Mislav Jurić

Tag: Computers

  • Linux Tutorial Series – 21 – Parent and current (working) directory – what do these terms mean?

    Here is the video version, if you prefer it:

    Maybe you heard the terms “parent directory” and “current directory”, “working directory” or “current working directory”. “What do these terms mean?” you might ask yourself. Well, fear not, because I have come to alleviate you from your ignorance! (imagine epic music playing in the background)

    Working directory (or its synonyms), in the context of using the Linux command line, refers to the directory you are currently located in. (Barrett, 2016)⁠Let me elaborate:

    I just started a new Terminal session and this is what I get as output:

    mislav@mislavovo-racunalo:~$

    See the ~ between the : and $? Well, that is my working directory. ~ actually stands for my home directory, so instead of ~, if we wanted to be fully correct, there should be /home/mislav. If you start a Terminal session, your working directory should also be ~ as well. From within the Terminal, you can change directories (using the cd command), but that is not the topic of this post.

    Now, more importantly, why is it important to know in which directory you are in? A good question. It’s like I asked it myself. Let’s look at the following example:

    mislav@mislavovo-racunalo:~$ ls

    anaconda3 grep-hadoop-example Python-3.7.4

    'Calibre Library' hadoop-example stanfordnlp_resources

    ...

    (… here means output continues)

    The ls command lists directory contents. (“LS(1),” n.d.)⁠ But contents of what directory, exactly? Well, if you don’t explicitly say what directory, it is assumed that you want the ls to list the contents of the working directory.

    So that’s why it is useful! Imagine if you were inside the directory you desire to operate upon and every time you wanted to call a command you needed to write out the full “trajectory” (also called a path) to the directory you wanted to operate on (as in ls /home/mislav while already being in /home/mislav). That’s tedious and programmers don’t like tedious. Thus, when calling a command (in our case, ls), it assumes you want to operate on the current directory.

    Lastly, parent directory is the directory directly above the current directory. (Shotts, 2019)⁠ For example, if I was in the folder

    /home/mislav

    the parent directory of the mislav directory is the home directory. (3 uses of the word directory in one sentence, whew!)

    Hope you learned something useful!

    References

    Barrett, D. J. (2016). Linux pocket guide (3rd ed.). O’Reilly Media. Pages 17-19

    LS(1). (n.d.). Retrieved December 29, 2019, from http://man7.org/linux/man-pages/man1/ls.1.html

    Shotts, W. (2019). The Linux Command Line, Fifth Internet Edition. Retrieved from http://linuxcommand.org/tlcl.php. Pages 31-32

  • Linux Tutorial Series – 20 – Linux directory hierarchy

    Here is the video version, if you prefer it:

    In this article, let’s talk about the Linux directory hierarchy. Here is how it looks like:


    Figure 1 – Linux directory hierarchy (modeled after Figure in (Ward, 2014)⁠, page 40)

    Here is a description of each of the directories: (Ward, 2014)⁠ (Barrett, 2016)

    • bin/ – programs (executables) you run in the shell are located here
    • boot/ – files for booting the system
    • dev/ – device files (your hardware devices represented as files)
    • etc/ – configuration files for your system
    • home/ – personal directories of all of the users
    • lib/ – files needed to successfully run some programs (those files are also known as libraries)
    • lost+found/ – damaged files that were recovered by a disk recovery tool⁠
    • media/ – files that enable access to disks
    • mnt/ – files that enable access to disks
    • opt/ – packages you might have paid extra money for (“What does ‘opt’ mean (as in the ‘opt’ directory)? Is it an abbreviation?,” n.d.)⁠
    • proc/ – operating system statistics
    • run/ – cross-distribution location for the storage of files that do not require preserving across reboots (system restarts); this is very complicated to read – I would read that as “files that can evaporate after every reboot” (“RunDirectory,” n.d.)⁠
    • sbin/ – place for system executables (only the superuser can run these)
    • srv/ – “This main purpose of specifying this is so that users may find the location of the data files for particular service, and so that services which require a single tree for readonly data, writable data and scripts (such as cgi scripts) can be reasonably placed.” (“1.19. /srv,” n.d.)⁠
    • sys/ – provides device and system interface
    • tmp/ – temporary files
    • usr/ – system files
    • var/ – program runtime information

    That’s pretty much it. Within those directories you may have subdirectories, which have their own meanings, but this article should give you the “one layer deep” explanation of what is going on. If you need additional explanation of a particular directory, use Google. I have found it useful to remember the general layout of what is where as I have described above, but if I ever find myself in need of the specifics of some particular directory or subdirectory I Google it.

    Hope this helped!

    References

    1.19. /srv. (n.d.). Retrieved December 22, 2019, from https://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/html/srv.html

    Barrett, D. J. (2016). Linux pocket guide (3rd ed.). O’Reilly Media. Pages 21-23

    RunDirectory. (n.d.). Retrieved December 22, 2019, from https://wiki.debian.org/ReleaseGoals/RunDirectory#A.2Frun

    Ward, B. (2014). How Linux Works: What Every Superuser Should Know (2nd ed.). No Starch Press. Pages 40-42

    What does “opt” mean (as in the “opt” directory)? Is it an abbreviation? (n.d.). Retrieved December 22, 2019, from https://stackoverflow.com/questions/12649355/what-does-opt-mean-as-in-the-opt-directory-is-it-an-abbreviation

  • Linux Tutorial Series – 19 – Directories and files

    Here is the video version, if you prefer it:

    In Linux, you will find both directories and files. Think of directories like folders in Windows or like drawers or folders in everyday life – they are used to store files within them and give structure to your files. (“Directory (computing),” n.d.)⁠ Files are resources for storing information. (“Computer file,” n.d.)⁠

    Directories also have a hierarchy. So we can have directory1/directory2. That means that directory2 is a child directory of directory1. Imagine this as a folder within a folder. When we list the “hierarchical trajectory” from some directory to some other directory, we are talking about a path. (“Path (computing),” n.d.)⁠

    Hope you learned something useful!

    References

    Computer file. (n.d.). Retrieved February 23, 2020, from https://en.wikipedia.org/wiki/Computer_file

    Directory (computing). (n.d.). Retrieved February 23, 2020, from https://en.wikipedia.org/wiki/Directory_(computing)

    Path (computing). (n.d.). Retrieved December 29, 2019, from https://en.wikipedia.org/wiki/Path_(computing)

  • Linux Tutorial Series – 18 – Exiting a terminal session

    Here is the video version, if you prefer it:

    How do you exit a shell session in Linux? You type exit or press CTRL + D. (Shotts, 2019)⁠

    mislav@mislavovo-racunalo:~$ exit

    References

    Shotts, W. (2019). The Linux Command Line, Fifth Internet Edition. Retrieved from http://linuxcommand.org/tlcl.php. Page 29

  • Linux Tutorial Series – 17 – The clear command

    Here is the video version, if you prefer it:

    If your Terminal window ever gets clogged up with old commands and old command output, type in clear to clear your Terminal window, as so:

    mislav@mislavovo-racunalo:~$ clear

    Keep this in mind if things get messy.

    Hope you learned something useful!

  • Linux Tutorial Series – 16 – Command history and cursor movement

    Here is the video version, if you prefer it:

    Did you know you can use the Up/Down arrows on your keyboard to see previous commands you executed in the Linux shell? Did you know that you can use Left/Right arrows to move your cursor? (Shotts, 2019)⁠

    If you did not, now you do. If you did, great for you!

    Hope this helped.

    References

    Shotts, W. (2019). The Linux Command Line, Fifth Internet Edition. Retrieved from http://linuxcommand.org/tlcl.php. Page 27

  • Linux Tutorial Series – 15 – Talking about time – date and cal

    Here is the video version, if you prefer it:

    Today, let’s talk about two time-related commands in the shell. They are called date and cal. (Shotts, 2019)⁠

    date gives you the current time:

    mislav@mislavovo-racunalo:~$ date

    Sun 22 Dec 2019 12:11:15 PM CET

    cal gives you the calendar:

    mislav@mislavovo-racunalo:~$ cal

    December 2019

    Su Mo Tu We Th Fr Sa

    1 2 3 4 5 6 7

    8 9 10 11 12 13 14

    15 16 17 18 19 20 21

    22 23 24 25 26 27 28

    29 30 31

    Obviously, applications of this are vast. Let’s say you freeze yourself and wake up 70 years in the future. Of course you’re not going to ask some human what year is it! That would be ludicrous! Instead, you will find the first computer with Linux and run the commands you learned from this article. I just saved your life 70 years in the future. You are welcome.

    References

    Shotts, W. (2019). The Linux Command Line, Fifth Internet Edition. Retrieved from http://linuxcommand.org/tlcl.php. Page 28

  • Linux Tutorial Series – 14 – Starting a shell session

    Here is the video version, if you prefer it:

    To start a shell session, find Terminal on your Linux distribution (via the graphical user interface) and click on it. That should start a shell session, which means you can type in commands!

    We will be writing some commands in the very next article, so stay tuned!

  • Linux Tutorial Series – 13 – What is a command?

    Here is a video version, if you prefer it:

    This may be a very simple question – what is a command? What is a command in the context of the Linux shell environment?

    Commands are, in essence, running a program with options and arguments. (Barrett, 2016)⁠ If you write, for example, ls -l file.txt, you are calling a program called ls with the option -l and the argument file.txt. But wait a minute – how does the operating system know where to find the ls program? This is not the focus of this article so we don’t currently care. As far as we are right now concerned, the operating system “does its magic” so it can find the program ls and call it with the specified options.

    There are a lot of things you can do with commands – commands can be piped, meaning output of one command is input to another and there can exist scripts which within themselves contain lots of commands. But again, essentially, a command is just a single program, with its options and arguments.

    Hope you found this useful!

    References

    Barrett, D. J. (2016). Linux pocket guide (3rd ed.). O’Reilly Media. Pages 3-4

  • Linux Tutorial Series – 12 – What is a shell?

    Here is the video version, if you prefer it:

    The shell, the shell… We all heard that. We know you can type some command in the shell in a Linux environment and get some output. But what does the shell actually mean?

    “A shell is a program that runs commands”, says (Ward, 2014)⁠. That is basically it. You type some commands in, the shell executes them, then you get some output. Shell scripts, another popular term, are essentially just commands typed in a file called a shell script; so the shell has the same job – execute commands.

    There are multiple kinds of shells. You can find more information here: (“5 Most Frequently Used Open Source Shells for Linux,” n.d.)

    Before I end, it is important to note that programs like Terminal are not actually shells – they are graphical user interfaces running shell on your behalf. (Barrett, 2016)⁠ Figure 1 depicts this. This program with a graphical user interface, called a terminal emulator, interacts with the shell. (Shotts, 2019)⁠

    Figure 1 – Relationship between graphical user interfaces to the shell and the shell itself (modeled after figure on page 15 of (Barrett, 2016)⁠)

    Hope you learned something new!

    References

    5 Most Frequently Used Open Source Shells for Linux. (n.d.). Retrieved December 22, 2019, from https://www.tecmint.com/different-types-of-linux-shells/

    Barrett, D. J. (2016). Linux pocket guide (3rd ed.). O’Reilly Media. Page 15

    Shotts, W. (2019). The Linux Command Line, Fifth Internet Edition. Retrieved from http://linuxcommand.org/tlcl.php. Page 26

    Ward, B. (2014). How Linux Works: What Every Superuser Should Know (2nd ed.). No Starch Press. Page 12