Lock screen gnome

["Peter Baumgarten" <me@peterbaumgarten.com>]

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I just installed guixsd with gnome, but I can not lock the screen when hit the meta key + L 
 
Is there anything extra I need to do add this functionality below is the config.scm I am using 
 
(use-modules (gnu) (gnu system nss)) 
(use-service-modules desktop) 
(use-package-modules certs gnome gnuzilla emacs video) 
 
(operating-system 
 (host-name "guix") 
 (timezone "Europe/Paris") 
 (locale "en_US.utf8") 
 
 ;; Use the UEFI variant of GRUB with the EFI System 
 ;; Partition mounted on /boot/efi. 
 (bootloader (bootloader-configuration 
 (bootloader grub-efi-bootloader) 
 (target "/boot/efi"))) 
 
 (file-systems (cons* (file-system 
 (device (file-system-label "my-root")) 
 (mount-point "/") 
 (type "btrfs")) 
 (file-system 
 (device (file-system-label "my-boot")) 
 (mount-point "/boot") 
 (type "ext2")) 
 (file-system 
 (device "/dev/sda1") 
 (mount-point "/boot/efi") 
 (type "vfat")) 
 %base-file-systems)) 
 
 (swap-devices '("/dev/sda3")) 
 
 (users (cons (user-account 
 (name "me") 
 (group "users") 
 (supplementary-groups '("wheel" "netdev" 
 "audio" "video")) 
 (home-directory "/home/me")) 
 %base-user-accounts)) 
 
 ;; This is where we specify system-wide packages. 
 (packages (cons* nss-certs ;for HTTPS access 
 gvfs ;for user mounts 
 icecat ;main web browser 
 emacs ;emacs 
 youtube-dl ;download youtube videos 
 %base-packages)) 
 
 ;; Add GNOME and/or Xfce---we can choose at the log-in 
 ;; screen with F1. Use the "desktop" services, which 
 ;; include the X11 log-in service, networking with 
 ;; NetworkManager, and more. 
 (services (cons* (gnome-desktop-service) 
 %desktop-services)) 
 
 ;; Allow resolution of '.local' host names with mDNS. 
 (name-service-switch %mdns-host-lookup-nss)) 
 

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