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

"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 pythonfrom subprocess import Popen, PIPEproc = 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 pythonfrom pipes import quotefrom pexpect import run # $ pip install pexpectout, returncode = run("sh -c " + quote(shell_command), withexitstatus=1)signal = returncode - 128 # 128+nprint out, signal

Or using pty stdlib module directly:

#!/usr/bin/env pythonimport osimport ptyfrom select import selectfrom subprocess import Popen, STDOUT# use pseudo-tty to capture output printed directly to the terminalmaster_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        breakos.close(slave_fd)os.close(master_fd)print "".join(buf), p.returncode-128

Came back here: it works like a charm with subprocess from python3 and if you are on linux, there is a backport to python2 called subprocess32 which does work quite well

Older solution: I used pexpect and it works

def cmd_line_call(name, args):    child = pexpect.spawn(name, args)    # Wait for the end of the output    child.expect(pexpect.EOF)     out = child.before # we get all the data before the EOF (stderr and stdout)    child.close() # that will set the return code for us    # signalstatus and existstatus read as the same (for my purpose only)    if child.exitstatus is None:        returncode = child.signalstatus    else:        returncode = child.exitstatus    return (out, returncode)    

PS: a little slower (because it spawns a pseudo tty)

proc = (subprocess.Popen(called, stdout=subprocess.PIPE, stderr=subprocess.PIPE))print(proc.stdout.read())print(proc.stderr.read())

This should work better.
Personally i'd go with:

from subprocess import Popen, PIPEhandle = Popen(called, shell=True, stdout=PIPE, stderr=PIPE)output = ''error = ''while handle.poll() is None:    output += handle.stdout.readline() + '\n'    error += handle.stderr.readline() + '\n'handle.stdout.close()handle.stderr.close()print('Exit code was:', handle.poll())print('Output was:', output)print('Errors were:', error)

And probably use epoll() if possible for the stderr as it sometimes blocks the call because it's empty which is why i end up doing stderr=STDOUT when i'm lazy.