Backup for /etc/passwd , /etc/group , /etc/shadow

/etc/passwd /etc/group /etc/shadow are very essential file systems for Linux. You should not be surprised that linux does do a backup of the /etc/passwd /etc/group /etc/shadow. They are represented by

#  /etc/passwd-
#  /etc/group-
#  /etc/shadow-

So in case your any of your /etc/passwd /etc/group /etc/shadow are corrupted, just do a copy and replace

Note: listed with the appropriate access permissions
  File:             Owner:  Group:  Permissions:
/etc/passwd      root     root   rw- r-- r--
/etc/group root     root   rw- r-- r--
/etc/shadow root     root   rw- --- ---