In this video, you'll learn about the system V init legacy boot procedure. So what is this
about? Well, this is about how we booted before system D. System D has been the standard for
over a decade. So you won't find many systems anymore that use system V, also known as system
V, which is named after the system V Unix distribution that already used this way of
booting. System D booting replaces the system V legacy boot, where slash sbin slash init
was the PID1 loaded by the kernel and responsible for booting everything else. Now in system
V boot, the run level was used to define the state that the system should start in. And
the etc init tab file was used to set the default run level in which the system would
enter. So in system V boot, we had etc init tab to set the default run level. And you
could use init or tell init commands to manage the current run level temporarily. Where run
level five was for graphical, run level three was for multi-user. So if you would be in
graphical, and you wanted to go to multi-user, you would use init three. And to start a
different run level while booting, the number of the run level could be added at the end of
the line that boots the kernel in grub. System V services were managed with service
commands. So you would have service followed by the name of the service, followed by start,
stop, status, or restart to perform one of the respective operations on them. And every
now and then you still might have to do that if system D is not available. Now the service
commands are for managing services individually. If you wanted to make sure that the service
was toggled to be automatically enabled or disabled, you would use check config. So check
config, httpd on would make sure that on Red Hat the httpd service would be started
automatically. System V booting is legacy. It's old. And for that reason, you should not
search for system V compatibility while using system D, but use system D solutions. So nobody
is using these options anymore unless you encounter a distribution where you get a system
CTL command not found. If that is the case, use the service command instead. But fortunately,
that's going to be pretty rare.