Gfrktyl

Here are the version details of the Debian machine I'm using:

root@my-host-name:~# cat /etc/debian_version

8.9

root@my-host-name:~# uname -a

Linux my-host-name 3.16.0-4-amd64 #1 SMP Debian 3.16.43-2+deb8u2 (2017-06-26) x86_64 GNU/Linux

root@my-host-name:~#

To do my work, I log into this machine as root and execute this command:

/usr/java/jre1.8.0_131/bin/java -jar /usr/local/jenkins/jenkins.war

This application runs a web server which I then access from elsewhere.

I have created a regular, non-privileged "jenkins" user under which to run this account. When the machine boots, I'd like the command shown above to automatically run as this new "jenkins" user. Similarly, when the machine is shut down, I'd like this process to be taken down gracefully.

I suppose what I'm saying is that I want this application to run as a service. (Please correct me if I am not precisely correct in my use of the term "service".)

How may I accomplish this?

ADDITIONAL INFORMATION ADDED AFTER FIRST ANSWER POSTED

I appear to have both systemd and init.

root@my-host-name:~# ps -elf | grep system

4 S root       156     1  0  80   0 - 10379 -      Jul31 ?        00:00:00 /lib/systemd/systemd-udevd

4 S root       157     1  0  80   0 -  7480 -      Jul31 ?        00:00:00 /lib/systemd/systemd-journald

4 S root       420     1  0  80   0 -  7083 -      Jul31 ?        00:00:00 /lib/systemd/systemd-logind

4 S message+   422     1  0  80   0 - 10713 -      Jul31 ?        00:00:00 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation

4 S Debian-+   812     1  0  80   0 -  8914 -      Jul31 ?        00:00:00 /lib/systemd/systemd --user

4 S root       993     1  0  80   0 -  6809 -      Aug01 ?        00:00:00 /lib/systemd/systemd --user

0 R root      5305  4936  0  80   0 -  3182 -      02:51 pts/0    00:00:00 grep system

root@my-host-name:~# ps -elf | grep init

4 S root         1     0  0  80   0 - 44052 -      Jul31 ?        00:00:01 /sbin/init

0 R root      5307  4936  0  80   0 -  3182 -      02:51 pts/0    00:00:00 grep init

Will they conflict? How do they interplay?

Also, my /etc/systemd/system directory is a maze of directories and links to directories:

root@my-host-name:/etc/systemd/system# ls -l

total 48

drwxr-xr-x 2 root root 4096 Apr 13 03:45 bluetooth.target.wants

lrwxrwxrwx 1 root root   37 Apr 13 03:45 dbus-org.bluez.service -> /lib/systemd/system/bluetooth.service

lrwxrwxrwx 1 root root   40 Apr 13 03:44 dbus-org.freedesktop.Avahi.service -> /lib/systemd/system/avahi-daemon.service

lrwxrwxrwx 1 root root   40 Apr 13 03:45 dbus-org.freedesktop.ModemManager1.service -> /lib/systemd/system/ModemManager.service

lrwxrwxrwx 1 root root   53 Apr 13 03:45 dbus-org.freedesktop.nm-dispatcher.service -> /lib/systemd/system/NetworkManager-dispatcher.service

lrwxrwxrwx 1 root root   32 Apr 13 03:45 display-manager.service -> /lib/systemd/system/gdm3.service

drwxr-xr-x 2 root root 4096 Apr 13 03:37 getty.target.wants

drwxr-xr-x 2 root root 4096 Apr 13 03:45 graphical.target.wants

drwxr-xr-x 2 root root 4096 Apr 13 03:37 halt.target.wants

drwxr-xr-x 2 root root 4096 Apr 13 03:45 hibernate.target.wants

drwxr-xr-x 2 root root 4096 Apr 13 03:45 hybrid-sleep.target.wants

drwxr-xr-x 2 root root 4096 Jul 13 09:21 multi-user.target.wants

drwxr-xr-x 2 root root 4096 Apr 13 03:37 paths.target.wants

drwxr-xr-x 2 root root 4096 Apr 13 03:37 poweroff.target.wants

drwxr-xr-x 2 root root 4096 Apr 13 03:37 reboot.target.wants

drwxr-xr-x 2 root root 4096 Apr 13 03:44 sockets.target.wants

lrwxrwxrwx 1 root root   31 Apr 13 03:45 sshd.service -> /lib/systemd/system/ssh.service

drwxr-xr-x 2 root root 4096 Apr 13 03:45 suspend.target.wants

lrwxrwxrwx 1 root root   35 Apr 13 03:37 syslog.service -> /lib/systemd/system/rsyslog.service

Does this state anything additional about the startup mechanism my Debian machine uses? Given this directory content, is it still correct to put the proposed jenkins.service directly in /etc/systemd/system, or must I try to figure out this pattern of links and try to replicate it?

You are likely running systemd as your inint system. To configure your service, you need to create the necessary unit file for example /etc/systemd/system/jenkins.service.

[Unit]

Description=Jenkins

After=network.target



[Service]

Type=simple

ExecStart=/usr/java/jre1.8.0_131/bin/java -jar /usr/local/jenkins/jenkins.war

User=jenkins



[Install]

WantedBy=multi-user.target

To enable the service to be run at boot, run systemctl enable jenkins. systemctl start jenkins.service starts the service from command line.
For full documentation, see man pages. Systemd home page also has plenty of material for further study.

In case you are using SysV style init, you need to write an init script which starts your daemon in /etc/init.d/, for example /etc/init.d/jenkins (and mark it executable).

#!/bin/sh

### BEGIN INIT INFO

# Provides:          jenkins

# Default-Start:     2 3 4 5

# Default-Stop:      1

### END INIT INFO



EXEC="/usr/java/jre1.8.0_131/bin/java"

ARGS="-jar /usr/local/jenkins/jenkins.war"

USER="jenkins"

PIDFILE="/run/jenkins.pid"



. /lib/lsb/init-functions



case "$1" in

  start)

    start-stop-daemon --start --background --chuid $USER 

                       --make-pidfile --pidfile $PIDFILE --exec $EXEC -- $ARGS

    ;;

  stop)

    start-stop-daemon --stop --pidfile $PIDFILE --exec $EXEC

    ;;

  *)

    echo "Usage: /etc/init.d/jenkins {start|stop}"

    exit 1

    ;;

esac



exit 0

Note that you must fork your service in your init script, otherwise your script doesn't exit, in this example start-stop-daemon does forking (--background) and changing user (--chuid). To study how other services are started in your system using init scripts you can study the files in /etc/init.d/.

To enable the service to start at boot time, run update-rc.d jenkins enable. To start the service run your new script /etc/init.d/jenkins start.

LSB compatible init scripts are also systemd backwards compatible. Remember to source /lib/lsb/init-functions for systemctl to work transparently when executing the script directly.

Debian wiki for LSBInitScripts provides more details about available options, such as starting the service after/before other service.