用popen启动服务：命令不停止

Question

I try to make a backup script in python and start, stop a service with popen... Stopping the service is working, but unfortunatly starting the service works, but blocks the rest of the execution, the scripts stays there, why ?

Seems to be somehow linked with the httpd service... :-(

the program config element is like "service;httpd;start" or "/etc/init.d/myprog;start"

class execute(actions):
    def __init__(self,config,section,logger):
        self.name="execute"
        actions.__init__(self,config,section,logger)

    def process(self):
        try:
            program=self.config.get(self.section,"program").split(";")
            self.logger.debug("program=%s" % program)
            p = subprocess.Popen(program, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
            stdout, stderr = p.communicate()

            if stdout:
                self.logger.info(stdout)
            if stderr:
                self.logger.error(stderr)

            return p.returncode

        except Exception:
            self.logger.exception(Exception)

Answer 1

You have to open a stdin as a pipe as well, and then close it (if you use read() and write() instead of communicate()).

p = subprocess.Popen(..., stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
p.stdin.close()
print "Stdout:", p.stdout.read()
print "Stderr:", p.stderr.read()

If it doesn't work, and you don't really need any checks, just close all pipes after call to Popen, what will cause program execution and detachment from pipes.

Warning: This will make program run as a daemon if it doesn't terminate on its own.

After doing this you may call wait() to see whether it'll block as well. And use exitcodes to check for eventual errors.

There are not much of them. Just service started or not. Sometimes even it returns that service is running, but service crashes.

To check whether service script is still running, but without blocking, use:

if p.poll()==None: print "Still running"

Else, poll() returns the exit code.

This works neatly for starting and stopping a service:

from subprocess import Popen, PIPE
service = "brltty"
p = Popen(["service", service, "start"], stdin=PIPE, stdout=PIPE, stderr=PIPE)
# Note: using sequence uses shell=0
stdout, stderr = p.communicate()
print "Stdout:", stdout
print "Stderr:", stderr

Don't forget to change start to stop :D :D :D

Answer 2

The call to p.communicate() waits for the process to terminate.

Refer to: subprocess documentation

Interact with process: Send data to stdin. Read data from stdout and stderr, until end-of-file is reached. Wait for process to terminate . The optional input argument should be a string to be sent to the child process, or None, if no data should be sent to the child.

You can try to use p.poll() instead. This method doesn't wait for a process to terminate.