ubuntu into recovery mode
original wozhaosini finally released on 2013-09-23 15:27:13 reading number 34987 Favorites
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default ubuntu is not the root user, if you are not careful this time performed usermod -G groupname username, the username lose other the original group, including the original sudo group, belongs to the group groupname, so ubuntu is completely lost root privileges
Solution:
1, into the recovery mode ubuntu:
When turned on, hold down the shift key to enter recovery mode
2, enter the root shell interface
3, if the filesystem is read-only, to execute the following commands (in a way to re-write mounts the root):
mount -o remount,rw /
4, using the following command to add the group to sudo usrname
usermod -a -G sudo username
