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Day 03 Applied Practice

Permissions and Users

Understand rwx permissions, change them with chmod, change ownership with chown, and understand sudo.

~1 hour Hands-on Precision AI Academy

Today’s Objective

Understand rwx permissions, change them with chmod, change ownership with chown, and understand sudo.

Permissions and Users is one of the most important topics in Linux in 5 Days. This lesson builds the foundation you need before moving to more advanced concepts — take time with each example and run the code yourself.

Reading Permissions

ls -la output
LS -LA OUTPUT
-rwxr-xr--  1 bo  staff  1234 Apr 10 script.sh
│└──┬──┘└──┬──┘└──┬──┘
│ │ │ └─── others: read only (r--)
│ │ └────────── group: read+execute (r-x)
│ └───────────────── owner: read+write+execute (rwx)
└───────────────────── file type: - = file, d = directory
chmod: Change Permissions
CHMOD: CHANGE PERMISSIONS
# Symbolic mode
chmod +x script.sh # add execute for everyone
chmod -w file.txt # remove write for everyone
chmod u+x script.sh # add execute for owner only
chmod go-w file.txt # remove write from group and others

# Octal mode (more common in practice)
chmod 755 script.sh # rwxr-xr-x (owner all, others read/exec)
chmod 644 file.txt # rw-r--r-- (owner rw, others read)
chmod 600 secret.key # rw------- (owner only)
chmod 700 private_dir/ # rwx------ (owner only)
chown and sudo
CHOWN AND SUDO
# Change owner
chown bo file.txt
chown bo:staff file.txt  # owner:group
chown -R bo ./mydir/ # recursive

# sudo: run as root
sudo apt install nginx
sudo systemctl restart nginx
sudo nano /etc/nginx/nginx.conf

# Switch to root (avoid where possible)
sudo -i

# See who has sudo access
cat /etc/sudoers
Permissions 755 for directories, 644 for files, 600 for secrets. This is the pattern you'll use 90% of the time. 755 = owner can do anything, everyone else can read and traverse. 600 = owner only, no one else.
📝 Day 3 ExerciseFix Permission Problems
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Supporting Resources

Go deeper with these references.

Linux Die
Linux Command Reference Comprehensive reference for Linux commands, flags, and shell built-ins.
→
DigitalOcean
Linux Basics Tutorial Series Step-by-step tutorials for new Linux users with practical examples.
→
GitHub
Bash Guide Community bash guide covering scripting, arrays, functions, and error handling.
→

Day 3 Checkpoint

Before moving on, make sure you can answer these without looking:

Continue To Day 4
Processes and System Monitoring
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