Linux – How to add a linux user with a random or invalid password from a script

This might sound like a silly idea, but if the users aren't actually doing anything, you could do:

cat /etc/passwd | cut -f 1 -d : >/tmp/users.list

Then edit /tmp/users.list to only contain the users you want. Then do:

for i in `cat /tmp/users.list`
do
    userdel $i
    useradd -m $i
done

However, many Redhat based distributions will create you a new home directory when you first login, providing it is specified in /etc/passwd where the directory should be.

To test that, do an "su - " and see if it does "the right thing". If it doesn't, the above script will work quite nicely, I think.

Type "man adduser" at a shell prompt. It will give you documentation on how to use adduser. In general, man will give you documentation on any CLI command.

But you really want to use useradd and not adduser.

In short:

useradd -c "Real Name" -m -g primarygroup -G secondarygroup1,secondarygroup2 username

Oh, and if you want to set the password at the same time, you have to pre-encrypt it. I continually rewrite this little program to do Unix-standard salt encryption:

#include <stdio.h>
#include <unistd.h>

int main(int argc, char *argv[]) {

        char *salt;

        if (argc < 2 || argc > 3) {
                fprintf(stderr, "Usage: %s string [salt]\n", argv[0]);
                exit(1);
        } else {
                if ( argc == 2 ) {
                        salt = argv[1];
                } else {
                        salt = argv[2];
                }
                printf("%s\n", crypt(argv[1], salt));
                exit(0);
        }
}

With this compiled as crypt, you can then add the option:

-p `crypt password`

Ideally, you don't ever want to put passwords in a command line, though, as there are multiple places it can show up (ps output, shell history, etc.), none of which are particularly secure.