After trying to install the Gnome desktop in my Ubuntu 16.04 I couldn’t boot again my computer after rebooting.

When I pressed ctrl+alt+f2 the message: «A start job is running for Hold until boot finishes up» appeared.

After a little Google searching I was able to figure out the issue. It was a problem with Gdm. So I had to use again LightDM.

To fix it follow these steps:

• When booting press ESC key to enter in the Grub menu.
• Start Recovery mode.
• Select a Root session to be able to execute commands.
• Mount the filesystem in write mode again:  mount  -o remount, rw
• Reconfigure lightdm : dpkg-reconfigure lightdm
• Reboot

After these steps your computer should boot again.

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