Setting the password non-interactively in Linux using bash shell

Manually resetting passwords of a large chunk of users is a painfully boring task & is definitely not the best use of our time. In this article I'll share just a couple of methods of somewhat automate this process. So here we go!

Method 1: use chpasswd
Using chpasswd we can set or reset login passwords for many users non-interactively. WE just need to add the username & password in a text file in the form of a key-value pair & serve the resultant text file as input to chpasswd command & our work is done. Here's a demo:

I've created a user named testuser & I want to set its password to 123. So, I've added the key-value pair in a text file shown below:

[root@centops ~]# cat pass.txt
testuser:123
[root@centops ~]#

Now we just need to feed it to chpasswd.

[root@centops ~]# chpasswd <pass.txt

Method 2: use stdin

This is another simple method wherein we echo out the password to passwd <user name> command via --stdin. Here's an example:

[root@centops ~]# echo "456"  | passwd testuser --stdin

Changing password for user testuser.

passwd: all authentication tokens updated successfully.

Method 3: use expect

Expect is an awesome tool for supplying input to interactive programs to automate them. Here's the expected expect code to accomplish a non-interactive password reset:

#!/usr/bin/expect

set timeout 10

set user [lindex $argv 0]

set password [lindex $argv 1]

spawn passwd $user

expect "password:"
send "$password\r"
expect "password:"
send "$password\r"

expect eof


The test looks like this:

# ./e3.sh testuser 123

spawn passwd testuser
Changing password for user testuser.
New password:
BAD PASSWORD: it is WAY too short
BAD PASSWORD: is too simple
Retype new password:
passwd: all authentication tokens updated successfully.