In subversion I was getting the error “post-commit hook failed (exit code 255) with no output” after trying to configure my post-commit hook to send email notifications. At first I thought the problem must have been related to the mailer, but I ran the mail command manually and it worked fine. Eventually I figured out that the problem was that the hooks/post-commit file hadn’t been marked executable. So it was a simple chmod +x to fix the problem.