GuidesSuexec and Apache: A Tutorial Page 8

Suexec and Apache: A Tutorial Page 8




The suexec wrapper isn’t perfect, and some aspects of its
design result in it being less than ideally suited to all environments. Here
are some of the more common questions, changes, and enhancements that come up
again and again:

Q:
The single --suexec-docroot value is irksome. I have 50
virtual hosts with DocumentRoot values like /vhost1,
/vhost2, and so on. The only way I can get suexec to
work with these is to use --suexec-docroot=/, which hardly seems
secure.
A:
This is unfortunately the way it is with the suexec that comes
with Apache up through version 1.3.11. The value you specify for
--suexec-docroot must be an ancestor of all of the
non-~username documents that use it. This restriction
may be lifted in a future version, but even then it would require
settings specified at compile-time, such as with something like
--suexec-docroot=/vhost1,/vhost2.
Q:
I only want suexec to be used in certain directories or
user accounts.
A:
As of Apache 1.3.11, suexec is an all-or-nothing proposition.
If it’s available and enabled, it will be used in all cases when a CGI script
is invoked. A future version of Apache may provide a means of controlling this
with greater granularity.
Q:
Why don’t the Apache CGI error messages say there’s a problem with
suexec?
A:
Because Apache really doesn’t know that for a fact. All it knows is that
called an internal function to invoke the CGI, and the interaction with the
script failed as described in the error message. The error might have been
caused by a failure to meet suexec‘s requirements, or it may have
been the result of a bona fide error in the script itself.
Q:
Why aren’t suexec‘s error messages logged in the Apache
server log?
A:
In order for the messages from suexec to appear in the main
server’s log, they would have to actually be passed to Apache so that Apache
did the logging. Not only is this inappropriate for the Web server to do, but
there would be additional confusion about into which error log the
messages should go.

Going Further

There are a few articles on the Web about working with the
suexec wrapper. Don’t neglect the man page included
with the source; you can view it directly with

    % cd ./apache-1.3/src/support/
    % man ./suexec.8
  

You can also find some documentation at the following URLs:

  • http://www.apache.org/docs/suexec.html>
  • http://www.apache.org/docs/suexec_1_2.html>
    (this is largely obsolete)

In Conclusion

The suexec application is a double-edged sword. It allows you to
execute scripts under other personæ than the basic server
user–but it can also cut you unexpectedly if you’re not careful. A single
misconfiguration can break all of your CGI scripts, so consider and plan
carefully, and test thoroughly, before implementing the wrapper on your
production systems.

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