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forever.c
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forever.c
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// https://linux.die.net/man/2/waitpid
// cc forever.c -O -o forever
#include <sys/wait.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <time.h>
int main(int argc, char *argv[], char *envp[]) {
if (argc < 2) {
fprintf(stderr, "Usage: %s /usr/bin/other_executables [options]\n", argv[0]);
exit(1);
}
// detach from the terminal parent
setsid();
signal (SIGHUP, SIG_IGN);
int status;
for(;;){
time_t forkTime=time(NULL);
pid_t pid = fork();
if( 0 > pid ){ // failure of fork
int errsv = errno;
fprintf(stderr, "failed to fork, error no: %d \n", errsv);
exit(1);
}
if ( 0 == pid ) { //child
fprintf(stderr, "child pid: %d, spawning...\n", getpid());
char *cwd = getenv("CWD");
if(cwd != NULL && strlen(cwd) > 0) {
chdir(cwd);
}
char **args=&argv[1]; // start from the second parameter
execve(args[0], args, envp); // exec binary with arguments and environment variables in child process
int errsv = errno;
fprintf(stderr, "failed to execute, error no: %d \n", errsv);
exit(1); // break loop in the monitored process in case it forks itself
}else{ //parent
fprintf(stderr, "start monitoring %d\n", pid);
pid_t w = waitpid(pid, &status, WUNTRACED); // block the main thread
if (WIFEXITED(status)) {
fprintf(stderr, "exited, status=%d\n", WEXITSTATUS(status));
} else if (WIFSIGNALED(status)) {
fprintf(stderr, "killed by signal %d\n", WTERMSIG(status));
} else if (WIFSTOPPED(status)) {
fprintf(stderr, "stopped by signal %d\n", WSTOPSIG(status));
}
time_t now=time(NULL);
if( 180 > (now - forkTime) ){ // If the child process keeps exiting within 180 seconds, stop to resume it anymore.
fprintf(stderr, "abnormally resume, please check manually.\n");
exit(1);
}
}
}
}