[SFS] Fwd: 12 DAYS OF LINUX TECH TIPS #8

[David L. Willson]

Hm. Interesting question. I have noticed that, but I just assumed it was a newbie mistake, or an oldbie trying to make an article friendly to DOS/Windows users. But, now that I think about it, it doesn't make sense. Any newbie that is going to use the Linux shell successfully, can make the leap between command shell prompts; it's not that hard. 

I wonder if there is any distro or Bash install that defaults to '>' rather than '$' and '#'... I don't have a Windows box handy, but I wonder about Bash in CygWin and Git. How's it set up? 

-- 
David L. Willson 
Teacher, Engineer, Evangelist 
COA LFCS CCAH RHCE CLP 
Mobile 720-333-LANS(5267) 
http://sofree.us 

This is a good time for a r3VOLution. 

----- Original Message -----

> It confuses me when linux/unix groups use the`>_` in icons to mean
> linux. Where is that a default prompt on a linux/unix system?
> It is the default prompt on dos other than the "drive spec" that
> usually precedes it..

> On Fri, Dec 14, 2018 at 7:56 AM DLWillson < DLWillson at thegeek.nu >
> wrote:

> > Highly enjoyable. Today it's at.
> 

> > David L. Willson
> 
> > 720-333-LANS
> 

> > -------- Original message --------
> 
> > From: Linux Journal < subs at linuxjournal.com >
> 
> > Date: 12/14/18 5:30 AM (GMT-07:00)
> 
> > To: dlwillson at thegeek.nu
> 
> > Subject: 12 DAYS OF LINUX TECH TIPS #8
> 

> > 
> 
> > 12 Days of Tech Tips #8 		view in browser »
> 
> > 
> 
> > 12 DAYS OF LINUX TECH TIPS FOR YOU THIS HOLIDAY SEASON! JOIN US
> > TODAY
> > FOR TECH TIP #8 		Terminal
> 
> > 
> 
> > Schedule One-Time Commands with the UNIX at Tool
> 
> > 
> 
> > Kyle Rankin
> 
> > 
> 
> > Cron is nice and all, but don't forget about its cousin at .
> 

> > When I first started using Linux, it was like being tossed into the
> > deep end of the UNIX pool. You were expected to use the command
> > line
> > heavily along with all the standard utilities and services that
> > came
> > with your distribution. At lot has changed since then, and
> > nowadays,
> > you can use a standard Linux desktop without ever having to open a
> > terminal or use old UNIX services. Even as a sysadmin, these days,
> > you often are a few layers of abstraction above some of these core
> > services.
> 

> > I say all of this to point out that for us old-timers, it's easy to
> > take for granted that everyone around us innately knows about all
> > the command-line tools we use. Yet, even though I've been using
> > Linux for 20 years, I still learn about new (to me) command-line
> > tools all the time. In this "Back to Basics" article series, I plan
> > to cover some of the command-line tools that those new to Linux may
> > never have used before. For those of you who are more advanced,
> > I'll
> > spread out this series, so you can expect future articles to be
> > more
> > technical. In this article, I describe how to use the at utility to
> > schedule jobs to run at a later date. at vs. Cron
> 

> > at is one of those commands that isn't discussed very much. When
> > people talk about scheduling commands, typically cron gets the most
> > coverage. Cron allows you to schedule commands to be run on a
> > periodic basis. With cron, you can run a command as frequently as
> > every minute or as seldom as once a day, week, month or even year.
> > You also can define more sophisticated rules, so commands run, for
> > example, every five minutes, every weekday, every other hour and
> > many other combinations. System administrators sometimes will use
> > cron to schedule a local script to collect metrics every minute or
> > to schedule backups.
> 

> > On the other hand, although the at command also allows you to
> > schedule commands, it serves a completely different purpose from
> > cron. While cron lets you schedule commands to run periodically, at
> > lets you schedule commands that run only once at a particular time
> > in the future. This means that at fills a different and usually
> > more
> > immediate need from cron. Using at
> 

> > At one point, the at command came standard on most Linux
> > distributions, but these days, even on servers, you may find
> > yourself having to install the at package explicitly. Once
> > installed, the easiest way to use at is to type it on the command
> > line followed by the time you want the command to run: $ at 18:00
> 

> > The at command also can accept a number of different time formats.
> > For instance, it understands AM and PM as well as words like
> > "tomorrow", so you could replace the above command with the
> > identical: $ at 6pm
> 

> > And, if you want to run the same command at that time tomorrow
> > instead: $ at 6pm tomorrow
> 

> > Once you press enter, you'll drop into an interactive shell: $ at
> > 6pm
> > tomorrow
> 
> > warning: commands will be executed using /bin/sh
> 
> > at>
> 

> > From the interactive shell, you can enter the command you want to
> > run
> > at that time. If you want to run multiple commands, press enter
> > after each command and type the command on the new at> prompt. Once
> > you're done entering commands, press Ctrl-D on an empty at> prompt
> > to exit the interactive shell.
> 

> > For instance, let's say I've noticed that a particular server has
> > had
> > problems the past two days at 5:10am for around five minutes, and
> > so
> > far, I'm not seeing anything in the logs. Although I could just
> > wake
> > up early and log in to the server, instead I could write a short
> > script that collects data from ps , netstat , tcpdump and other
> > command-line tools for a few minutes, so when I wake up, I can go
> > over the data it collected. Since this is a one-off, I don't want
> > to
> > schedule something with cron and risk forgetting about it and
> > having
> > it run every day, so this is how I would set it up with at : $ at
> > 5:09am tomorrow
> 
> > warning: commands will be executed using /bin/sh
> 
> > at>
> 
> > at> /usr/local/bin/my_monitoring_script
> 

> > Then I would press Ctrl-D, and the shell would exit with this
> > output:
> > at> <EOT>
> 
> > job 1 at Wed Sep 26 05:09:00 2018
> 
> > Managing at Jobs
> 

> > Once you have scheduled at jobs, it's useful to be able to pull up
> > a
> > list of all the at jobs in the queue, so you know what's running
> > and
> > when. The atq command lists the current at queue: $ atq
> 
> > 1   Wed Sep 26 05:09:00 2018 a kyle
> 

> > The first column lists the number at assigned to each job and then
> > lists the time the job will be run and the user it will run as.
> > Let's say that in the above example I realize I've made a mistake,
> > because my script won't be able to run as a regular user. In that
> > case, I would want to use the atrm command to remove job number 1:
> > $
> > atrm 1
> 

> > If I were to run atq again, I would see that the job no longer
> > exists. Then I could sudo up to root and use the at command to
> > schedule the job again. at One-Liners
> 

> > Although at supports an interactive mode, you also can pipe
> > commands
> > to it all on one line instead. So, for instance, I could schedule
> > the above job with: $ echo /usr/local/bin/my_monitoring_script | at
> > 5:09am tomorrow
> 
> > Conclusion
> 

> > If you didn't know that at existed, you might find yourself coming
> > up
> > with all sorts of complicated and convoluted ways to schedule a
> > one-off job. Even worse, you might need to set an alarm clock so
> > you
> > can wake up extra early and log in to a problem server. Of course,
> > if you don't have an alarm clock, you could use at : $ echo "aplay
> > /home/kyle/alarm.wav" | at 7am tomorrow
> 

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