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Linux directories and paths: pwd, ls, mkdir, cd, absolute vs relative paths and ~

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Let's start. Last class we logged in to our EC2 server with SSH and saw that an operating system is mostly files and folders. Today we actually walk around inside the server. Where am I? What is in here? How do I make a folder, go into it, come back out, and jump to any folder in one line? By the end of the class you will read a path like /home/ec2-user/calendar/weeks and know exactly where it points. Keep your server running and type every command with me.

What you will learn in this class

  • A short SSH recap and the four errors you will meet most
  • Linux users: root and ec2-user, and why you log in as ec2-user
  • When an idle SSH session drops, and how to get back fast
  • The Linux tree: everything starts at / (root)
  • Your home directory, and pwd
  • Reading a path
  • Files vs folders (directories)
  • mkdir: one folder or many
  • ls and ls -r
  • cd into a folder, and what the prompt tells you
  • Going up: cd .., cd ../.., cd ../../..
  • cd alone, cd -, and moving sideways
  • mkdir -p: folders inside folders in one line
  • Absolute paths, relative paths and ~
  • Worked scenario 1: the calendar (four ways to make week1)
  • Worked scenario 2: one to five (three ways to make 22)
  • Names with spaces
  • Tab completion, and what to do when names start the same
  • clear and history
  • Practice task

1. Quick recap: logging in with SSH

Why. Every Linux class starts with logging in to the server. If SSH fails, nothing else works. The full step-by-step, with all the fixes, is in the previous chapter: Inside an EC2 server: EBS, ENI, instance states, connecting with SSH, and what Linux is.

What. The command has four parts:

ssh -i Downloads\firstserver.pem ec2-user@3.3.3.3

  1. ssh: the program.
  2. -i: the identity file (your private key) comes next.
  3. Downloads\firstserver.pem: the path to the key. Type Dow and press Tab, then fir and press Tab, so there are no typos.
  4. ec2-user@3.3.3.3: the user name, @, and your server's public IPv4. 3.3.3.3 is a placeholder; use your own.

Paste the IP with Ctrl+V or right-click. Both work in the PowerShell of Windows 10 and 11, and in Windows Terminal.

The four errors you will meet most:

Error Usual cause Fix
Permission denied (publickey) wrong key for this server, or wrong user name use the key chosen at launch; ec2-user on Amazon Linux
No such file or directory typo in the key path use Tab completion
Permission denied again user name typed wrong: ec2user, or a space inside ec2-user@... it is ec2-user, with a hyphen, and no spaces
Connection timed out the public IP changed after a stop and start copy the new public IP from the console

If SSH still won't work:

  1. Check the OpenSSH client with ssh -V. If PowerShell says ssh is not recognized, add the OpenSSH Client optional feature, or install the latest PowerShell from Microsoft. Then open a new window.
  2. Use EC2 Instance Connect: select the instance → Connect → EC2 Instance Connect → Connect. A terminal opens in the browser.
  3. PuTTY is an older third-party tool. You rarely need it now, because Windows has ssh built in.

Classroom line

Miss one sentence and you won't follow the next.

Correction

In class, red error text was blamed on "an old PowerShell", and we heard that Ctrl+V doesn't paste. Red text only means the command failed. One common cause is a missing OpenSSH client; check with ssh -V. And Ctrl+V does paste in current PowerShell and Windows Terminal; right-click works too.

2. Linux users: root and ec2-user

Why. The prompt says ec2-user. Who is that, and why not log in as the administrator?

What.

  1. root is the administrator of a Linux system. It can do anything, including delete the whole system.
  2. ec2-user is the normal default login user on Amazon Linux. On Ubuntu the default user is ubuntu.
  3. Linux has many more accounts for system programs, but these two matter for logging in.
  4. We log in as ec2-user. When a task needs admin rights, we put sudo in front of that one command, for example sudo yum install tree -y.

How AWS sets this up.

  1. You choose a key pair at launch. The key pair is not tied to any user.
  2. At first boot, AWS puts the public half of that key into the default user's file ~/.ssh/authorized_keys: ec2-user on Amazon Linux, ubuntu on Ubuntu.
  3. That is why your key works for ec2-user.
  4. Direct SSH login as root is blocked, for safety. Use sudo instead.

Correction

In class it was said that AWS won't give a key for root because the key belongs to ec2-user, and that Linux has two users by default. The key pair isn't tied to a user; AWS installs it for the default user at first boot, and root SSH login is disabled on purpose. Linux has many system accounts; root and ec2-user are the two that matter for login.

3. When an idle SSH session drops

Why. You leave the terminal for a while, come back, and you are suddenly at your Windows prompt (PS C:\Users\ravi>). Your server is fine. Only the connection dropped.

What. AWS does not close idle SSH sessions by default. The drop usually comes from your home router or Wi-Fi, which forgets quiet connections after some idle minutes, or from your laptop going to sleep.

How to get back fast.

  1. Press the Up Arrow key in PowerShell. Your last command, the ssh -i ... line, comes back.
  2. Press Enter. You are logged in again.
  3. To stop the drops, add a keep-alive: ssh -o ServerAliveInterval=60 -i Downloads\firstserver.pem ec2-user@3.3.3.3. SSH then sends a small message every 60 seconds, so the router keeps the connection.

Correction

In class the drop was described as happening "after 10 to 15 minutes", as if it were a fixed rule. There is no such AWS rule. How long it takes depends on your router, Wi-Fi or laptop sleep settings.

4. The Linux tree: everything starts at /

Why. On Windows you think in drives: C:\, D:\. Linux has no drive letters. Everything hangs from one top point.

What.

  1. The top of everything is /, called root (the root directory).
  2. Under / are the system directories: bin, sbin, etc, home, root, dev, opt, usr, var and more.
  3. /home holds one folder per user: /home/ec2-user, /home/ubuntu, /home/ravi.
  4. Your own work goes inside your home folder, /home/ec2-user.
  5. Careful with the word "root". / is the root directory. /root (with a name after the slash) is the home folder of the root user. They are different places.
Linux starts at one top directory: / (root) / bin sbin etc home root dev opt usr var ec2-user ubuntu ravi your folders and files go here /home/ec2-user = home of user ec2-user/root = home of the root user,not the same as //etc = settings, /var = logs and data/bin, /usr = programs, /dev = devices Like C:\ on Windows (a simplification): everything on the system is somewhere under /.

Figure 1. The Linux tree starts at / (root). Under it are bin, sbin, etc, home, root, dev, opt, usr and var. /home holds a folder for each user; your files go under /home/ec2-user.

What the main directories hold (for now, just recognise the names):

Directory Holds
/bin, /usr/bin commands like ls and mkdir
/sbin system admin commands
/etc settings (configuration files)
/home one home folder per user
/root home of the root user
/var logs and changing data, e.g. /var/log
/dev devices, like disks
/opt extra software you install

Correction

The class board called / "like C:\ on Windows". That is a fair picture to start with, but / is not a folder like the others: it is the single top of the whole tree, and even other disks appear somewhere under it.

5. Your home directory, and pwd

Why. "Where am I?" is the first question every time. Before you create or delete anything, know where you are standing.

What. pwd means print working directory. It prints the full path of the directory you are in now.

How.

  1. Log in.
  2. Type pwd and press Enter.
  3. You see /home/ec2-user.
  4. After login you always land in your home directory.

6. Reading a path

Why. Paths are how Linux says "go here". Read one slowly once, and you can read all of them.

What. Take /home/ec2-user/ravi/one:

  1. The first / is root, the top.
  2. Every other / only separates names. Read it as "go inside".
  3. So: start at root → into home → into ec2-user → into ravi → into one.
Reading a path: /home/ec2-user/ravi/one / home / ec2-user / ravi / one first / = root, the top every other / just separates names: go inside Read it as: start at root → into home → into ec2-user → into ravi → into one.Below root there are four directories here: home, ec2-user, ravi and one. pwd prints this kind of path.

Figure 2. The path /home/ec2-user/ravi/one: the first / is root; every other / separates names. Read it as root, then into home, ec2-user, ravi and one.

Worked example: count the levels.

  1. /home/ec2-user has two directories below root: home and ec2-user.
  2. Counting root itself, that is three levels: /, home, ec2-user.
  3. /home/ec2-user/ravi/one has four directories below root.

Correction

The board said /home/ec2-user "has three folders: /, home and ec2-user". / is not a folder inside the path; it is the top. Say "two directories, or three levels counting root".

7. Files vs folders

Why. Everything you create will be one of these two. They behave differently.

What.

  1. A file holds content. You open it to read it or write in it: notes, a web page, a script.
  2. A folder is a container. It holds files and other folders. Think of a tiffin box: the box itself is not food; it holds the food, and even smaller boxes.
  3. Windows says folder. Linux says directory. Same thing. This course uses both words.

Classroom line

A folder is like a tiffin box.

File vs folder (directory) File: holds contentyou read it and write in it folder = tiffin box noteslist one a folder inside a folder Folder: a container for files and other foldersWindows says folder; Linux says directory. Same thing.

Figure 3. A file holds content you read and write. A folder (a directory, in Linux) is a container like a tiffin box: it holds files and other folders.

8. mkdir: make one folder, or many

Why. Before you can organise anything, you need folders.

What. mkdir means make directory.

How.

  1. mkdir ravi makes one folder named ravi.
  2. Linux prints nothing. No output means success. Linux stays quiet when all is well.
  3. ls shows ravi.
  4. Several at once: mkdir raja rani aws. Each name is a separate folder.
  5. Try the same name again: mkdir ravi.
  6. Error: mkdir: cannot create directory 'ravi': File exists. Two items in the same folder can't share a name.

Ravindra Bagale's Tip

mkdir -p ravi gives no error if ravi already exists. Useful in scripts. Section 13 shows the real job of -p.

9. ls and ls -r

Why. After every change, look. ls is how you look.

What. ls means list. It lists the files and directories in the directory you are in.

How.

  1. ls → aws raja rani ravi. Alphabetical order.
  2. ls -r → ravi rani raja aws. The -r option reverses the order (Z to A).
  3. A brand-new server shows nothing for ls in your home folder. That is normal.

The -r is an option: a letter after a dash that changes how a command behaves. You will meet many: ls -l, ls -a, ls -R.

10. cd into a folder, and what the prompt tells you

Why. Making folders is half the job. You also need to go into them.

What. cd means change directory.

How.

  1. Start at home. The prompt is [ec2-user@ip-172-31-5-10 ~]$.
  2. cd ravi
  3. The prompt now ends in ravi ]$ instead of ~ ]$.
  4. pwd → /home/ec2-user/ravi.
  5. mkdir one makes one inside ravi.
  6. cd one
  7. pwd → /home/ec2-user/ravi/one.

Reading the prompt [ec2-user@ip-172-31-5-10 ~]$:

  1. ec2-user: who you are.
  2. ip-172-31-5-10: the server's name, built from its private IP (the IP here is an example).
  3. ~: where you are. The prompt shows only the last part of the path, and shows ~ when you are at home.
  4. $: a normal user. A root shell shows #.
Handwritten board. Left column: mkdir ravi, cd ravi, then mkdir one at the ravi prompt, pwd, /home/ec2-user/ravi, cd one, pwd arrow /home/ec2-user/ravi/one. Right column: mkdir 'my folder', and mkdir 'my folder' 'your folder'.

From the class board: Left: mkdir ravi, cd ravi, mkdir one; pwd shows /home/ec2-user/ravi; cd one; pwd shows /home/ec2-user/ravi/one. Right: a folder name with a space goes in quotes, one or several at once.

Classroom line

Pay attention, and do your own work yourself.

Correction

~ in the prompt was described as a kind of status mark. It is the short form of your home path. The shell shows ~ instead of /home/ec2-user to keep the prompt short.

11. Going up: cd .., cd ../.., cd ../../..

Why. You went into a folder. How do you come out?

What. .. (two dots) means the parent directory: one level up. Each ../ climbs one more level.

How.

  1. Suppose you are in /home/ec2-user/ravi/one.
  2. cd .. → /home/ec2-user/ravi (one level up).
  3. Go back: cd one.
  4. cd ../.. → /home/ec2-user (two levels up).
  5. Go back: cd ravi/one.
  6. cd ../../.. → /home (three levels up).
  7. Check with pwd after every step.

Worked example: a common mistake.

  1. You are in /home (after cd ../../..).
  2. You type cd myfolder.
  3. Error: -bash: cd: myfolder: No such file or directory.
  4. Why? myfolder is inside ec2-user, not inside /home.
  5. Fix: cd ec2-user/myfolder.

Correction

In class cd ../../../.. (four levels) was typed while saying "three levels", so the result didn't match the board. Three levels up is cd ../../..: count one .. per level, and check with pwd before and after.

12. cd alone, cd -, and moving sideways

Why. Typing many ../ is slow. Two shortcuts save you every day.

What.

  1. cd alone takes you home (/home/ec2-user) from anywhere.
  2. cd - takes you back to the previous directory, and prints where it went. Press it again to switch back. It works like a back and forward switch.
  3. Sideways: to reach a folder next to yours, go up, then down in the same line.

Classroom line

There's a shortcut here too: to go back where you came from.

Worked example: a full walk. Suppose your home has one/two and myfolder side by side.

  1. cd ~/one/two then pwd → /home/ec2-user/one/two.
  2. cd .. → /home/ec2-user/one.
  3. cd ../myfolder → /home/ec2-user/myfolder (up to home, then into myfolder).
  4. cd ../.. → /home.
  5. cd → /home/ec2-user.
  6. cd - → prints /home and goes there.

Sideways from deeper. From /home/ec2-user/one/two, cd ../../myfolder reaches myfolder in one step. Back again: cd ../one/two.

Moving around with cd / home ec2-user (~) one two myfolder $ pwd/home/ec2-user/one/twostart here $ cd ../home/ec2-user/oneup one level $ cd ../myfolder/home/ec2-user/myfolderup, then sideways $ cd ../../homeup two levels $ cd/home/ec2-useralone: home $ cd -/homeback to previous The orange box shows where you are after each command. cd prints nothing; pwd tells you where you are.

Figure 4. Animation: pwd, cd .., cd ../myfolder, cd ../.., cd and cd -. The orange box shows where you are after each command.

Classroom line

What is our job? To solve the problem in the least time.

13. mkdir -p: folders inside folders, in one line

Why. Real projects need nested folders: project/src/css. Making them one by one with cd in between is slow.

What. Spaces and slashes mean different things to mkdir:

  1. mkdir india maharashtra pune → spaces = three separate folders, side by side.
  2. mkdir -p india/maharashtra/pune → slashes = one inside the other: pune inside maharashtra inside india.
  3. -p means parents (--parents): create any missing parent folders on the way, and give no error if they already exist.
  4. Without -p, mkdir india/maharashtra/pune fails when india doesn't exist yet: No such file or directory.
Side by side, or one inside another? mkdir india maharashtra punethree names = three folders, side by side ~ india maharashtra pune ls in ~ shows all three:india maharashtra pune mkdir -p india/maharashtra/puneslashes = one inside the other; -p makes the parents ~ india maharashtra pune cd into all three, then pwd:/home/ec2-user/india/maharashtra/pune Without -p, mkdir india/maharashtra/pune fails if india does not exist yet: No such file or directory.

Figure 5. mkdir india maharashtra pune makes three folders side by side. mkdir -p india/maharashtra/pune makes them one inside another.

Handwritten board: a tree india, arrow to maharashtra, arrow to pune; below it the command mkdir -p india/maharashtra/pune.

From the class board: india contains maharashtra, which contains pune. One command makes all three: mkdir -p india/maharashtra/pune.

Worked example: prove it.

  1. cd (go home).
  2. mkdir -p india/maharashtra/pune
  3. cd india then ls → maharashtra.
  4. cd maharashtra then ls → pune.
  5. cd pune then pwd → /home/ec2-user/india/maharashtra/pune.

A question from class: months with jan, feb and mar.

  1. mkdir -p months/jan/feb/mar makes them nested: feb inside jan, mar inside feb. Usually not what you want.
  2. Side by side, the simple way: mkdir months, cd months, mkdir jan feb mar.
  3. Or, from home, give each full path separated by spaces: mkdir -p months/jan months/feb months/mar.
  4. Bonus shortcut (more in the next class): mkdir -p months/{jan,feb,mar}. The shell expands the braces into the three paths of step 3.

Classroom line

What will just typing it get you? Short-term satisfaction... What is the main aim? To understand a new concept.

14. Absolute paths, relative paths and ~

Why. Every command that takes a path (cd, mkdir, ls, cp) accepts all three kinds. Knowing them lets you work on any folder without walking to it first.

What.

  1. Absolute path: starts with /. It starts from root, so it means the same place no matter where you are. Example: /home/ec2-user/calendar/weeks.
  2. Relative path: does not start with /. It starts from where you are now. .. means the parent; a plain name means a folder inside the current one. Example: ../weeks.
  3. Tilde path: starts with ~. ~ means your home directory. Example: ~/calendar/weeks.

~ depends on who is logged in:

  1. Logged in as ec2-user: ~ = /home/ec2-user.
  2. Logged in as ubuntu: ~ = /home/ubuntu.
  3. Logged in as ravi: ~ = /home/ravi.
  4. / is always the top of the whole tree. ~ is your own folder inside it.
~ means the home of whoever is logged in /home ec2-user logged in as ec2-user: ~ = /home/ec2-user ubuntu logged in as ubuntu: ~ = /home/ubuntu ravi logged in as ravi: ~ = /home/ravi The shell (bash) turns ~ into that path before the command runs. / is the top of the whole tree; ~ is your own folder in it.

Figure 6. ~ means the home of whoever is logged in: /home/ec2-user, /home/ubuntu or /home/ravi. The shell turns ~ into that path.

Correction

In class it was said that "the Linux backend replaces ~". It is the shell (bash) that turns ~ into your home path, before the command runs. One result: inside quotes, '~/x' is not expanded, so leave ~ outside quotes.

15. Worked scenario 1: the calendar

Why. This is the board scenario that makes the three kinds of path click.

Set it up (from home):

  1. mkdir calendar
  2. cd calendar
  3. mkdir months weeks days
  4. cd months
  5. mkdir jan feb mar
  6. pwd → /home/ec2-user/calendar/months. You are in months.

The task: make week1 inside weeks, while you are in months. Four ways:

  1. Walk there, then make it: cd .., then cd weeks, then mkdir week1.
  2. Relative, stay where you are: mkdir ../weeks/week1 (up to calendar, into weeks, make week1).
  3. Absolute, works from anywhere: mkdir /home/ec2-user/calendar/weeks/week1.
  4. Tilde: mkdir ~/calendar/weeks/week1.
You are in months. Make week1 inside weeks: four ways ~ (/home/ec2-user) calendar monthsyou are here jan feb mar weeks week1new days 1. Walk there, then make itcd ..; cd weeks; mkdir week1 2. Relative (from where you are)mkdir ../weeks/week1 3. Absolute (starts with /, works from anywhere)mkdir /home/ec2-user/calendar/weeks/week1 4. Tilde (~ = your home)mkdir ~/calendar/weeks/week1 All four make the same folder: /home/ec2-user/calendar/weeks/week1

Figure 7. You are in months. Make week1 inside weeks by walking there, with a relative path, an absolute path or a tilde path. All four make /home/ec2-user/calendar/weeks/week1.

Check: ls ~/calendar/weeks → week1. If you try all four with the same name, the second one onwards says File exists, because week1 is already there. To practise all four, use a new name each time: week1, week2, week3, week4.

Classroom line

Real study happens when you build situations in your own mind.

16. Worked scenario 2: one to five

Set it up:

  1. cd
  2. mkdir -p one/two/three/four/five
  3. cd one/two/three/four
  4. pwd → /home/ec2-user/one/two/three/four. You are in four.

The task: make 22 inside two. Three ways:

  1. Absolute: mkdir /home/ec2-user/one/two/22. (mkdir -p works too; it gives no error when the parents exist.)
  2. Relative: mkdir ../../22. The first .. goes from four to three; the second goes from three to two.
  3. Tilde: mkdir ~/one/two/22.
You are in four. Make 22 inside two ~ (/home/ec2-user) one two 22new three fouryou are here five 1st .. : up to three2nd .. : up to two Absolutemkdir /home/ec2-user/one/two/22 Relative: four → three → twomkdir ../../22 Tildemkdir ~/one/two/22 Same result each time: /home/ec2-user/one/two/22.mkdir -p makes missing parents and gives no errorif they already exist.

Figure 8. Animation: you are in four. Two .. steps climb to two, and 22 appears inside two. Absolute, relative and tilde paths give the same result.

Handwritten board: a tree from / to home to ec2-user, then a chain of circles 1, 2, 3, 4, 5 with 22 branching off 2; on the right three commands: mkdir /home/ec2-user/1/2/22, mkdir ../../22, mkdir ~/1/2/22.

From the class board: The class board used folders named 1 to 5 under ec2-user. From inside 4, three ways to make 22 inside 2: mkdir /home/ec2-user/1/2/22, mkdir ../../22 and mkdir ~/1/2/22.

Check: ls ~/one/two → 22 three.

Classroom line

Go back and forth like this yourself; make up your own situations.

17. Names with spaces

Why. On Windows, "My Folder" is normal. In the shell, a space separates arguments, so it causes surprises.

What.

  1. mkdir my folder makes two folders: my and folder.
  2. mkdir 'my folder' makes one folder named my folder. Double quotes work too: mkdir "my folder".
  3. Several names with spaces: mkdir 'my folder' 'your folder'.
  4. To go in: cd 'my folder', or type cd my and press Tab. Tab writes cd my\ folder/.
  5. The backslash \ is an escape character: it tells the shell "the next space is part of the name".
Folder names with a space mkdir my folderthe space splits it: TWO folders, my and folder my folder mkdir 'my folder'quotes keep it together: ONE folder ("my folder" works too) my folder cd my\ folderbackslash escapes the space; Tab writes this for you my folder Easiest: avoid spaces. Use my-folder or my_folder.

Figure 9. mkdir my folder makes two folders. mkdir 'my folder' makes one. cd my\ folder escapes the space; Tab writes it for you.

Worked example.

  1. mkdir 'my folder'
  2. cd my + Tab → cd my\ folder/ → Enter.
  3. mkdir 'inside folder'
  4. pwd → /home/ec2-user/my folder.
  5. ls → inside folder.

Classroom line

Go on. Create folders with spaces... Press Tab and see what happens.

Ravindra Bagale's Tip

At work, avoid spaces in file and folder names. Use my-folder or my_folder. Scripts, URLs and other people's commands will thank you.

18. Tab completion, and what to do when names start the same

Why. On the job, nobody types long paths letter by letter. Tab is faster and makes no spelling mistakes.

What.

  1. Type the first few letters of a name and press Tab. If only one name matches, the shell completes it.
  2. If several names match, one Tab completes only the letters they share, or does nothing.
  3. Press Tab twice to see the matching names.
  4. Type one or two more letters until only one name matches, then press Tab.

Worked example 1: tata, twelve, taja (and two).

  1. In a fresh folder: mkdir tata twelve taja two.
  2. cd t + Tab → nothing happens: four names start with t.
  3. Tab Tab → taja/ tata/ twelve/ two/.
  4. cd taj + Tab → cd taja/.
  5. cd .., then cd tat + Tab → cd tata/.

Worked example 2: amazon, amma, aman.

  1. mkdir amazon amma aman
  2. cd ama + Tab → stops at ama, because amazon and aman both start with ama.
  3. cd amaz + Tab → cd amazon/.
  4. cd aman + Tab → cd aman/.
  5. cd amm + Tab → cd amma/.
Tab completion when names start the same $ ls taja tata twelve two $ cd t[Tab] → nothing: four names start with t $ cd t[Tab][Tab] → shows the choices taja/ tata/ twelve/ two/ $ cd tajtype more letters, then [Tab] $ cd taja/completed Second example$ lsaman amazon amma cd ama + Tab→ stops at ama (amazon, aman) cd amaz + Tab→ cd amazon/ cd aman + Tab→ cd aman/

Figure 10. Animation: cd t + Tab does nothing (four matches); Tab Tab lists them; cd taj + Tab completes taja. In the second example ama is not unique, so type amaz or aman.

Correction

The class example typed ama and Tab to reach amazon. With aman also present, ama is not unique, so Tab stops at ama. Type amaz, then Tab.

19. clear and history

clear.

  1. clear (or Ctrl+L) wipes the screen.
  2. Only the screen. Your files and folders are untouched.

history.

  1. history prints a numbered list of commands you ran.
  2. Handy to see what you did, or to copy a long command again.
  3. !45 runs command number 45 again.
  4. The Up Arrow walks back through the same list.

Classroom line

While I'm explaining, don't type along... when I'm showing, just watch.

Correction

history was described as a way to see everything that was run on a server. It shows only the commands of this user's shell (saved in ~/.bash_history), and a user can edit or clear it. It is not an audit log. On AWS, account actions are recorded by CloudTrail; that comes later in the course.

20. Practice task

Classroom line

Don't look at someone else's screen... put in the effort yourself.

Try at home

Task 1: build and walk a tree

  1. Log in and run pwd. Write down what it shows.
  2. mkdir -p school/class1/divA school/class2
  3. cd school/class1/divA, then pwd.
  4. Go to class2 in one command, without going home. (cd ../../class2)
  5. Use cd - twice and watch where you land.
  6. Use cd alone, then pwd.

Task 2: three ways

  1. From inside divA, make notes inside school with a relative path. (mkdir ../../notes)
  2. Make exams inside school with an absolute path.
  3. Make results inside school with a ~ path.
  4. ls ~/school should show class1 class2 exams notes results.

Task 3: spaces and Tab

  1. mkdir 'my notes' 'my marks'
  2. Go into my marks using Tab. What does Tab type?
  3. Make three folders that start the same: mkdir data date dance.
  4. Practise reaching each one with the fewest letters + Tab.

Task 4: your own situations

  1. Draw a folder tree on paper, at least four levels deep.
  2. Make it with one mkdir -p line.
  3. Pick any two folders in it. Move between them with an absolute path, a relative path and a ~ path.
  4. Run history and read back what you did.
  5. When you finish, stop the instance from the console.

Classroom line

Don't forget to stop the server.

Correction

At the end of class it was said that the IP changes "on reboot". A reboot keeps the same public IP. The auto-assigned public IP changes when you stop and then start the instance (an Elastic IP stays). Also, a stopped instance still pays for its EBS disk; see the previous chapter.

Ravindra Bagale's Tip

Before every mkdir, cp or rm, ask yourself "where am I?" and run pwd if you are not sure. Most beginner mistakes happen in the wrong folder, not with the wrong command. For a compact reference of these commands, see 3.2 Navigation and 3.3 Working with files and directories.

Recap

In short

  1. SSH: ssh -i <key> ec2-user@<public IP>. Use Tab for the key path. Paste with Ctrl+V or right-click.
  2. Errors: publickey (wrong key or user), no such file (key path), timed out (IP changed after stop/start).
  3. Log in as ec2-user; use sudo for admin work. The key pair isn't tied to a user; root SSH login is blocked.
  4. An idle SSH drop comes from your router, Wi-Fi or sleep, not AWS. Up Arrow + Enter reconnects; ServerAliveInterval=60 keeps it alive.
  5. / is the top of the whole tree. /root is the root user's home, a different place.
  6. You land in /home/ec2-user. pwd prints where you are.
  7. In a path, the first / is root; the others separate names.
  8. A file holds content; a folder (directory) holds files and folders.
  9. mkdir a b c makes three folders. No output = success. Same name again = File exists.
  10. ls lists; ls -r lists in reverse.
  11. cd name goes in. The prompt shows ~ at home.
  12. cd .. up one; cd ../.. up two; cd ../../.. up three.
  13. cd alone = home. cd - = back to the previous directory.
  14. mkdir -p a/b/c makes nested folders; spaces make side-by-side folders.
  15. Absolute starts with /; relative starts from where you are; ~ is your home (the shell expands it).
  16. Calendar: four ways to make week1. One to five: three ways to make 22.
  17. Spaces: quote the name or escape with \. Better: avoid spaces.
  18. Tab completes; Tab Tab lists; type more letters when names start the same.
  19. clear wipes the screen only. history lists this user's commands; it is not an audit log.
  20. Stop the server after practice. Reboot keeps the public IP; stop and start changes it.

Samjla ka? Aaj ghari swatahachya situation banva, absolute, relative ani ~ teenhi vaapra. Pudhchya class madhe files.

Ravindra Bagale, trainer: linkedin.com/in/ravindra-bagale. The folder names (ravi, calendar, india/maharashtra/pune, one to five, tata, amazon), the user name ravi and the addresses 3.3.3.3 and 172.31.5.10 are examples for learning. Command outputs were checked with GNU bash and coreutils, the same tools Amazon Linux 2023 uses; AWS behaviour is from AWS's own documentation as of October 2026.