I have a script which is doing some stuff, e.g. automated testing. For an unknown reason it is getting (seamingly) randomly terminated by a SIGTERM signal - the goal is to try to identify who is sending the signal - the PID of the sender.
I've tried using the signal library, but it seems that it does not provide enough information about the sender, in case of using a handler setting like signal.signal(signal.SIGTERM, some_handler) - the handler is only passed the signal number (15 in the case), and current stack, which are not helpful.
I also tried using ctypes and creating a handler (based on answer to this), after some changes i managed to get the handler to accept siginfo_t - but the values for siginfo_t.contents.si_pid and siginfo_t.contents.si_code do not make sense to me, as they don't resemble the sender's PID, and the code is not 15.
The code I used is listed below:
#!/usr/bin/env python3
import sys
import os
import time
from ctypes import Structure, Union, POINTER, CFUNCTYPE, CDLL, byref, sizeof, \
c_short, c_int, c_uint, c_long, c_ulong, c_char_p, c_void_p
SIGTERM = 15
SA_SIGINFO = 4
class sigset_t(Structure):
_fields_ = [
("__val", c_ulong * (1024 // (8 * sizeof (c_long)))),
]
class sigval_t(Union):
_fields_ = [
("sival_int", c_int),
("sival_ptr", c_void_p),
]
class siginfo_t(Structure):
_fields_ = [
("si_signo", c_int),
("si_errno", c_int),
("si_code", c_int),
("_pad", c_int * 29),
("si_pid", c_uint)
]
sa_sigaction_functype = CFUNCTYPE(None, c_int, POINTER(siginfo_t), c_void_p)
sa_handler_functype = CFUNCTYPE(None, c_int, use_errno=True)
class SIGACTION(Structure):
_fields_ = [
# ("sa_handler", sa_handler_functype),
("sa_sigaction", sa_sigaction_functype),
# ("sa_mask", sigset_t),
("sa_mask", siginfo_t),
("sa_flags", c_int),
("sa_restorer", c_void_p),
]
libc = CDLL(None)
def sighandler(sig, siginfo_t, something): # Signal handler function
libc.puts.argtypes = [c_char_p]
libc.puts.restype = c_int
libc.puts("Custom signal handler called for signal {0:d}".format(sig).encode())
# print(str(siginfo_t.contents))
print("Sender PID: " + str(siginfo_t.contents.si_pid))
print("Signal Number: " + str(siginfo_t.contents.si_signo))
def main(*argv):
libc.sigaction.argtypes = [c_int, POINTER(SIGACTION), POINTER(SIGACTION)]
libc.sigaction.restype = c_int
signal_number = SIGTERM
act = SIGACTION(
# sa_handler=sa_handler_functype(sighandler),
sa_sigaction=sa_sigaction_functype(sighandler),
sa_flag=SA_SIGINFO)
res = libc.sigaction(signal_number, byref(act), None)
print("sigaction result: {0:d}".format(res))
print("PId {0:d} waiting for SIG {1:d}...".format(os.getpid(), signal_number))
while 1:
time.sleep(0.1)
if __name__ == "__main__":
main(*sys.argv[1:])
print("\nDone.")
And the values I get when the handler is called (signal is sent by process with PID 14783):
siginfo_t.contents
si_code: 11340640
si_errno: 1
si_pid: 2
si_signo: 1
This is my first time using ctypes and C in general (hence, the code may not make too much sense), so any help with clarifying why do I get invalid values and how to fix it would be appreciated, thanks.
Python 3.8, tested on Ubuntu 18.04.5 LTS
