mybonk-wiki

Baby rabbit holes

Ordered list of “basic” skills that need to be acquired to enjoy the ride.

Applies to Linux, whatever the distribution, although we use NixOS ourselves and have a section dedicated to it.

Go through this slowly. It is tempting to speed-read through a book, call it done, and move on to the next book.

To get the most out of this, take your time understanding each section.

For every 5 minutes you spend reading you should spend 15 minutes tinkering around with what you just read. Play around, copy/past, break things, have fun.

A good general cheat sheet page: https://github.com/ruanbekker/cheatsheets#readme

UNIX vs. Linux? What’s the difference?

Good read on how Unix started and influenced Linux: [https://www.redhat.com/sysadmin/unix-linux-history]

First steps with command-line

A shell is a user interface for access to an operating system’s services.

A terminal is a program that opens a graphical window and lets you interact with the shell.

It is common that the keyboard layout the system is configured with is different from the keyboard you actually use (e.g. system keyboard configured US layout but you use a keyboard with a French layout), read this article “https://www.baeldung.com/linux/console-change-keyboard-layout” to fix this.

A CLI (command-line interface) is what deal with when you interact with the shell.

RTFM!

The most important command is man which stands for “manual”. It explains what the command is and how to use it. Don’t spend hours on youtube, read the manuals. e.g.

  $ man git

  NAME
          git - the stupid content tracker

  SYNOPSIS
          git [-v | --version] [-h | --help] [-C <path>] [-c <name>=<value>]
              [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
            [-p|--paginate|-P|--no-pager] [--no-replace-objects] [--bare]
            [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
            [--config-env=<name>=<envvar>] <command> [<args>]


  DESCRIPTION
          Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.

  [...]

• Hit h for help and q to leave the manual.
• scroll through the manual using ‘arrow up’ and ‘arrow down’.
• Jump pages up and down using ‘space bar’ and ‘Shift + space bar’.
• Search for a term in a manual using / e.g. /ignore then hit:
  • n for next match
  • Shift + n for previous match
• Search for a term in all the manuals: Use apropos.

Most common commands

• System version
  • OS name and version in Linux:
    • cat /etc/os-release
  • Linux kernel version:
    • hostnamectl
• Terminal / iTerm2 (features).
  • iTerm2 hotkeys:
    • toggle maximize window: Cmd + Alt + =.
    • toggle full screen: Cmd + Enter.
    • make font larger: Cmd + +.
    • make font smaller: Cmd + -.
  • Clear the terminal window: clear.
  • Reset your terminal when it gets messed up by control sequences: reset.
• Shell:
  • bash and its history (sh, csh, tsh, ksh …).
  • zsh pronounced Z shell, is bash on steroids with extended features and support for plugins and themes, most noticeably:
    • Automatic cd: Just type the name of the directory without cd.
    • Recursive path expansion: e.x. “/u/lo/b” expands to “/usr/local/bin”.
    • Spelling correction and approximate completion: Minor typo mistakes in file or directory names are fixed automatically.
    • Plugin and theme support: This is the greatest feature of Zsh. Use Oh My Zsh manage these effortlessly (list of plugins HERE).
  • fzf (Fuzzy Finde: A tool that can change your tech life into “before” and “after” parts.

• Environment variables in Linux-based systems:

  • Read “how environment variables work” (www.howtogeek.com/668503/how-to-set-environment-variables-in-bash-on-linux)
    • $ printenv: Print all the environment variables.
      • $SHELL: The default shell being used on the system (e.x. zsh, bash …).
      • $PATH: Instructs the shell which directories to search for executables, it allows to run commands without having to specify its full path.
      • .etc…
    • $ export EDITOR=vi
    • $ echo $EDITOR
    • .etc…
• Shell commands you must know really well :
  • man: User manual of given command.
  • apropos: Search all the man pages using keywords to find commands and their functions (read this).
  • whatis: Display manual documentation pages in various ways.
  • pwd, ls, cd, type, mkdir, mv, rm, ln, which, stat, whereis, cat, head, tail, more, tee …
  • uname -a, hostname, whoami, passwd, chown, chgrp, chmod, …
  • uptime: Tell how long the system has been running.
  • ip a: Tells you the IP address of your system.
  • su/sudo, doas: Used to assume the identity of another user on the system (they are both similar tools, doas has been ported from the OpenBSD project and could be assumed “safer” than sudo as it is less error-prone e.g. when setting up somewhat complicated patterns in /etc/sudoers).
  • history
    • echo "$HISTFILE"
    • history | grep [string]: Find any record in history.
    • history -c: Remove all records.
    • history -d 1234: Remove record number 1234.
      • IMPORTANT: In Zsh this command does not work, it is an alias to fc which doesn’t have an option to delete records from the history. <workaround>
    • Don’t forget to explore ‘i-search’ and ‘reverse-i-search’ using Ctrl + s and Ctrl + r respectively; Read this if ‘i-search’ using Ctrl + s does not work.
  • alias
  • grep:
    • On a file:
      • Most basic use: all the lines containing ‘keyword’:

        $ grep 'keyword' /path/to/file.log
        

      • To also show the 5 lines before and the 2 lines after the keyword occurrences as well as highlighting the occurrences in color: $ grep -B 5 -A 2 --color 'keyword' /path/to/file.log
      • Exclude a single pattern using the the -v flag: grep -v "pattern" file:

        # journalctl -n 50 |grep -v  "sudo"
        

      • Exclude multiple patterns using the -e flag combined with the -v flag:

        # journalctl -n 50 |grep -v -e  "sudo" -e "background"
        

    • On directories: Find all files containing specific text
      • Search all the files in a given directory:

        grep -rnw '/path/to/somewhere/' -e 'pattern'
        

      • Only search through those files with .c or .h extensions:

        grep --include=\*.{c,h} -rnw '/path/to/somewhere/' -e "pattern"
        

      • Exclude searching all the files with .o extension:

        grep --exclude=\*.o -rnw '/path/to/somewhere/' -e "pattern"
        

      • Exclude one or more directories using the --exclude-dir parameter. For example, this will exclude the dirs dir1/ , dir2/ and all of them matching *.dst:

        grep --exclude-dir={dir1,dir2,*.dst} -rnw '/path/to/search/' -e "pattern"
        

    • tee: a command in command-line interpreters using standard streams which reads standard input and writes it to both standard output and one or more files, effectively duplicating its input. It is primarily used in conjunction with pipes and filters. The command is named after the T-splitter used in plumbing.
  • watch: Execute a program periodically showing output in fullscreen e.g.
  • $ watch 'du -ac -d0 /data/bitcoind/blocks'
  • $ watch -n 2 'bitcoin-cli -getinfo | grep progress'
  • md5sum: Calculates and verifies 128-bit MD5 hashes as a compact digital fingerprint of a file. There is theoretically an unlimited number of files that will have any given MD5 hash.
  • sha256: Similar to md5 but based on 256-bits, considered more secure and less prone to theoretical collisions.
  • Command to search for files through directories:
    • find /search/directory/ -name "matching file search criteria" -actions
    • find /dir/to/search -name "pattern" -print
    • find /dir/to/search -name "file-to-search" -print
    • find /dir/to/search -name "file-to-search" -print [-action]

The importance of Git / GitHub

“If your work is not on Github it does not exist”
-Ben Arc

GitHub (or GitLab or other alternative) is a platform on the Internet used for storing, tracking, and collaborating on projects. It makes it easy to share all sorts of files and collaborate with peers in an asynchronous but coordinated way. GitHub also serves as a social networking site where developers can openly network, collaborate, and pitch their work.

• Manual: $ man git
• How to fork a repository (instructions here).
• What is a “pull request”? (video explanation): https://www.youtube.com/watch?v=For9VtrQx58.

• What is stash/pop, when to use them: https://www.youtube.com/watch?v=urSlkC-6lZE.

• Commonly used:
  • Your identity
    • The first thing you should do when you install Git is to set your user name and email address. This is important because every Git commit uses this information, and it’s immutably baked into the commits you start creating:

      $ git config --global user.name "John Doe"
      $ git config --global user.email johndoe@example.com
      

  more ~/.gitconfig

  git config -l

  git config user.name

  git clone https://github.com/mybonk/mybonk-core.git

  git remote show origin

  git remote set-url: You may need to change the connection type to GitHub from https to ssh (if you use private-public keys to connect). This is done by using the git remote set-url and changing https://github.com/mybonk/mybonk-core.git by git@github.com://github.com/mybonk/mybonk-core.git.

  $ git remote set-url origin git@github.com://github.com/mybonk/mybonk-core.git
  

  git status

  git show

  git log main --graph

  git branch

  git switch

  git checkout origin/main / git checkout origin/main <file_name>

  git add . / git add -a / git add -A

  git mv filename dir/filename

  git restore --staged file-to-unstage.txt: Unstage a file in the Git index and undo a git add operation. Command introduced in 2019 as (Git 2.23). Are NOT recommended git rm (may remove the file not only from the index, but also from the repo altogether) and git reset (is “too powerful” and may result in rewriting of branch history).

  git commit -m "commit message"

  git push / git push -u origin main

  git pull

  git reflog

  git remote set-url origin https://git-repo/new-repository.git / git remote set-url <remote_name> <ssh_remote_url> / git remote -v

  git diff <dir or file name>

  git log / git log --oneline / git log -S "signet" --pretty=format:'%h %an %ad %s'

  git blame README.md (also try the options -e, -w, -M, -C, -L 1,5 )

  git stash push / git stash list / git stash pop / git stash apply

Good to know

• What is the difference between merge and rebase?
• How to Setup Passwordless Authentication for git push in GitHub.
• Switch to another branch (on the command line).
• Switch GitHub account in terminal (on the command line).

Git front ends

Using one of the following might saves you time by simplifying your interactions with Git.

• Lazygit: Nice command-line based Git front-end.
• Source Tree: Graphical GUI desktop client. Here is are good simple tutorials to get started.

• Ungit: “The easiest way to use git. On any platform. Anywhere.”

• Magit!: Version control system Git, implemented as an Emacs package.

GitHub CLI

Command-line tool that brings pull requests, issues, GitHub Actions, and other GitHub features to your terminal, so you can do all your work in one place.

Authenticate with your GitHub account:

$ gh auth login

Text processing

• vi (cheat-sheet HERE)
  • $ vi +132 myfile: Open myfile on line 132
• sed (https://www.gnu.org/software/sed/manual/sed.html): “stream editor” for editing streams of text too large to edit as a single file, or that might be generated on the fly as part of a larger data processing step: Substitution, replacing one block of text with another.
• awk (https://github.com/onetrueawk/awk/blob/master/README.md): Programming language. Unlike many conventional languages, awk is “data driven”: you specify what kind of data you are interested in and the operations to be performed when that data is found.
• jq: Lightweight and flexible command-line JSON parser/processor. reference
• rg (also known as ripgrep): Recursively search the current directory for lines matching a pattern, very useful to find whatever document containing whatever text in whatever [sub]directory.
  • $ rg what_i_am_looking_for MyDoc_a.php MyDoc_b.php Look for string ‘what_i_am_looking_for’ in MyDoc_a.php and MyDoc_b.php
  • $ rg what_i_am_looking_for MyDoc.php -C 2: Return results with context, displaying 2 lines before and 2 lines after the match in the output. Also try the options -B and -A (number of lines before and after the match).
  • $ rg 'Error|Exception' MyDoc.php: Searches the file for either Error or Exception.
  • $ rg 't.p' MyDoc.php: Looks for a t and a p with any single character in between.
  • $ rg ssl -i: Recursively searches for instances of ssl in a case-insensitive manner.
  • $ rg service /etc/var/configuration.nix -i: Recursively searches a specific directory for instances of service in a case-insensitive manner.
  • rg -g 'comp*' key Searches only for the pattern key in files beginning with the substring comp.
  • -l option to only list the files having a match without additional details/
  • -i option for case-insensitive search.
  • -S option for smart case search.
  • -F option to treat the search string as a string literal (regex syntax).
  • $ rg --type-list List of the available file types.
  • $ rg key -t json Restricts the search for the pattern key to json files only.
• more, less, most: Terminal pagers. They are used to view files page by page, and/or line by line, each having their own prominent feature or advantage.
• pandoc: Pandoc is best described as a “universal document converter”. It can convert between numerous markup and word processing formats including various flavors of Markdown, HTML, Word docx, pdf .etc…
  Example to render README.md so that it is nicely formatted and readable on a terminal:

  $ pandoc -t plain README.md | less
  

File processing

• $ tar -xvf myfile.tar.gz: Untar a file.

File system / Block devices

• lsblk: List information about the system’s available or the specified block devices (e.g. disks, USB sticks …).
• Test block device performances: hdparm -t --direct /dev/sda1 (if not installed run nix-shell -p hdparm).
• df: “Disk Free” displays disk usage:
  • df -hT. -h for “human readable”, add -T to display the type of the filesystem.
  • df -hT .. ‘.’ for whatever partition the current directory is residing on.
  • df -hT -t ext4. -t ext4 to display only filesystems of type ext4.
  • df -hT -x squashfs -x overlay -x tmpfs -x devtmpfs to hide given filesystem types from the output.
• du: “Disk Usage” to get space usage of directory/subdirectory.
  • $ du -h /data. -h for “human readable”.
  • $ du -s /data. -s for “summary”.
  • $ du -ah --time. Shows the time of the last modification to any file in the directory or subdirectory. --time with the -ah flags is very useful e.g. someone writes files somewhere by accident and you need to find where.
• fdisk: Dialog-driven program to see and manipulate disk partition table:
  • fdisk -l: List the system’s partition scheme.
  • fdisk -l | grep "Disk /": See all the available disks.
  • fdisk /dev/sdc: Enter the interactive mode to manipulate the partition table of the disk /dev/sdc

• mkfs.ext4 /dev/sdc1: Formats the partition /dev/sdc1 in ext4 file system format.

• Interesting threads about ZFS:
  • “what is the point of ZFS with only 1 disk”.
  • “benefit/risk of ZFS with only 1 disk” (also includes the commands for a little ZFS experimentation).

    cURL

    Great tutorial on how to use cURL: https://curl.se/docs/httpscripting.html

• $ curl -O https://testdomain.com/testfile.tar.gz: Download the file testfile.tar.gz.
• $ curl -o mydownload.tar.gz https://testdomain.com/testfile.tar.gz (little ‘o’): Download to the file mydownload.tar.gz.
• $ curl -I https://www.google.com: Query the header of a server (same as -head).
• $ curl -k https://localhost/my_test_endpoint: Ignore invalid or self-signed certificates (same as --insecure).
• Make a POST request (through parameters and JSON):
  • $ curl --data "param1=test1&param2=test2" http://test.com
  • $ curl -H 'Content-Type: application/json' --data '{"param1":"test1","param2":"test2"}' http://www.test.com
• $ curl -X 'PUT' -d '{"param1":"test1" "param2":"test3"}' \http://test.com/1: Specify a type of request (here ‘PUT’).
• $ curl -u <user:password> https://my-test-api.com/endpoint1: Basic Authentication for various protocols (same as -user).
• Update name resolution: test an API before deploying and want to hit in the endpoint in the test machine rather than the actual endpoint, you can pass in a custom resolution for that request: Works similarly to /etc/hosts host-resolution.
• Upload a file: curl with the -F option emulates a filled-in form when the user has clicked the submit button. This option causes curl to POST data using the Content-Type multipart/form-data:
  • $ curl -F @field_name=@path/to/local_file <upload_URL>
  • $ curl -F @field_name=@path/to/local_file_1, @field_name=@path/to/local_file_2, @field_name=@path/to/local_file_3, <upload_URL>
• $ curl -w "%{time_total}\n" -o /dev/null -s www.test.com: Use -w to display information (stdout) after a transfer. total_time is one of the interesting parameters curl returns

wget

• Download a complete remote directory, includes no parent and recursive to only get the desired directory.$ wget --no-parent -r http://WEBSITE.com/DIRECTORY

Cryptography

• The difference between seed words and private key: https://youtu.be/Y_A3j8GzaO8

Remote Access

Spare yourself the pain, learn good habits, save tones time and avoid getting locked out of your system by really understanding how SSH (a.k.a Secure Shell or Secure Socket Shell) works, how it allows you to connect a remote machine, execute commands, upload and download files.

• For history, what is the difference between Telnet and ssh
• OpenSSH
• .ssh client configuration (~/.ssh/config)
• How to setup and manage ssh keys: https://goteleport.com/blog/how-to-set-up-ssh-keys/
  • ssh-keygen e.x. $ ssh-keygen -t ecdsa -b 521, ssh-keygen -R 5.72.114.57
  • passphrase
  • ssh-copy-id: Copy your public key on the server machine’s ~/.ssh/authorized_keys
  • ssh-add
  • ssh-agent, will save you a LOT of time (key management, auto re-connect e.g. when your laptop goes to sleep or reboots …).

Use ssh auto login (auto login using public and private keys pair to be specific) as it is also significantly more secure than basic password-based login. Bellow is a real time illustration of ssh failed login attempts initiated from the Internet (bots, hackers, you name it) on a machine with password authentication left enabled (instead of using ssh auto login).

For reference:

$ssh root@192.168.0.155
#

IP addresses (here 192.168.0.155) are not “human friendly”. You can associate an IP address to an arbitrary name, easier to remember. This can be configured in your ssh configuration file ~/.ssh/config. Here is an example in its simplest form:

Host console_jay
  HostName 192.168.0.155
  User root

You can now use the following simple syntax instead to connect:

$ssh console_jay

This is all very nice until you change environment or move your hardware to another network: A new IP address will be assigned to the machine and the shorthand console_jay will no longer work, you now have to figure out what the new IP address of your machine (scan the network or physically connect to serial) which is frustrating and time consuming.

A more effective way to deal with this issue and streamline remote access altogether is to use WireGuard/Tailscale. Tailscale basically hides all the nitty gritty of ssh by managing the VPN for you in the background.

Have a look at this Tailscale Quick tutorial.

To enable Tailscale:

• Create credentials on https://login.tailscale.com.
• Install and run the Tailscale service on each machines you want to have remote access to.
• Attach each of the machines to the VPN.

With tailscale on you can now refer to your remote machine anytime anywhere through its Tailscale “Magic DNS” name:

$ tailscale ssh console_jay@dab-dominant.ts.net

Or even just:

$ tailscale ssh console_jay

Note that Tailscale’s “Magic DNS” and ssh commands are transparently wrapped through the Tailscale VPN. So $ ssh console_jay will work as well as $ tailscale ssh console_jay.

Commonly used:

# tailscaled
$ tailscale help
$ tailscale login
$ tailscale up
$ tailscale down
$ tailscale status
$ tailscale netcheck
$ tailscale ssh console_jay

rsync

rsync uses a delta transfer algorithm and a few optimizations to make the operation a lot faster compared to scp. The files that have been copied already won’t be transferred again (unless they changed since). Can be run ad-hoc on the command line or configured to run as a deamon on the systems to keep files in sync.

rsync allows to restart failed transfers - you just reissue the same command and it will pick up where it left off, whereas scp will start again from scratch.

rsync needs to be used over SSH to be secure:

• Example 1: From local to local (instead of using scp):

  $ rsync -avhW --progress --exclude --exclude '*/*.lock' /unmountme/bitcoind/{blocks,chainstate,indexes} /data/bitcoind
  

• Example 2: Same thing but also gives a visual indication of the copy progress as well as completion time estimate (‘ETA’):

  $ rsync -avhW --stats --exclude '*/*.lock' --human-readable /unmountme/bitcoind/{blocks,chainstate,indexes} /data/bitcoind | pv -lep -s $(find /unmountme/bitcoind/{chainstate,blocks,indexes} -type f | wc -l)
  

  Network

  ### Speed test

• https://www.speedtest.net ### Scanners

• findssh: Super quick command line tool that scans an entire IPv4 subnet in less than 1 second. Without NMAP. It is extremely quick but sometimes it misses some hosts so run it a couple of time to be sure it scanned them all.

  Example to scan the complete network for sshd listening:

  $ python3 -m findssh -b 192.168.0.1 -s ssh -v
  searching 192.168.0.0/24
  DEBUG:asyncio:Using selector: EpollSelector
  DEBUG:root:[Errno 111] Connect call failed ('192.168.0.19', 22)
  (IPv4Address('192.168.0.82'), 'SSH-2.0-OpenSSH_8.4p1 Debian-5+d')
  (IPv4Address('192.168.0.136'), 'SSH-2.0-OpenSSH_9.1')
  (IPv4Address('192.168.0.106'), 'SSH-2.0-OpenSSH_8.4p1 Debian-5+d')
  DEBUG:root:[Errno 111] Connect call failed ('192.168.0.150', 22)
  (IPv4Address('192.168.0.100'), 'SSH-2.0-OpenSSH_7.4')
  DEBUG:root:[Errno 111] Connect call failed ('192.168.0.44', 22)
  

• Angry IP Scanner: Scans LAN and WAN, IP Range, Random or file in any format, provides GUI as well as CLI.

### Tor

• .onion
• tor hidden services
• Tor browsers (https://www.torproject.org/download/)
• torify / torsocks

### I2P

• Tor vs I2P (https://www.cloudwards.net/i2p-vs-tor/)

tmux & tmuxinator

… or alternatives like GNU Screen, Terminator, Byobu, .etc…

tmux for beginners:

• part 1: https://dev.to/iggredible/tmux-tutorial-for-beginners-5c52
• part 2: https://dev.to/iggredible/useful-tmux-configuration-examples-k3g

$tmux source-file ~/.tmux.conf

$tmux new -s MY_SESSION

$tmux list-keys

$tmux list-sessions / $tmux ls

$tmux kill-session -t name_of_session_to_kill : Kills a specific session.

$tmux kill-session -a : Kills all the sessions apart from the active one.

$tmux kill-session : Kills all the sessions.

tmux kill-server : Kills the tmux server.

tmux-resurrect and tmux-continuum: Tmux plugins to persist sessions across restarts.

tmux shortcuts

• Sessions
  • List sessions and switch to a different session: Prefix + s (or tmux ls followed by tmux attach -t SESSION).
  • Detach a session: Prefix + d or tmux detach
  • Kill a session: tmux kill-session -t MY_SESSION
• Windows:
  • Create a window: Prefix + c or tmux new-window -n MY_WINDOW
  • Close a pane / window: Ctrl + d or Prefix + x
  • Switch to a different window: Prefix + n (next), Prefix + p (previous) and Prefix + N (where N is the window index number, zero-based).
  • Kill a window: tmux kill-window -t MY_WINDOW
• Panes
  • List all the panes: Prefix + q (or tmux list-panes).
  • Jump into a specific pane: Prefix + q followed by the pane number you want to jump into.
  • Move to next pane: Prefix + o
  • Switch to last pane: Prefix + ;

    tmuxinator

tmuxinator is a tool that allows you to easily manage tmux sessions by using .yaml files to describe the layout of a tmux session, and open up that session with a single command.

• tmuxinator new [project]: Create a new project file with given name and open it in your editor.
• tmuxinator list: List all tmuxinator projects.
• tmuxinator copy [project] [copy_of_project]: Copy an existing project to a new project and open it in your editor.
• tmuxinator delete [project_a] [project_b] ...: Deletes given project(s).
• tmuxinator start -p your_tmuxinator_config.yml: Start tmuxinator using custom configuration file (as opposed to it picking it up from default location like ˜/.config/tmuxinator\).
• tmuxinator start console -n "console_jay" extra_param="any_string": Start a session console, assign it project name “console_jay” and extra arbitrary parameter “extra_param” to pass value “any_string”.
• tmuxinator stop [project]: Stop a tmux session using a project’s tmuxinator config.

processes

• ps, pstree, top
• systemd
  • man systemd.unit
  • man systemd.service
  • man systemd.directives
• hostnamectl: Query and change the system hostname and related settings.
  • hostnamectl status
  • hostnamectl hostname: Query hostname.
  • hostnamectl hostname <name>: Change hostname.

• systemctl

  • systemctl status
  • systemctl status bitcoind
  • systemctl start bitcoind
  • systemctl restart bitcoind
  • systemctl stop mempool fulcrum
  • systemctl enable --now bitcoind

  • systemctl disable bitcoind

  • systemctl list-unit-files --type service -all: List all the services on your system and their status.
  • Show all the running processes: systemctl --type=service --state=running (where --state can be any of running, dead, exited, failed or inactive).
  • systemctl daemon-reload: Reload systemd files. If you change a service file in /etc/systemd/system/, they will be reloaded.
  • systemctl cat bitcoind: Show the service definition.
  • systemctl show bitcoind: Show the service parameters.
• journalctl
  • Show only kernel messages: journalctl -k
  • Show messages from a specific boot (most recent by default or from specified BOOT_ID): journalctl -b
  • As previous but displays only the errors, if any: journalctl --no-pager -b -p err
  • List previous boots: journalctl --list-boots
  • Display the timestamps in UTC: journalctl --utc
  • journalctl --since "2015-01-10" --until "2015-01-11 03:00"
  • journalctl --since yesterday
  • journalctl --since 09:00 --until "1 hour ago"
  • journalctl -p err -b where option ‘-p’ can be any of:
    • 0: emerg
    • 1: alert
    • 2: crit
    • 3: err
    • 4: warning
    • 5: notice
    • 6: info
    • 7: debug
  • journalctl --no-full
  • journalctl --no-pager
  • journalctl -b -u bitcoind -o json

  • journalctl -b -u bitcoind -o json

  • journalctl -u bitcoind.service
  • journalctl -u bitcoind.service -u clightning.service --since today
• logger: Write messages directly to Log Files.

certificate

• authority
• expiration
• update

  http vs. https

  OS-layer firewall

What is the difference between IPtables and UFW Linux firewalls?

UFW is built upon IPtables, IPtables a very flexible tool but it’s more complex as compared to UFW. Also IPtables requires a deeper understanding of TCP/IP, which might not be the case with every Linux user, so UFW is the solution. UFW allows the user to configure firewall rules easily using IPtables under the hood. Hence, for an average Linux user UFW is the best way to get started with setting up different firewall rules.

We discuss and use UFW in our scope.

In NixOS the following commands are replaced by parameters in the configuration file (networking.firewall.allowTCPPorts .etc…) you should not run them manually.

• $ sudo ufw allow 9999: Open port 9999.
• $ sudo ufw enable: In case ufw is not running (check with sudo ufw status).
• $ netstat -ano: See what ports are open and what processes uses to them.

partitions / filesystems

• findmnt: Lists all mounted filesytems or search for a filesystem. It is able to search in /etc/fstab, /etc/fstab.d, /etc/mtab or /proc/self/mountinfo. If device or mountpoint is not given, all filesystems are shown.
  • /
  • /mnt
  • /var
  • /etc
  • /tmp
  • /lib
  • .etc…

UEFI vs. Legacy Boot

Other tools / resources

• SSHFS: Tool to safely mount a remote folder from a server to a local machine. The client extends the SSH file transfer protocol, which helps locally mount a remote file system as a disk image securely.
• Gocryptfs: Tool to perform file-based encryption. It’s fast, lightweight, well-documented. In contrast to disk-based encryption software, which operates on whole disks, gocryptfs works on individual files that can be backed up or synchronized efficiently using standard tools like sshfs or rsync. Read more about it HERE.
• VirtualBox: By Oracle Corporation. Simple, Cross-platform, Open-source, great performances, all-in-one, virtual machine program. Even though it is primarily fit for desktop usage, it can be run in headless mode.
• QEMU: Open-source machine virtualizer and emulator. It supports a wide range of hardware architectures and guest operating systems. Coupled with KVM it runs VMs that perform well because KVM is hardware-level virtualization and QEMU is a software-level virtualization. Technically, QEMU is a type-2 hypervisor.
• QuickEMU: Terminal-based tool that lets you rapidly create optimized desktop virtual machines and manage them with ease. The tool chooses the best configuration by default as per available system resources. It also downloads the image for the selected operating system. All you have to do is install the operating system as you would normally do and get started.
• QuickGUI: Makes it convenient to utilize Quickemu’s abilities to quickly create and manage multiple VMs without needing to configure anything. What’s more interesting: you do not need elevated privileges to make it work.
• KVM: “Kernel-based Virtual Machine” Baked into Linux. You can run VMs out of the box. It is a “type-1 hypervisor” a.k.a “hardware-based”. It converts the Linux host into a hypervisor to run virtual machines with bare metal performance. You can create guest/virtual machines of different operating systems too. Have a look at QuickEMU and QuickGUI for tools to make your life easier.
• WSL: Windows Subsystem for Linux to run ELF64 Linux binaries on Windows (if you have Windows system but would like to run Linux programs and commands this is what you need if you prefer not to use a full fledged virtual machine).
• multitail: MultiTail lets you view multiple files like the original tail program. The difference is that it creates multiple windows on your console (ncurses). It can also monitor wildcards: if another file matching the wildcard has a more recent modification date, it will automatically switch to that file.
• websocketd: Small command-line tool that will wrap an existing command-line interface program, and allow it to be accessed via a WebSocket. WebSocket-capable applications can now be built very easily. As long as you can write an executable program that reads STDIN and writes to STDOUT, you can build a WebSocket server. No networking libraries necessary.
• wscat: WebSocket cat.
• Benchmaring
  • time: The simplest, shell built-in, tool to measure a command execution time.
  • Use the $ free -m command to check your Linux memory usage.
  • lshw: Small tool to extract detailed information on the hardware configuration of the machine. It can report on memory, firmware version, mainboard configuration, CPU version and speed, cache configuration, bus speed, etc. in various output format. e.x. $ lshw -short, $ lshw -json…
  • powertop: Tool to access various powersaving modes in userspace, kernel and hardware. Monitors processes and shows which utilizes the most CPU allowing to identify those with particular high power demands.
  • stress-ng: Stress test a computer system in various selectable way.
  • Byte UNIX Bench: Since 1983, provide a basic indicator of the performance of a Unix-like system; hence, multiple tests are used to test various aspects of the system’s performance.
  • geekbench: Simple tool to quickly benchmark a system’s performance (How to run on Linux)
  • iperf3: Simple tool to quickly benchmark the maximum achievable bandwidth on IP networks.
    • Run iperf3 as a server: iperf3 -s
    • Run an iperf3 server on a specific port: iperf3 -s -p port
    • Start bandwidth test: iperf3 -c server
    • Run iperf3 in multiple parallel streams: iperf3 -c server -P streams
    • Reverse direction of the test. Server sends data to the client: iperf3 -c server -R
  • lscpu: Part of util-linux, command to display information about the CPU architecture.
  • lsmem: Part of util-linux, command to list the ranges of available memory with their online status.
  • memtester: Effective userspace tester for stress-testing the memory subsystem. It is very effective at finding intermittent and non-deterministic faults.
  • memusage: Profile memory usage of a program.
  • dmesg: Shows Kernel Messages.
  • dmesg -n 1: Temporarily suppress all kernel logging to the console.
• inxi: A full featured CLI system information tool, example:
  • $ inxi -Fxzb --usb
• tree: Outputs a depth-indented listing of files making it easy to visualize the organization of files and directories within a given path. With no arguments the tree lists the files in the current directory. When directory arguments are given, the tree lists all the files or directories found in the given directories each in turn.
• pv: Pipe Viewer, command-line tool that allows to monitor data being sent through pipe. It provides the ability to monitor progress of a given application (time elapsed, completed progress, data transfer speed, ETA).
• glances utility: System cross-platform monitoring tool. It allows real-time monitoring of various aspects of your system such as CPU, memory, disk, network usage etc. as well as running processes, logged in users, temperatures, voltages etc.
• htop: Similar to glances above.

• btop: Similar tool to glances and htop above.

• VPN / tunnels
  • Wireguard This VPN technology is built into the kernel; Client apps widely available (e.x. Tailscale), allows to connect to your local network remotely using a simple QR code to authenticate.

  • Tailscale: Quick tutorial Rapidly deploy a WireGuard-based VPN, a “Zero-config VPN”: Automatically assigns each machine on your network a unique 100.x.y.z IP address, so that you can establish stable connections between them no matter where they are in the world, even when they switch networks, and even behind a firewall. Tailscal nodes use DERP (Designated Encrypted Relay for Packets) to proxy encrypted WireGuard packets through the Tailscale cloud servers when a direct path cannot be found or opened. It uses curve25519 keys as addresses.

  • Zerotier: Another VPN alternative.
  • ngrok: Exposes local networked services behinds NATs and firewalls to the public internet over a secure tunnel. Share local websites, build/test webhook consumers and self-host personal services.
    • Sign up (or login) to get a TOKEN then run: $ ngrok config add-authtoken TOKEN
    • $ ngrok http 8000
• ecash system
  • How To Make a Mint: The Cryptography Of Anonymous Electronic Cash by Laurie Law, Susan Sabett, Jerry Solinas, NSA (National Security Agency), 18 June 1996. (Did the NSA create bitcoin?).
  • Cashu: Cashu is a free and Open-source Chaumian ecash system built for Bitcoin. Cashu offers near-perfect privacy for users of custodial Bitcoin applications. Nobody needs to knows who you are, how much funds you have, and whom you transact with.
• XSATS.net: bitcoin/sats to and from world currencies, spot price or for any given date.
• md5calc: Website to calculate the Hash of any string.

Common bitcoin-related commands

• Check bitcoin deamon is running:

  $ systemctl status bitcoind
  

Using bitcoin’s command line interface bitcoin-cli

bitcoin-cli is the most straightforward way to execute bitcoin RPC commands (full list of RPC commands), here are some of the most commonly used:

• $ bitcoin-cli -getinfo
• $ bitcoin-cli getblockchaininfo
• It is a good idea to pipe through jq to get pretty JSON output formatting or extract specific data, for instance:
  • $ bitcoin-cli getblockchaininfo | jq '.'
  • $ bitcoin-cli getblockchaininfo | jq '.verificationprogress'
• General Info
  • $ bitcoin-cli help
  • $ bitcoin-cli help getblockchaininfo
  • $ bitcoin-cli getblockchaininfo
  • $ bitcoin-cli getpeerinfo
  • $ bitcoin-cli getnetworkinfo
  • $ bitcoin-cli getmininginfo
• Block Info
  • $ bitcoin-cli getblockcount
  • $ bitcoin-cli getbestblockhash
  • $ bitcoin-cli getblock <hash>
  • $ bitcoin-cli getblockhash <index>
• Transaction Info
  • $ bitcoin-cli getwalletinfo
  • $ bitcoin-cli createwallet
  • $ bitcoin-cli listreceivedbyaddress 0 true: List of accounts on the system.
  • $ bitcoin-cli setaccount 1GBykdD628RbYPr3MUhANiWchoCcE52eW2 myfirstaccount: To associate an existing address (here : 1GBykdD628RbYPr3MUhANiWchoCcE52eW2) to an account name.
  • $ bitcoin-cli sendfrom myfirstaccount 1AYJyqQHCixxxxxxffevxxxxQosCWqn1bT 0.15: Send bitcoins (here : 0.15) to an address (here : 1AYJyqQHCixxxxxxffevxxxxQosCWqn1bT)
  • $ bitcoin-cli getrawmempool
  • $ bitcoin-cli getrawtransaction <txid>
  • $ bitcoin-cli decoderawtransaction <rawtx>

Using bitcoin JSON-RPC API calls

The bitcoin JSON-RPC API allows to interact with bitcoin deamon in a varierty of ways: cURL, JavaScript, Python …

First you need to make sure Bitcoin Core is setup to accept Remote Procedure Calls (RPC):

For instance you could run getnetworkinfo using the following cURL:

curl -u public:2S8PWBZ71wMXdrsAxL21 -d '{"jsonrpc": "1.0", "id": "curltest", "method": "getnetworkinfo", "params": [] }' -H 'content-type: text/plain;' http://mybonk-jay:8332/

Most noticably you need to use the option -u (or --user) to pass valid crenentials (here username public and password 2S8PWBZ71wMXdrsAxL21) allowing you to connect else you will get an 401 Unauthorized error. Username is either public or priviledged, their password in /etc/nix-bitcoin-secrets/bitcoin-rpcpassword-{public|priviledged}.

Also make sure that the method you call (getnetworkinfo, getpeerinfo, listwallets…) is indeed in the RPC whitelist else you will get a

You can use curl with the -v (verbose) parameter to see the headers sent: The text after the Basic keyword is the base64 encoded text string of the username:password combination that was passed with the -u parameter.

Authorization: Basic cHVibGljOjJTOFBXQlo3MXdNWGRyc0F4TDIx

To manually generate the base64 encoded credentials on Linux, you can simply call:

$ echo -n "username:password" | base64 -w0
cHVibGljOjJTOFBXQlo3MXdNWGRyc0F4TDIx

To test this end to end, you can remove -u username:password and substitute with -H Authorization: Basic cHVibGljOjJTOFBXQlo3MXdNWGRyc0F4TDIx and it will still authenticate just fine:

$ curl -v -d '{"rpc": "1.0", "id": "curltest", "method": "getnetworkinfo", "params": [] }' -H 'content-type: text/plain;' -H 'Authorization: Basic cHVibGljOjJTOFBXQlo3MXdNWGRyc0F4TDIx' http://mybonk-jay:8332/

In conculsion, you could even run these RPC commands without using cURL: You would just need to base64 encode the username:password combination and set the HTTP Authorization header with the type as Basic along with the base64 encoded string.

Common clightning-related commands

This is a nice cheatsheet for https://github.com/grubles/cln-cheatsheet

• Check bitcoin deamon is running:

  $ systemctl status clightning
  

  Using clightning’s command line interface lightning-cli

  lightning-cli is simply a wrapper over core-lightning JSON RPC to interact with the lightning deamon, and print the result.

  $ lightning-cli --version
  $ lightning-cli help
  

• Complete list of all JSON-RPC commands: HERE
• Simple examples:

  $ lightning-cli --version
  $ lightning-cli help
  $ lightning-cli getchaininfo
  $ lightning-cli getinfo
  

  Something fun to do is to stream stats from one node (the “source”) to another (the “destination”):

• On the “source” machine run the following command to send 100 times between 2000 and 65000 sats using keysend to node with pubkey 0278e764e98cf94ef1f33684bac0f7cc85b3d445465cc4c0171d07107079aaf4cc (replace by the pubkey of your destination node):

  $ for i in {1..100}; do lightning-cli keysend 0278e764e98cf94ef1f33684bac0f7cc85b3d445465cc4c0171d07107079aaf4cc `shuf -i 2000000-65000000 -n 1`; done
  

• Now on the “destination” machine run the following command to observe lightning channels grow as the payments are processed:

  $ watch "lightning-cli listfunds | jq '.channels[] | .our_amount_msat'"
  

Another example is sending funds onchain using lightning-cli, which is also possible.

• Generate a new bitcoin address (bech32 address format by default):

  $ lightning-cli newaddr
  {
    "bech32": "tb1qmws65ajdzfk3etqzumfk9ujumjhj8tgvk7rwys"
  }
  

• Now send funds to the address you have generated in the previous step:

  $ lightning-cli withdraw tb1qmws65ajdzfk3etqzumfk9ujumjhj8tgvk7rwys 10000000
  

  The command will take a couple of seconds to complete and will return the txid (transaction id) along with other data. The command withdraw has a few optional parameters, have a look at its documentation.

Using clightning JSON-RPC API calls

Similarly to the bitcoin JSON-RPC, the clightning JSON-RPC API allows to interact with clightning deamon in a varierty of ways: cURL, JavaScript, Python …

Corelightning documentation is very well done with clear examples.

Podcasts

• Citadel Dispatch #37, Sep 2021: Building software from source code, reproducible builds, reducing trust, coin selection, coin control, coinjoin
• Citadel Dispatch #42, Nov 2021: Security focused bitcoin nodes with @nixbitcoinorg, @n1ckler, and @seardsalmon
• nixbitcoin-dev with Stefan Livera: A security focused bitcoin node.

Other projects and references

• Seed-signer: Bitcoin only, Open-source, offline, airgapped Bitcoin signing device. Can also DIY.
• Blockstream Jade: Bitcoin only, Open-source hardware wallet. Can also DIY.
• Hardware Wallets comparison and audit.
• BIP39: Play around and understand 12 vs 24 word seed (mnemonic) length, does it make a difference? Entropy, splitting scrambling … (don’t forget to generate a random mnemonic and select the option “Show split mnemonic cards” to see how much time it would take to brute-force attack).
• Other package managers:
  • Homebrew
    • $ brew search android-platform-tools
    • $ brew install android-platform-tools
    • $ brew info android-platform-tools
    • $ brew remove android-platform-tools
  • apt
  • Tea

    Federations

• FEDIMINT (by Fedi):
  • Explanation video by Obi and Justin (Bitcoin Miami 2023): https://www.youtube.com/watch?v=_ByXD659Tcc.
  • Fedimint on GitHub.
  • Telegram:
    • @fedimint
    • @fedibtc
  • Discord.
• LIQUID (by Blockstream)
  • …
  • ..

For developers

• Great Nix language tour: https://nixcloud.io/tour
• The difference between RPC and REST
• HTTP-TRACKER Chrome extension: Allows to inspect HTTP request headers, cookies, data, response Headers, cookies and even add/modify request headers before sending requests.
• Poetry2nix: Developping Python with Poetry & Poetry2Nix: Reproducible, flexible, Python environments.
• Polar: One-click Bitcoin Lightning Networks for local app development & testing.
• Rust: Multi-paradigm, general-purpose programming language that emphasizes performance, type safety, and concurrency. It enforces memory safety—ensuring that all references point to valid memory—without requiring the use of a garbage collector or reference counting present in other memory-safe languages.
• Cargo: Package manager for Rust.
• Just: Just is a handy little tool to save and run project-specific commands.
• DuckDNS: Allows to get free dynamic DNS (forces ‘KYC’ by login using Github, Twitter, reddit or Google account). Good for testing.
• How to compile Bitcoin Core and run the unit and functonal tests: https://jonatack.github.io/articles/how-to-compile-bitcoin-core-and-run-the-tests
• asciinema: Record and share your terminal sessions, the simple way.

Books

• Introduction to the Mac command line (on GitHub).
• Learn Bitcoin from the command line (on GitHub)
• Mastering the Lightning Network (on GitHub).
• The NixOS and Flakes book: The NixOS and Flakes book.

NixOS/Nix specific

If you are actualy running NixOS operating system (as opposed to just Nix which is the package manager), you can lookup the currently active NixOS configuration. For example:

$ nixos-version
23.05.20230915.360a7d3 (Stoat)

Of course you also use the traditional Linux commands to know more:

• OS name and version in Linux:
  • cat /etc/os-release

      BUG_REPORT_URL="https://github.com/NixOS/nixpkgs/issues"
      BUILD_ID="23.05.20230915.360a7d3"
      DOCUMENTATION_URL="https://nixos.org/learn.html"
      HOME_URL="https://nixos.org/"
      ID=nixos
      LOGO="nix-snowflake"
      NAME=NixOS
      PRETTY_NAME="NixOS 23.05 (Stoat)"
      SUPPORT_END="2023-12-31"
      SUPPORT_URL="https://nixos.org/community.html"
      VERSION="23.05 (Stoat)"
      VERSION_CODENAME=stoat
      VERSION_ID="23.05"
    

• and: $ hostnamectl

     Static hostname: mybonk-jay
         Icon name: computer-vm
           Chassis: vm 🖴
        Machine ID: b93a6b5ab0384df583b2f691e312314c
           Boot ID: 82b819d538bd4a1a93ec046fc81111e5
    Virtualization: kvm
  Operating System: NixOS 23.05 (Stoat)
    OS Support End: Sun 2023-12-31
  OS Support Expired: 10month 5d
            Kernel: Linux 6.1.52
      Architecture: x86-64
   Hardware Vendor: 
    Hardware Model: vServer
  Firmware Version: 20171111
     Firmware Date: Sat 2017-11-11
  

Common Nix commands

• Nice Nix cheat sheet:
  • https://github.com/brainrake/nixos-tutorial/blob/master/cheatsheet.md
• Search the Nix ecosystem:
  • https://search.nixos.org: Search Nix packages, NixOS options, Flakes.
  • https://noogle.dev: Search nix functions based on type, name, description, example, category .etc..
• NixOS the “traditional” vs. the “Flakes” way:
  • Flakes have been introduced with Nix 2.4
  • Although still flagged as “experimental” feature it is the way forward, we advise you to learn Flakes already.
• nix --version: Get running nix version.
• nix-info -m
• nix-shell: Start an interactive shell based on a Nix expression. This is distinct from nix shell (great explanation of the difference between ‘nix-shell’ and ‘nix shell’).
• nix-build: Build a Nix expression. This is distinct from nix build.
• nix-channel
• nix-collect-garbage
• nix-copy-closure
• nix-deamon
• nix-env
• nix-hash
• nix-instantiate (same as nix-instantiate default.nix)
  • nix-instantiate --eval: Very easy way to evaluate a nix file.
  • nix-instantiate --eval --strict: --strict tries to evaluation the entire result (otherwise may return <CODE> blocks).
  • nix-instantiate --eval --json --strict: Always use --strict with --json (otherwise <CODE> blocks may result in json not being able to parse).
  • Similarly with Flakes enabled you could use nix eval -f default.nix. Note that nix eval behaves as --strict (tries to evaluation the entire result).
• nix-prefetch-url
• nix-store

nix repl

• Use nix repl to interactively explore the Nix language as well as configurations, options and packages.
  • Video: Running Nix Code: nix eval and nix repl.

  

    $ nix repl
    Welcome to Nix 2.15.0. Type :? for help.
  
    nix-repl>  
  

  • Use :? to get help on the commands

  • Use :q to quit nix-repl.

  • You can use autocomplete (tab, tab) from within nix-repl.
  • Get the documentation of a built-in function :doc, for instance:

    nix-repl> :doc dirOf
    

  • Show the logs for a derivation use :log, for instance:

      nix-repl> builtins.readFile drv
      "Hello world"
      nix-repl> :log drv
      Hello world
    

  • load nixos configuration from a nix file (not Flake):

    $ nix repl --file '<nixpkgs/nixos>' -I nixos-config=./configuration.nix
    

  • Add everything that you see passed to modules: options, config, pkgs, lib, and the other “Special ones”:

    $ nix repl>:l <nixpkgs/nixos>
    

  • Similarly on Flake systems:

    $ nix repl>:lf /etc/nixos
    $ nix repl>nixosConfigurations.<hostname>
    

Garbage collection:

• Ref. the options keep-derivations (default: true) and keep-outputs (default: false) in the Nix configuration file.
• nix-collect-garbage --delete-old: Quick and easy way to clean up your system, deletes all old generations of all profiles in /nix/var/nix/profiles. See the other options below for a more “surgical” way to garbage collect.
• nix-env --delete-generations old: Delete all old (non-current) generations of your current profile.
• nix-env --delete-generations 10 11 23: Delete a specific list of generations
• nix-env --delete-generations 14d: Delete all generations older than 14 days.
• nix-store --gc --print-dead: Display what files would be deleted.
• nix-store --gc --print-live: Display what files would not be deleted.
• After removing appropriate old generations (after having used nix-env with an argument --delete-generations) - you can run the garbage collector as follows: nix-store --gc

Nix debugging

• lib.debug.traceSeq <arg1> <arg2>: Print a fully evaluated value.

Search NixOS/Nix packages on the command line

You can search for packages using search.nixos.org:

But you can also search for packages straight from the command line, there are 2 methods to do this:

Method 1

Just use nix-shell’s autocomplete feature: Press the < tab > key as you enter the name, you’ll see all Nix package names that begin with the text you entered (takes a second or two to complete):

$ nix-shell -p asciiq
asciiquarium

Note: Nix shell autocomplete applies only on the Nix package names (not its description nor any other metadata).

Method 2

Use the nix terminal app with search:

$ nix search nixpkgs asciiquarium
* legacyPackages.x86_64-linux.asciiquarium (1.1)
  Enjoy the mysteries of the sea from the safety of your own terminal!

* legacyPackages.x86_64-linux.asciiquarium-transparent (2023-02-19)
  An aquarium/sea animation in ASCII art (with option of transparent background)

Notes:

• Whereas the nix-shell “autocomplete” seen earlier (Method 1) applies only on the Nix package names, nix search does a full-text search.
• The command to be used if Flakes are enabled is nix search nixpkgs asciiquarium else it is nix search asciiquarium.
• Add the --json flag to get more information in the output (and pipe through jq to get it in a nice readable format):

  $ nix search nixpkgs --json asciiquarium | jq
  
  evaluating 'legacyPackages.x86_64-linux'
  evaluating 'legacyPackages.x86_64-linux'{
    "legacyPackages.x86_64-linux.asciiquarium": {
      "description": "Enjoy the mysteries of the sea from the safety of your own terminal!",
      "pname": "asciiquarium",
      "version": "1.1"
    },
    "legacyPackages.x86_64-linux.asciiquarium-transparent": {
      "description": "An aquarium/sea animation in ASCII art (with option of transparent background)",
      "pname": "asciiquarium-transparent-unstable",
      "version": "2023-02-19"
    }
  }
  
  

Run a package without having to install it

This is a great feature of NixOS. For example I can open a shell with the asciiquarium package available in it:

$ nix-shell -p asciiquarium

Now get this: that command didn’t actually install anything. When I leave the shell (with exit or ctrl+d), asciiquarium is no longer there, and it doesn’t pollute my user environment.

Alternatively, if you have Flakes enabled you can us the following command (more information here):

$ nix shell nixpkgs#asciiquarium

You can play around with plenty of nifty little programs kids love:

$ nix-shell -p asciiquarium cmatrix fortune cowsay sl figlet toilet oneko

.etc…

• asciiquarium: Enjoy the mysteries of the sea from the safety of your own terminal.
• cmatrix: Shows a scrolling ‘Matrix’ like screen on the terminal.
• fortune: Simple program that displays random poignant, inspirational, silly or snide phrases from a database of quotations.
• cowsay: Simple little ASCII art tool that prints a picture of a cow with a speech bubble message; you can enter the following command to “pipe” the output of the aforementioned fortune command to create your own wise cow. Try out $ fortune | cowsay
• sl: Animated ASCII steam locomotive with a few nice hidden options
• figlet: ASCII banner creator
• pipes: Animated pipes terminal screensaver.
• toilet: More ASCII fonts. For some reason, they named it toilet.
• oneko: Adds an animated cat to your terminal who will follow your mouse (get it?)
• bastet: Tetris on the command-line.
• ninvaders: Space Invaders on a command-line.
• moon-buggy: Jump, fire, on a command-line.

Many other little games are bundled in a package. The package bsdgame for instance has cool command-line games.

Various

• nix-community/awesome-nix: “A curated list of the best resources in the Nix community.”.

• If you are using an SSD it may be useful to enable TRIM support as well as set filesystem flags to improve the SSD performance: ` fileSystems.”/”.options = [ “noatime” “nodiratime” “discard” ]; `

Others

• Crypto Pals
  • Page: www.cryptopals.com. Be scared of the emerged part of the iceberg in cryptography. Take this challenge!
• Déclaration des Droits de l’Homme et du Citoyen de 1789 https://www.conseil-constitutionnel.fr
  • Document (site of Conseil Constitutionnel of France): https://www.conseil-constitutionnel.fr/node/3850/pdf
• The Declaration of Independence of Cyberspace (John Perry Barlow)
  • Document: https://cryptoanarchy.wiki/people/john-perry-barlow
  • Audio, red by the author: https://www.youtube.com/watch?v=3WS9DhSIWR0
• Users Manual for The Human Experience (Michael W. Dean)
  • pdf book: https://michaelwdean.com/UMFTHE/Users_Manual_for_The_Human_Experience-eBook.pdf
  • audiobook on YouTube: https://www.youtube.com/watch?v=xpJMFBpGR2s
• How Learning Works (Published by Jossey-Bass)
  • Document: https://firstliteracy.org/wp-content/uploads/2015/07/How-Learning-Works.pdf

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