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- [Scott] Understanding how long a computer
has been running for,
and how hard it's working
are important aspects of system maintenance.
The uptime command tells us both of these things.
This shows me the current time,
and from the current time,
how long the system has been powered on,
and booted.
In my case, it's been up for 18,
well, just about 19 hours.
Uptime is a sensitive topic for some people.
It can be considered a point of pride
to have a system that hasn't been restarted
in a long time,
but sometimes it can be an indication
of likely problems to have a system
with hundreds or thousands of days of uptime.
On the one hand,
a system with long uptime
is probably pretty stable.
That's a good thing.
But if a system hasn't been restarted
in a very long time,
it could also indicate that some of the software
on the system is out of date.
On modern systems,
restarting for software updates is pretty much
a thing of the past,
but some distros,
and especially older ones do need restarts
to install system level software,
like kernel updates now and again.
If you're inheriting a system to manage,
very long uptime could also be a red flag
for problems when it does restart.
Maybe that system has been online and untouched
because there was a problem
getting a service running,
and nobody wants to go through that process again
if they can help it.
Of course, that's not to say you should restart
your systems all the time.
It's just something to keep in mind
if you see a system
with a surprisingly long uptime.
It's also important to keep an eye out
for very short up times.
If you're looking at a system
that has a short uptime,
it could be that it was just restarted
on purpose.
Or it could have been restarted accidentally.
Perhaps the machine crashed and rebooted.
Or maybe it's a container
that just popped into existence.
As you explore your systems and environment,
you'll get a sense of what kind of uptimes
are suitable for your machines.
Back in the terminal,
I can see that there's two users connected here,
and over here is the load average.
The load average is a quick snapshot
of how hard the system is working,
and how hard it has been working
in the recent past.
The three numbers left to right
indicate the load on the system
over the past one minute, five minutes,
and 15 minutes.
Load means how much work the processor
is able to get done
versus how many processes are competing
for its resources.
1.00 means that the CPU
is working at a break even rate.
It's at 100% utilization,
but nothing additional is waiting.
It's being used to its capacity but no more.
Anything over 1.00 means one
or more processes are having to wait
to be worked on,
and anything under 1.00
means that the CPU has some time to idle.
It's not working at full capacity all the time.
If you see a number significantly
higher than 1.00
it doesn't necessarily mean your system
is having problems.
It just means that some process
or other will need to wait a little bit
to have its work processed.
Systems will often spike up over 1.00
when they're doing their normal tasks.
What you want to keep an eye out for
is systems with a consistently high load average.
If you have more than one processor
or more than one processor core,
higher numbers may be normal.
1.00 is one core at 100% capacity.
So a dual core machine would be
at full capacity at 2.00
and an eight core machine would be at
full capacity at 8.00 and so on.
So if you connect into your 12 core
powerhouse machine,
and see it at a 9.00 load average,
it's only really at about three quarters
of its full processing capacity.
If your system is running close
to its full all the time,
that can be okay as long as it's expected.
Maybe it's a processing node
or a database server with many clients.
But if your system is consistently
over the 100% line,
and especially if it's over by a lot,
it may be worth investigating why.
Maybe it's time to add more processors
to a virtual machine.
Or move some tasks to other machines.
Or maybe it's time to upgrade
to a more powerful system.
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