Weird backtick problem

I'm installing TWiki on a server that I don't control, and I have boiled
a bizarre problem down to this: a (Perl) program that executes a command
in backticks will work in the cgi-bin directory, but hangs in the
htdocs/wiki/bin directory. The program is no longer than

print `/bin/ls`;

(after the content-type header) and it makes no difference what the
command in the `` is. If I put anything else besides backticks in the
program it executes properly. I have a .htaccess in the wiki/bin
directory with a SetHandler cgi-script directive. The cgi-bin directory
has no .htaccess file. htdocs is a sibling of cgi-bin. mod_perl is not
running.

I got nowhere with extensive googling. There were some postings alleging
a similar problem on Windows servers but this is Linux. As a last resort
I will have to figure out how to install TWiki by moving its programs to a
cgi-bin directory out of its main tree, but I'd still like to know what
the heck is going on here. The important thing to note is that programs
*are* working in the wiki/bin directory, except for when they employ
backticks; but programs using backticks *do* work in the cgi-bin
directory. I can even run a CGI program in cgi-bin that uses
backticks of its own to executes a program in wiki/bin that also contains
backticks, and *that* works.

--
Peter Scott
http://www.perlmedic.com/
http://www.perldebugged.com/

On Fri, 06 Oct 2006 19:31:19 +0000, I wrote:
> a (Perl) program that executes a command
> in backticks will work in the cgi-bin directory, but hangs in the
> htdocs/wiki/bin directory.

Forgot to mention. This is Apache 1.3.37.

--
Peter Scott
http://www.perlmedic.com/
http://www.perldebugged.com/

Peter Scott wrote:
> On Fri, 06 Oct 2006 19:31:19 +0000, I wrote:
>> a (Perl) program that executes a command
>> in backticks will work in the cgi-bin directory, but hangs in the
>> htdocs/wiki/bin directory.
>
> Forgot to mention. This is Apache 1.3.37.
>
Not sure if I read your prob correctly, but how's about adding a script
alias for the wiki/bin.

You'll need to let apache know which dirs hold executables, otherwise
they won't work.

Hope this helps

Pete

On Sat, 07 Oct 2006 14:29:08 +0200, Yamaska wrote:

> Peter Scott wrote:
>> On Fri, 06 Oct 2006 19:31:19 +0000, I wrote:
>>> a (Perl) program that executes a command
>>> in backticks will work in the cgi-bin directory, but hangs in the
>>> htdocs/wiki/bin directory.
>
> Not sure if I read your prob correctly, but how's about adding a script
> alias for the wiki/bin.
>
> You'll need to let apache know which dirs hold executables, otherwise
> they won't work.

My .htaccess says

SetHandler cgi-script
Options +ExecCGI

I tried putting a ScriptAlias in there and got a 500, but I don't see the
point since it is just going to point to the same directory anyway.
Remember, the programs in this directory *do run* - they just can't
execute a command in backticks.

I experimented some more. The problem is with fork(): when executed in the
cgi-bin directory, it works. But in this directory, it returns undef,
with $! set to EAGAIN (resource temporarily unavailable), which explain
the hangs on backticks, 'cos it's just going to keep trying to fork. So I
don't even have to exec() anything to have the problem.

Did some more googling to no effect. This is not running under SSL. It
happens every time. I don't see how the system can have a different limit
depending on the directory. I've looked through httpd.conf and can't see
anything weird.

--
Peter Scott
http://www.perlmedic.com/
http://www.perldebugged.com/