Fix CTRL-Z handling: Signal SIGSTOP to PGID

Fix #3501

src/terminal_unix.go

@@ -7,6 +7,8 @@ import (
 	"os/signal"
 	"strings"
 	"syscall"
+
+	"golang.org/x/sys/unix"
 )
 
 func notifyOnResize(resizeChan chan<- os.Signal) {
@@ -14,7 +16,12 @@ func notifyOnResize(resizeChan chan<- os.Signal) {
 }
 
 func notifyStop(p *os.Process) {
-	p.Signal(syscall.SIGSTOP)
+	pid := p.Pid
+	pgid, err := unix.Getpgid(pid)
+	if err == nil {
+		pid = pgid * -1
+	}
+	unix.Kill(pid, syscall.SIGSTOP)
 }
 
 func notifyOnCont(resizeChan chan<- os.Signal) {