Linux Password Trick With Immutable Bit Using chattr Command

With the help of utility called chattr, you can changes the file attributes on a Linux second extended file system. The operator + causes the selected attributes to be added to the existing attributes of the files; - causes them to be removed; and = causes them to be the only attributes that the files have.

1) Login as the root user.

2) Type the following command to write protect /etc/shadow file:
# chattr +i /etc/shadow

3) Login as user vivek and type the passwd command to change password:

$ passwd

Changing password for user vivek.
Changing password for vivek
(current) UNIX password: OLDPASSWED
New password: NEWPASSWD
Retype new password:NEWPASSWD
passwd: all authentication tokens updated successfully.

4) Now logout and try to login with the new password. However, system will not accept your new password. You still need to use the old password. A file with the 'i' attribute cannot be modified: it cannot be deleted or renamed, no link can be created to this file and no data can be written to the file. Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this attribute.

5) Get the list of Linux second extended file system using the lsatter command (run as root user :-) )

# lsattr /etc/shadow

----i-------- /etc/shadow

6) To see all Linux second extended file system attributes read the man page
man chattr
man lsattr

7) Please note that even root user is not allowed to change the password. You can remove the attribute using the following command:

# chattr -i /etc/shadow
# lsattr /etc/shadow

------------- /etc/shadow

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