2、將標準輸入,標準輸出,標準錯誤都重定向/dev/null
daemon 實現大致如下:
int daemonize(int nochdir, int noclose)
{
int fd;
switch (fork()) {
case -1:
return (-1);
case 0:
break;
default:
_exit(EXIT_SUCCESS);
}
if (setsid() == -1)
return (-1);
if (nochdir == 0) {
if(chdir("/") != 0) {
perror("chdir");
return (-1);
}
}
if (noclose == 0 && (fd = open("/dev/null", O_RDWR, 0)) != -1) {
if(dup2(fd, STDIN_FILENO) < 0) {
perror("dup2 stdin");
return (-1);
}
if(dup2(fd, STDOUT_FILENO) < 0) {
perror("dup2 stdout");
return (-1);
}
if(dup2(fd, STDERR_FILENO) < 0) {
perror("dup2 stderr");
return (-1);
}
if (fd > STDERR_FILENO) {
if(close(fd) < 0) {
perror("close");
return (-1);
}
}
}
return (0);
}
#include <signal.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
static int fd = -1;
void sigroutine(int dunno) {
switch (dunno) {
case SIGUSR1:
fprintf(stderr, "Get a signal -- SIGUSR1 \n");
if (fd != -1) close(fd);
fd = open("/tmp/console_temp.log", O_RDWR|O_APPEND|O_CREAT, 0600);
if (fd == -1) break;
dup2(fd, STDIN_FILENO);
dup2(fd, STDOUT_FILENO);
dup2(fd, STDERR_FILENO);
break;
case SIGUSR2:
fprintf(stderr, "Get a signal -- SIGUSR2 \n");
if (fd != -1) close(fd);
fd = open("/dev/null", O_RDWR, 0);
if (fd == -1) break;
dup2(fd, STDIN_FILENO);
dup2(fd, STDOUT_FILENO);
dup2(fd, STDERR_FILENO);
break;
}
return;
}
int main() {
signal(SIGUSR1, sigroutine);
signal(SIGUSR2, sigroutine);
daemon(1,0);
for (;;){
fprintf(stderr,"test \n") ; // 不斷打印test
sleep(1);
}
return 0;
}
$ ps -ef| grep daemon_example
root 11328 1 0 19:15 ? 00:00:00 ./daemon_example
如上,進程後臺運行了,拿到pid 11328
#!/bin/bash
pid=$1
ps -p $pid>/dev/null
if [ ! $? -eq 0 ] ; then
echo pid does not exist!
exit 1
fi
echo pid $pid
trap "kill -usr2 $pid && exit 1" HUP INT QUIT TERM
kill -usr1 $pid
echo it works,please wait..
sleep 1
tail -f -n 0 /tmp/console_temp.log
echo done!
pid 11328
it works,please wait..
test
test