MATE: no screen lock after suspend

[mehlon]

Describe the bug
When using the MATE desktop, the screen lock is not activated after suspending to RAM.

To Reproduce
Steps to reproduce the behavior:

1. Set services.xserver.desktopManager.mate.enable = true;
2. Suspend the screen with systemctl suspend.
3. Wake the screen up again.

Expected behavior
The screen lock should activate, asking the user to input their password.

Metadata
Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

• system: "x86_64-linux"
• host os: Linux 4.19.106, NixOS, 19.09.2166.ce9f1aaa39e (Loris)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.3.3
• channels(root): "nixos-19.09.2166.ce9f1aaa39e, u-20.09pre215033.ddc2f887f5f"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute: nixpkgs.mate
# a list of nixos modules affected by the problem
module: services.xserver.desktopManager.mate

[worldofpeace]

Anything in your journal on display-manager.service?

[mehlon]

Relevant: https://ubuntu-mate.community/t/how-to-lock-screen-on-suspend/16836

Anything in your journal on display-manager.service?

Nope. Nothing new is added to journalctl -u display-manager.service -e after suspending.

[mehlon]

This happens with both lightdm and sddm. So presumably it's a problem with MATE itself, not the display manager.

[stale]

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[AshleyYakeley]

Ran into this.

[AshleyYakeley]

Workaround for home-manager:

services.screen-locker =
{
    enable = true;
    lockCmd = "mate-screensaver-command --lock";
};