$ sudo nixos-rebuild switch
(...)
removing user ‘guixbuilder7’
removing user ‘guixbuilder3’
removing user ‘guixbuilder10’
removing user ‘guixbuilder1’
removing user ‘guixbuilder6’
removing user ‘guixbuilder9’
removing user ‘guixbuilder4’
removing user ‘guixbuilder2’
removing user ‘guixbuilder8’
removing user ‘guixbuilder5’
(...)