How to test for services in Linux?

Question

I've been assigned a project to write some kind of a script that will perform a sanity check on a Linux server implementation to determine if it has a number of dependencies installed before source code is deployed to it. I need to check for the presence of applications such as PHP, Nginx, PostgreSQL, etc and likely confirm version numbers for these as well. These dependencies are required for the given source code to be able to run properly on the server.

The problem is, I'm not sure how to approach this due to my novelty in working with Linux. I've done some research on this and thought that the solution might be to use a combination of combing through the list of running services with a command such as "chkconfig --list" and pinging individual applications with commands such as "php -v" and then asserting the that results from these equate to what I'm looking for.

Pardon if that makes no sense whatsoever, I really am new to this. I was then thinking I could place these "tests" inside of a shell script or something that could be run whenever a test on the server needed to be executed. I would aggregate the true/false results of my assertions and output whether the sanity check passed based on that. Any guidance would be greatly appreciated.

Thank you.

Revision: In lieu of a shell script, I was also thinking I could write this in Python. Does anybody know of any good Python libraries that allow querying of system services?

Answer 1

If your target systems are managed by reasonable people, the software will be managed by the packaging system. On Redhat, Fedora, CentOS or SUSE systems that will be RPM. On any system derived from Debian it will be APT.

So your script can check for one of those two packaging systems. Although be warned that you can install RPM on a Debian system so the mere presence of RPM doesn't tell you the system type. Packages can also be named differently. For example, SUSE will name things a bit differently from Redhat.

So, use uname and/or /etc/issue to determine system type. Then you can look for a particular package version with rpm -q apache or dpkg-query -s postgresql.

If the systems are managed by lunatics, the software will be hand-built and installed in /opt or /usr/local or /home/nginx and versions will be unknown. In that case good luck.