How to Kill a Process or Capture Signals (SIGTERM, SIGKILL) in Python?

Kill Current Process

We can kill a process itself or let the process commit suicide by sending the SIGKILL signal to itself. We can do this via os.kill:

1
2
3
4

import os
import signal
 
os.kill(os.getpid(), signal.SIGKILL)

import os
import signal

os.kill(os.getpid(), signal.SIGKILL)

The SIGKILL will terminate the Python process immediately. Alternatively, we can graceful terminate a process by sending the SIGTERM signal, which is a gentle way to ask the process to terminate itself. In this way, the process can finish up some work e.g. clean up, before being killed.

1
2
3
4

import os
import signal
 
os.kill(os.getpid(), signal.SIGTERM)

import os
import signal

os.kill(os.getpid(), signal.SIGTERM)

Kill the Parent Process

We can pass the parents PID to os.kill via os.getppid():

1
2
3
4

import os
import signal
 
os.kill(os.getppid(), signal.SIGKILL)

import os
import signal

os.kill(os.getppid(), signal.SIGKILL)

The Children Processes are also terminated when their parents are killed.

Capture or Trap the Signals (SIGTERM) in Python

The SIGKILL can’t be captured and handled as the process is terminated straight away. But for other signals (we can check by “kill -l” command), we can capture and handle them:

1
2
3
4
5
6
7
8
9
10
11
12
13

 1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL       5) SIGTRAP
 6) SIGABRT      7) SIGBUS       8) SIGFPE       9) SIGKILL     10) SIGUSR1
11) SIGSEGV     12) SIGUSR2     13) SIGPIPE     14) SIGALRM     15) SIGTERM
16) SIGSTKFLT   17) SIGCHLD     18) SIGCONT     19) SIGSTOP     20) SIGTSTP
21) SIGTTIN     22) SIGTTOU     23) SIGURG      24) SIGXCPU     25) SIGXFSZ
26) SIGVTALRM   27) SIGPROF     28) SIGWINCH    29) SIGIO       30) SIGPWR
31) SIGSYS      34) SIGRTMIN    35) SIGRTMIN+1  36) SIGRTMIN+2  37) SIGRTMIN+3
38) SIGRTMIN+4  39) SIGRTMIN+5  40) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8
43) SIGRTMIN+9  44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9  56) SIGRTMAX-8  57) SIGRTMAX-7
58) SIGRTMAX-6  59) SIGRTMAX-5  60) SIGRTMAX-4  61) SIGRTMAX-3  62) SIGRTMAX-2
63) SIGRTMAX-1  64) SIGRTMAX

 1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL       5) SIGTRAP
 6) SIGABRT      7) SIGBUS       8) SIGFPE       9) SIGKILL     10) SIGUSR1
11) SIGSEGV     12) SIGUSR2     13) SIGPIPE     14) SIGALRM     15) SIGTERM
16) SIGSTKFLT   17) SIGCHLD     18) SIGCONT     19) SIGSTOP     20) SIGTSTP
21) SIGTTIN     22) SIGTTOU     23) SIGURG      24) SIGXCPU     25) SIGXFSZ
26) SIGVTALRM   27) SIGPROF     28) SIGWINCH    29) SIGIO       30) SIGPWR
31) SIGSYS      34) SIGRTMIN    35) SIGRTMIN+1  36) SIGRTMIN+2  37) SIGRTMIN+3
38) SIGRTMIN+4  39) SIGRTMIN+5  40) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8
43) SIGRTMIN+9  44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9  56) SIGRTMAX-8  57) SIGRTMAX-7
58) SIGRTMAX-6  59) SIGRTMAX-5  60) SIGRTMAX-4  61) SIGRTMAX-3  62) SIGRTMAX-2
63) SIGRTMAX-1  64) SIGRTMAX

For example, we can use the signal.signal to write a handler to trap the signals. Sending a SIGTERM to following and the console will print “Received Signal 15”, and if the program receives SIGINT – which is basically pressing the Ctrl + C shortcut to interrupt, it will print “Received Signal 2”.

1
2
3
4
5

def capture_signal(signal_number, frame):
    print('Received Signal {}'.format(signal_number))
    sys.exit(1)
 
signal.signal(signal.SIGTERM, handler)

def capture_signal(signal_number, frame):
    print('Received Signal {}'.format(signal_number))
    sys.exit(1)

signal.signal(signal.SIGTERM, handler)

The second parameter “frame” is a frame object:

1

<frame at 0x7f798c22a4c0, file 'signal_test.py', line 130, code run>

<frame at 0x7f798c22a4c0, file 'signal_test.py', line 130, code run>

Conclusion

We can use the os.kill to either kill a process itself, the parent process or any other process (as long as the current user running the process has permissions). To retrieve the current process ID, we can do os.getpid(), the parent process’s ID can be retrieved by os.getppid().

The SIGKILL can’t be captured and handled. To view a list of all Signals, we can do “kill -l“.

–EOF (The Ultimate Computing & Technology Blog) —