- All right.
Let's talk about at.
At means the at daemon.
So sudo systemctl status of atd
is showing that atd is active and running.
That's good.
So as an ordinary user, I am going to open at teatime
and there we are opening the at shell
and in there I'm going to use logger TEATIME,
and then I'm done.
Now, this is also particular about at.
You need to use control D.
Control D is the end of file sign.
That is what you can use to close editor-like things
or secondary cells, Control D.
We haven't seen control D very often, so far.
And there, you can see that at TEATIME stands for 16:00:00.
Of course you can also use real time,
at 10:20 for instance.
wall COFFEETIME,
wall is Linux commanded to writes to all users
that are currently logged in,
and oops this is not doing what I wanted.
So I need to repeat it at 20:21.
Let me do this real fast
because otherwise I will be too slow again.
Okay.
Typo in coffee, who cares about typo in coffee?
What I care about is that I want to see
that this is working.
Wall by the way is for write all,
and write all will write to all the users
that currently have a terminal session open.
It might not work because of security restrictions.
In the old days, wall was a nice way to pass messages
to all users currently connected to a system.
Nowadays, security might be preventing this.
Atq, atq is showing us what exactly
is scheduled for execution
and the interesting thing here
is that we don't see the 10:20 anymore,
but we do see the 10:21.
And yeah, as I mentioned the wall is not so very successful
but that's a wall problem,
that's not an f problem.
Atq is showing that the 10:21 job has been executed anyway.
You wanna see a convincing example, okay.
Then, at 10:22 touch /tmp/1022,
control D,
and there we will see in a couple of seconds
that this is running.
Atq for at query is showing
that the job is waiting for execution.
Let me use at rm.
Atrm is what you can use to remove a job
if you don't want it anymore.
So atrm 1 makes that the job should now be gone.
Is it?
Yes, it is.
So the only thing we need to do now is to wait
until it is 10:22.
There we go.
It is 10:22 and ls -l on tmp.
We can see file with the name 10:22.
It has been created at 10:22.
So that is how you can use at.
At is useful but it is connected to a current,
a current terminal session
and that might limit it a little bit
in what you want to do
but it can be useful in particular for individual user jobs.