linux - [Solved-5 Solutions] How to make child process die after parent exits - ubuntu - red hat - debian - linux server - linux pc
Linux - Problem :
How to make child process die after parent exits ?
Linux - Solution 1:
Child can ask kernel to deliver SIGHUP (or other signal) when parent dies by specifying option PR_SET_PDEATHSIG in prctl() syscall like this:
prctl(PR_SET_PDEATHSIG, SIGHUP);
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Linux - Solution 2:
By running the "original" code in the "child" and the "spawned" code in the "parent" (that is: you reverse the usual sense of the test after fork()). Then trap SIGCHLD in the "spawned" code
Linux - Solution 3:
If you're unable to modify the child process, you can try something like the following:
int pipes[2];
pipe(pipes)
if (fork() == 0) {
close(pipes[1]); /* Close the writer end in the child*/
dup2(0, pipes[0]); /* Use reader end as stdin */
exec("sh -c 'set -o monitor; child_process & read dummy; kill %1'")
}
close(pipes[0]); /* Close the reader end in the parent */
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- This runs the child from within a shell process with job control enabled. The child process is spawned in the background.
- The shell waits for a newline (or an EOF) then kills the child.
- When the parent dies--no matter what the reason--it will close its end of the pipe.
- The child shell will get an EOF from the read and proceed to kill the backgrounded child process.
Linux - Solution 4:
On Mac OS X you can use kqueue:
void noteProcDeath(
CFFileDescriptorRef fdref,
CFOptionFlags callBackTypes,
void* info)
{
// LOG_DEBUG(@"noteProcDeath... ");
struct kevent kev;
int fd = CFFileDescriptorGetNativeDescriptor(fdref);
kevent(fd, NULL, 0, &kev, 1, NULL);
// take action on death of process here
unsigned int dead_pid = (unsigned int)kev.ident;
CFFileDescriptorInvalidate(fdref);
CFRelease(fdref); // the CFFileDescriptorRef is no longer of any use in this example
int our_pid = getpid();
// when our parent dies we die as well..
LOG_INFO(@"exit! parent process (pid %u) died. no need for us (pid %i) to stick around", dead_pid, our_pid);
exit(EXIT_SUCCESS);
}
void suicide_if_we_become_a_zombie(int parent_pid) {
// int parent_pid = getppid();
// int our_pid = getpid();
// LOG_ERROR(@"suicide_if_we_become_a_zombie(). parent process (pid %u) that we monitor. our pid %i", parent_pid, our_pid);
int fd = kqueue();
struct kevent kev;
EV_SET(&kev, parent_pid, EVFILT_PROC, EV_ADD|EV_ENABLE, NOTE_EXIT, 0, NULL);
kevent(fd, &kev, 1, NULL, 0, NULL);
CFFileDescriptorRef fdref = CFFileDescriptorCreate(kCFAllocatorDefault, fd, true, noteProcDeath, NULL);
CFFileDescriptorEnableCallBacks(fdref, kCFFileDescriptorReadCallBack);
CFRunLoopSourceRef source = CFFileDescriptorCreateRunLoopSource(kCFAllocatorDefault, fdref, 0);
CFRunLoopAddSource(CFRunLoopGetMain(), source, kCFRunLoopDefaultMode);
CFRelease(source);
}
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Linux - Solution 5:
This type of solution is useful when the code in the child can't be modified.
int p[2];
pipe(p);
pid_t child = fork();
if (child == 0) {
close(p[1]); // close write end of pipe
setpgid(0, 0); // prevent ^C in parent from stopping this process
child = fork();
if (child == 0) {
close(p[0]); // close read end of pipe (don't need it here)
exec(...child process here...);
exit(1);
}
read(p[0], 1); // returns when parent exits for any reason
kill(child, 9);
exit(1);
}
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There are two small caveats with this method:
- If you deliberately kill the intermediate process, then the child won't be killed when the parent dies.
- If the child exits before the parent, then the intermediate process will try to kill the original child pid, which could now refer to a different process. (This could be fixed with more code in the intermediate process.)
def run(*args):
(r, w) = os.pipe()
child = os.fork()
if child == 0:
os.close(w)
os.setpgid(0, 0)
child = os.fork()
if child == 0:
os.close(r)
os.execl(args[0], *args)
os._exit(1)
os.read(r, 1)
os.kill(child, 9)
os._exit(1)
os.close(r)