Capture PID of child process

[klappnase]

Hello, everyone,

I am running python2.2.2 on a linux box.
I want to call a shell command and get the PID of this child process
so I have the possibility to abort the child process while it is still
running.

I tried the popen2 module for that:

self.pp = popen2.Popen3(cmd)
cmdpid = self.pp.pid

However I found that the PID returned by self.pp.pid is not the PID of
the process of interest, but the PID of a subshell in which this child
process is running.
So if I do

os.kill(cmdpid, 9)

the subshell is killed, but the process I actually wanted to stop is
happily running on.

Does anyone have a clue what to do about that? Any help would be very
appreciated.

Thank you in advance

Michael

 

[Michael Hudson]

Hello, everyone,

I am running python2.2.2 on a linux box.
I want to call a shell command and get the PID of this child process
so I have the possibility to abort the child process while it is still
running.

I tried the popen2 module for that:

self.pp = popen2.Popen3(cmd)
cmdpid = self.pp.pid

However I found that the PID returned by self.pp.pid is not the PID of
the process of interest, but the PID of a subshell in which this child
process is running.
So if I do

os.kill(cmdpid, 9)

the subshell is killed, but the process I actually wanted to stop is
happily running on.

Does anyone have a clue what to do about that? Any help would be very
appreciated.

If you don't actually want to let a shell near your cmd string, you
can pass a list of strings to popen2.Popen3's constructor, and then
pp.pid will be the PID of the child process you're interested in.

This doesn't seem to be documented anywhere! But you can read the
source, I hope.

Cheers,
mwh

 

[Bernhard Herzog]

self.pp = popen2.Popen3(cmd)
cmdpid = self.pp.pid

However I found that the PID returned by self.pp.pid is not the PID of
the process of interest, but the PID of a subshell in which this child
process is running.

If cmd is a string popen will start a sub-shell so that'd the pid you
get. You could try to prefix your command with exec so that your
command's process replaces the shell process (see the shell
documentation).

Alternatively you could use a list of strings as the command so that no
shell is used in the first place, i.e. "prog param" would become
["prog", "param"]. This approach has the advantage that you don't have
to worry about shell quoting but it's less portable because it's not
even documented (I'll file a bug report for that).

Bernhard

 

[Bernhard Herzog]

Alternatively you could use a list of strings as the command so that no
shell is used in the first place, i.e. "prog param" would become
["prog", "param"]. This approach has the advantage that you don't have
to worry about shell quoting but it's less portable because it's not
even documented (I'll file a bug report for that).

As it turns out, there already is a bug report:
http://python.org/sf/666700

Bernhard

 

[P]

Hello, everyone,

I am running python2.2.2 on a linux box.
I want to call a shell command and get the PID of this child process
so I have the possibility to abort the child process while it is still
running.

I tried the popen2 module for that:

self.pp = popen2.Popen3(cmd)

I modified this a bit to create my own class,
which allows me to kill the whole process group
and wait for completion. See the fslint_backend
class in http://www.pixelbeat.org/fslint/FSlint-2.02.tar.gz

Pádraig.