Since I did the upgrade to 15.04 there is a very strange behaviour whenever I lock the screen.

Right after the screen is locked and the monitor turns black the computer goes to sleep (or suspend mode, I don't know exactly what's the correct term for this). To wake it up I have to first press the enter key. Then the computer is revived, but the monitor is all grey and I have to click on it for the login screen to show up. This is the moment where I can finally introduce my password to login. And of course, going to sleep it means that my network connection is disconnected every time (very annoying because it terminates all my active connections).

This never happened before, everything worked fine with the lock screen process up until the upgrade. I checked the settings for power management and light locker but there are no options that I can use to forbid the computer to go to sleep when the screen is locked.

What should I do ?

2 Answers 2


This behaviour has been around since at least Ubuntu 14.04 (i.e. kernel 3.13) and is reported as Bug #1350513. On Sony models Ctrl+Alt+F1 and Ctrl+Alt+L can start the shut-down procedure; on Lenovo models it sends the system to sleeping mode.

In all likelihood these are all symptoms of a same issue with the kernel. I would suggest you jump over to Launchpad and report there in detail your computer model and all the procedures that unexpectedly send the system to sleeping mode.

  • thanks for your answer, the thing is that this started to happen after I upgraded to 15.04 (kernel 3.19), didn't have the problem with 14.10, for instance. I will go to launchpad and report the issue.
    – misterjinx
    Apr 29, 2015 at 11:41

Perhaps it is related with this change of terminals:

One thing that changes for users is the fact that locking with LightDM means that a new virtual terminal is opened. In a default single-user session, the user’s X session rests at VT7 (reachable with the keyboard-shortcut Ctrl+Alt+F7). When you lock your session, LightDM sends a lock signal, light-locker locks the session on VT7 and you get forwarded to VT8, where you’re presented with the login greeter, which serves as the unlock dialog.

The aforementioned change introduces one inconvenience you might (or might not) notice: when light-locker switches the VT, there is some screenflickering and it could take a second or two on older machines.

The behaviour you described happened to me in 14.04 and continues to do so in 16.04. I never had 15.04, but you see/saw it there too. I do not know any actual answer, but wanted to point at that quote nonetheless :)

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