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

Where,

  • -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"'
Output:

sa3tHJ3/KuYvI

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:
$ password="1YelloDog@"
$ pass=$(perl -e ‘print crypt($ARGV[0], “password”)’ $password)
$ echo $pass
Output

paU5t8Al/qf6M

Sample shell script to add a user

Based upon above discussion here is a sample shell script:

#!/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[0], “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:
$ ./adduser.sh
Only root may add a user to the system

Run as root:
# ./adduser
Output:

Enter username : roja
Enter password : HIDDEN
User has been added to system!

Now user roja can login with a password called HIDDEN.

——————- another hint —-

I just want to send one script which I have made for changing password of any user from remote machine.
Here I have created one file called “host” which contents host ips.

Shell script code

#!/bin/bash
read -p "Enter Username: " username
read -ers -p "Enter New password for user $username: " paswd
echo
read -ers -p "Enter Root Password: " rpaswd
echo
password=`python file ${paswd}`;
echo "$username $password $npaswd"
cat host | while read line
do
#####expect####
status=$(expect -c "
spawn ssh $line usermod -p $password $username
expect {
password: { send \"$rpaswdn\"; exp_continue }
}
exit
")

echo ""
echo "$status" > log.txt
#####end of expect#######
done

python code - file [for crypt()]

import crypt; import sys; print crypt.crypt(sys.argv[1],”salt”);

————————–

To display user list just type:

cut -d: -f1 /etc/passwd

gawk -F: ‘{ if ( $3>500 ) print $1 }’/etc/passwd