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Table of Contents
Services - System and service managers
init
System V style init script /etc/init.d/name.
The traditional System V init system had limitations. For example, some services need to start after other services (for example, you can't mount NFS filesystems until the network is running), but the only way in System V to handle that is to set the links in the rc#.d directory such that one is before the other. You might need to re-number everything later when dependencies are added or changed.
invoke-rc.d
invoke-rc.d is a wrapper around running the System V style init script /etc/init.d/name directly, obeying runlevel constraints as well as any local policies set by the system administrator.
The policy may cause the command not to be run at all, based on the current runlevel and whether the daemon should be run in that runlevel.
By default, Debian does not differentiate between runlevels 2-5, but as the local administrator, you can change what is run in each runlevel. invoke-rc.d will honor these local policies and not start a daemon if the runlevel is wrong.
According to the man page, all access to init scripts by Debian packages' maintainer scripts should be done through invoke-rc.d.
service
service runs a System V init script in as predictable environment as possible, removing most environment variables and with current working directory set to /.
service works in most Linux distributions including Debian and Ubuntu.
systemd
systemd is the new system and service manager for Linux. It is a replacement for init system and can manage system startup and services. It starts up and supervises the entire system.
systemctl only works on systemd based Ubuntu like version 16.04 LTS and above.
systemd jobs start when they have to.
System V
See init.
Upstart
Upstart jobs start as soon as they can.