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Re: lightdm (testing): Long waiting time after login

On 16/05/18 19:28, work@hllmnn.de wrote:
I just did a fresh install of testing with XFCE. After entering the login
credentials the screen was black for 30-60 seconds before the desktop
environment showed up. Assuming a bug in XFCE, I performed another fresh install
with MATE, but a similar effect occured: after login the background image is
shown for 30-60 seconds before the desktop is fully loaded.

What happens if you wiggle your mouse or provide keyboard activity while waiting? For example, if you wiggle your mouse vigorously for two seconds or press the Alt key 20 times? Does the wait end sooner?

In Linux 4.16, the getrandom system call (without the GRND_NONBLOCK flag) blocks until sufficient entropy is available in the pool. This is the documented behaviour, and Linux 4.16 now enforces it to fix CVE-2018-1108. This has caught out several services that try to use getrandom (without the GRND_NONBLOCK flag) at early boot, including plymouth (via fontconfig) and gdm3. What you see might have the same cause. For details of my investigation, see:

Wiggling your mouse or providing keyboard activity adds entropy to the pool. If this reduces the waiting time, you might be affected by the same bug.

Kind regards,

Ben Caradoc-Davies <ben@transient.nz>
Transient Software Limited <https://transient.nz/>
New Zealand

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