PHP `require_once` includes wrong file

Question

I have a development tree on a Linux Ubuntu 14.04-LTS machine like this, with three identical branches:

main -+-- leonardo --- project --- htdocs -+- panel --- index.php
      |                                    |
      |                                    +- config.php
      |
      +-- federico --- project --- htdocs -+- panel --- index.php
      |                                    |
      |                                    +- config.php
      |
      +-- carlo ------ project --- htdocs -+- panel --- index.php
      |                                    |
      |                                    +- config.php
    ..... (you get my drift).

There are neither soft links nor hard links. The config.php file is in svn-ignore and is different between all branches

There is an Apache server and there is a virtualHost for each developer, so I can see my development version at http://leonardo.project.local or Federico's at http://federico.project.local .

While investigating the current weirdness, the two files are these:

<?php // this is panel/index.php
    echo "I am " . __FILE__ . "\n";
    echo "I will include " . realpath('../config.php') . "\n";
    require_once '../config.php';

<?php // this is config.php
    echo "I am " . __FILE__ . "\n";
    exit();

The expected output of course would be:

I am leonardo/project/htdocs/panel/index.php
I will include /var/www/main/leonardo/project/htdocs/config.php
I am leonardo/project/htdocs/config.php

But the actual output is:

I am leonardo/project/htdocs/panel/index.php
I will include /var/www/main/leonardo/project/htdocs/config.php
I am federico/project/htdocs/config.php

The additional weirdness is that

    echo "I will include " . realpath('../config.php') . "\n";
    require_once realpath('../config.php');

works.

TL;DR require_once and realpath disagree about where '../config.php' actually is.

The really strange thing is that I do not see how a script running in leonardo/project/htdocs/panel/ could know about federico/project/htdocs/config.php; it ought to go four directories up, then explore very many subdirectories.

I'm almost beginning to suspect that this could be something filesystem- or even kernel- related.

The filesystem is ext4, the kernel is 3.13.0-55-generic #92-Ubuntu SMP Sun Jun 14 18:32:20 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux. The machine is a virtual x64 on the latest VMware Workstation.

Checks

• PHP's include_path only includes . and /usr/local/php5/pear.
• as stated earlier, no files in the branch are symlinks, and the inode counts for all involved files indicate there are no cross links. The files are indeed different.
• all files are really there, it's not a "last ditch include".
• from command line, in leonardo...panel, I run "cat ../config.php" and I get my config.php, as expected. It is only from PHP that the wrong file gets included.
• restarting Apache (just in case) availed nothing. I'll next try and reboot the whole VM, but to do that I need to freeze several services and it will take me a while.
• everything was hunky dory up to yesterday (I wasn't here then). There were no system updates, no reboots, and not even remote logins in the last three days. Uptime is now eight days.
• I'm an idiot: I can too know to the minute when this started happening by checking the integration test logs. Have asked for them, expecting them after lunch.

Answer 1

It's worth checking what your include_path is set to (this can be done using get_include_path).

require and include will behave differently given an absolute and relative path. When you use

require_once realpath('../config.php');

This is doing:

require_once '/var/www/main/leonardo/project/htdocs/config.php';

Which works as you'd expect.

The weirdness in the following:

require_once '../config.php';

occurs because PHP will check each entry in the include path for a matching file and return the first matching entry. Hence it's likely that the path to the federico config is being checked first.