upstart Flashcards
start and stop services in an asynchronous manner which also decreased the boot up time fora Linux system. This benefit came about
by Upstarts ability to start services in parallel of one another, rather than waiting on one service to start before it could start up the next one.
This flow is the main way that Upstart starts a system. And it may look just as sequential as the old Init system.
However, after the start-up event begins there are multiple other jobs that are running at the same time that we don’t have listed here.
hardly any Linux distributions use it anymore. The focus of looking at Upstart is to demonstrate a type of initialization daemon that made a leap from being a static startup
or shutdown mechanism to one that actually kept track of what was going on with the system and reacting to it.
Upstart Init daemon
real time events
advantage of upstart over init
upstart monitors the services that it works with If a service stops working unexpectedly Upstart
will make attempts to get it running again.
monitoring
fire off the startup event
mountall
startup also runs the /etc/init/rc-sysinit.conf script
rc-sysinit.conf script
telinit
runlevel
/etc/init/rc.conf
login
upstart boot sequence
that will check and mount the drives that make up the file system using the mountall tool.
The startup event
checks to see if there is an /etc/init tab file to see if there are any configuration options set there.
/etc/init/rc-sysinit.conf script
calls telinit to switch into the default run level via the runlevel command.
rc-sysinit.conf script
start off many other jobs from Upstart to get the system ready and provides a compatibility mechanism to legacy scripts that may require specific run levels.
run level command for upstart not the same as init
When something on a Linux system changes and when an event is triggered it starts an Upstart
job that is then further divided into task and services.
event
By executing the joband passing the expected run level, as an argument.
/etc/init/rc.conf
what is requested of it and then return to a waiting state once it has finished. A service will not typically stop by itself.
The Upstart daemon will monitor each service and it will only kill a service if an event calls for it or if an administrator manually stops it.
task
condition at a point in time on the system.
job state
waiting state
initial state of a job. It isn’t doing anything yet but is just waiting to do something.
that the job itself is about to start.
starting state
means that the job is running.
running state