In your cronjob, replace the php5 entry with the following
(including the backticks):
which php5
If that still doesn't work, replace it simply with php, not php5:
which php
You can use 'env php' instead and it'll pick up the first one in $PATH (same sort of idea as 'which' though).
So the job would be:
env php -f /path/to/file.php
Also while the curl suggestion may work, it's going to (eventually) have timeout issues and stop working if the backup's become too large.
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