John Topley John Topley - 5 months ago 29
PHP Question

PHP is_writable() function always returns false for a writable directory

I'm trying to install a PHP-based software package in a Red Hat 7 Amazon EC2 instance (ami-8cff51fb) that has had Apache 2.4.6 and PHP 5.4.16 installed on it using yum. The installation fails because it says a particular directory needs to be writable by the webserver with 0755 or 0775 permissions.

The directory in question has 0775 permissions with

root:apache
ownership. I have verified that the httpd process is being run by the apache user and that the apache user is a member of the apache group.

If I edit
/etc/passwd
to temporarily give the apache user a login shell and then
su
to that account, I am able to manually create files as the apache user within the directory using the
touch
command.

I took a look at the source code of the installer script and identified that it's failing because PHP's
is_writable()
function is returning false for the directory in question. I created a separate test PHP script to isolate and verify the behaviour I'm seeing:

<?php
$dir = '/var/www/html/limesurvey/tmp';
if (is_writable($dir)) {
echo $dir, ' is writable';
} else {
echo $dir, ' is NOT writable';
}
?>


This outputs the NOT writable message. If I change
$dir
above to be
/tmp
then it correctly outputs that
/tmp
is writable.

If I change the directory permissions to 0777 and/or change the ownership to
apache:apache
then PHP still reports that the directory isn't writable. I even tried creating a
/test
directory set up with the same permissions and ownership and my test script still reports it as not writable.

I'm really at a loss as to explain this behaviour, so any ideas would be welcome!

Thanks in advance.




The directory listing for
/var/www/html/limesurvey
is given below. The
tmp
and
upload
directories have 0775 permissions as per Lime Survey's installation instructions.
test.php
is my test script mentioned above.

[ec2-user@ip-xx-x-x-xxx limesurvey]$ pwd
/var/www/html/limesurvey
[ec2-user@ip-xx-x-x-xxx limesurvey]$ ls -al
total 80
drwxr-xr-x. 20 root apache 4096 Mar 30 11:25 .
drwxr-xr-x. 3 root root 23 Mar 25 14:41 ..
drwxr-xr-x. 2 root apache 38 Mar 10 12:56 admin
drwxr-xr-x. 16 root apache 4096 Mar 10 12:56 application
drwxr-xr-x. 3 root apache 4096 Mar 10 12:56 docs
drwxr-xr-x. 2 root apache 4096 Mar 10 12:56 fonts
drwxr-xr-x. 19 root apache 4096 Mar 10 12:56 framework
-rw-r--r--. 1 root apache 429 Mar 10 12:56 .gitattributes
-rw-r--r--. 1 root apache 399 Mar 10 12:56 .gitignore
-rw-r--r--. 1 root apache 296 Mar 10 12:56 .htaccess
drwxr-xr-x. 4 root apache 4096 Mar 10 12:56 images
-rw-r--r--. 1 root apache 6652 Mar 10 12:56 index.php
drwxr-xr-x. 5 root apache 39 Mar 10 12:56 installer
drwxr-xr-x. 89 root apache 4096 Mar 10 12:56 locale
drwxrwxr-x. 2 root apache 39 Mar 25 14:41 logs
drwxr-xr-x. 4 root apache 49 Mar 10 12:56 plugins
-rw-r--r--. 1 root apache 61 Mar 10 12:56 README
drwxr-xr-x. 4 root apache 4096 Mar 10 12:56 scripts
-rw-r--r--. 1 root apache 380 Mar 10 12:56 .scrutinizer.yml
drwxr-xr-x. 5 root apache 4096 Mar 10 12:56 styles
drwxr-xr-x. 5 root apache 4096 Mar 10 12:56 styles-public
drwxr-xr-x. 12 root apache 4096 Mar 10 12:56 templates
-rw-r--r--. 1 root apache 159 Mar 30 11:11 test.php
drwxr-xr-x. 3 root apache 20 Mar 10 12:56 themes
drwxr-xr-x. 26 root apache 4096 Mar 10 12:56 third_party
drwxrwxr-x. 5 root apache 80 Mar 26 13:45 tmp
drwxrwxr-x. 6 root apache 79 Mar 10 12:57 upload


Running
namei -l /var/www/html/limesurvey/tmp
gives:

[ec2-user@ip-x-x-x-xxx ~]$ namei -l /var/www/html/limesurvey/tmp
f: /var/www/html/limesurvey/tmp
drwxr-xr-x root root /
drwxr-xr-x root root var
drwxr-xr-x root root www
drwxr-xr-x root root html
drwxr-xr-x root apache limesurvey
drwxrwxr-x root apache tmp

Answer

After much head-scratching, it transpired that SELinux was preventing the directory from being written to. I found a good tutorial that explains what's going on. I was able to fix it by running this command:

sudo chcon -R -t httpd_sys_rw_content_t tmp
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