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Documentation Akeeba Backup – User's Guide

Q202 - Unable to reliably calculate CRC

[Important]Important

Your backup will work properly, but there is a high chance of timeout errors with large files.

You have selected to use the ZIP archive format. Akeeba Backup / Akeeba Solo may be unable to reliably calculate the CRC checksums under some circumstances:

  • The "hash" PHP extension is not present or activated in your php.ini

  • The functionality of the "hash" PHP extension is blocked by your host

Under these circumstances, a seemingly broken ZIP archive can be produced by Akeeba Backup. The archive is not really corrupt. The ZIP format requires us to store a "signature" for each file. Calculating this signature on large files without the "hash" extension is impossible, therefore this "signature" is empty. Archiver applications pick up this empty "signature" and think that the archive is broken, as the empty "signature" violates the ZIP format.

Depending on the source of the problem, you can try several workarounds:

  • Recommended and easiest solution: Download Akeeba eXtract Wizard to easily and reliably extract backup ZIP archives.

  • Some archivers offer an option to ignore CRC errors, so you can use it to extract afflicted archives. Sometimes this option is entitled "Keep broken files" or "Ignore errors".

  • Switch to the latest PHP 5 version; after all, newest versions incorporate security-related bug fixes.

  • Download the PHP "hash" extension and / or enable it on your server; if you are on shared hosting you'll have to ask your host to do that for you.

  • If you manage your own server, remove any limitations regarding the "hash" extension (e.g. by editing disabled_functions in your php.ini).

  • Use the JPA Archive Format, which is much more efficient during archiving and extraction.

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