[Updating this post as I go. Last updated: 7/7/25]
I decided to go back to basics and refresh my Linux knowledge. Here I'm recapping everything I've learnt. Useful notes here
I created a docker container running Ubuntu to practice using:
docker run -dit --name linux-learning --hostname ubuntu-dev --restart unless-stopped --cpus="2" --memory="4g" --mount type=bind,source="C:/ubuntu-data",target=/data -v /var/run/docker.sock:/var/run/docker.sock -p 2222:22 -p 8080:80 --env TZ=Europe/London --env LANG=en_GB.UTF-8 ubuntu:latest /bin/bash
Some important directories
/sbin -> System binaries for administrative commands
/bin -> Essential user binaries
/lib -> Shared libraries and kernel modules
/boot -> Stores files needed for booting the system
/usr -> Contains most user-installed applications and libraries.
/var -> Stores logs, caches, and temporary files that change frequently.
/etc -> Stores system configuration files.
/opt -> Used for installing optional third-party software
Understanding User Management
Creating users
There are 2 ways you can create a new user: useradd or adduser
useradd-> Directly modifies system files like /etc/passwd, /etc/shadow, and /etc/group to create a new user but you need to specify all options manually and by default it doesn't create a home directory unless you specify the -m flag. You also have to manually set the password for the new user using the passwd command after creating the user. Useful when writing scripts as it doesn't prompt for additional details.
adduser-> It provides a user-friendly, interactive experience by prompting you to enter a password and additional user details like full name, phone, etc. It automatically creates the home directory and uses configuration from /etc/adduser.conf for defaults.
In my case this command wasn't available by default and I had to install it using apt install adduser. You can check if you have it installed in /sbin
To see which users have been created you can check the /etc/passwd file.
User passwords are encrypted and stored in the etc/shadow file. Passwords cant be decrypted once created but can be reset using sudo passwd username.
Switching users
When switching to another user you can use either su username or su - username.
su username allows you to become that user but keep your current environment such as paths and variables and is useful for quick command execution.
su - username means you fully switch to the other user's environment including their paths, shell settings and any startup scripts.
Groups
Groups are used to organise users and manage permissions their collectively.
groupadd-> to create a new group
cat /etc/group -> to view groups
usermod -aG groupname username -> to add a user to a group
gpasswd -d username groupname -> to remove a user from a group
Understanding File Management
File Navigation
h – Move left
l – Move right
j – Move down
k – Move up
0 – Move to the beginning of the line
^ – Move to the first non-blank character of the line
$ – Move to the end of the line
w – Move to the next word
b – Move to the previous word
gg – Move to the start of the file
G – Move to the end of the file
:n – Move to line number n
Editing Text
x – Delete a character
X – Delete a character before cursor
dw – Delete a word
dd – Delete a line
d$ – Delete from cursor to end of line
d0 – Delete from cursor to beginning of line
D – Delete from cursor to end of line
u – Undo last action
Ctrl + r – Redo an undone change
yy – Copy (yank) a line
yw – Copy (yank) a word
p – Paste after the cursor
P – Paste before the cursor
Working with Multiple Files
:e filename – Open a new file
:w – Save file
:wq – Save and exit
:q! – Quit without saving
:split filename – Split screen horizontally and open another file
:vsplit filename – Split screen vertically
Ctrl + w + w – Switch between split screens
File Permissions
Change file permissions with chmod for users, groups and others.
r = 4
w = 2
x = 1
Change ownership using chown
Change user: chown user filename
Change user and group: chown user:group filename
Change group: chown :group filename or chgrp newgroup filename
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