Linux – What does it mean a ! before the username field in /etc/passwd

linuxpasswordrhelusers

After doing some googling I could not find why in the /etc/passwd

shows a ! at the beginning of the line.

It looks like this:

!user:x:0:0:user:/home/user:/bin/bash

any ideas? my only guess is that perhaps the user no longer exist.

Best Answer

This essentially does nothing more than changing the username to !user, so if you try to login as user you will get:

No passwd entry for user 'user'

as the username has been changed to !user.

Now if you change the /etc/shadow too and set the username as !user, then you can login as the user !user using the same password used for user.

If you want to block a user from logging in using password, you should add a ! to the password field of /etc/shadow or better use passwd -l command.

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Even though these appliance type products are based on Linux it's generally a good idea not to try and customize them as though they're Linux boxes. They typically are missing most of the tools and are usually stripped down in various ways which can make this dangerous.

I've had experience with both Netgear's ReadyNAS box as well as the Thecus boxes and this has always been the case with both these types of products. You might want to consider doing a factory restore to get this back normal instead of hacking it your self.

You'll have to reconfigure the box but this is usually just setting the IP back up and potentially some user account creation.

I direct you to the actual pages from Synology that cover how to accomplish this:

User created without a password behaves as if he had one

A user is created by default as a locked account. The field that should contain the password hash in /etc/shadow will contain !!. When an account is locked, that account is available to root only (root can su but logins aren't allowed). If you 'unlock' the account which simply removes the !! you will be allowed to change the password.

[root@test ~]# su - test
[test@test ~]$ passwd
Changing password for user test.
Changing password for test.
(current) UNIX password:
[test@test ~]$ exit
logout
[root@test ~]# passwd -u test
Unlocking password for user test.
passwd: Warning: unlocked password would be empty.
passwd: Unsafe operation (use -f to force)
[root@test ~]# passwd -u test -f
Unlocking password for user test.
passwd: Success
[root@test ~]# su - test
[test@test ~]$ passwd
Changing password for user test.
New password:

Best Answer

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User created without a password behaves as if he had one

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