Ubuntu init process

History

sysVinit
upstart
systemd

ubuntu: sysVinit –> upstart(6.10+) –> systemd (15.04+)

Features of Upstart

Event Based

Start System faster (compare with previous method).
Dynamically start service when discovering new device
Dynamically stop service when device is removed

Systemd

Systemd is a collection of system management daemons, utilities and libraries which serves as a replacement of System V init daemon. Systemd functions as central management and configuration platform for UNIX like system.

systemctl

Systemctl is a systemd utility which is responsible for Controlling the systemd system and service manager.

Init script vs Service file

You may use service SCRIPT start|stop|statu.. manage jobs, but it’s different between using Init script and upstart or systemd service file. see man service.

System V init script

located in /etc/init.d/SCRIPT

Example: (from shadowsocks-go project)

#!/bin/bash
# Start/stop shadowsocks.
#
### BEGIN INIT INFO
# Provides:          shadowsocks
# Required-Start:
# Required-Stop:
# Should-Start:
# Should-Stop:
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: shadowsocks is a lightweight tunneling proxy
# Description:       Modified from Linode's nginx fastcgi startup script
### END INIT INFO

# Note: this script requires sudo in order to run shadowsocks as the specified
# user. 

BIN=/usr/bin/shadowsocks-local
CONFIG_FILE=/etc/shadowsocks/config.json
LOG_FILE=/var/log/shadowsocks
USER=nobody
GROUP=nobody
PID_DIR=/var/run
PID_FILE=$PID_DIR/shadowsocks.pid
RET_VAL=0

\[ -x $BIN \] || exit 0

check_running() {
  if [\[ -r $PID_FILE \]]; then
    read PID <$PID_FILE
    if [\[ -d "/proc/$PID" \]]; then
      return 0
    else
      rm -f $PID_FILE
      return 1
    fi
  else
    return 2
  fi
}

do_status() {
  check_running
  case $? in
    0)
      echo "shadowsocks running with PID $PID"
      ;;
    1)
      echo "shadowsocks not running, remove PID file $PID_FILE"
      ;;
    2)
      echo "Could not find PID file $PID_FILE, shadowsocks does not appear to be running"
      ;;
  esac
  return 0
}

do_start() {
  if [\[ ! -d $PID_DIR \]]; then
    echo "creating PID dir"
    mkdir $PID_DIR || echo "failed creating PID directory $PID_DIR"; exit 1
    chown $USER:$GROUP $PID_DIR || echo "failed creating PID directory $PID_DIR"; exit 1
    chmod 0770 $PID_DIR
  fi
  if check_running; then
    echo "shadowsocks already running with PID $PID"
    return 0
  fi
  if [\[ ! -r $CONFIG_FILE \]]; then
    echo "config file $CONFIG_FILE not found"
    return 1
  fi
  echo "starting shadowsocks"
  # sudo will set the group to the primary group of $USER
  sudo -u $USER $BIN -c $CONFIG_FILE >>$LOG_FILE &
  PID=$!
  echo $PID > $PID_FILE
  sleep 0.3
  if ! check_running; then
    echo "start failed"
    return 1
  fi
  echo "shadowsocks running with PID $PID"
  return 0
}

do_stop() {
  if check_running; then
    echo "stopping shadowsocks with PID $PID"
    kill $PID
    rm -f $PID_FILE
  else
    echo "Could not find PID file $PID_FILE"
  fi
}

do_restart() {
  do_stop
  do_start
}

case "$1" in
  start|stop|restart|status)
    do_$1
    ;;
  *)
    echo "Usage: shadowsocks {start|stop|restart|status}"
    RET_VAL=1
    ;;
esac

exit $RET_VAL

You can use update-rc.d command to update the system service definitions.

Systemd Unit file

Example (/etc/systemd/system/shadowsocks.service)

Prepare the executable file with the custom service.
Create a unit file in the /etc/systemd/system/ directory and make sure it has correct file permissions. Execute as root:

touch /etc/systemd/system/shadowsocks.service
chmod 644 /etc/systemd/system/shadowsocks.service

Edit shadowsocks.service file

Shadowsocks-local

[Unit]
Description=Shadowsocks local daemon
After=network.target

[Service]
ExecStart=/usr/bin/shadowsocks-local -c /etc/shadowsocks/config.json
PIDFile=/var/run/shadowsocks.pid
KillMode=process
Restart=on-failure
RestartSec=42s

[Install]
WantedBy=default.target

Shadowsocks-server

[Unit]                                                                          
Description=Go Shadowsocks server daemon                                          
Wants=network-online.target
After=network.target network-online.target multi-user.target
                                                                                 
[Service]                                                                        
ExecStart=/usr/bin/shadowsocks-server -u -c /etc/shadowsocks/config.json  
ExecReload=/bin/kill -HUP $MAINPID
PIDFile=/var/run/shadowsocks.pid                                                 
KillMode=process                                                                 
Restart=on-failure                                                               
TimeoutStopSec=30
                                                                                 
[Install]                                                                        
WantedBy=multi-user.target 
Alias=ss-server.service

Proxy setting

Environment="HTTP_PROXY=http://127.0.0.1:8118"
Environment="HTTPS_PROXY=http://127.0.0.1:8118"
Environment="NO_PROXY=pi.lan,127.0.0.1"

Check Environment setting [example home-assistant-@pi.servie]:

sudo systemctl show home-assistant@pi.service --property Environment
# Output:
# Environment=HTTP_PROXY=http://127.0.0.1:8118 HTTPS_PROXY=http://127.0.0.1:8118 NO_PROXY=pi.lan,127.0.0.1

Notify systemd that a new shadowsocks.service file exists by executing the following command as root

systemctl daemon-reload
# start shadowsocks service
systemctl start shadowsocks.service

You can check its status now by service shadowsocks status To add it to startup, using systemctl enable shadowsocks

Check details of running status

service shadowsocks status -l
# or
journalctl -xe

upstart job is configured in /etc/init/

Shell script with systemd unit

A sample with java web application.

dummy service

[Unit]                                                                          
Description=Dummy daemon                                          
Wants=network-online.target
After=network.target network-online.target multi-user.target
                                                                                 
[Service]                                                                        
ExecStart=/usr/bin/dummy 
ExecReload=/bin/kill -HUP $MAINPID
PIDFile=/var/run/dummy.pid                                                 
KillMode=process                                                                 
Restart=on-failure                                                               
TimeoutStopSec=30
                                                                                 
[Install]                                                                        
WantedBy=multi-user.target

dummy script to start

#/bin/bash

JAVA_HOME="${JAVA_HOME:-/usr/lib/jvm/default}"
JAVA_OPTS="-XX:+UnlockExperimentalVMOptions -XX:-UseJVMCICompiler"
JAVA_OPTS="${JAVA_OPTS} -Xms1024m -Xmx2048m -XX:PermSize=32m"
DUMMY_PROGRAM="/opt/dummy/dummy.jar"
START_CMD="${JAVA_HOME}/bin/java ${JAVA_OPTS} -jar ${DUMMY_PROGRAM}"

LOG_FILE=/var/log/dummy

init() {
	touch ${LOG_FILE}
}

check_running() {
	logger -i -t "It's running" -f ${LOG_FILE}
}

check_deps() {
	echo "Ok"
}

start() {
	eval ${START_CMD}
	echo "It's started"		
}

main() {
 init
 check_running
 check_deps
 start &
}

main "$@"

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