The update fails with "File checksum failed"

Why it happens

Joomla checks the downloaded update package against its official checksum before installing it. "Checksum failed" means the file on your server doesn't match: the download was cut off, damaged, or changed by something on the server (a proxy or security tool).

Fix it

1. Go to System → Update → Joomla and click Check for Updates to clear the old download, then try again.
2. Still failing? Download the update package for your exact version from downloads.joomla.org.
3. In Joomla Update, use the upload and update link below the update button, upload the package and install.
4. If it fails on several sites on the same host, ask your host whether a firewall or proxy changes downloads.

Good to know

• Never skip the check by installing files by hand over FTP: a half-copied core is much harder to fix.
• Use the "Update Package" for your version, not the full install package.