如果直接从 shell /tmp/a.out
运行,下面的可编译 C++ 程序会按预期捕获信号。
但是,如果 Debian 的 start-stop-daemon
触发此程序,则该程序无法捕获任何信号并静默终止。 (我现实生活中的多线程程序并没有静默终止。相反,段错误发生在 pthread 库中。)
文件“/tmp/t.cpp”:
#include <iostream>
#include <signal.h> //sigaction, signal()
#include <unistd.h> //sleep()
#include <cstring> //memset()
#include <cstdlib> //exit()
static int caught_signal;
void signal_handler(int signal_number)
{
std::cerr << "Caught signal# " << signal_number << std::endl;
caught_signal=signal_number;
}
void accept_signals()
{
struct sigaction actions;
memset(&actions,0,sizeof(actions));
actions.sa_handler=signal_handler;
int result;
if(
(result=sigaction(SIGTERM,&actions,NULL)) != 0
|| (result=sigaction(SIGHUP,&actions,NULL)) != 0
){
std::cerr << "sigaction() failed: " << result << std::endl;
exit(EXIT_FAILURE);
}
}
int main(int argc,char ** argv)
{
caught_signal=-1;
accept_signals();
while(true){
if(caught_signal >= 0){
switch(caught_signal){
case SIGHUP:{
std::cerr << "Reload" << std::endl;
break;
}
default:{ //SIGTERM
std::cerr << "Terminate" << std::endl;
return 0;
}
}
}
sleep(1);
}
return 0;
}
文件“/tmp/t.sh”:
#!/bin/sh
### BEGIN INIT INFO
# Provides: progam
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: My Program
# Description: Test signals.
### END INIT INFO
PATH=/sbin:/bin:/usr/sbin:/usr/bin
DAEMON=/tmp/a.out
NAME=progam
DESC="My Program"
SCRIPTNAME=/etc/init.d/$NAME
PIDFILE=/tmp/progam.pid
test -x $DAEMON || exit 0
#set -x
. /lib/lsb/init-functions
case "$1" in
start)
log_daemon_msg "Starting $DESC" $NAME
start-stop-daemon --start --oknodo --quiet --pidfile $PIDFILE --exec $DAEMON -b -m --
log_end_msg $?
;;
stop)
log_daemon_msg "Stopping $DESC" $NAME
start-stop-daemon --stop --retry TERM/10 --quiet --pidfile $PIDFILE --exec $DAEMON --remove-pidfile
log_end_msg $?
;;
reload|force-reload)
log_daemon_msg "Reloading $DESC" $NAME
start-stop-daemon --stop --signal HUP --retry 10 --quiet --pidfile $PIDFILE --exec $DAEMON -b -m
log_end_msg $?
;;
restart)
log_daemon_msg "Restarting $DESC" $NAME
$0 stop
$0 start
;;
status)
status_of_proc -p "$PIDFILE" "$DAEMON" "$NAME" && exit 0 || exit $?
;;
*)
echo "Usage: $SCRIPTNAME {start|stop|restart|reload|force-reload|status}" >&2
exit 1
;;
esac
exit 0
运行结果:
john@host:/tmp$ ./t.sh start
[ ok ] Starting My Program: progam
john@host:/tmp$ ps ax|grep a.out
8911 ? S 0:00 /tmp/a.out
8931 pts/4 S+ 0:00 grep a.out
john@host:/tmp$ ./t.sh stop
[ ok ] Stopping My Program: progam
john@host:/tmp$ ps ax|grep a.out
8961 pts/4 S+ 0:00 grep a.out
john@host:/tmp$ ./a.out&
[1] 8963
john@host:/tmp$ ps ax|grep a.out
8963 pts/4 S 0:00 ./a.out
8967 pts/4 S+ 0:00 grep a.out
john@host:/tmp$ kill -TERM 8963
john@host:/tmp$ Caught signal# 15
Terminate
ps ax|grep a.out
8973 pts/4 S+ 0:00 grep a.out
[1]+ Done ./a.out
john@host:/tmp$ exit
如果程序由上述 shell 脚本启动,为什么当信号到达时程序终止,我相信它会崩溃?
最佳答案
一个善良的灵魂帮助了我,如下所示: https://lists.debian.org/debian-user/2016/05/msg00283.html
启蒙节选如下:
程序和 shell 脚本都在正常工作。 start-stop-daemon
将标准错误等重定向到 /dev/null
。因此,C 函数 signal_handler()
的输出被丢弃。
关于c++ - start-stop-daemon 启动的 C 程序无法捕获信号,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/37076470/