I have been writing a lot about this Raspberry Pi iPad server project and Mosh pretty much seemed purpose-built to solve the “ssh on a mobile device that hates background processes and open connections” problem.
I was doing some clever shit with screen, but I gave mosh a go and it’s dead simple to configure and use with blink.
You literally just install the mosh server on the Pi:
sudo apt install mosh
And the Mosh client is built right into Blink, which is cool. I guess.
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.txtWhere “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=1Delete 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 rebootI 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 ddclientConfiguring 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 -noquietThese 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.
sudo apt-get install wavemonAnd you run it from the command line like so:
sudo wavemonYou 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.
sudo apt-get install nmapTo scan a single host (one IP address):
sudo nmap 192.168.50.1I 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
sudo apt-get install tcpdumpAnd 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
sudo apt-get install iperf3and also dead simple to run, assuming you have the right arguments:
On your remote end (aka the hosted server):
iperf3 -sOn 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.
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:
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 enableThen reboot the Pi to make sure the AP comes up:
sudo shutdown -r nowIt 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.
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
This Christmas, we upgraded the kids’ iPads, and I inherited my daughter’s old iPad Air 2. I had an iPad years ago, but I didn’t like it.
I like tablets, I just didn’t like the iPad. Tablets fill this weird gap between a smartphone and a PC, where you can do what you do what you do on your phone (texts, memes, and games) only more comfortably. A laptop is best used when seated, preferably at a desk or table; it’s portable. The smartphone is great when you are out of the house or office and moving around; it’s mobile. The tablet fits into that middle space: seated but not at a desk or table, such as in bed, on the couch, on a long flight, or riding a train. Staring at a screen of any kind in a car for a long time makes me nauseous, so I prefer audio for car trips.
I also hate tablets because they come close to doing what a netbook used to, before 10 inch screens went extinct. (Yes the GPD Pocket is a thing, it’s also the price of a gaming laptop. I already have too many laptops as it is, without dropping 12 Benjamins on another one because it’s cute.) Netbooks are great for note taking in a meeting or class, or for doing light system administration tasks where you need basic networking tools like ping, ssh, or more serious tools like network scanners or wifi analyzers. Android tablets do ok in this regard, but the lineup of network tools for iOS are not great.
The problem with a tablet is that it isn’t a netbook. The problem with a netbook is that it a tablet.
Since inheriting this iPad has cost me nothing (well, I paid for it years ago) I am going to try it again. This time I am also re-creating the netbook experience using recycled technology that I already have. I am trying to create a portable (not necessarily mobile) computing setup that is smaller than a laptop, charges off of 5v DC, does Unix shit reliably, stores files and streams media without Internet access, and fits in my man purse. The theme of this project is “modular off-grid solar powered computing made with shit laying around the house.”
Modular
The essential difference between a tablet and a netbook is the keyboard. The dream is to have either a netbook with a removable screen, or a tablet with a detachable keyboard. Those purpose-built devices are nice, but they are also expensive. For this hand-me-down project I decided to kludge pieces together instead.
Using a tablet keyboard is usually pretty lame, especially a keyboard with no touchpad. Taking my hand off the keyboard to touch the screen is a major distraction. I had a touch screen laptop for years and rarely used that feature. I think I have a decent little Bluetooth keyboard somewhere, one with that ThinkPad nipple-looking thing. It’s probably sitting in a box with a bunch of broken tablets.
As much as I dislike membrane keyboards, they will be significantly better than typing on the iPad when it is propped up in that tilted landscape mode.
Off grid
Traveling with a laptop can be kind of a waste, especially when you end up not using it very much. Wasted suitcase space isn’t that big a deal anymore since haven’t been on an airplane in a couple of years. Anymore, the traveling I do is outdoor stuff like car trips and camping. Tech in these scenarios is great for keeping the kids busy when it’s rainy, cold, or on long car rides. We travel a few times each year to my in-laws lake house where there is tons of nature, but not much access to the Internet. Offline media requires the kind of storage that tablets are notoriously short on.
In the before times, when international travel was a thing, I used a cheap Andoroid tablet and a Chromebook. The Chromebook had a real keyboard and real web browser, while the Android could run arbitrary apps from the Google Play Store. The combination was a decent small toolkit. Between having kids and COVID, I haven’t gone over seas in several years. All that gear is probably obsolete now anyways.
I hate electronic waste, and yet I seem to produce a lot of it.
Shit laying around the house
This project began as a plan to reuse a hand-me-down iPad. I set the old iPad up purely to get access to FaceTime, and as I loaded my old apps on it, I discovered that it was still decently powerful.
I have also collected a few Raspberry Pi’s over the years. I have done maker stuff with them, used them to demonstrate things at 2600, including a Pi PBX one time as a proof of concept. They’re handy little things. As I get more into amateur radio, Pi’s come in handy for different digital and packet modes.
The Pi also runs off 5v DC, albeit at higher than 2a. This isn’t a problem with modern phone chargers and portable battery banks, of which I also have a couple.
Adding Solar
Amateur radio has taught me about the importance of charging batteries in the field. “Field rechargeable” is probably a better term than “solar”. Solar is more of a guideline. If something can charge from USB, you can probably charge it off of solar. If you can charge it off of solar, you can probably charge it off either 5v USB, or 12v car electrical. Wall and car chargers for smartphones are great sources of USB power, and in the family travel scenario, car and wall power make more sense. USB ports in computers can also charge USB devices, although they tend to do it very slowly. The Pi 4 can’t run reliably from a laptop USB.
I have a folding solar panel with a 12v power output and USB outputs. I normally use it to charge my portable solar generator. That’s a stupid name for the device. It’s just a big 12v battery, it doesn’t generate anything. I already have a collection of USB battery banks laying around the house, so one of those should run the Pi for a pretty long time. I even have a USB battery bank with an integrated solar panel, though it takes multiple days worth of good sunlight to fully charge it. I haven’t tried laying out the solar panel with the solar banks plugged into it to see how it charges, but I am hoping to try it out when the weather is nicer.
Stay tuned for the next installment where I get started configuring the iPad.
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