The PATH to /home/timmy/grannys_house (Revisited)

Back in the old days, when Timmy wanted to visit granny’s house, all he had to do was have Lassie lead him there. In today’s more complicated computer world, it takes a bit more understanding.

We’re going to learn a bit about a very important subject in Linux. It’s called PATH. The path to a file or whatever on your Linux operating system is something that you need to understand when manipulating files from the command line. Another term we’ll look at briefly is the working directory.

When Timmy, as a regular user, opens his terminal from his GUI or from the post login command line (Run Level 3 – multi-user, no X running), his working directory is in /home/timmy. Whichever directory you are in at the time is known as the working directory. Timmy may navigate to another directory using the cd command. Let’s say he navigates to /usr/bin. At that time, his working directory becomes /usr/bin. See how this works?

Think of the Linux file system as a multi-room house. If you’re in bedroom4 right now, your working directory would be /house/bedroom4. If you walked out of that room and down the hall to bathroom02, then your working directory becomes /house/bathroom02. At that time, you may then use the command micturate. Heh! A little bathroom humor there.

OK, so now we know all about the working directory, right? Moving on…

Let’s say that Timmy wants to copy a .jpg that is in /usr/share/wallpaper over to the /home/timmy/grannys_house directory. He would open his terminal, which would then be sitting there with that blinking cursor waiting for Timmy’s next command:

timmy@lassies_machine~:$ |

Timmy’s working directory at this point is /home/timmy, as designated by the command line shorthand character ~ . If Timmy wants to copy the .jpg without actually going to the directory that it’s in to copy it, he must provide the proper path in his command.

timmy@lassies_machine~:$ cp /usr/share/wallpaper/cabin.jpg /home/timmy/grannys_house

The above command, using absolute path names, directs the shell (command line interpreter) to copy the cabin.jpg image from the /usr/share/wallpaper directory to the /home/timmy/grannys_house directory. If Timmy wanted to just make a duplicate of a file in his /home/timmy directory, then he could leave off the / character when showing the command line the proper path. This can be done because he’s already in the /home/timmy directory. It is his working directory. He can now use a relative path to direct the shell to make the copy.

timmy@lassies_machine~:$ cp cabin.jpg cabin.jpg_backup

In the above example, notice that there is no / being used. Timmy is simply making a backup copy of cabin.jpg. Both files are relative to his working directory, so the shell understands that Timmy just wants to make this duplicate right there in that same directory.

It’s really not rocket science, to use that worn out old cliché. The command line can be pretty simple once you get the hang of it folks. You know what I always say… Don’t fear the command line. I hope you’ve learned something here today. Remember to click the links within the article. You’ll find some more useful information and a few definitions for you there.

Later…

~Eric

Further reading:

Unix Commands @ Wikipedia

LinuxTutorial.info

Linfo.org

Paul Sheer’s Rute Users Tutorial and Exposition

Image credits: Timmy (Jon Provost) and Lassie image owned and copyright by Classic Media

Note: This article originally appeared on my old Nocturnal Slacker/Lockergnome Blog (now defunct).


Sometimes, You Just Have to Revert

For a couple weeks now, I’ve been having issues with Thunderbird 5 in my Arch Linux installation.

I have a few much-used extensions installed in my Thunderbird, and 5.x broke four of them when it updated in Arch from 3.1.11. I tried a few work-arounds. I tried to live without the extensions. This morning I decided that I just wasn’t going to deal with this any longer. I reverted. How’d I do that, you might be asking? Well, with Arch (in most instances), it’s pretty simple.Photobucket

First item of importance is that I had a backup of my Thunderbird 3.1.11 .thunderbird directory backed up on separate media (DVD). Second item is that I had not run pacman -Scc in a while. This command clears the cache of installed items in Arch. So, with those items being satisfied, I was able to revert using the magical pacman -U command.

#pacman -U thunderbird-3.1.11*

The asterisk denotes auto-completion at the command line. BASH will automatically add the remaining characters to the command.

Photobucket

And with that simple series of commands, my world is back to being wonderful once again. Oh, and to make sure that I don’t accidentally upgrade T-bird on my next pacman update session, I’ve added it to the ignore list in my pacman.conf file.

#vim /etc/pacman.conf

# Pacman won’t upgrade packages listed in IgnorePkg and members of IgnoreGroup
 IgnorePkg   =  thunderbird

There you have it. The wonderful simplicity of Arch package management.

Have fun… and learn something while you’re at it. :)

~Eric


The GNU/Linux Adventurer’s Backpack

If you are setting off on your new GNU/Linux adventure, there are some must have things that you’ll be needing to take along with you.

When you’re at the kitchen table packing that backpack for your big adventure, don’t forget to stuff these items in there with your lantern, matches, water purification pills, and lip balm. You’ll find this stuff will come in very handy along the trail.

A little history

Linux, which specifically means the kernel portion of the operating system, was born in 1991 when Finnish student Linus Torvalds decided he wanted something to run on his 80386 processor based PC. Linus turned the code for his new kernel loose on USENET.

Within a short while Softlanding Linux System (SLS) was born of a mating of Linus’ new kernel and Richard Stallman‘s GNU Operating System. The SLS project was taken over by Patrick Volkerding, who morphed it into Slackware Linux, the oldest still living GNU/Linux distribution. You can view the Linux family tree to see how things progressed from there.

Some handy documentation –

C’mon. Quit whining. Sometimes, it’s a good thing to read the fine manual. The “man” pages, short for manual, are available to you from within any GNU/Linux distribution. They’re already in your backpack even if you didn’t know it. To access a manual page for a certain command within Linux, just use this from the command line:

$ man <command or application name>

For example, let’s say you want to know how to use the ls command. You would type this into the command line:

$ man ls

LS(1)                            User Commands                           LS(1)

NAME
       ls – list directory contents

SYNOPSIS
       ls [OPTION]… [FILE]…

DESCRIPTION
       List  information  about  the FILEs (the current directory by default).
       Sort entries alphabetically if none of -cftuvSUX nor –sort.

       Mandatory arguments to long options are  mandatory  for  short  options
       too.

       -a, –all
              do not ignore entries starting with .<snip>

…and the manual page for the ls command will magically appear. Cool, huh? You can also refer to that same manual page by using online websites that make that same information available to you. You can use Linux Man Pages, Linux Man Pages Online, or other similar sites.

For some more in depth GNU/Linux documentation, you can check out The Linux Documentation Project (TLDP), LinuxDocs.org, or DistroWatch.com. The last provides brief synopses and reviews of most of the GNU/Linux distributions available today.

Which distribution to start the adventure? –

If you clicked on that DistroWatch link above, you’d see that there are many, many GNU/Linux distributions out there in the world. While choice is a good thing, numerous choices can sometimes be overwhelming for new adventurers; what trail should I take? Every GNU/Linux advocate will have their own favorite list of distributions that they recommend to all the new adventurers they run across. Following is my list of the five easiest transition distributions. What’s a transition distribution? I define that as a GNU/Linux distribution that is easy to install and use right out of the box for new adventurers who are mostly used to using Microsoft Windows products.

Ubuntu – this is the distro that took GNU/Linux from the desktops of geeks like me and put it on Gramps and Granny’s system. It did more to popularize the GNU/Linux operating system than any other distribution prior.

Linux Mint – this distro from the land of Eire is slam packed with all the great stuff you’d want in an operating system. It’s good to go right out of the box.

Mepis – while not the most popular GNU/Linux out there, this Debian-based distribution is a fine product, and most suitable for new adventurers.

PCLinuxOS – this distro is a branch of the old and venerable Mandrake/Mandriva GNU/Linux. It’s easy to install and to operate.

Ultimate Edition – this distribution gets its foundation from its Debian and Ubuntu roots. It is also easy to install and has loads and loads of useful software included the moment you boot up.

Vector Linux – this excellent distribution is based on Slackware Linux. It is easy to install and use.

OK, then. We have some history, some documentation, and a choice of distributions in our backpack now. We’re almost ready to begin the adventure. But wait! There are a few more very important items that we’ll be needing.

Tips and Tutorials –

Tutorials are documents that teach in a step-by-step fashion. They can cover a lot of information in a small space. They’re usually simplified so that amateurs and novices can follow along without the need to know the really complicated stuff underneath it all. Tips are just that; little tid-bits of information to make things go easier on your adventure.

There was once a man called Bruno, he was my friend. He was also a serious GNU/Linux advocate and teacher. He selflessly spent many hours of his daily life teaching others about GNU/Linux. Many of us who knew him learned from him and were inspired by him to carry on his tradition of teaching. While Bruno may no longer be with us, part of the legacy he left us is his Tips for Linux Explorers site. Yes, some of the info there is a bit dated, but most of it is still very relevant and helpful.

As far as tutorials go, there are many sites with wonderful GNU/Linux tutorials. Here are a few that I use regularly: The Linux Tutorial, YoLinux Tutorials, Linux Survival, HowtoForge, Tutorialized, and Linux Planet Tutorials. Believe me, if there’s something you want to accomplish within GNU/Linux, there is a tutorial somewhere that will show you how. Remember, when searching for answers to your GNU/Linux questions, Google is your friend.

More good reading –

5 Things Every Aspiring Linux User Should Know – another article that may be useful to new Linux Adventurers.

New to Linux? Here’s Your Hitchhiker’s Guide to Linux Forum Galaxy! – by Megatotoro

Some Advanced Reading –

The books listed below are somewhat advanced. I wouldn’t recommend that new Adventurers dive into them right off. Give yourself some time to climb a bit higher on that learning curve, then give these books below a peak or two. The more you experience GNU/Linux, the more the information in these books below will make sense to you. I put them here because they are excellent learning tools… when you reach that level.

Linux – Rute User’s Tutorial and Exposition by Paul Sheer

LINUX: Rute Users Tutorial and Exposition is the only Linux sysadmin’s guide proven by 50,000+ Web users. It presents in-depth coverage of all aspects of system administration: user management, security, networking, Internet services, packages, config files, shell scripting, and more. It also contains detailed cross-references to LPI and RHCE certification topics, making it invaluable for exam preparation. (description from Amazon.com) *This book is also available online in .pdf format.

Linux Pocket Guide by Danial J. Barrett

Linux Pocket Guide is organized the way you use Linux: by function, not just alphabetically. It’s not the ‘bible of Linux; it’s a practical and concise guide to the options and commands you need most. It starts with general concepts like files and directories, the shell, and X windows, and then presents detailed overviews of the most essential commands, with clear examples. You’ll learn each command’s purpose, usage, options, location on disk, and even the RPM package that installed it. (description from Amazon.com)

A Practical Guide to Linux – Commands, Editors, and Shell Programming by Mark G. Sobell

Packed with hundreds of high-quality, realistic examples, this book gives you Linux from the ground up: the clearest explanations and most useful knowledge about everything from filesystems to shells, editors to utilities, and programming tools to regular expressions. Sobell has also added an outstanding new primer on Perl, the most important programming tool for Linux admins seeking to automate complex, time-consuming tasks. (description from Amazon.com)

Understanding the Linux Kernel by Bovet & Cesati

Understanding the Linux Kernel will acquaint you with all the inner workings of Linux, but it’s more than just an academic exercise. You’ll learn what conditions bring out Linux’s best performance, and you’ll see how it meets the challenge of providing good system response during process scheduling, file access, and memory management in a wide variety of environments. This book will help you make the most of your Linux system. (description from Amazon.com)

The Debian System by Krafft

The Debian GNU/Linux operating system approaches Linux system administration differently than other popular Linux distributions, favoring text-based configuration mechanisms over graphical user interfaces (GUIs). Debian may appear simplistic and even slightly outdated, but it is actually very robust, scalable, and secure. Debian’s open development cycle and strict quality control by the developers help Debian to constantly gain popularity, despite its reputation as an operating system just for professionals and hardcore computer hobbyists. (description from Amazon.com)

And lastly, but never last, this most necessary thing to have in your GNU/Linux adventurer’s backpack:

Community –

We come into this world alone and we leave it alone, but fortunately, while in this world, we have each other. Were it not for the GNU/Linux – Open Source community, there wouldn’t be any GNU/Linux; or if there were, it would be some ghastly thing used by a few uber-geeks in the darkness of night on their own desktop systems. Joyfully, that isn’t so because we have community; arguably the most important ingredient in the brewing pot.

There is a large and very active GNU/Linux – Open Source community every where in the world. You can access and interact with that community in many ways; boards and forums, USENET Groups, mailing lists, websites and portals, blogs like this one, etc. Community means a lot to me. Below you’ll find my list of favorite places where I go to learn what I need to continue on my own adventure:

Boards and Forums

Scot’s Newsletter Forums – Bruno’s All Things Linux – a Linux support forum and much more. This site is run by Scot Finnie, Editor-in-chief of ComputerWorld.com.

Jeremy’s LinuxQuestions.org – a Linux support forum and community dedicated to assisting adventurers of all skill levels and abilities.

TechSupportGuy Forums – Linux and Unix – another excellent Linux community forum.

The Linux Foundation’s Linux.com Community – a relatively new and growing community with many helpful members.

Just Linux Forums – a great community resource.

Linux Forums – search this place for great tips and assistance as you travel along in your adventure.

Also, don’t forget… nearly every distribution of GNU/Linux has its own very helpful support community. Check out the main websites for links to their forums and such. All the distros mentioned above have their own forums. Check ‘em out.

Linux News Sites

Tux Machines – Susan Linton’s wonderful Linux community site.

Linux Today – news you can use.

Linux Insider – more informative Linux news.

LXer Linux News – the world is talking about GNU/Linux and Free/Open Source Software.

The above are just a sampling. There are literally hundreds of top level, informative Linux news sites on the Net. Search!

Linux Learning Blogs

Linux Operating System – Guillermo Garron’s very helpful and informative blog.

Linuxaria – Ricardo Capecchi’s bi-lingual Everything About Linux blog.

All About Linux – a self-professed “very” popular blog about Linux, Open Source, and Free Software.

Linux Notes from Dark Duck – helpful information on choosing and running Linux on your systems.

Dedoimedo – a place to learn a lot about a lot. A unique experience, I might add.

There are many more sites out there, too. Each distribution usually has a handful of dedicated bloggers and teachers running from their own websites. Don’t forget to search online. You’ll find some wonderful stuff.

One other thing you can do when starting out on your adventure is to register with The Linux Counter and be counted as part of the community. Proudly display your Linux Registered User number for all to see. Sorry, they’re out of stock on the super-dooper decoder rings, though. You may find one in that Cap’n Crunch serial box on your kitchen table. ;)

I’ve tried to make this as all-inclusive as I could, but of course, I’ve failed miserably. GNU/Linux is a topic that volumes have been written about. How could I possibly give you all that information in one short article? Oh well. I hope that what you do find here will help you along in your adventure. I leave you with three bits of wisdom that I learned early on when I first started out on my adventure:

  • First and foremost, GNU/Linux is NOT MS Windows. Please don’t expect it to be.
  • Secondly, KEEP notes! You will find this an immeasurably important practice to discipline yourself into doing regularly. I don’t care if your notes are on your iPad or your main system or on a dead tree note book (my choice medium). Just keep notes. You won’t regret it.
  • Lastly, but again NEVER last, the community is there for you. Take from it all that is offered, so that you can learn and expand your horizons on your great GNU/Linux adventure. We ask only one thing from you in return; when the time comes that you have reached a level of knowledge where you can comfortably (and accurately) do so, please give back to the community that supported you. This way there will always be those willing to help the new GNU/Linux Adventurers coming along the trail.

Happy adventuring!

~Eric

P.S. I intend this document to be a living device. I will probably be amending it from time to time.

Addenda:

I – 08 May 2011

a. added Vector Linux to suggested starting distributions

b. added an advanced book list for those who would like to go a bit deeper in their studies

II – 28 February 2012

a. added link to 5 Things Every Aspiring Linux User Should Know

III – 22 August 2012

a. added Megatotoro’s New to Linux? Here’s Your Hitchhiker’s Guide to Linux Forum Galaxy!


Multi-booting My Way (Not Necessarily the Easy Way)

The following is a brief step-by-step on how I’ve been multi-booting different operatings systems on my machines for the past few years.

It’s not necessarily the easy way to do things. It is the way I first learned and the way that I’m most comfortable with using. I’m posting it here, as I believe it may be helpful to some Linux Explorers out there. This tutorial is based on GRUB Legacy. I do not use the new GRUB2 on my machines.

Here we go…

I have multiple drives on my system, so multi-booting becomes a bit more interesting. Currently, I have three hard drives installed. They are /dev/sda, /dev/sdb, and /dev/sdc. We won’t concern ourselves at all with /dev/sdc because it is primarily used as a common storage/backup drive. My operating systems are installed on /dev/sda and /dev/sdb.

I use /dev/sda (1st boot device in my BIOS) as the drive that has my primary operating system and my secondary operating system on it. I break my drives down into numerous partitions because I always install GNU/Linux operating systems on at least two partitions; /(root) and /home. I also have a common /swap partition on each drive that I plan on installing GNU/Linux distributions on.

My /dev/sda partitions look like this:

/dev/sda1   *       16065    51215219    25599577+  83  Linux <– Slackware /(root)
/dev/sda2        51247350   153645659    51199155   83  Linux <– Slackware /home
/dev/sda3       153661725   488392064   167365170    5  Extended
/dev/sda5       153661788   204860879    25599546   83  Linux <– Arch /(root)
/dev/sda6       204877008   307275254    51199123+  83  Linux <– Arch /home
/dev/sda7       307307448   311403959     2048256   82  Linux swap / Solaris
/dev/sda8       311420088   488392064    88485988+  83  Linux <– Archives

My /dev/sdb partitions look like this:

/dev/sdb1   *       16384    51216383    25600000    7  HPFS/NTFS/exFAT <– MS Windows XP
/dev/sdb2        51232768   102432767    25600000    7  HPFS/NTFS/exFAT <– MS Windows Programs
/dev/sdb3       102453181   488270159   192908489+   5  Extended
/dev/sdb5       102453183   106550639     2048728+  82  Linux swap / Solaris
/dev/sdb6       106565823   137289599    15361888+  83  Linux <– CentOS tester 1 /(root)
/dev/sdb7       137304783   188501039    25598128+  83  Linux <– CentOS tester 1 /home
/dev/sdb8       188516223   219239999    15361888+  83  Linux <– Foresight tester 2 /(root)
/dev/sdb9       219255183   270451439    25598128+  83  Linux <– Foresight tester 2 /home
/dev/sdb10      270466623   301190399    15361888+  83  Linux <– Debian tester 3 /(root)
/dev/sdb11      301205583   352401839    25598128+  83  Linux <– Debian tester 3 /home
/dev/sdb12      352417023   383140799    15361888+  83  Linux <– vacant tester 4 /(root)
/dev/sdb13      383155983   434352239    25598128+  83  Linux <– vacant tester 5 /home
/dev/sdb14      434367423   488270159    26951368+  83  Linux <– common storage

You get the above information on your drives using the fdisk -l command as root from the command line.

Alright then, let’s say that I now want to install Fedora Core Linux on my tester 4 partitions of /dev/sdb. Here’s how I would do that step-by-step:

1) Begin the Fedora installation setting /dev/sdb5 as swap, /dev/sb12 as /(root), and /dev/sdb13 as the /home partition from Fedora’s installer.

2) When the Anaconda installer reaches the point where it asks where I want to install the GRUB bootloader, I choose to SKIP installation of GRUB.

3) Once the install is finished, I reboot my main operating system (Slackware) and from the command line I mount the newly installed Fedora /(root) partition:

root_Slackware/home/vtel57:# mount /dev/sdb12 /mnt/tmp

*Note: I have a /mnt/tmp directory in my Slackware. If you don’t have a /mnt/tmp, just mount in /mnt. You’ll be fine.

4) I list the contents of the Fedora /boot directory:

root_Slackware/home/vtel57:# ls /mnt/tmp/boot

5) I copy down the vmlinuz and initrd information. You’ll be looking for the vmlinuz-<kernel version> and the initrd-<kernel version>.img files specifically. You’ll need that information for the next step.

6) I edit my /boot/grub/menu.lst file to add the new Fedora Core entry. Note: my MBR-controlling GRUB is in my secondary OS, Arch Linux. I can still mount and modify it from within Slackware, though.

root_Slackware/home/vtel57:# mount /dev/sda5 /mnt/tmp

root_Slackware/home/vtel57:# vim /mnt/tmp/boot/grub/menu.lst

I’ll add this entry to the file:

# Fedora Core

title          fedora (t4)

root         (hd1,11)

kernel     /boot/vmlinuz-<kernel version> root=/dev/sdb12 ro

initrd       /boot/vmlinuz-<kernel version>.img

7) I reboot and choose “fedora (t4)” from the GRUB menu to boot my new Fedora installation.

That’s it, folks. Straightforward, but not necessary the easiest way to do this. That’s the beauty of GNU/Linux. You can do it your way.

Have fun!

~Eric

P.S. I’m still working on the next shell scripting lesson. It’s going to be about variables and parameters, a necessary lesson for further BASH learning. Unfortunately, it’s also kinda’ complicated, so it’s taking me a bit to figure out how to formulate a lesson and still stay loyal to my primary goal here… keeping it as simple as possible. Stay tuned…


A Few More Shell Basics

In our last lesson here, I scratched the surface of the basics needed to start scripting in BASH. Today, we’ll learn a few more things.

Here are some fundamentals that we need to cover real quick. It’s nothing too complicated.

chmod - You’ve seen this command in action before, I’m sure. It’s important when it comes to writing shell scripts because it allows the script to become executable. This is, of course, a necessity if we want the script to actually run and do something.

#! - These two symbols used in this particular order at the beginning of a script specifies which shell we want to use to run this script. We will primarily be talking about BASH here in these lessons, but let’s say we wanted to write a script that used the tcsh shell instead. The first line of the script would be:

#!/bin/tcsh

The operating system would check that first line initially to determine what shell we intended when we wrote the script. It would then call up that shell and run the script. You’ll see that a lot when programming in BASH. Now you know what it does.

# – This symbol signifies a comment. You’ve probably seen this many times already in configuration files like GRUB’s menu.lst or your distribution’s repository configuration file, maybe. It’s not at all uncommon to find this symbol used in many different programming languages to alert the OS (and the user) that the data on the same line following the # is an informational comment of some sort. Comments are GOOD things when programming. Make lots of comments. They will help you and maybe others who use your program or script down the road. Here’s an example of a commented snippet of script:

#!/bin/bash
# ZIP-100 mknod script – 07222006 – Bruno
mknod /dev/hdb4 b 3 64
#End script

You can see the initial #! telling the OS what shell to use. In the next line, you can see the # symbol followed by some informational data. This was an actual script that I used to need to run at boot to get my ZIP-100 drive to be recognized by the OS. Newer kernels later on solved the issue by using udev, but that’s a whole ‘nother subject. I just wanted you to see what a comment looks like in a BASH script.

; and <newline> - These two devices, when used in the shell, denote a transition from one command to another. For example, if I had three commands called c1, c2, and c3, I could run them on the same line using the ; (semi-colon) to separate them. Or I could just put each of them on a new line. Here’s what I mean…

$ c1;c2;c3 <ENTER to execute>

$ c1 <ENTER>
$ c2 <ENTER>
$ c3 <ENTER>

Pretty simple so far, huh? OK. Let’s continue…

\ – The backward slash is used to continue a command from one line to the next. Like this:

$ echo “She sells seashells \

> by the seashore.” <ENTER>

She sells seashells by the seashore.

Without the \, the line would have been broken when displayed by the echo command’s output. Like this:

$ echo “She sells seashells

> by the seashore.” <ENTER>

Sea sells seashells

by the seashore.

See the difference? Cool! OK, then… just a few more for today. We don’t want to get a headache by stuffing too much in there at one time.

| and & – These two are very cool, and you’ll see them a lot. The first one is called a “pipe”, and that’s just what it does. It pipes output of one command into the input of another. The ampersand (&) symbol tells the shell to run a command in the background. I should briefly diverge here for a moment and mention foreground and background operations so you’ll understand what they are.

A quick sidebar lesson…

You can run a command in the foreground (actively running before your eyes) or in the background (hidden from view but still going). The way to do this is to use the bg and fg command modifiers in the command line. Let’s look a a couple simple examples. Let’s say Mary wants to run some big admin job in the background while she does other stuff in the foreground. It’s pretty easy to do. First she starts big_job01 from the command line.

mary@workplace:~$ big_job01

bla-bla-bla-big_job_running_now-bla-bla-bla

With big_job01 running actively in the foreground, Mary doesn’t have a cursor blinking at the command line. She cant do any other work because she has to watch big_job01 outputting. To change this, Mary will “background” big_job01 to bring back her command line cursor so she can do other things.

CTRL+Z

What this combination of keystrokes will do for Mary is it will stop the process big_job01, giving this notification:

1]+  Stopped                 big_job01

Now Mary will get her cursor back and she can send the big_job01 to the background and get it running again.

mary@workplace:~$ bg 1

She can check to see that it’s in the background and running by listing the jobs.

mary@workplace:~$ jobs -l

1]+  4107 Running                 big_job01 &

Note the following & in the above line. That’s telling Mary that big_job01 is running in the background. Cool, huh? Now Mary can go on about her other chores in the foreground as she normally would. When big_job01 finishes, the command line will give Mary a notification like this:

1]+ Done                                         big_job01

OK, there you have it… a bit about backgrounding and foregrounding operations within the shell. Now let’s go back to what we were talking about before.

( and ) – The parenthesis are used in shell scripting to group commands. The shell will actually create a copy of itself, called a sub-shell, for each group. Groups are seen by the shell as jobs and process IDs are created for each group. Sub-shells have their own environment; meaning they can have their own variables with values different from other sub-shells or the main shell. A bit confusing, huh? Well, let’s see a quick example and then wrap up this lesson so we can all go watch C.S.I. on TV.

$ (c1 ; c2) & c3 &

In the above example, grouped command c1 and c2 would execute sequentially in the background while executing command c3 in the background. Remember that we can background commands by using the ampersand (&) symbol and separate commands by using the semi-colon (;). The prompt would return immediately after hitting ENTER on the line above because both jobs would be running in background. The shell would run the grouped commands  c1 and  c2 as one job and c3 as another job. Clear as chocolate pudding, huh? Don’t worry. It’ll all come together… I hope.

Until next time….

~Eric


Beginning Shell Scripting

OK, let’s continue on with our lessons about the Linux Shell and the command line.

Today, we’re going to learn how to write a script that you can run from the command line that will actually do stuff. It’s a very simple script, so don’t expect anything spectacular. I was wondering what I could use as an example script for this lesson when I remembered a question someone at LinuxQuestions.org asked the other day about how to tell which users are currently logged into a Linux system. Let’s make a little script to give us that information.

Let’s say that Mary wants to see who is logged in on the Linux system that she maintains for her company. She could easily do this with one simple command from the command line:

mary@workplace:~$ who

bill           pts/4       April 10 09:12

james       pts/5       April 10 09:30

marjory    pts/11     April 10 10:02

ken           pts/16     April 10 10:31

That was pretty easy, right? What if Mary wanted to check this periodically during the day? Well, she could write a small shell script with the proper permissions that she could execute any time she wanted from the command line or the terminal within her graphical user interface. Let’s find out how she might do that.

Mary would first open the vim editor with the file name that she plans to use for this script:

mary@workplace:~$ vim onsys

Vim would faithfully carry out the command and open up ready to edit file onsys. At which point, Mary would enter these lines to create her script:

# custom who script – mary – 10 Apr 11

date

echo “Users currently logged into the system:”

who

# end of script

Here’s what Mary actually did… she made a comment in the first line that begins with the character #, so that the shell knows to ignore that line. In the next line, she sets the command “date” so the script will output the date along with whatever else she requests it to do. In line 4, she uses the built-in echo command to tell the shell to display whatever is being asked for following the echo command. In this case, Mary wants the script to display Users currently logged into the system: when she runs it. The next command that Mary enters into this little script is the built-in who command. And lastly, is her notation that the script has ended.

Now, to make this script work, Mary needs to make it executable. In other words, she has to change the file’s permissions to allow herself (and other, if she wants) to execute (make it run) the script onsys. She will do that this way:

mary@workplace:~$ chmod +x onsys

If she now listed the permissions for this file, they would look like this:

mary@workplace:~$ ls -l onsys

-rwxr-xr-x 1 mary users 94 Apr 10 15:21 onsys

What this means is that everyone on the system can read and execute this script, but only mary can write to (change) it.

OK, so Mary wants to test her script now, so she just types in the script name at the command line (assuming the script is in her working directory):

mary@workplace:~$ onsys

Sun Apr 10 15:48:09 EDT 2011

Users currently logged into the system:

bill           pts/4       April 10 09:12

james       pts/5       April 10 09:30

marjory    pts/11     April 10 10:02

ken           pts/16     April 10 10:31

And so, there you have it. Mary wrote a simple script using shell built-in commands to perform a function that she does repetitively every day. That’s what scripts do. They perform tasks for us at our bidding. Of course, scripts can get much more complicated; so complicated in fact as to be considered applications in their own right. A script is just a series of encoded commands and variables designed to do something, which is basically what an application is also.

Start yourself a directory in your /home directory where you can create and play around with scripting and scripts. It can really be fun. You can “automate” a lot of every day stuff that you do on your computer using custom-made scripts. Yes, you can do it. It ain’t rocket science. It is similar to the technology used to program rockets, though.

Have FUN!

~Eric


Pimp My Bash Prompt

In the next couple lessons here at Nocturnal Slacker v1.0 we’ll be discussing the Bourne Again Shell (BASH) in a bit more detail.

With that in mind, though, how ’bout we play around with a neat trick that will customize your BASH prompt whenever you go to the command line? Sound like fun? OK, here we go…

There’s a file in your /home/<your_username> directory called .bashrc. You’ll need to use the -a (all) option when listing (ls) that directory because the preceding . means it’s a hidden file. So, let’s see how joe would do this…

joe@mysystem:~$ ls -a .bashrc

.bashrc

There we go. So Joe now knows that he does have a .bashrc file in his /home directory. Now, let’s say that Joe wants a cool BASH prompt like mine:

vtel57_Slackware~:$

… that shows his username, his operating system, and his working directory. To do this, Joe is going to have to add a little data to his .bashrc file. He’ll edit the file using the VIM command line editor. Remember that from a previous lesson? Here goes Joe…

joe@mysystem:~$ vim .bashrc

And poof! Up comes VIM with the .bashrc file ready to be edited. It’s almost like magic, huh?

# /home/joe/.bashrc

# custom prompt
PS1=”\u | archlinux\w:$ “

Joe is going to edit the .bashrc file to add the little bit in purple that you see above. What that will do is tell BASH to start up the command line with a prompt the shows Joe’s usersname (u), his distribution (ArchLinux) separated by the | (pipe) character; and his working directory (\w). After saving the file, this is what Joe’s command line prompt will look like once he starts his next BASH session:

joe | archlinux~:$

Pretty neato, huh? Remember the ~ denotes the home directory. If Joe was to change directories (cd) to say /boot/grub, then his prompt would now change too to show the new working directory.

joe | archlinux~:$ cd /boot/grub

joe | archlinux/boot/grub:$

Again, pretty neato, huh? This way, Joe will always know what directory he’s in at any given time. That will help prevent Joe from making any command line boo-boos.

That’s it, guys and gals. Pretty simple stuff. See? You’re not near as scared of that mean ol’ command line as you used to be, huh? Use your imagination when customizing your prompt. I’ve seen some pretty cool ones out there. Here’s the one my friend securitybreach and fellow Admin from Scot’s Newsletter Forums – Bruno’s All Things Linux uses:

╔═ comhack@Cerberus 02:27 PM
╚═══ ~/->

How’s that for spiffy? For further reading see HERE and HERE.

Have a great weekend wherever you may be!

~Eric


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