Environment

• PHP -V output: PHP 5.3.5-1ubuntu7.2 with Suhosin-Patch (cli) (built: May 2 2011 23:00:17) Copyright (c) 1997-2009 The PHP Group Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies
• cat /etc/issue output: Ubuntu 11.04
• Apache2 -V ouput: Server version: Apache/2.2.17 (Ubuntu) Server built: Sep 1 2011 09:31:14
• Browser About output: Firefox 6.0.2

PS -AUX Ouput

root      2943  0.0  0.3 206420 12428 ?        Ss   Sep19   0:20 /usr/sbin/apache2 -k start
www-data 18658  0.0  0.2 208552 11096 ?        S    Sep25   0:00 /usr/sbin/apache2 -k start
www-data 18659  0.0  0.3 208976 12036 ?        S    Sep25   0:00 /usr/sbin/apache2 -k start
www-data 18660  0.0  0.3 210532 12476 ?        S开发者_开发百科    Sep25   0:00 /usr/sbin/apache2 -k start
www-data 18661  0.0  0.3 210276 11820 ?        S    Sep25   0:00 /usr/sbin/apache2 -k start
www-data 18662  0.0  0.2 206948 10236 ?        S    Sep25   0:00 /usr/sbin/apache2 -k start
www-data 20037  0.0  0.3 208976 12128 ?        S    08:22   0:00 /usr/sbin/apache2 -k start
www-data 20039  0.0  0.3 209132 11748 ?        S    08:23   0:00 /usr/sbin/apache2 -k start
www-data 20120  0.0  0.3 209004 12000 ?        S    09:04   0:00 /usr/sbin/apache2 -k start

File Permissions

drwxr-xr-x 2 www-data www-data   4096 2011-09-26 15:24 .
drwxr-xr-x 4 www-data www-data   4096 2011-08-26 11:31 ..
-rw-r--r-- 1 root     root     161976 2011-08-26 16:26 market.txt
-rw-r--r-- 1 root     root          0 2011-09-26 14:55 test1.txt
-rw-r--r-- 1 root     root          0 2011-09-26 14:55 test2.txt
-rw-r--r-- 1 root     root          0 2011-09-26 14:55 test3.txt
-rw-r--r-- 1 root     root          0 2011-09-26 14:55 test4.txt
-rw-r--r-- 1 root     root          0 2011-09-26 15:02 test5.txt

Code

rename($file, "$dest/$file");

Question

When I run the above code on the files listed in the File Permissions section above, it properly moves the file from its current location to a new location and removes the original. How is this possible when apache2 is running as www-data and the files are owned by root and only have read access for non-root users? On the PHP documentation it says:

Warnings may be generated if the destination filesystem doesn't permit chown() or chmod() system calls to be made on files — for example, if the destination filesystem is a FAT filesystem.

Does rename() call either of those system functions during the process? If so, why? Not that it matters anyway as www-data should not be able to chown/chmod a file owned by root anyway.

Can anyone explain to me how this is occuring?

Additional Information

• I have tried this with the PHP script owned by root and by www-data and it works.

I tried to provide as much pertinent info as possible but let me know if you need anything else.

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Moves don't "remove" originals, unless the move takes place across filesystem boundaries. Within a single filesystem, a move simply rewrites the relevant directory entries so it APPEARS that you've copied/deleted the file, but all you've done is a bit of housekeeping. Since www-data owns the directories in question, it can rewrite the directory entries representing those files all it wants, and never touch the actual files.

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When moving files you are not editing the files themselves, but rather the directory they are part of. In your case that directory is owned by www-data (the apache process)