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Linux Tutorial Series

Linux Tutorial Series – 129 – Package management

Here is the video version, if you prefer it:

Let’s talk about package management today. What is package management and why do we need it?

Let’s start with why do we need it. We need it because packages are a convenient way to deliver software – we deliver software like a package. Package management is a term for installing, modifying and removing packages. The alternative to installing software from a package is to install the software from source, but that is for another article.

Different Linux distributions use different packaging systems. (Shotts, 2019) A package consists of files that contain the software we are installing. Packages are available in repositories. Each distribution has its own repository with packages. If a software depends on something to run (such as an external piece of code to calculate something), then we say that that external piece of code is a dependency. Package managers (programs that manage packages) take care of dependencies when installing packages.

There are high-level package management tools (such as apt and apt-get in Debian-like distributions) and low-level package management tools (such as dpkg in Debian-like distributions). We will use those to manage our packages.

Hope you learned something new!

A caveat: In the following articles I will cover package management operations (installing, removing, …) using package manager that is used in Debian and Debian-like Linux distributions. I won’t cover other distributions. In case you have another distribution, I suggest using Google to find the equivalent commands.

References

Shotts, W. (2019). The Linux Command Line, Fifth Internet Edition. Retrieved from http://linuxcommand.org/tlcl.php. Pages 196-199

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Linux Tutorial Series

Linux Tutorial Series – 128 – Other compression and archiving commands

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There are other compression commands (such as bzip2) and archiving commands (such as zip). (Shotts, 2019)⁠

zip may be useful; its syntax is:

zip zipFile fileToArchive

where zipFile is the newly created zip file and fileToArchive is the file you want to compress.

If your fileToArchive is a directory, use:

zip -r zipFile fileToArchive

To unzip use:

unzip zipFile

I never used bzip2 so far, but just know that it exists.

Hope you learned something useful!

References

Shotts, W. (2019). The Linux Command Line, Fifth Internet Edition. Retrieved from http://linuxcommand.org/tlcl.php. Pages 261-262; 268-270

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Linux Tutorial Series

Linux Tutorial Series – 127 – The tar command

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The tar command is used to create an archive of files or to extract files from an already existing archive of files. (Ward, 2014) To create an archive of files, use the following syntax:

tar cvf archiveName.tar file1 file2 …

cvf mean the following – c enters the create mode (telling tar to create a new archive), v is the flag for verbose output (so you know what is happening) and f means that the next argument will be the name of the to-be-constructed archive.

⁠To extract files from an already existing archive, use the following syntax:

tar xvf archiveName.tar

v and f mean the same things as I explained above, but x is the extract mode, telling tar to extract the archive provided as the argument.

Memorize these two commands by heart. That’s what I did.

When extracting files, it is always a good idea to extract them in a newly created folder. That way, if the extracted files make a mess, you can always move that folder to the location you want to (or delete it). There are options in tar to check the archives contents, but I haven’t used them – I used the method of extracting the archive in a new folder.

Hope you learned something useful!

References

Ward, B. (2014). How Linux Works: What Every Superuser Should Know (2nd ed.). No Starch Press. Page 37

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Linux Tutorial Series

Linux Tutorial Series – 126 – The gzip command

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The gzip command is used to compress one or more files. (Shotts, 2019)⁠ Here is its syntax:

gzip fileName

Interesting options include:

-v – verbose mode (informative output is displayed)

-t – test the integrity of the compressed file

-d – decompress

For decompression you can use gunzip command as follows:

gunzip fileName

That way you can decompress a file compressed with gzip.

Thank you for reading!

References

Shotts, W. (2019). The Linux Command Line, Fifth Internet Edition. Retrieved from http://linuxcommand.org/tlcl.php. Pages 259-261

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Linux Tutorial Series

Linux Tutorial Series – 125 – Compression – Why is it used?

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Before we talk about compressing files in Linux, let’s first talk about what compression is and more importantly, why is it used.

Compression is used to encode information in a way to take up less space (space being measured in computer memory in this case). Decompression is the reverse process – reading the information that was compressed and reconstructing the original.

Let’s say I have 10 letters A in a row:

AAAAAAAAAA

and let’s say I need 1 memory unit to represent the letter A. I also need 1 memory unit to represent any other letter or a digit. Then I have 10 memory units in total.

However, I could think: “OK, how can I transfer the same information, but using less memory units?”. One way is to send the information over like this:

A10

and that there’s an agreement between me (the sender) and the receiver that A10 means “A repeated 10 times”. That way (assuming, as I stated above, that every letter and digit takes up 1 memory unit) I have represented the occurrence of A 10 times in a row with only 3 memory units. 10/3 would be the compression ratio, the ratio between uncompressed and compressed information.

Data compression can be lossless or lossy – lossless means that no information is lost (like in our example) and lossy compression means that we lose some information in the compression procedure, but we can gain a close approximation when decompressing it. (Shotts, 2019)⁠

Those are the very basics of compression and why it is used. There is an entire field called Information Theory that deals with compression. There is also the Hutter prize, which aims to reward the person who can advance state-of-the-art in compression: (“Hutter Prize,” n.d.)⁠ The compression algorithms used today are more elaborate than the basic one I explained above, of course, but you get the idea.

Hope you learned something interesting!

References

Hutter Prize. (n.d.). Retrieved February 10, 2020, from http://prize.hutter1.net/

Shotts, W. (2019). The Linux Command Line, Fifth Internet Edition. Retrieved from http://linuxcommand.org/tlcl.php. Page 259

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Linux Tutorial Series

Linux Tutorial Series – 124 – Checkpoint

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Going on, we will talk about file compression and commands related to package management. Both are used relatively frequently. If you are a “regular” desktop user, then using a graphical user interface (GUI) to compress and decompress archives is going to be enough most (if not all) of the time. Still do read through it, because sometimes you may have to use the command line and it pays to know what the tutorials you found on Google are telling you. In relation to package management, that is something you will use very frequently both as a regular desktop user and as a software engineer (or some other career choice) using Linux, so do pay close attention.

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Linux Tutorial Series

Linux Tutorial Series – 123 – Review

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We talked about file modes and permissions. Let’s review that on an example:

-rw-r--r--

First character (looking from left to right) tells us if we are talking about a file or a directory or something else, the next three characters tell us user permissions, the next three tell us group permissions and the next three tell us world permissions.

Then we talked about the following:

  • chmod is used to change file permissions
  • chown is used to change file owner
  • umask defines the default permissions (keep in mind the octal to binary conversion we talked about and how it relates to permissions)
  • passwd is used to change users password
  • adduser is used to add users
  • userdel command is used to delete users
  • /etc/passwd keeps users and their IDs, while /etc/sudoers keeps the list of users who can execute the sudo command

Hope you refreshed your memory!

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Linux Tutorial Series

Linux Tutorial Series – 122 – A tidbit about users vol 4 – passwd and sudoers

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Have you ever wondered where information about regular users and superusers is kept? The answer is /etc/passwd and /etc/sudoers, respectively.

/etc/passwd maps users to their IDs. It also stores the home directory of the user. Encrypted user passwords are stored in /etc/shadow. (Ward, 2014)⁠ What does “encrypted” mean? It means that passwords are not stored as plain text – they are stored as some jibberish, but there are certain mechanisms which can figure out if a password you enter is valid by manipulating the aforementioned jibberish.

/etc/sudoers is the file containing users that can use the sudo command.

If you need any details on these files, I think that a Google search can do wonders. I just wanted to cover these files conceptually, so that you heard of them and know what they store.

Hope you learned something new!

References

Ward, B. (2014). How Linux Works: What Every Superuser Should Know (2nd ed.). No Starch Press. Pages 43; 153-157

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Linux Tutorial Series

Linux Tutorial Series – 121 – A tidbit about users vol 3 – userdel command

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If you ever need to delete users, use the userdel command, as follows:

userdel username

You need to have superuser permissions. Make sure that no processes from the user you are trying to delete are running, or otherwise userdel will fail to execute. (“How to Delete/Remove Users in Linux (userdel Command),” n.d.)

Hope you learned something useful!

References

How to Delete/Remove Users in Linux (userdel Command). (n.d.). Retrieved February 10, 2020, from https://linuxize.com/post/how-to-delete-users-in-linux-using-the-userdel-command/

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Linux Tutorial Series

Linux Tutorial Series – 120 – A tidbit about users vol 2 – adduser

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If you ever need to add a user to your computer (I had to once), then use adduser. It must be run as the superuser, so be sure to prefix it with sudo. (“How to Add and Delete Users on Ubuntu 18.04,” n.d.)⁠ Its usage is as follows:

adduser username

You can find more details in the reference above. A low-level alternative to adduser is useradd, but I had adduser available on the machine I was adding the user on (it had Debian 9 on it).

Hope you learned something new!

References

How to Add and Delete Users on Ubuntu 18.04. (n.d.). Retrieved February 10, 2020, from https://linuxize.com/post/how-to-add-and-delete-users-on-ubuntu-18-04/