how can I know whether the plugin is used by any jobs in jenkins

Question

Jenkins had 600+ plugins, in the real system, we are used to install lots of plugins.

And sometimes, we want to remove some plugins to make system more clean or replace

Answer 1

I can't comment because I don't have enough reputation, but if I could, I would point out that the broken link provided by coffeebreaks for the small scriplet script mentioned in the accepted answer can be found on the Internet Archive, at this link:

https://web.archive.org/web/20131103111754/http://scriptlerweb.appspot.com/script/show/97001

In case that link breaks, here is the content of the script:

import jenkins.model.*;
import hudson.ExtensionFinder;

List finders = Jenkins.instance.getExtensionList(ExtensionFinder.class);

for (finder in finders) {
  println(">>> " + finder);
  if (finder instanceof hudson.ExtensionFinder.GuiceFinder) {
    println(finder.annotations.size());
    for (key in finder.annotations.keySet()) {
       println(key);
    }
  } else if (finder instanceof ruby.RubyExtensionFinder) {
    println(finder.parsedPlugins.size());
    for (plugin in finder.parsedPlugins) {
      for (extension in plugin.extensions) {
        println("ruby wrapper for " + extension.instance.clazz);
      }
    }
  } else if (finder instanceof hudson.cli.declarative.CLIRegisterer) {
    println(finder.discover(Jenkins.instance));
    for (extension in finder.discover(Jenkins.instance)) {
      println("CLI wrapper for " + extension.instance.class);
      // not sure what to do with those      
    }
  } else {
    println("UNKNOWN FINDER TYPE"); 
  }
}