Upload: Failed to Write File to Disk

WordPress received the file and could not save it. The upload itself worked, so the problem is on the server side and is almost always one of four things.

1. Disk space

df -h .
# or in the host panel, look at disk usage

A full disk produces exactly this error. The usual consumers are backups stored on the server, old cache files, and log files nobody rotated.

# the biggest directories
du -sh * | sort -h | tail -10

# anything large in wp-content
du -sh wp-content/* | sort -h | tail

2. Permissions and ownership

The uploads directory must be writable by the user PHP runs as:

ls -la wp-content/ | grep uploads
# should be drwxr-xr-x and owned by the web server user

chmod 755 wp-content/uploads
find wp-content/uploads -type d -exec chmod 755 {} \;
find wp-content/uploads -type f -exec chmod 644 {} \;

3. The temporary directory

PHP writes uploads to a temp directory before WordPress moves them. If that directory is missing or not writable, the move fails. Check what PHP is using:

<?php echo sys_get_temp_dir(); ?>

If it is wrong or unwritable, point WordPress at a directory you control:

// wp-config.php
define( 'WP_TEMP_DIR', ABSPATH . 'wp-content/temp/' );
// then create that directory, 755, correct ownership

4. Inode limit

An inode is one file or directory. Shared hosts cap the count, and a site with a large media library plus a cache plugin generating a file per page can reach it while still having plenty of disk space free. The symptom is identical.

df -i .
find . -type f | wc -l

# where the files are
for d in wp-content/*/; do echo "$(find "$d" -type f | wc -l) $d"; done | sort -rn

The usual answers are clearing the cache directory, removing on-server backups, and unregistering image sizes you do not use.

Which one is it?

Clue	Cause
Started suddenly, nothing changed	Disk full or inode limit
Started after a migration	Permissions or ownership
Only large files fail	PHP upload limits, not this error
Every file fails including tiny ones	Permissions or temp directory
Disk shows free space but it still fails	Inodes

Preventing it

• Store backups off-server, not in wp-content.
• Rotate or disable debug logs.
• Unregister image sizes you do not use, then regenerate thumbnails.
• Set a cache lifetime so cached files are cleared rather than accumulating.
• Monitor both disk usage and inode count, not just disk.

Common questions

Why do some uploads work and others fail?

If only large files fail you are looking at upload_max_filesize or post_max_size, which produce a different error. This one usually affects everything.

Can I just set 777?

It will work and it is a real security risk on shared hosting. Fix ownership instead.

The host says there is plenty of space

Ask specifically about the inode count. It is a separate limit and support often does not mention it unprompted.