Php validate user

moxum used Ask the Experts™
I would like to validate a user against the normal linux security file.

Eg. I have a user named "user1" with the password "apassword" that can login to a shell. I want to have a php function that returns if the "shell" password for a specified username is correct.


function valid_password( $username ) {
//code here

Please advice.
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I found on the Internet a link:
that suggests a code like:

    function valid_user ($user, $passwd) {
        $autharray = file("/etc/shadow");
        for ($x = 0; $x < count($autharray); $x++) {
            if (eregi("^$user:", $autharray[$x])) {
                $passwd = explode(":", $autharray[$x]);
                $salt = substr($passwd[1],0,2);
                $cryptpw = crypt($pass,$salt);
                if ($cryptpw == $passwd[1]) {
                    return "OK";
        return "NOT OK";

It sould work if you use /etc/passwd to store the passwords. If you use shadow passwords I think that you should use an external program. I recommend Checkpassword from:

From PHP you can use function posix_getpwnam() which does same as unix getpwnam(3). For username as argument it returns array with info about user.

This will not be complete solution for you since linux uses shadow passwords, so for passwd field it will return 'x' or '*', so you want be able to use it like that.

One of solutions for this is to write and call C program, which will obtain real, of course crypted, password from /etc/shadow via getspnam() function. Example of this can be found on

Beside all this, note that accessing files like /etc/passwd from PHP is security risk, and it's not bad idea to think, do you really want and need to do that.

Just short on code from phpbuilder: this actually suggests to read /etc/shadow directly from PHP, which means to run your PHP script as root and read /etc/shadow. This is not a security risk, this is HUGE security risk.
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The man wanted to know how can be done. I tried to tell him. I agree that using php to read /etc/shadow is not a good practice.
I also suggested an external program. It's his choice to pick one of the possible ways to solve this problem.



how about pam?

I think I will go for this one...

Thanks for your idea's anyway.

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