186 Linux basics [1d]

Our workstations and servers run Linux. This lesson covers the command-line tools you need every day, from file and process handling to SSH and shell scripts.

Important

Work on this lesson in advisor mode.

Learning goals

• You can look around a Linux system from the shell: files and directories, running processes, disk usage, open network ports, installed packages.
• You can explain file ownership and the nine permission flags, and change them.
• You can make a script executable and run it directly, in bash and in Ruby, using a shebang line.
• You can connect to a server with SSH and copy files to and from it, and you can explain why you log in as the deploy user and what that user may and may not touch.
• You can edit a file in a terminal editor (e.g. vim or nano) and have made it your $EDITOR.
• You use the shell efficiently: history search, tab completion, pipes, and job control to suspend and resume programs.
• You can configure your shell and tools through their dotfiles, e.g. ~/.bashrc, ~/.ssh/config, ~/.gitconfig.
• You can find out how any command works, e.g. with man, tldr or --help.

Resources

Read what's new to you, skim what's familiar, skip what you already master. Stop when you can meet the learning goals.

Your agent can also generate an overview, a tutorial or an explanation for anything here, tailored to what you already know. Just ask.

Pick one introduction

• 📘 Learn Enough Command Line to be Dangerous Show archive.org snapshot — free to read online; also in our library Show archive.org snapshot
• ▶️ The Missing Semester: Course overview + the shell Show archive.org snapshot and shell tools and scripting Show archive.org snapshot — MIT lectures with notes and exercises

For specific goals

• 📄 CLI tricks every developer should know Show archive.org snapshot — history, completion, pipes, aliases
• 📄 Linux file permissions explained Show archive.org snapshot — owner, group, the nine flags, chmod
• 📄 Job control Show archive.org snapshot — Ctrl+Z, bg, fg, jobs
• 📄 Vim cheat sheet Show archive.org snapshot — enough vim to edit a file on a server; or use nano
• 🎮 tldr — install with sudo apt install tldr; tldr ssh shows usage examples for any command (run tldr -u first if pages are missing)
• 📄 Deployments in our opsComplete deck — why you log in as the deploy user and what that user may touch

Exercises

Get around the system

Solve each task in your terminal. The commands in parentheses are hints — learn them with man, tldr or --help (get more colorful man pages).

• Find out how full your disk is, and which subdirectory of your home directory takes the most space. (df -h, du -h)
• Start bin/dev in your MovieDB, then from a second terminal: which processes belong to it, and on which TCP ports do they listen? Kill one of them by name. (ps, top, ss --listening --tcp, kill, pkill -f)
• Check whether a package is installed, search the package index for one you'd like, install it, and bring your system up to date. (dpkg -l, apt-cache search, sudo apt install, apt update, apt dist-upgrade)
• Connect to your staging server, copy a file to it and back. (ssh, scp)
• Fetch a page from your staging app and inspect the response headers; look up the server's IP. (curl, dig)
• In your MovieDB logs, find every request to a movie page — including in rotated logs. (grep with |, less, zgrep)
• Create a symbolic link and explain how it differs from a copy; update a file's timestamp without editing it. (ln -s, touch)

Configuration files

Make one improvement to each of the following files and demonstrate it:

• ~/.bashrc — e.g. an alias or a prompt tweak
• ~/.ssh/config — a Host alias, so ssh <shortname> reaches your staging server
• ~/.gitconfig — e.g. a git alias or a useful setting

Note that changes to your ~/.bashrc don't affect already opened shells.

Terminal editor

To edit files from within a terminal, you'll need a CLI editor.

• Choose an editor ( vim Show archive.org snapshot or nano Show archive.org snapshot )
  • If you chose vim, learn how to exit Show archive.org snapshot an open editor:
    • :q to exit
    • :wq to save (write) and exit
    • :q! to exit without writing
• Persist your choice in the $EDITOR variable. It defines the default for commands like git commit:

# Example with vim

# open the configuration file
vim ~/.bashrc

# navigate to the end of the file,
# press "i" to switch to insert mode
# then type out the line you want to add
export EDITOR=vim

# persist your changes
:wq

Note

While you could locally set $EDITOR to a graphical editor like gedit, this is not possible for remote shells to our servers. Getting accustomed to a CLI editor will pay off in the long term.

Terminal shortcuts

Understand what the following shortcuts do in a terminal:

• Up-arrow
• Tab
• CTRL+R
• CTRL+Z / jobs / fg / bg Show archive.org snapshot
  • This allows you to faux-multitask within a single shell. E.g. you can temporarily suspend a running vim editor, take a look around the system, then return to your vim editor.

File ownership

Understand access rights and ownership of files:

• What does "ownership" mean for files?
• Each file has 9 flags, 3 read, 3 write, and 3 executable flags. What do they mean?
• Write a simple bash script that prints a message. How can you execute it?
• Write the same script in Ruby. What do you have to do to just call it from the command line without using the ruby command directly? Learn about the "shebang".