I have placed a systemd service file in usr/lib/systemd/system/testfile.service.Here is the service file:[Unit]Description=Test service[Service]Type=notifyExecStart=/bin/dd.shExecReload=/bin/kill -HUP $MAINPIDKillMode=processRestart=on-failureRestartSec=30s[Install]WantedBy=multi-user.targetI tried to start the service at boot time by trying these two ways Created a softlink for the file from   /usr/lib/systemd/systemd to /etc/systemd/system/multi-user.target.wants (manually and by using systemctl enable command) and rebooted the system, testfile service started successfully at boot time .created a dependency in the existing up and running service file like After=testfile.service and Wants=testfile.service, then rebooted the system testfile service started successfully.But when I place the file /usr/lib/systemd/system and without any 1 or 2 solution approach service is not started, I feel that placing the service file in /usr/lib/systemd/system/ is enough for any service to start automatically , without creating the softlinks to wants directory or creating the dependency with the other services.Please let me know, how to start a service at boot time  which is present in /usr/lib/systemd/system directory without 1 or 2 solution approaches?I have also created preset files in usr/lib/systemd/system-preset/ to disable and enable few services, seems like those preset files were not executed , services which i have disabled in the preset file are still enabled after the boot up. Please let me know how to debug this issue.
start a service a at bootime in systemd
systemd;systemd boot
You should store your custom unit files in /etc/systemd/system/. After you create them, you have to enable them with systemctl enable name, which creates necessary symlinks.