How to fix "Failed to write file to disk" in WordPress

Failed to write file to disk.

Common causes

• The hosting account has reached its disk quota
• The partition holding /tmp or upload_tmp_dir is full
• The temp directory is not writable by the PHP user
• Large local backups or cache folders filling the account
• wp-content/uploads ownership changed after a migration (shows the 'could not be moved' variant)

How to fix it

1. Check disk usage. In cPanel open Disk Usage; in hPanel check Hosting > Resources. On a VPS run df -h and look at both / and /tmp.
2. Free up space. Remove old backup archives (e.g. wp-content/updraft, wp-content/ai1wm-backups), cache folders and unused themes. Move backups to off-site storage.
3. Set a writable temp directory. Point upload_tmp_dir to a folder in your home directory (outside public_html) that your account owns, and set WP_TEMP_DIR to the same path.
4. Check uploads permissions. wp-content/uploads and its year/month subfolders should be 755 and owned by the PHP user. Avoid 777.
5. Retry with a smaller file. If small files work and large ones fail, the temp partition is nearly full or size-limited. Ask your host to check it.

SSH diagnostics

df -h /tmp ~
du -sh ~/public_html/wp-content/* | sort -h | tail
php -i | grep -E 'upload_tmp_dir|sys_temp_dir'
ls -ld ~/public_html/wp-content/uploads

How to stop it happening again

• Store backups off-site instead of inside wp-content
• Set up disk usage alerts in your hosting panel
• Optimize images before upload to slow storage growth