How to get the OS on which PHP is running?

PHP Does not provide any function to get the name of the distribution, php_uname is similar to Linux command uname, does not provide any info about the distribution itself.

Neither php_uname nor PHP_OS give sufficient info. about the distribution but the OS type (e.g. Linux / Windows).

I think the best way to know what is the running OS/distribution is to read /etc/os-release, the good thing is this file has read permission for all system users and the bad thing is it may not work on shared hosting.

Here I wrote a very simple PHP function which reads and convert os-release to an array:

    function getOSInformation()
    {
        if (false == function_exists("shell_exec") || false == is_readable("/etc/os-release")) {
            return null;
        }

        $os         = shell_exec('cat /etc/os-release');
        $listIds    = preg_match_all('/.*=/', $os, $matchListIds);
        $listIds    = $matchListIds[0];

        $listVal    = preg_match_all('/=.*/', $os, $matchListVal);
        $listVal    = $matchListVal[0];

        array_walk($listIds, function(&$v, $k){
            $v = strtolower(str_replace('=', '', $v));
        });

        array_walk($listVal, function(&$v, $k){
            $v = preg_replace('/=|"/', '', $v);
        });

        return array_combine($listIds, $listVal);
    }

This function prints something like this:

Array
(
    [name] => Ubuntu
    [version] => 16.04.2 LTS (Xenial Xerus)
    [id] => ubuntu
    [id_like] => debian
    [pretty_name] => Ubuntu 16.04.2 LTS
    [version_id] => 16.04
    [home_url] => http://www.ubuntu.com/
    [support_url] => http://help.ubuntu.com/
    [bug_report_url] => http://bugs.launchpad.net/ubuntu/
    [version_codename] => xenial
    [ubuntu_codename] => xenial
)

Held og lykke [1] ;-)

[1] Danish phrase means good luck.

Just bear in mind that PHP_OS actually contains the platform on which PHP was built. This may not be the same platform as that on which it is deployed. Therefore php_uname('s') is more reliable.

As of PHP 7.2.0 we have a new Predefined Constant to get the operating system family i.e. PHP_OS_FAMILY. It returns a string Either of 'Windows', 'BSD', 'OSX', 'Solaris', 'Linux' or 'Unknown'.

PHP has many predefined constants that are often useful.

Here, PHP_OS is the one you are looking for.

For instance, on my current machine, this code :

var_dump(PHP_OS);

Gives :

string 'Linux' (length=5)

You have some examples and comparisons with what the php_uname function can get you on the manual page of php_uname ; for instance (quoting) :

<?php
echo php_uname();
echo PHP_OS;

/* Some possible outputs:
Linux localhost 2.4.21-0.13mdk #1 Fri Mar 14 15:08:06 EST 2003 i686
Linux

FreeBSD localhost 3.2-RELEASE #15: Mon Dec 17 08:46:02 GMT 2001
FreeBSD

Windows NT XN1 5.1 build 2600
WINNT
*/

if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
    echo 'This is a server using Windows!';
} else {
    echo 'This is a server not using Windows!';
}

That page also says :

For the name of just the operating system, consider using the PHP_OS constant, but keep in mind this constant will contain the operating system PHP was built on.