Permissions set to 777 and file still not writeable - php

Question

I have set file permissions to 777 yet I cannot write to the file with PHP.
I can clearly see in my FTP client that the file has 0777 permissions and when I do:
echo (true === is_writable('file.txt')) ? 'yes' : 'no';
I get 'no';
I also tried:
echo (true === chmod('file.txt', 0777)) ? 'yes' : 'no';
With the same result.
The directory listing goes something like this:
public_html
public 0777
css 0755
js 0755
file.txt 0777
And I'm using .htaccess file to redirect all traffic to the public subfolder. Of course, I have excluded the file from rewriting (it is accessible from the browser I checked):
RewriteRule ^(file).* - [L]
Why is that?

Answer 1

I guess Apache runs as a different user/group than the user/group owning the file. In which case, the file itself needs to be 0777.
public only needs to be 0777 if you plan on adding files to the folder using PHP. Even if the folder itself is not 0777, if the file is and the folder has at least 5 for the user (read/execute), you should be able to write to the file.
In the end, your file tree should look like this:
public_html
public
file.txt 0777
Naturally, you won't be able to change those permissions using PHP, but you can do so from your FTP client.
If it still isn't working, PHP might be running in safe mode or you might be using an extension such as PHP Suhosin. You might get better result changing the owner of the file to the same user/group that is running the script.
To get the user/group id of the executing user, you may use the following:
<?php
echo getmyuid().':'.getmygid(); //ex:. 0:0
?>
Then, you may use chown (in the terminal) to change the owner of the file:
> chown 0:0 file.txt

Answer 2

In opencart i faced this error after installing vqmod and giving all necessary permissions.
after researching a bit, found it.
"MODS CACHE PATH NOT WRITEABLE" is actually refering to vqmod folder itself and not the cache folder.
sudo chmod -R 777 vqmod
in your root directory.....

Answer 3

You have to chmod the file right after you create it.
function Doo_Chmod($path, $chmod = null)
{
if (file_exists($path) === true)
{
if (is_null($chmod) === true)
{
$chmod = (is_file($path) === true) ? 644 : 755;
if (in_array(get_current_user(), array('apache', 'httpd', 'nobody', 'system', 'webdaemon', 'www', 'www-data')) === true)
{
$chmod += 22;
}
}
return chmod($path, octdec(intval($chmod)));
}
return false;
}

Answer 4

Not strictly related to the above question, still, I will put it here for future visitors, as I came here reading the title.
From arch wiki:
File attributes
Apart from the file mode bits that control user and group read, write
and execute permissions, several file systems support file attributes
that enable further customization of allowable file operations. This
section describes some of these attributes and how to work with them.
Warning: By default, file attributes are not preserved by cp, rsync,
and other similar programs. chattr and lsattr
For ext2 and ext3 file systems, the e2fsprogs package contains the
programs lsattr and chattr that list and change a file's attributes,
respectively. Though some are not honored by all file systems, the
available attributes are:
a: append only
c: compressed
d: no dump
e: extent format
i: immutable
j: data journalling
s: secure deletion
t: no tail-merging
u: undeletable
A: no atime updates
C: no copy on write
D: synchronous directory updates
S: synchronous updates
T: top of directory hierarchy
For example, if you want to set the immutable bit on some file, use
the following command:
# chattr +i /path/to/file
To remove an attribute on a file just change + to -.
For a file, with no additional attributes, the lsattr looks like this:
$ lsattr /etc/hosts
-------------e- /etc/hosts