How To Automatically Create User Accounts in Unix ( Linux )

The simplest way to automatically  add a new user to your system is to do run a Perl script  like this:

#!/usr/bin/perl
 use strict;
 use warnings;
 use Fcntl ':flock'; # import LOCK_* constants

# The file we are going to change (Testing on Back Track 5R2)

my $pw_file = "/etc/passwd";
 my $group_file = "/etc/group";
 my $shadow_file = "/etc/shadow";

# Login name
 my $login;    # Login name
 print "Login: ";
 $login = <STDIN>;
 chomp($login);

if ($login !~ /[A-Z_a-z0-9]+/) {
 die("No login specified");
 }

open PW_FILE, "<$pw_file" or die("Could not read $pw_file");
 # Lock the file for the duration of the program
 flock PW_FILE, LOCK_EX;

# Check login info.
 my $check_uid = getpwnam($login);
 if (defined($check_uid)) {
 print "$login already exists\n";
 exit (8);
 }

# Find the highest UID.  We'll be that +1
 my @pw_info = <PW_FILE>;

my $uid = 0;    # UID for the user

# Find biggest user
 foreach my $cur_pw (@pw_info) {
 my @fields = split /:/, $cur_pw;
 if ($fields[2] > 60000) {
 next;
 }
 if ($fields[2] > $uid) {
 $uid = $fields[2];
 }
 }
 $uid++;

# Each user get his own group.
 my $gid = $uid;

# Default home dir.
 my $home_dir = "/home/$login";

print "Full Name: "; # Get user full name
 my $full_name = <STDIN>;
 chomp($full_name);

my $shell = "";    # Get user shell to use
 while (! -f $shell) {
 print "Shell: ";
 $shell = <STDIN>;
 chomp($shell);
 }

print "Setting up account for: $login [$full_name]\n";

open PW_FILE, ">>$pw_file" or
 die("Could not append to $pw_file");
 print PW_FILE
 "${login}:x:${uid}:${gid}:${full_name}:${home_dir}:$shell\n";

open GROUP_FILE, ">>$group_file" or
 die("Could not append to $group_file");
 print GROUP_FILE "${login}:x:${gid}:$login\n";
 close GROUP_FILE;

open SHADOW, ">>$shadow_file" or
 die("Could not append to $shadow_file");
 print SHADOW "${login}:*:11647:0:99999:7:::\n";
 close SHADOW;

# Create the home directory
 mkdir($home_dir);
 chmod(0755, $home_dir);
 system("cp -R /etc/skel/.[a-zA-Z]* $home_dir");
 system("find $home_dir -print ".
 "-exec chown ${login}:${login} {} \\;");

# Set the password for the user
 print "Setting password\n";
 system("passwd $login");

flock(PW_FILE,LOCK_UN);
 close(PW_FILE);

How It Work:

• Lock the /etc/passwd file
• Get the user name
• Lock the password file
• Make sure the user doesn’t exist
• Genarate a user ID for the new user
• Create an entry in /etc/passwd
• Create an entry in /etc/shadow
• Create an entry in /etc/groups
• Create the user home directory
• Set the initial password for new user
• Unlock the /etc/passwd file

Example on BackTrack Linux:

Add New User

And:

Add New User

 

Source:

1.Perl for System Administration.http://docstore.mik.ua/orelly/perl/sysadmin/index.htm