Manjaro OpenRC Cheat Sheet

Amidst preparations for my third year at university, I've put together a sort of reference sheet to help me remember all the common commands needed when using Manjaro with OpenRC. It's not complete, but I'll continue to update it with various useful commands I stumble upon. You can find it below.

If you have any that you find useful, post a comment below! I'd love to see what you come up with - I might even add it to this list (crediting you of course)!

Cast List

• sudo pacman: Main package manager
• yaourt: pacman wrapper, also has AUR support. Swap out pacman for yaourt to include the AUR.
• sudo rankmirrors: Finds and selects the fastest repository mirrors.
• sudo rc-update - Enable and disable services
• sudo service - Start, stop, and query the status of services

Commands

Package Management

Command	Description
rankmirrors -i -m rank -d	Interactively re-find the fastest mirrors
pacman -Sy	Synchronise local repository metadata
pacman -Syy	Redownload all repository metadata
pacman -Syua	Sync with mirrors and update all packages
pacman -Fs filename	Search repositories for packages that contain filename
pacman -Ss search_string	Search repositories for package name or description that contain a search string
pacman -S package_name	Install package_name and any dependencies required
pacman -Rs package_name	Remove package_name and all dependencies not needed by anything else
pacman -Dk	Check that all required dependencies are installed
pacman -Q	List all installed packages and their versions
pacman -Qe	List all packages that were installed manually
pacman -Qd	List all packages that were isntalled automatically
pacman -Sii package_name	See which packages require package_name to be installed

Services

Command	Description
rc-update	List all services and their runlevels
rc-update add service_name default	Add service_name to the default runlevel
rc_update delete service_name default	Remove service_name from the default runlevel
service service_name start	Start service_name
service service_name stop	Stop service_name
service service_name status	Query the status of service_name

Sources and Further Reading

• Manjaro
• OpenRC
• Package manager command conversion tables
• pacapt, a command that provides a pacman-like interface on top of other package managers

Arduino Runtime Exception List

Just yesterday I was at the Hardware Meetup at C4DI, and I (along with a few other people - thank you for helping :D) was attempting to fix a series of nasty runtime errors. All it gave me was a message in the serial monitor that an exception had occurred, an error code, and a raw stack dump. This wasn't very helpful at all. Even more unhelpful was the lack of help out there on how to decode this information.

I did, however, manage to find a page that contains a list of the different error codes and their meanings. It's not much, but it's a start. It helped us at least to work out what was wrong with it :-)

Arduino Exception Reference

If you're running Windows, then Microsoft have created Visual Micro - a what looks like a perfectly brilliant debugger for the arduino. Apparently you can inspect variables, see the digital pin statuses, and get intellisense lovelyness :D Since I'm running linux, I can't get my hands on it - hopefully someone will build an alternative for linux and other OSes soon!

I also discovered a weird oddity with UDP Multicast in C#. I'm going to investigate further and write up another post that will (hopefully) follow this one.

Arduino quick reference guide

This post was going to be about how I connected my robot to a WiFi network and controlled it wirelessly, but I've been having some issues with getting that to work :-( Since I wanted to make a post anyway, I thought I'd post about a quick reference guide I found instead :-)

(Download as: png, svg | Original source)

I found this decided to print it out and laminate it. It's been really useful - I'm really glad I decided to print it out now. It was originally made by a guy called Mark Liffiton. You can find its Github repository here. The version I have posted here is tweaked very slightly to have colour on the reset button, which the original doesn't have.

Next I'm going to attempt to find a similar sort of thing for the esp8266 (upon which the Wemos D1 R2 is based) API, because I'm constantly having to look up various functions all over the place and it wastes a lot of time :-)

Have you found a handy reference sheet? Post about it in the comments below!

Drive Naming Schemes in Linux

If you've used linux before, you'll probably have seen your flash drive or hard drive appearing as /dev/sdc4 at one point or another. You may have a cd drive which appeared as /dev/sr2 or /dev/cdrom. If you're really lucky, you might even have a tape drive that appears as /dev/st0.

What do all of these letters mean? I was wondering the same thing, so I looked it up and am writing up what I found in this post.

It would appear that in linux devices have a prefix and then an identifier. Before I explain the identifiers, I should outline each of the prefixes that I've come across (or looked up) first. You can find them below.

sd*

By far the most common device name prefix that I have come across is sd. This apparently originally stood for SCSI (SATA?) Device, but today it represents any regular block device that can be used for storage. This includes hard drives and flash drives for example.

hd*

The hd prefix originally stood for Hard Disk and was used for IDE drives, but it was dropped as of Linux 2.6.19 and sd* is now used instead.

sr*

sr stands for SCSI ROM and is used for CD / DVD drives (It might be used for blu-rays too, but I don't have one to check. Please post in the comments if you do!). On my machine, I have a number of symbolic links leading back to this drive in my /dev called cdrom, cdrw, dvd, and dvdrw.

st*

I have not come across a device with this prefix yet. If you have one, please post in the comments below! It stands for SCSI Tape drive.

Identifiers

The numbers and / or letters after the prefix refer to the device number, and, if appropriate, partition on the device. For example, /dev/sdb4 refers to the 4th partition on the 2nd disk, /dev/sr2 refers to the 3rd CD / DVD drive, and /dev/hdc3 refers to the 3rd partition on the 3rd IDE hard drive.

Sources

• Super User - What does /dev/sda for linux mean?
• Ask Ubuntu - What is the Linux drive naming scheme?
• The Linux Documentation Project - Drive Naming in Linux

Mobile Network Types

At the moment I am rather busy with my coursework, but I still have some time to make a quick post.

This is just a small post to tell you about a quick reference I put together in 5 minutes. It tells you what the different types of mobile network are (like HPSA and EDGE) and how fast they should be.

Link: Mobile Network Types

I have also been looking at Windows 10 in a virtual machine, so I will have a (long!) post coming out soon all about my thoughts and suggestions.

Terminal Reference Sheet

While browsing my stackedit markdown documents, I found a reference sheet for the linux terminal. While originally posted on novitiate, I thought that it might be of use to someone on this website too. The reference sheet was originally designed for the raspberry pi, but it works for other bash like shells too :)

You can find it below.

Basic Linux Terminal Reference Sheet

Command	Function
ls	List the contents of the current directory
cd orange	Change the current directory to the sub-folder orange
cd ..	Change the current directory to the parent folder
cd ~	Change the current directory to your home folder
rm banana.txt	Delete the file banana.txt
rmdir pineapple	Delete the directory pineapple, but only if it is empty
rm -rf mango	Delete the directory mango, even if it has files and folders inside it
mkdir cheese	Create a new folder called cheese
mv kiwi.py cake.py	Rename kiwi.py to cake.py
cp bread.7z cherry.7z	Copy bread.7z to cherry.7z
mv cabbage oranges/tangerines	Move the folder cabbage to the folder tangerines inside the folder oranges
sudo command	Execute command as the root (administrator) user
sudo apt-get update	Update the package list
sudo apt-get upgrade	Update the currently installed packages
sudo apt-get install foo	Install the package foo
rpi-update	Update the Raspberry Pi's firmware1
raspi-config	Start the Raspberry Pi configuration utility
nano apple.txt	Edit the file apple.txt in the nano command line text editor
exit	Exit the terminal
sudo shutdown -h now	Shutdown
sudo reboot	Restart
top	View a list of processes using your CPU most intensively
CTRL + C	Keyboard shortcut to exit most programs
CTRL + Z	Keyboard shortcut to suspend the currently active process and return focus to the terminal
fg	Resume the currently suspended process
jobs	Display a list of jobs attached to the current terminal
bg 2	Put the job with the id 2 into the background2
disown 2	Disown the job with the id 2 so that it will not be terminated when the terminal is terminated2
help | less	Pipe the output of the command help into the command less, which lets you scroll through large amounts of output with the arrow keys (press q to quit).
cat cakes.log | View the contents ofcakes.log. Tip: add	lessto pipe it intoless` so that you can browse the file with the arrow keys.
man less	Display the manual page about the command less
help less	Display some basic help about the command less
ssh [email protected]	Connect to the device at the IP 192.168.0.3 with the username pi and start a remote terminal session

Links to other useful lists

• http://www.techradar.com/news/computing/pc/how-to-get-to-grips-with-your-raspberry-pi-s-command-line-interface-1161712
• https://help.ubuntu.com/community/UsingTheTerminal
• http://ss64.com/bash/
• http://explainshell.com/

If you have any other commands or links to useful lists / references, please leave a comment below.

Have you found a cool bash reference? Post a comment below and I will consider adding it to the list.