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My Linux Upskill Challenge - Day 2

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My Linux Upskill Challenge - Day 2

Introduction

I’ve started following the Linux Upskill Challenge to sharpen my Linux knowledge and hands-on skills. It’s a series of 21 lessons designed to be completed daily, but I’ll be going through them at my own pace. I’ll share my journey and notes here as I move forward.

Day 2 - Basic navigation

RTFM

  • In this lesson, I learned a new acronym: RTFM – “Read the F***ing Manual.” 😆
  • When you’re learning and using Linux (or anything else) and have questions, of course, you’re always free to Google it or ask ChatGPT.
  • However, the best system administrators are those who first RTFM.

This is something we’re starting to forget nowadays!

  • Linux systems offer several ways to access documentation. But if—after searching—you still need help, you can always ask a well-written question in forums, Reddit, Discord, or other communities.

I think this is even more relevant today, especially when writing good prompts in the “GPT era.

Looking for Documentation

  • The man command is a great place to start—most installed applications have their own manual.

  • For instance, you can find the manual for these commands:

    • man cp
    • man mv
    • man grep
    • man ls
    • even man man 🙂

  • That said, man output can be overwhelming for some commands or too minimal for others. That’s where tldr comes in—it provides simplified, community-written man pages for common Linux (and other OS) commands.

  • tldr is another tool for viewing documentation. I installed it using sudo apt install tldr, but it didn’t work right away on my EC2 instance.

  • I got the following error:

tldr: /home/ubuntu/.local/share/tldr: createDirectory: does not exist (No such file or directory)
  • I fixed it with these two commands:
mkdir -p ~/.local/share/tldr
tldr --update
  • The second command pulls the latest pages from the official GitHub repo (make sure your server has internet access!).
  • I tried tldr with the same commands as before, and yes—it showed me much more simplified info.
  • I also learned about the apropos command, which is equivalent to man -k.
  • Both are useful when you kind of know what a command does and want to search for keywords in the manual.
  • For example, if you search for the phrase “remove file” using apropos "remove file", you’ll get results like this:
ubuntu@ip-172-31-92-220:~$ apropos "remove file"
git-rm (1)           - Remove files from the working tree and from the index
rm (1)               - remove files or directories
ubuntu@ip-172-31-92-220:~$ man -k "remove file"
git-rm (1)           - Remove files from the working tree and from the index
rm (1)               - remove files or directories

  • Some commands—especially shell built-ins—don’t have man pages.

  • For those, you can use the help command instead.

  • Example: use help export instead of man export.

  • I found exceptions like echo, which works with both man echo and help echo.

  • The best way to check if a command is a shell built-in is to use the type command.

  • Lastly, there’s the info command. It gives more detailed documentation, sometimes written in a tutorial style and with hypertext navigation.

Linux Essentials Exam 010-160 Objectives - 2.3

  • I discovered a command that gives you documentation about the Linux file system: man hier.

  • / is the top-level directory (called root) for all other folders.

  • 🧭 To find out where you are in the file system, use pwd—this is like your GPS in Linux. 🛰 ⇒ 20250611T1211-pwd

  • By default, you’ll start in the /home/<user> directory, unless you’re logged in as root, in which case you’ll be in /root.

  • You can move between directories using cd:

    • cd .. takes you “up” one level.
      • cd . keeps you in the same folder. đŸ€”

  • You can use either relative or absolute paths to move around:

    • For example, if you first do cd /var, then both cd log and cd /var/log will get you to the same place.

  • Just running cd returns you to your home directory, as does cd ~.

  • You can also use ~ as a shortcut to move into folders inside your home directory from anywhere.

    • For instance, if you’re in /var/log and want to go to /home/ubuntu/data/example, just use cd ~/data/example.
ubuntu@ip-172-31-92-220:/var/log$ cd ~/data/example/
ubuntu@ip-172-31-92-220:~/data/example$

Listing Files in a Folder

  • I used ls with different options (“switches”) to list files.

  • For example: ls, ls -l -L, and ls -l -t -r -a (or just ls -ltra).

  • Files or folders that start with a . are hidden. Use ls -a to see them.

  • You can combine switches and provide a folder path (argument):
    e.g., ls -ltra /var/log

  • Entries that start with d are directories.

  • Some terminals show these in a different color—if not, try --color=auto.

  • Example:

    ls -l /var/log/
total 2880
-rw-r--r--  1 root      root              1810 Jun 11 09:31 alternatives.log
-rw-r--r--  1 root      root             38322 May 21 21:10 alternatives.log.1
drwxr-x---  2 root      adm               4096 Jun 11 00:22 apache2
-rw-r-----  1 root      adm                  0 May  8 12:36 apport.log
drwxr-xr-x  2 root      root              4096 Jun 11 09:32 apt
-rw-r-----  1 syslog    adm              75999 Jun 11 12:45 auth.log
-rw-r-----  1 syslog    adm             103911 Jun  7 21:55 auth.log.1
-rw-r-----  1 syslog    adm              17215 May 31 23:55 auth.log.2.gz
-rw-r-----  1 syslog    adm              15940 May 24 23:17 auth.log.3.gz
-rw-r-----  1 syslog    adm               1728 May 17 19:35 auth.log.4.gz
-rw-r--r--  1 root      root             61237 Feb 16 14:53 bootstrap.log
-rw-rw----  1 root      utmp              3600 Jun 10 17:42 btmp
...

ls -loutput breakdown

  • Each line corresponds to a file or a directory, each field at the beginning of each line means something different.
  • The first field is the file type & permissions, contains 10 characters where:
    • The first character indicates the file type, as per the following table.
    • The next nine characters (e.g., rw-rw----) corresponds to the file permissions, which is covered on this note: Linux file permissions
SymbolType of fileDescription
ddirectoryA container of another files
-normal fileA regular file like text, images, binaries or compressed files, etc..
lsymbolic linkA link to another file
ssocket fileThis is a special file used for inter-process communications (IPC)
pNamed pipe (FIFO)A method for unidirectional communication between processes.
bblock device fileThese are files that represent block devices (e.g. hard drives, USB drives)
ccharacter device fileThese are character devices (e.g., keyboards, serial ports, sound cards)
  • The next field is the Link Count, it indicates the number of hard links to this file(e.g., 1)
  • The next field is the user who owns the file (e.g,root)
  • The next field is the group who owns the file (e.g,adm)
  • The next one is File Size in bytes ((e.g,4096))
  • Then is the Date modified (e.g,Jun 11 00:22)
  • And the Filename (e.g,apache2)

File list sort options

  • By default lssort the results in alphabetical order

  • The option -tsort the files based on the timestamp

ls -lt /var/log
  • The option -Swill sort the files based on the file size.
ls -lS /var/log
  • The option -r will revers the result or any other options.
ls -ltr /var/log
ls -lSr /var/log

Basic Directory Manipulation

  • I created a new folder with mkdir test, then moved into it with cd test.
  • You can repeat this to build nested folder structures.
mkdir test
cd test
  • To move a folder into another directory, I used mv:
  • Created a folder test2, then moved example from test to test2.
mv test/example test2
  • To remove an empty directory, use rmdir.
  • To remove a non-empty one, use rm -r.

Basic File Manipulation

  • To create a new (empty) file: touch newfile.txt
  • To move it: mv newfile.txt test2
  • To delete it: rm
touch newfile.txt
mv newfile.txt test2
rm test2/newfile.txt

A Bit More Advanced Directory Navigation (Stack-Based)

  • I learned about pushd and popd, which let you move between folders using a stack (LIFO order).
  • It’s different from cd ..—with pushd you can hop to /etc, then /var/log, and then jump back in reverse order using popd.
  • Use dirs to see the current directory stack.
pushd /etc
pushd /var/log
dirs
popd
popd
  • If you run pushd without arguments, it swaps your current and previous directories—similar to cd -, but it remembers your path history.

So these are my notes for the Day 2 – Basic Navigation of the Linux Upskill Challenge.

Additional Resources

Nota diaria: 2025-05-01

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