Can't detach child process when main process is started from systemd
Solution is to add
KillMode=process
to the service block. Default value is control-group
which means systemd cleans up any child processes.
From man systemd.kill
KillMode= Specifies how processes of this unit shall be killed. One of control-group, process, mixed, none.
If set to control-group, all remaining processes in the control group of this unit will be killed on unit stop (for services: after the stop command is executed, as configured with ExecStop=). If set to process, only the main process itself is killed. If set to mixed, the SIGTERM signal (see below) is sent to the main process while the subsequent SIGKILL signal (see below) is sent to all remaining processes of the unit's control group. If set to none, no process is killed. In this case, only the stop command will be executed on unit stop, but no process be killed otherwise. Processes remaining alive after stop are left in their control group and the control group continues to exist after stop unless it is empty.
Admin
Updated on June 27, 2022Comments
-
Admin almost 2 years
I want to spawn long-running child processes that survive when the main process restarts/dies. This works fine when running from the terminal:
$ cat exectest.go package main import ( "log" "os" "os/exec" "syscall" "time" ) func main() { if len(os.Args) == 2 && os.Args[1] == "child" { for { time.Sleep(time.Second) } } else { cmd := exec.Command(os.Args[0], "child") cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true} log.Printf("child exited: %v", cmd.Run()) } } $ go build $ ./exectest ^Z [1]+ Stopped ./exectest $ bg [1]+ ./exectest & $ ps -ef | grep exectest | grep -v grep | grep -v vim snowm 7914 5650 0 23:44 pts/7 00:00:00 ./exectest snowm 7916 7914 0 23:44 ? 00:00:00 ./exectest child $ kill -INT 7914 # kill parent process [1]+ Exit 2 ./exectest $ ps -ef | grep exectest | grep -v grep | grep -v vim snowm 7916 1 0 23:44 ? 00:00:00 ./exectest child
Note that the child process is still alive after parent process was killed. However, if I start the main process from systemd like this...
[snowm@localhost exectest]$ cat /etc/systemd/system/exectest.service [Unit] Description=ExecTest [Service] Type=simple ExecStart=/home/snowm/src/exectest/exectest User=snowm [Install] WantedBy=multi-user.target $ sudo systemctl enable exectest ln -s '/etc/systemd/system/exectest.service' '/etc/systemd/system/multi-user.target.wants/exectest.service' $ sudo systemctl start exectest
... then the child also dies when I kill the main process:
$ ps -ef | grep exectest | grep -v grep | grep -v vim snowm 8132 1 0 23:55 ? 00:00:00 /home/snowm/src/exectest/exectest snowm 8134 8132 0 23:55 ? 00:00:00 /home/snowm/src/exectest/exectest child $ kill -INT 8132 $ ps -ef | grep exectest | grep -v grep | grep -v vim $
How can I make the child survive?
Running go version go1.4.2 linux/amd64 under CentOS Linux release 7.1.1503 (Core).
-
Alexis Wilke almost 8 yearsWould there be a way to move the process out of the group instead?
-
DonutGaz about 5 yearsThis saved me. Thank you.
-
rien333 over 3 yearsToday, the manual tells us that "If set to 'process', only the main process itself is killed (not recommended!)". Any idea why this is discouraged?