Creates the necessary files for running pgagent as a service in ubuntu (or debian), and then starts the service

deploy-pgagent.sh

#!/bin/bash

###
### It goes without saying that pgagent has to be installed in the system first
### On Ubuntu, after adding the PGDG apt repo, the installation can be done with 
### sudo apt install pgagent
###

### generate the conf file in /etc

echo "#/etc/pgagent.conf" >> /etc/pgagent.conf
echo "CONNECT_STRING=\"user=postgres dbname=postgres\"" >> /etc/pgagent.conf
echo "LOGLEVEL=1 #warning" >> /etc/pgagent.conf
echo "LOGFILE=\"/var/log/postgresql/pgagent.log\"" >> /etc/pgagent.conf
echo "RUN_AS=postgres:postgres" >> /etc/pgagent.conf

### generate the init.d script in /etc/init.d

echo "#!/bin/sh" >> /etc/init.d/pgagent.sh
echo "#" >> /etc/init.d/pgagent.sh
echo "# start/stop pgagent daemon." >> /etc/init.d/pgagent.sh
echo "set -e" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo "### BEGIN INIT INFO" >> /etc/init.d/pgagent.sh
echo "# Provides:          pgagent" >> /etc/init.d/pgagent.sh
echo "# Required-Start:    \$network \$local_fs postgresql" >> /etc/init.d/pgagent.sh
echo "# Required-Stop:     \$network \$local_fs postgresql" >> /etc/init.d/pgagent.sh
echo "# Default-Start:     S 2 3 4 5" >> /etc/init.d/pgagent.sh
echo "# Default-Stop:      0 1 6" >> /etc/init.d/pgagent.sh
echo "# Short-Description: pgAgent" >> /etc/init.d/pgagent.sh
echo "### END INIT INFO" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo ". /lib/lsb/init-functions" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo "path2bin=\"/usr/bin/pgagent\"" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo "if ! test -f \$path2bin; then" >> /etc/init.d/pgagent.sh
echo "    log_failure_msg \"\$path2bin not found\"" >> /etc/init.d/pgagent.sh
echo "    exit 1" >> /etc/init.d/pgagent.sh
echo "fi" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo "RUN_AS=\"\"" >> /etc/init.d/pgagent.sh
echo "CONNECT_STRING=\"\"" >> /etc/init.d/pgagent.sh
echo "LOGLEVEL=0" >> /etc/init.d/pgagent.sh
echo "LOGFILE=\"/var/log/postgresql/pgagent.log\"" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo "if [ -f /etc/default/pgagent ]; then" >> /etc/init.d/pgagent.sh
echo "  . /etc/default/pgagent" >> /etc/init.d/pgagent.sh
echo "elif [ -f /etc/pgagent.conf ]; then" >> /etc/init.d/pgagent.sh
echo "  . /etc/pgagent.conf" >> /etc/init.d/pgagent.sh
echo "fi" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo "if [ \"\$CONNECT_STRING\" = \"\" ]; then" >> /etc/init.d/pgagent.sh
echo "    log_failure_msg \"CONNECT_STRING not specified\"" >> /etc/init.d/pgagent.sh
echo "    exit 1" >> /etc/init.d/pgagent.sh
echo "fi" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo "opts=\"--quiet --oknodo --exec \$path2bin\"" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo "case \"\$1\" in" >> /etc/init.d/pgagent.sh
echo "    start)" >> /etc/init.d/pgagent.sh
echo "        log_begin_msg \"Starting PgAgent daemon...\"" >> /etc/init.d/pgagent.sh
echo "        if pidof \$path2bin > /dev/null; then" >> /etc/init.d/pgagent.sh
echo "                log_begin_msg \"Already running\"" >> /etc/init.d/pgagent.sh
echo "                log_end_msg 0" >> /etc/init.d/pgagent.sh
echo "                exit 0" >> /etc/init.d/pgagent.sh
echo "        fi" >> /etc/init.d/pgagent.sh
echo "        if [ \"\$RUN_AS\" != \"\" ]; then" >> /etc/init.d/pgagent.sh
echo "                opts=\"-c \$RUN_AS \$opts\"" >> /etc/init.d/pgagent.sh
echo "                if [ ! -f \"\$LOGFILE\" ]; then touch \$LOGFILE; fi" >> /etc/init.d/pgagent.sh
echo "                chown \$RUN_AS \$LOGFILE" >> /etc/init.d/pgagent.sh
echo "        fi" >> /etc/init.d/pgagent.sh
echo "        OPTIONS=\"-l \$LOGLEVEL -s \$LOGFILE \$CONNECT_STRING\"" >> /etc/init.d/pgagent.sh
echo "        start-stop-daemon --start \$opts -- \$OPTIONS" >> /etc/init.d/pgagent.sh
echo "        log_end_msg \$?" >> /etc/init.d/pgagent.sh
echo "        ;;" >> /etc/init.d/pgagent.sh
echo "    stop)" >> /etc/init.d/pgagent.sh
echo "        log_begin_msg \"Stopping PgAgent daemon...\"" >> /etc/init.d/pgagent.sh
echo "        start-stop-daemon --stop \$opts" >> /etc/init.d/pgagent.sh
echo "        log_end_msg \$?" >> /etc/init.d/pgagent.sh
echo "        ;;" >> /etc/init.d/pgagent.sh
echo "    force-reload)" >> /etc/init.d/pgagent.sh
echo "        \$0 restart" >> /etc/init.d/pgagent.sh
echo "        ;;" >> /etc/init.d/pgagent.sh
echo "    restart)" >> /etc/init.d/pgagent.sh
echo "        \$0 stop" >> /etc/init.d/pgagent.sh
echo "        \$0 start" >> /etc/init.d/pgagent.sh
echo "        ;;" >> /etc/init.d/pgagent.sh
echo "    status)" >> /etc/init.d/pgagent.sh
echo "        if ! pidof \$path2bin > /dev/null; then" >> /etc/init.d/pgagent.sh
echo "                log_success_msg \"PgAgent isn't running\"" >> /etc/init.d/pgagent.sh
echo "                exit 3" >> /etc/init.d/pgagent.sh
echo "        fi" >> /etc/init.d/pgagent.sh
echo "        log_success_msg \"PgAgent running\"" >> /etc/init.d/pgagent.sh
echo "        exit 0" >> /etc/init.d/pgagent.sh
echo "        ;;" >> /etc/init.d/pgagent.sh
echo "    *)" >> /etc/init.d/pgagent.sh
echo "        log_success_msg \"Usage: \$0 {start|stop|force-reload|restart|status}\"" >> /etc/init.d/pgagent.sh
echo "        exit 1" >> /etc/init.d/pgagent.sh
echo "        ;;" >> /etc/init.d/pgagent.sh
echo "esac" >> /etc/init.d/pgagent.sh
echo "" >> /etc/init.d/pgagent.sh
echo "exit 0" >> /etc/init.d/pgagent.sh

### make the service shell file executable

sudo chmod +x /etc/init.d/pgagent.sh

### let the system know about it, enable it, start it and show the status

sudo systemctl daemon-reload
sudo update-rc.d pgagent.sh defaults
sudo update-rc.d pgagent.sh enable
sudo service pgagent start
sudo service pgagent status

Credits go to
https://gist.github.com/peterneave/83cefce2a081add244ad7dc1c53bc0c3

Tested and known to work on Ubuntu 18.04