История изменений

$ sudo dpkg-reconfigure gdm

dpkg-query: package 'gdm' is not installed and no information is available
Use dpkg --info (= dpkg-deb --info) to examine archive files.
/usr/sbin/dpkg-reconfigure: gdm is not installed

$ sudo apt-get install gdm
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package gdm is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'gdm' has no installation candidate

$ sudo dpkg-reconfigure gdm

dpkg-query: package 'gdm' is not installed and no information is available
Use dpkg --info (= dpkg-deb --info) to examine archive files.
/usr/sbin/dpkg-reconfigure: gdm is not installed