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cplater avatar Server

What would prevent php-fpm (8.0.16) from being able to write to an NFS mounted filesystem?

rs flag
cplater

I have a php-fpm (8.0.16) instance that cannot write files to an NFS share. I am using a simple php script for testing:

<?php

ini_set('display_errors', 1);
ini_set('error_reporting', E_ALL);

$fp = fopen('test.txt', 'a');

fwrite($fp, 'test');

When running via php-fpm, in a directory that is an NFS share, the following error is received:

Warning: fopen(test.txt): Failed to open stream: Read-only file system in /path/to/nfs/share/test-write.php

However, the following code:

<?php

ini_set('display_errors', 1);
ini_set('error_reporting', E_ALL);

$fp = fopen('/tmp/test.txt', 'a');

fwrite($fp, 'test');

works as expected.

The script works when run from the command line as the same user that is used to run php-fpm both in an directory on an NFS share, and in /tmp. Additionally, the script works as expected on earlier versions of php via php-fpm.

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djdomi avatar
za flag
djdomi
seems that www-data has no write access to the devices. or depending on what user you decide to use and mount. moreover apparmor can also play in thus party
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de flag
kofemann
According to the error message, the NFS volume exported in read-only mode
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cplater avatar
rs flag
cplater
@kofemann I've ruled that out by writing to the NFS volume via CLI. I can run the same php file as the user:group apache:apache from php (cli) and it works.
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cplater avatar Server
rs flag
cplater

In the systemd php-fpm.service file there was a setting:

# Mounts the /usr, /boot, and /etc directories read-only for processes invoked by this unit.
ProtectSystem=full

This is what was preventing php-fpm from being able to write to the NFS share as it was mounted in a subdirectory of /usr.

As mentioned here you can override this using systemctl edit php-fpm.service and adding paths that need write access:

[Service]
ReadWritePaths=\path\that\needs\write\access
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