Linux Add user failed

Recently changed the development machine, the development machine has only one user, must pass through the springboard machine to log on. Now want to use a different user to access the machine, but do not have permission to execute AddUser error.

Later found is because the operation of the students Shadow, passwd these several files with chattr lock, as long as the unlock can add users ~ command as follows:

sudo chattr-i/etc/shadow
sudo chattr-i/etc/gshadow
sudo chattr-i/etc/passwd
sudo chattr-i/etc/group

Of course, you can use chattr +i to lock it up after you've added it.

Linux Add user failed