System run level.
These are the wrong levels in the system, in an operating system that brings the system in a different
mode, in windows, you do have a safe mode.
That's one of the Modra system brings up and it doesn't have networking is just bring you a single user
mode.
And another operating system had different modes just like that.
In Linux, we have six different kind of system run levels.
The main run rate levels that are significantly used many times by system administrators is the first
one is zero.
Every time you type zero, of course, proceeding with the command in it, I and I t followed by space
and zero, it was shut down your computer or your computer completely.
It will not reboot or completely powered off.
Then you have in it one.
It is a single user mode, usually aliased as small case as are upper uppercase as you could type in
it.
Space s or a proccess.
It will function the same way as if you type one.
Then the most commonly used is six.
When you type in its basics, it will reboot your system.
This command is equivalent to command as if typing reboot the other level.
Run levels are run level two, which will bring the system in multi-user mode.
Without networking, there won't be any network.
You cannot communicate to other computers.
Then you have level three, which is a multi user mode with networking, which is most of the time is
the one that is used by us, but it does not have GUI and the run level five, which is multiuser mode
with networking and with Cooey for our environment.
We do have a GUI, so most of the time I run level is five, but if there is no GUI, you are going
to see that you will be rebooted into the wrong level three.
So we'll try a couple of these run levels in our Linux machine.
Let's log into it.
To run any of the system run level commands, you have to be route.
You could be fired if you are rude, of course, by running, who am I and the first man you have to
run is zero, which is in it zero space minus zero.
This will completely shut down my computer.
It's now going to reboot.
I have to go into my Oracle virtual box to power it on.
Or if it's a physical server, you actually have to be in front of the computer in front of the rack
wherever it is racked in the shelf you have to power on to bring it back online.
If you type in it one, it will bring down the system and reboot it back in a single user mode.
Sometimes you do need to bring your Linux machine to single user mode if you wanted to troubleshoot
some issues or reset a password or so on.
And then we have in it six, which is just like as if you typing reboot, then the other one level is
multiuser two, three and five.
Now how do you find out which run levels you are in the command to find out is who space minus are are.
It's the option that tells you what one level you are and you will see here.
It's telling you you are in level five.
Why?
Because they're going if I wanted to bring it into one level and three without agoI, I could do it.
Three, it will reboot system.
And there you go.
See, it brought it back to run level three.
There is no GUI.
I want to type it in my login credential and now if I type who minus or you'll see now the run level
has changed to three because there is no GUI.
If I wanted to just type in it six, it would automatically bring the system back online and it will
be automatically enrolled level five.
So that's about system level.
You could try every single option that you see it here, try to practice it and of course, run man
on and it command.