Boot stuck at "A start job is running for Create Volatile Files and Directories"

This message will appear when the /tmp directory is full or has too many files/directories inside it. Since it prevents a successful boot, we will need to modify the boot options to fix it 

 First, restart the affected system (Ctrl-Alt-Del or power cycle it) and upon reaching Grub, press the E key to begin editing the boot option 

 Scroll to the bottom and find the section including root=/* and "ro". This is the area we will be editing. Server versions of Ubuntu normally mention "maybe-ubiquity" after this, whereas desktop versions normally include "quiet splash" 

 

 Change the "ro" (read-only) to "rw" (read-write) and add init=/bin/bash after it (ensuring there's a double space after rw) 

 

 Now we're effectively running in single-user (root) mode. We can now run the commands needed to reset the /tmp directory: 

 Move the existing directory: 

 mv /tmp /old.tmp 

 Make a new directory: 

 mkdir /tmp 

 Set the correct permissions: 

 chmod 1777 /tmp 

 Now we can reboot. The normal "reboot" command doesn't work in this mode, so a Ctrl-Alt-Del is the easiest way!