session > When the screensaver is activated
3. If you want to have a real screensaver, you'll need to install and configure xscreensaver or gnome-screensaver. Otherwise if you're okay with a blank screen, go to the Display tab in Power Manager and adjust the times as desired

Related Solutions

Ubuntu – How to prevent the Sleep button from locking the screen

You can remap the key using ~/.Xmodmap. Use xev (in a terminal) to find the offending keycode, then assign a different keysym, e.g. XF86WakeUp. Append this line to ~/.Xmodmap (create that file if it does not yet exist):

keycode 150 = XF86WakeUp

After logging out and logging in again your key should be mapped. If you don't want to log out, you can also use xmodmap ~/.Xmodmap to reload the key mappings.

Using xev to actually find the keycode of the key that you want to remap might be not so easy: if the key is already bound to an action (e.g. in the Gnome keyboard properties), xev does not show the keycode. As an example, this is the kind of xev output that you want to see:

KeyPress event, serial 41, synthetic NO, window 0x5800001,
    root 0xb3, subw 0x0, time 312883, (737,182), root:(946,647),
    state 0x0, keycode 180 (keysym 0x1008ff18, XF86HomePage), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

You can see the keycode (180) in the third line after the word "keycode". If you don't get such a block that starts with "KeyPress event", your key probably is already bound. You can try to use a non-Gnome desktop like LXDE or KDE and use xev there.

Ubuntu – How to lock AND blank the screen from the keyboard in 14.04

Open System Settings and navigate to Keyboard -> Shortcuts. Open the "System" section, click on "Lock screen" and press Backspace. This will disable the system lock screen shortcut.

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