Capture “Segmentation fault” message for a crashed subprocess: no out and err after a call to communicate()

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"Segmentation fault" message might be generated by a shell. To find out, whether the process is kill by SIGSEGV, check proc.returncode == -signal.SIGSEGV.

If you want to see the message, you could run the command in the shell:

#!/usr/bin/env python
from subprocess import Popen, PIPE

proc = Popen(shell_command, shell=True, stdout=PIPE, stderr=PIPE)
out, err = proc.communicate()
print out, err, proc.returncode

I’ve tested it with shell_command="python -c 'from ctypes import *; memset(0,1,1)'" that causes segfault and the message is captured in err.

If the message is printed directly to the terminal then you could use pexpect module to capture it:

#!/usr/bin/env python
from pipes import quote
from pexpect import run # $ pip install pexpect

out, returncode = run("sh -c " + quote(shell_command), withexitstatus=1)
signal = returncode - 128 # 128+n
print out, signal

Or using pty stdlib module directly:

#!/usr/bin/env python
import os
import pty
from select import select
from subprocess import Popen, STDOUT

# use pseudo-tty to capture output printed directly to the terminal
master_fd, slave_fd = pty.openpty()
p = Popen(shell_command, shell=True, stdin=slave_fd, stdout=slave_fd,
          stderr=STDOUT, close_fds=True)
buf = []
while True:
    if select([master_fd], [], [], 0.04)[0]: # has something to read
        data = os.read(master_fd, 1 << 20)
        if data:
            buf.append(data)
        else: # EOF
            break
    elif p.poll() is not None: # process is done
        assert not select([master_fd], [], [], 0)[0] # nothing to read
        break
os.close(slave_fd)
os.close(master_fd)
print "".join(buf), p.returncode-128

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