How to get process's grandparent id

Question

How can i get process id of the current process's parent?
In general given a process id how can I get its parent process id?
e.g. os.getpid() can be used to get the proccess id, and os.getppid() for the parent, how do I get grandparent,

My target is linux(ubuntu) so platform specific answers are ok.

Answer 1

I do not think you can do this portably in the general case.

You need to get this information from the process list (e.g. through the ps command), which is obtained in a system-specific way.

Answer 2

linux specific:

os.popen("ps -p %d -oppid=" % os.getppid()).read().strip()

Answer 3

I don't think you can do this in a portable Python fashion. But there are two possibilities.

1. The information is available from the ps command so you could analyze that.
2. If you have a system with the proc file systems, you can open the file /proc/<pid>/status and search for the line containing PPid:, then do the same for that PID.

For example the following script will get you your PID, PPID and PPPID, permissions willing:

#!/bin/bash
pid=$$
ppid=$(grep PPid: /proc/${pid}/status | awk '{print $2'})
pppid=$(grep PPid: /proc/${ppid}/status | awk '{print $2'})
echo ${pid} ${ppid} ${pppid}
ps -f -p "${pid},${ppid},${pppid}"

produces:

3269 3160 3142
UID        PID  PPID  C STIME TTY          TIME CMD
pax       3142  2786  0 18:24 pts/1    00:00:00 bash
root      3160  3142  0 18:24 pts/1    00:00:00 bash
root      3269  3160  0 18:34 pts/1    00:00:00 /bin/bash ./getem.sh

Obviously, you'd have to open those files with Python.

Answer 4

If you have a POSIX-compliant 'ps' command, which allows you to specify the columns you want, like this: ps -o pid,ppid

You could then try:

import os
import re

ps = os.popen("ps -o pid,ppid")
ps.readline()    # discard header
lines = ps.readlines()
ps.close

procs = [ re.split("\s+", line.strip()) for line in lines ]

parent = {}
for proc in procs:
    parent[ int(proc[0]) ] = int(proc[1])

Now you can do:

parent[ parent[pid] ]

You could even write a function to list a process' ancestors:

def listp(pid):
    print(pid)
    if parent.has_key(pid):
        listp( parent[pid] )

Answer 5

from __future__ import with_statement

def pnid(pid=None, N=1):
    "Get parent (if N==1), grandparent (if N==2), ... of pid (or self if not given)"
    if pid is None:
        pid= "self"

    while N > 0:
        filename= "/proc/%s/status" % pid
        with open(filename, "r") as fp:
            for line in fp:
                if line.startswith("PPid:"):
                    _, _, pid= line.rpartition("\t")
                    pid= pid.rstrip() # drop the '\n' at end
                    break
            else:
                raise RuntimeError, "can't locate PPid line in %r" % filename
        N-= 1

    return int(pid) # let it fail through


>>> pnid()
26558
>>> import os
>>> os.getppid()
26558
>>> pnid(26558)
26556
>>> pnid(N=2)
26556
>>> pnid(N=3)
1