Using the Raspberry Pi to Turn an iPad into a Real Computer, part 5: The Networky Bits

Now that I have the Pi set up as both a wireless client, and a Wireless Access Point, it’s time to get the different network tools configured.

Frequently visited networks
The web GUI doesn’t handle connecting to networks. The GUI looks like it will, but it doesn’t actually accomplish anything. I am sure there is a way to configure around the problem, but I haven’t dug into it. Instead, in typical Chris fashion, I just use a super ugly hack based on like 15 minutes of research into the problem. I’ll figure out how to do it the right way in the future (yeah, right.) but for now I just change the SSID and PSK entries in /etc/wpa_supplicant/wpa_supplicant.conf and reboot the Pi.

I used this command to put the SSID info and passphrase into a file:

wpa_passphrase "Totally A Starbucks" LOLnotreallySBUX | tee sbux.txt

Where “Totally A Starbucks” is the SSID for your wireless network (put the name in quotes), and LOLnotreallySBUX is the pre-shared key for your wireless network. I created a different file for each network I want to connect to (home, work, etc.) and then created copies of wpa_supplicant.conf for each network. I call them, creatively enough, home, work, hotspot, and phone.

country=US
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
ap_scan=1

update_config=1

Delete any/all network entries, and then use the CTRL+R command in nano to read in the contents of your various files (sbux.txt, in the example above). Then save the file. The sbux.txt file in the example above will look like this:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
ap_scan=1

update_config=1
network={
        ssid="Totally A Starbucks"
        #psk="LOLnotreallySBUX"
        psk=3f825ee60dff2f77fccfd2a74ac08023d69e1a66918687ec513afe438a2bd1fd
}

You will need one “wpa_supplicant.conf” source file for each network. You could call them wpa_supplicant.conf.home, or just home. Then I created shell scripts to copy the home file to wpa_supplicant.conf like so:

#!/bin/sh
sudo cp /etc/wpa_supplicant/home /etc/wpa_supplicant/wpa_supplicant.conf
sudo reboot

I put the shell scripts in the /usr/local/bin directory, so that I could call them simply by typing home.sh or work.sh at the command prompt, and then wait for the Pi to boot back up. It ain’t pretty, but it works… every time.

Stupid (mobile) SSH tricks

Speaking of ugly shell scripts that ignore modern practices in favor of dubious hacks from 20 years ago, using SSH on a tablet is super glitchy. In order to conserve battery power, tablets and smart phones don’t like to run processes in the background. In order to conserve mobile data, tablets and smart phones don’t like to keep network connections open for any length of time. Most smartphone apps are front ends to websites or APIs, so you only need processing and network connection when the app is open. This is fine for just about every mobile app, but it murders SSH. There is a lot of talk about mosh in the Blink documentation. It’s literally a mobile-shell. It’s purpose-built to solve this problem.

So naturally, I am not going to use it yet. I’ll look into mosh at a later date (LOL). Instead I am going to create a Rube Goldberg contraption that is held together with awful shell scripts.

Because my SSH session to the Pi gets dropped a lot, I set up a host in Blink so that I can quickly connect to the Pi just by typing ssh@raspad.

On the Pi, I installed screen so that I can keep a session running and not lose whatever I was doing when the connection drops. To save a few keystrokes, I created another shell script in /usr/local/bin called “scr”:

#!/bin/sh
screen -DR 

I tried some different forms of alias, but this one actually works on the Pi.

Now, all I have to type is ssh raspad to connect to the Pi, and scr to connect to my existing screen session. And if no screen session is available, it creates a new one.

The virtual keyboard on the iPad is different in some ways from a “real” keyboard. There is no CRTL key, no arrow keys, and no F keys (F1, F2, etc.)

Most of the time, my primary workstation is a Windows PC. I have a special .screenrc that I use with PuTTy. For the life of me, I cannot figure out how to press F10 in Blink. So I just changed my .screenrc on the Pi to use F3-F6:

startup_message off

# Window list at the bottom.
# I got the long line of vars from https://bbs.archlinux.org/viewtopic.php?pid=423481#p423481
hardstatus alwayslastline
hardstatus string "%{.kW}%-w%{.W}%n %t%{-}%{=b kw}%?%+w%? %=%c %d/%m/%Y" #B&W & date&time

# From Stephen Shirley
# Don't block command output if the terminal stops responding
# (like if the ssh connection times out for example).
nonblock on

# Allow editors etc. to restore display on exit
# rather than leaving existing text in place
altscreen on

# bind F3 to detach screen session (to background)
bindkey -k k3 detach

# bind F4 to create a new screen
bindkey -k k4 screen

# Bind F5 and F6 to previous and next screen window
bindkey -k k5 prev
bindkey -k k6 next

Nah, fuck that. Just use Mosh.

Mobile Networking

The more work that goes into this little project, the more this is starting to look like a mobile home lab. While I do not have plans to remotely access the Pi from the Internet, nor do I have plans to serve anything from the Pi to the Internet, there are reasons to use dynamic DNS and an overlay network.

I have written about NeoRouter before as a means for gaining remote access to my home network. I also use it on my internal network to get access to my lab servers from my wireless network. My internal wired network (which is my lab, basically) is separated from the family wireless network. Most of the time, it’s to protect the family from my lab. Sometimes it’s the other way around. My modernized smuggling server sits on my lab network, and I use NeoRouter to access its various web interfaces.

Dynamic DNS is another thing that sounds like it’s mostly for remote access, but comes in handy for other things. I used to use it with my mobile phone to do VOIP when I traveled overseas, back what that was humanly possible. The tool that I prefer to use is DDclient.

sudo apt-get install ddclient

Configuring DDclient depends on the dynamic DNS provider that you are signed up with. But once you have it configured, you can test it with this command:

sudo ddclient -daemon=0 -debug -verbose -noquiet

These are the kinds of tools that you set up before you need them. I am not sure if I will ever need them, but it would be nice to have them running properly if I did.

Cool Networking Tools
Now that you can connect to the Pi reliably, and you can get the Pi to connect to the different wireless networks that you may come into contact with in a semi-automated fashion, it’s time to break out the nifty networking tools to run in your screen session.

1. WaveMon
   For whatever reason, iOS lacks a decent WiFi scanner. Wavemon is a command line Wi-Fi analyzer. The Wi-Fi settings will show you nearby access points, and will use a couple of bars to show you the quality of your connection, but that’s it. To get useful signal info, you need to use Wavemon:

   sudo apt-get install wavemon

   And you run it from the command line like so:

   sudo wavemon

   You need root privileges to do scans for nearby access points. There are other mischievous tools that you can put to work from there, but mostly I use Wi-Fi scanners to see how crowded a given channel is when helping my friends and family set up their wireless networks.
   

2. Nmap
   So you found a wireless network to connect to, let find out what’s on it. Nmap is probably the most complicated command line tool in existence. I am by no means and expert on using it. In fact, I really only know how to do like 3 things with it, so I’m not going to go into using Nmap pretty much at all. What I can tell you is that if the wireless network you are on has AP-host isolation enabled, you won’t see any of the wireless clients. Fortunately, the tool is small and requires very little power. This makes it ideal for running on the Raspberry Pi.
   To install Nmap:

   sudo apt-get install nmap

   To scan a single host (one IP address):

   sudo nmap 192.168.50.1

   I don’t remember if you need to be root to run Nmap effectively. Most of my experience with these tools is from Kali Linux (of which there is a Raspberry Pi distribution) where everything runs as root.
   To scan a a whole network (all the IP’s in a subnet):

   sudo nmap 192.168.50.0/24

   

3. TCPdump
   We are on the wireless network and we have scanned it for cool things. Now let’s see what kind of chatter is happening. I don’t do it very often, but every once in a while, being able to monitor network traffic comes in handy. On a “real” computer, I prefer to use Wireshark, but tcpdump will work in a pinch. You install it like any other commandline tool:

   sudo apt-get install tcpdump

   And like most scanning and monitoring tools, you need to run it at root. Like Nmap, TCPdump is super complicated. If you want to monitor traffic on your hostAP network, you will need to specify the uap0 interface for your scans. You can filter your results by pretty much anything. For example, you filter ICMP traffic like this:

   sudo tcpdump -i uap0 protocol icmp

   

4. iPerf3
   Now that you have seen what’s happening inside your wireless network, it’s time to test network thruput. For this task, I like to use iperf3. You need another computer to run iperf3 to send data to, but any Unix host should be capable of running it. I use it on my admin workstation when I am tinkering at home, and I run it on my hosted VM to test Internet links.
   Like WaveMon or Nmap, it’s dead simple to install:

   sudo apt-get install iperf3

   and also dead simple to run, assuming you have the right arguments:
   On your remote end (aka the hosted server):

   iperf3 -s

   On your local machine (in this case, the Pi):

   iperf3 -c hostname

   

Now that the Pi has expanded the iPad’s ability to connect and to troubleshoot networks, it’s time to add features that normal people will appreciate, like storage and media streaming.

Using the Raspberry Pi to Turn an iPad into a Real Computer, part 4: RaspAP

My previous post was about pre-configuring the Pi for headless booting that automatically connects to your wireless network.

This is fine for your home network, but it will be difficult to get connected to the Pi when you are traveling. Also, if you are planning to leave the Pi at home, and never use it while traveling, that is waste of a Raspberry Pi. There is a global shortage of Pi’s; they are pretty much impossible to get, even at Pandemic-Profiteering prices. If you just want to do occasional Unix shit on an iPad when you are at home, just use a VM. If you do want to use the Pi out in the field, I recommend RaspAP.

If the headless install went well, you should be able to log into the Pi via SSH and run the RaspAP installer script. I learned about RaspAP from this video:

All did not go well for me in the beginning. I couldn’t connect to the Pi wirelessly to save my life. If I plugged it in to a switch, connecting was not a problem. I tried and tried dozens of different things. I even tried a completely different Pi. It turns out that I was making a few mistakes:

1. You absolutely have to use the 32bit version of Raspberry Pi OS lite. Not 64 bit. Not the default version that you click on accidentally. 32bit. Lite. No exceptions.
2. I was getting owned by my own paranoid network security.

You see, the monster that we fear most is the one that we see in the mirror. Spies sweep for bugs, thieves keep things in safes, and hackers enable AP-Host isolation on their wireless networks. Host isolation keeps devices that are connected to an access point from talking to each other. They can see and talk to hosts that are on the same wired network as the AP, so you can connect to servers. The reverse is also true, servers on the wired network can see and talk to hosts that are connected to the AP. What absolutely doesn’t work with AP-Host isolation is an iPad that is connected via WiFi connecting to a RaspberryPi that is also connected to WiFi. You get nothing. Good day sir.

One way to remedy this situation is to use a server on the wired network as a jump box for SSH, and some Stupid SSH Tricks(tm) for mapping port 80 on the Pi to a local port on your iPad or laptop. Rather than deal with the keyboard situation on the iPad, I just used PuTTy on my windows laptop for the initial setup.

Begin the RaspAP install by running the quick installer:
curl -sL https://install.raspap.com | sudo bash

(I’m a Debian guy that still uses su instead of sudo, so I probably over use sudo in all of these examples.)

At this point, the order of operations is critically important. DO NOT START THE HOTSPOT! You need to configure the WiFi Client AP Mode under Hotspot|Advanced before you do anything. You can’t change the AP Mode while the AP is running, and running the AP shuts down wlan0 on the Pi, so you can’t connect to the Pi while the AP is up, and shutting off the AP cuts off your access to the Pi. I had to re-image my SD card a few times because of this error. I guess you can fix this using the wired Ethernet, but I haven’t figured out how.

To enable WiFi Client AP Mode, open the hotspot menu, set the SSID and pre-shared key options for your AP, and then click “save”. Then enable the WiFi Client AP Mode under the Advanced tab. THEN AND ONLY THEN can you start the hotspot.

Now configure hostapd to start at boot:

sudo update-rc.d hostapd defaults
sudo update-rc.d hostapd enable

Then reboot the Pi to make sure the AP comes up:

sudo shutdown -r now

It will take a few minutes for the AP to be visible to the iPad, and once the AP is visible, you should wait for a minute or two before connecting.

The thing to remember from here on out (that you can add as a host in Blink) is that when you are connected to the Pi AP, the Pi’s static IP is 192.168.50.1. From there you can add those sweet delicious network tools that are missing from iOS. My next post will cover some of those tools.

Using the Raspberry Pi to Turn an iPad into a Real Computer, part 3: Pi OS install

In my last post, I talked about setting up the iPad for access to the Raspberry Pi. Now the work on the Pi begins. Before you can do anything with the Pi, you need to install the basic OS. I tried a bunch of things, and in the end, I chose to go with a fully headless install. The Pi is going to be headless for the rest of its life, so it might as well start that way.

Imaging
Most Pi tutorials recommend Balena Etcher or Win32DiskImager to burn your image to an SD card. I have used both tool tons of times and they are both great. In fact, I have been using Win32DiskImager to read my SD cards back to an image file to make incremental backups of this project. Making backups when you hit a major milestone is super important. Also, SD cards fail all the time, so it pays to have good backups.

For this project, I went with Raspberry Pi Imager because you can configure a bunch of stuff during the imaging process. You do this by clicking the little gear icon to the lower right of the “Write” button.

Also, carefully note in the picture above that I chose the “Raspberry Pi Os Lite (32-Bit) option. You may be saying to yourself “Nah son, I’m 64bit for life.” and I am here to tell you that for this project, 64bit is a grave mistake. The RaspAP installer shits itself on 64bit Raspberry Pi OS, and you will catch hell trying to make it work. Don’t be like me. Just run the 32bit version.

Most of the initial config is going to happen with SSH, so scroll down to enable it:

Obviously the Pi needs to connect to the Internet for the initial setup, so you will want to enable Wifi, and program it to connect to your wireless network:

The next item is also important. Configuring the location sets the radio properties for the WiFi adapter, as well as the UTF-8 character set which can affect scripts running later:

At this point, you are ready to boot the Pi. You will need a way to find the IP for the Pi. You can look it up in the DHCP lease table on your router (or other DCHP server). You could run NMAP to scan your wireless subnet and look for an IP running SSHD. If you know the IP of the Pi’s wireless card in advance, you could set up a DHCP reservation. Since I am recycling this Raspberry Pi, I already had a reservation set up from it’s previous life as an amateur radio workstation.

What you don’t want to do is set a static IP just yet. In the next step, we will be setting a static IP, so that you never have to determine the IP of the Pi again.

One thing that I add to Raspberry Pi servers is to reboot them on a regular basis. This step probably isn’t necessary on newer model Pi’s, but between the small amount of memory and the unreliable nature of SD card storage, the 2b would lock up from time to time. To get around this problem I just set up a cron job to reboot the Pi every morning at 4am:
sudo crontab -e

At first you will be prompted to choose an editor. Personally, I prefer nano. Once the file is open in your editor, scroll to the bottom of the file and enter:
0 4 * * * /sbin/shutdown -r now

In my next post, I will cover installing RaspAP, which requires a full update and reboot:
sudo apt update
sudo apt full-upgrade
sudo shutdown -r now

Using the Raspberry Pi to Turn an iPad into a Real Computer, part 2: The iPad

In my last post, I talked about why I wanted to do this project, which was mostly about not wanting an old iPad to sit in a box with all my other crap. It was also about a clever use of a Raspberry Pi. While 99% of the work in this project is setting up the Pi, this post is about setting up the iPad.

Growing up the iPad
My daughter got the iPad when she was 4. We bought it refurbished from Amazon. As much as I dislike Apple as a company, and as a platform, the quality of their hardware is impressive. We put the iPad in a pink foam bumper case. It was subjected to all manner of child induced terrors: spilled milk, sticky fingers, being left to die in random places. Despite being 2 years old when we got it, and her using it for probably 5 years, it’s still in pretty good shape. The screen cracked in one corner.

I cleaned it up, and I put it in a cheap folio case.

Blink
The only real modification I made to the iPad was to install a Unix shell app called Blink. Blink has some essential tools like ping and ssh, along with the ability to map hostnames to IP addresses in a manner similar to /etc/hosts.

The app is $20 per year, it’s meant to be used for home automation, and includes a lot of that. If you aren’t into that you can just shake your iPad every day or two and keep using the app for free.

The iPad’s on screen keyboard doesn’t have some essential keys, like CTRL or arrow keys. If you are going to spend time in the Unix shell, you should probably have a hardware keyboard.

Keyboard
My wife has a Bluetooth keyboard that she uses to live-Tweet TV episodes sometimes. It doesn’t have a touchpad, it runs off of AAA batteries instead of being rechargeable, but it does have arrow keys. The F-keys (F1-F10) behave a little strangely, which I will go into more in the next post about configuring the Pi.

The most practical solution would be a keyboard with a dedicated CTRL key, arrow keys, and a touchpad. If I end up using this gear a lot, I might splurge on a cool keyboard.

I spent a little while shopping for 60% mechanical keyboards. Buying a keyboard is definitely outside of the “shit laying around the house” constraint. A retro-gray keyboard would give the iPad some cool Unix style. A 60% keyboard doesn’t solve the touchpad problem, however, and a lot of 60% layouts don’t have dedicated arrow keys.

Battery
The Raspberry Pi doesn’t have a built-in battery, so using it portably requires a battery bank. I have a small collection of batteries thanks to amateur radio and owning a couple of smartphones with terrible battery life.

The Raspberry Pi 4b requires more amperage than the previous models. I have plugged the Pi into the battery for testing purposes, but I haven’t tested how long the battery lasts with the Pi plugged in. These batteries can completely charge two tablets from 0 to 100% simultaneously, so I am pretty sure I can get several hours of use with the Pi. Of course, in a situation where I am charging the iPad and my 4G hotspot, that duration lowers significantly.

And now, the fun begins: Setting up the Raspberry Pi