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.

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Day 2 - Basic navigation

• URL: https://linuxupskillchallenge.org/02/
• Previous Lesson: My Linux Upskill Challenge: Day 1

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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.

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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.

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• 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.

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• 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

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• 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.

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

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Navigate the File Structure

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. 🤔

• 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$

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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
  ...

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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

Symbol	Type of file	Description
d	directory	A container of another files
-	normal file	A regular file like text, images, binaries or compressed files, etc..
l	symbolic link	A link to another file
s	socket file	This is a special file used for inter-process communications (IPC)
p	Named pipe (FIFO)	A method for unidirectional communication between processes.
b	block device file	These are files that represent block devices (e.g. hard drives, USB drives)
c	character device file	These 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)

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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.

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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

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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.

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Additional Resources

• Difference between help, info and man command
• GNU Texinfo
• Explore the Linux File System
• Linux File System – YouTube
• Simple Terminal Commands on Ubuntu – YouTube
• Solaris Unix Commands

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Related notes

• My Linux Upskill Challenge: Day 1
• My Linux Upskill Challenge: Day 3

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Nota diaria: 2025-05-01