[mod_python] os.system() call does not work within mod_python script

Arno Wilhelm quirxi at aon.at
Sun May 15 06:59:43 EDT 2005


thanks for your help.

I have resolved the issue now. User apache is not allowed to issue (almost) any 
command. I had to load the suexec module that uses the command suexec2 in order 
to get that to work!

The only command that worked without the suexec_module was the echo command:
system( "/bin/echo Hello_mod_python >> /tmp/dummy.log 2>&1" )

Any other command from within a mod_python script did not show any results, 
except an empty /tmp/dummy file (but not even an error message) at all!

When I load the suexec_module in apache2.conf like this:

LoadModule suexec_module      modules/mod_suexec.so
SuexecUserGroup root root

apache2 seems to issue the command with the help of the suexec2 utility:

# suexec2 -V
  -D AP_DOC_ROOT="/var/www"
  -D AP_GID_MIN=100
  -D AP_HTTPD_USER="apache"
  -D AP_LOG_EXEC="/var/log/apache2/suexec_log"
  -D AP_SAFE_PATH="/usr/local/bin:/usr/bin:/bin"
  -D AP_UID_MIN=1000
  -D AP_USERDIR_SUFFIX="public_html"

See also this website for more details:

Thanks and greetings,


Graham Dumpleton wrote:
> On 15/05/2005, at 8:08 AM, Arno Wilhelm wrote:
>> Hello,
>> I have got a proble for which I cannot find a proper solution:
>> Whenever a user on his browser hits a certain page (served by 
>> mod_python) the mod_python should send a SIGUSR signal to a certain 
>> process in order to force a update on him like this
>> # os.system( "kill -s SIGUSR1 26199" )
>> Whenever I make this call from within a python script it works. But 
>> whenever I try to build it into the mod_python script that is handled 
>> by apache it does not work. After that I have experimented with other 
>> os.system calls from within mod_python scripts and all of them seem to 
>> be ignored somehow.
>> Could someone here possibly shed some light on this issue, since I am 
>> on the end of my knowledge.
> A few things to consider.
> 1. Set full pathnames to the programs in the command.
> The PATH setup for Apache may not be that useful. It may reference
> some standard locations, but not much. Thus, if you expect program
> to be found by searching PATH, it may not work.
> 2. Don't rely on the current working directory to be anything specific.
> Normally current working directory would be '/' and nothing to to do
> with where any Python request handler will be. Any references to files
> should always be as absolute paths.
> 3. Apache usually runs as user "nobody" or some other special user.
> Because Apache runs as a special user, it often will not have the
> necessary privileges to be able to write to directories or send signals
> to processes running as another user.
> 4. Log output of scripts to a directory in "/tmp".
> As a way of working out problems, send the output of any commands to
> a log file in "/tmp". Ie., run your command as:
>   os.system( "kill -s SIGUSR1 26199 >> /tmp/dummy.log 2>&1" )
> This will allow you to see any errors. With the way that Apache works,
> you might not otherwise see errors generated by a call to os.system()
> until Apache is shutdown and certain buffers are flushed out.
> Graham

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