I'm having a bit of a permissions nightmare.

I have a directory called 'data'. It's owned by user1 and it's group is 'user1'. Directory permissions are 775.

Within 'data' is a file called 'thefile'. It's permissions are 664.

On my system apache runs as user www-data.

the group 'user1' has www-data added to it.
user1:x:500:www-data

I have a php script that is owned by user1.
When I run the script from the command line logged in as user1 it works fine and it can write to 'thefile'.

When I try to invoke the script via a web browser it fails with a permission problem writing to 'thefile'. It fails even though the file has a group othat includes www-data (apache).

I know that the answer will make me feel fairly dumb but I'm over banging my head against this.

Suggestions much appreciated.

The scenario you have mentioned should work without problems. Do you have SELINUX enabled ?

No, no SELinux, no apparmor. I'll go back over everything I've set up and see if there's some seemingly minor error.

Check your php.ini file. There might be some system functions that is now allowing to write to the file.