The following compilable C++ program catches signals as expected if it
runs directly from shell /tmp/a.out.
However, this program fails to catch any signal and silently terminates
if it is fired by Debian's start-stop-daemon. (My real life multiple
threaded program does not silently terminates. Instead, segmentation
fault occurs from pthread libray.)
---
(
Better code formatted message can be found here:
http://stackoverflow.com/questions/37076470/c-program-launched-by-start-stop-daemon-fails-to-catch-signals
)
File "/tmp/t.cpp":
#include
#include //sigaction, signal()
#include //sleep()
#include //memset()
#include //exit()
static int caught_signal=-1;
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(,0,sizeof(actions));
actions.sa_handler=signal_handler;
int result;
if(
(result=sigaction(SIGTERM,,NULL)) != 0
|| (result=sigaction(SIGHUP,,NULL)) != 0
){
std::cerr << "sigaction() failed: " << result << std::endl;
exit(EXIT_FAILURE);
}
}
int main(int argc,char ** argv)
{
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;
}
---
File "/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
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: $SCRIPTNAME
{start|stop|restart|reload|force-reload|status}" >&2
exit 1
;;
esac
exit 0
---
Running results:
john@host:/tmp$ ./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/4S+ 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/4S+ 0:00 grep a.out
john@host:/tmp$ ./a.out&
[1] 8963
john@host:/tmp$ ps ax|grep a.out
8963 pts/4S 0:00 ./a.out
8967 pts/4S+ 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/4S+ 0:00 grep a.out
[1]+ Done./a.out
john@host:/tmp$ exit
---
Why the program terminates, which I believe crashes, when signals arrive
if it is launched by the aforementioned shell script?
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