Cryptic errors from mod_fcgid and Perl

For future reference, the cryptic error from mod_fcgid:

[Thu Feb 12 22:10:27 2009] [warn] (104)Connection reset by peer:
    mod_fcgid: read data from fastcgi server error.
[Thu Feb 12 22:10:27 2009] [error] [client X.X.X.X] Premature end of
    script headers: dispatch.fcgi

means that dispatch.fcgi failed to start. Possible reasons are:

1. Missing Perl modules. Unfortunately, I don’t know where the stderr output ends up. Try running the script directly; e.g. perl dispatch.fcgi.
2. Missing Perl modules that you installed locally (e.g. local::lib) but Apache doesn’t have it in $PERL5LIB.

Remember that the folder must not be group-writable, and that any executable must be run from the directory root that suEXEC was compiled for! These will fail with a more useful error though, complaining of “suexec policy violation: see suexec log for more details” (the log is at /var/log/httpd/suexec.log for CentOS systems).