systemctl daemon-reload

systemctl start servicename

# systemctl get-default
multi-user.target

systemd-analyze critical-chain
systemctl --failed

Value for unit DefaultDependencies is set to yes by default. it will add following dependencies:

• Conflicts=shutdown.target to stop service during shutdown
• Conflicts=umount.target to umount mounts durign shutdown
• Requires=basic.target and After=basic.target

If services are defined with DefaultDependencies=no, they will be started unconditionally even in emergency mode, wchich can be wrong.

local-fs.target is configured to go to OnFailure=emergency.target. File /etc/fstab is parsed by systemd-fstab-generator to generate .mount units, which are Required.

To let mounts fail without switching to emergency mode, special attribute are introduced to fstab. http://www.freedesktop.org/software/systemd/man/systemd.mount.html

Kernel commandline:

systemd.unit=emergency

systemd.log_level=debug systemd.log_target=console console=ttyS0,38400

Create directory “dev-mmcblk0.device.wants” and put symlink to service inside it. List of devices:

systemctl --all --full -t device