Our regular reader Imtiaz asks:
How do I add a user with password? I’d like to take input such as username, password from keyboard and add to the system under Linux.
A. You can easily write a shell script that reads username, password from keyboard and add to /etc/passwd and /etc/shadow file using useradd command (create a new user command).
General syntax is as follows:
useradd -m -p encryptedPassword username
- -m : The user’s home directory will be created if it does not exist.
- useradd -p encryptedPassword : The encrypted password, as returned by crypt().
- username : Add this user to system
Task: Create an encrypted password
You need to create encrypted password using perl crypt():
$ perl -e 'print crypt("password", "salt"),"\n"'
Above will display the crypted password (sa3tHJ3/KuYvI) on screen. The Perl crypt() function is a one way encryption method meaning, once a password has been encrypted, it cannot be decrypted. The password string is taken from the user and encrypted with the salt and displayed back on screen.
You can store an encrypted password using following syntax:
$ pass=$(perl -e 'print crypt($ARGV, "password")' $password)
$ echo $pass
Sample shell script to add a user
Based upon above discussion here is a sample shell script (Download link):
#!/bin/bash # Script to add a user to Linux system if [ $(id -u) -eq 0 ]; then read -p "Enter username : " username read -s -p "Enter password : " password egrep "^$username" /etc/passwd >/dev/null if [ $? -eq 0 ]; then echo "$username exists!" exit 1 else pass=$(perl -e 'print crypt($ARGV, "password")' $password) useradd -m -p $pass $username [ $? -eq 0 ] && echo "User has been added to system!" || echo "Failed to add a user!" fi else echo "Only root may add a user to the system" exit 2 fi
Close and save the script:
Only root may add a user to the system
Run as root:
Enter username : roja Enter password : HIDDEN User has been added to system!
Now user roja can login with a password called HIDDEN.
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