If you are running Linux Mint 19 Tara, you are likely affected by the issue announced on [The Linux Mint Blog][1] and described in depth [on the forums][2].

Summarizing the relevant forum post:

The issue concerns the base-file 19.0.2 update. The package content is empty and updating it results in creating the `/var/run directory`, which should be a symbolic link towards `/run`, preventing many system services from running correctly.

The solution:

 1. boot in recovery mode:

 - Boot your computer
 - Press <kbd>Shift</kbd> while booting to force the boot menu to show up
 - Select Advanced options for Linux Mint 19
 - Select the "recovery mode" boot option
 - When the Recovery Menu appears, select "root - Drop to root shell prompt"
 - Press Enter

 2. You will then be able to type commands. Run the following ones:

 ```
 mount -o rw,remount /
 rm -rf /var/run
 ln -s /run /var/run
 ```

 3. Reboot. Your computer should now boot normally and let you log in.

 4. To completely fix the issue, open a terminal and type:

 ```
 wget linuxmint.com/tmp/base-files_19.0.1_all.deb
 sudo dpkg -i base-files_19.0.1_all.deb
 ```


 [1]:https://blog.linuxmint.com/?p=3969
 [2]:https://forums.linuxmint.com/viewtopic.php?f=143&t=331605