Let’s say someone asks you to estimate the total bandwith used by a particular subnet, or a particular service such as https on port 443. I provide a crude way to do that using tcpdump on a not-too-busy server.
The code
I call it bandwidth.sh. By the way, I ran it on a Checkpoint Gaia appliance so it works there as well.
Running tcpdump with the -v switch gives us packet length. We find that length and sum it up. Here we used a filter epxression of 216.71/16 to capture only the traffic from that subnet.
The number of packets to capture has to be tuned to how busy it gets. Now it’s set to only capture 1000 packets. And you see my crude timings are truncated at the second. So 1000 packets in one second or about 1.5 MBytes/sec = 12 Mbps is the maximum sensitivy of this approach. I doub it will really work for interfaces with more thn 100 Mbps, even after you scaled up the count (and don’t forget to change the denominator in the kbps line!
Here’s a sample output:
1000 packets captured
2002 packets received by filter
0 packets dropped by kernel
5 kbps at Wed Nov 3 12:09:45 EDT 2021
I think it’s important to note the number of packets dropped by the kernel. So if it gets too busy as I underatdn it, it will at least try to tell yuo that it couldn’t capture all the data and at that point you can no longer trust this method. Perhaps with enhanced statistical methods it could be salvaged.
I don’t run it continuously to also give the kernel a breather. It probably doesn’t make much difference, but every two minutes seems plenty frequent to me…
Conclusion
We have demonstrated a crude but better-than-nothing script to calculate bandwidth for a given tcpdump filter expression. It won’t win any awards, but it contains some worthwhile ideas. And it seems to work at low bandwidth levels.
This post builds on the success of previous posts and uses elements from them. I don’t honestly expect anyone to repeat all the ingredients I have assembled here. But I have created them in a fairly modular way so you can pick out those elements which will help your project.
But, it is true, I have gotten the user experience of recording audio from, e.g., a band practice, down to a click of the ENTER button to start the recording, another click to stop it, and a click of the UP ARROW button to process the audio recording – turn it into a video – and upload it to YouTube, mark it as UNLISTED, and send the link to me in an email. Pretty cool if I say so myself. I am refining things as I write this to make it more reliable.
This write-up is not terribly detailed. It presumes at least a medium skill level with linux.
Ingredients
RPi 3 or RPi 4
Raspberry OS desktop running Pixel desktop environment
tiger VNC, i.e., the package tigervnc-scraping-server
chromium-browser (but it comes with)
xdotool (apt-get install xdotool)
xsel (apt-get install xsel)
YouTube account
crontab entries – see below
you do not need an HDMI display, except for the OS setup
#!/bin/bash
# DrJ 8/2021
# Control the livestream of audio to youtube
# works in conjunction with an attached keyboard
# I use bash interpreter to give me access to RegEx matching
HOME=/home/pi
log=$HOME/audiocontrol.log
program=ffmpegwireless9.sh
##program=tst.sh # testing
PGM=$HOME/$program
# de-press ENTER button produces this:
matchE="1, 28, 0"
# up arrow
matchU="1, 103, 0"
epochsOld=0
cutoff=3 # seconds
DEBUG=1
ledtime=10
#
echo "$0 starting monitoring at "$(date)
# Note the use of script -q -c to avoid line buffering of the evread output
script -q -c $HOME/evread.py /dev/null|while read line; do
[[ $DEBUG -eq 1 ]] && echo line is $line
# seconds since the epoch
epochs=$(date +%s)
elapsed=$((epochs-$epochsOld))
if [[ $elapsed -gt $cutoff ]]; then
if [[ "$line" =~ $matchE ]]; then
# ENTER button section - recording
echo "#################"
echo We caught this input: $line at $(date)
# see if we are already running our recording program or not
pgrep -f $program>/dev/null
# 0 means it's been found
if [ $? -eq 0 ]; then
# kill it
echo KILLING $program
pkill -9 -f $program; pkill -9 arecord; pkill -9 ffmpeg
pkill -9 -f blinkLED
echo Shine the PWR LED
$HOME/shineLED.sh
else
# start it
echo Blinking PWR LED
$HOME/blinkLED.sh &
echo STARTING $PGM
$PGM > $PGM.log.$(date +%m-%d-%y:%H:%M) 2>&1 &
fi
epochsOld=$epochs
elif [[ "$line" =~ $matchU ]]; then
# UP ARROW button section - processing
echo "###########"
echo processing commencing at $(date)
$HOME/blinktwiceLED.sh &
echo start processing of the recording
$HOME/process.sh >> process.log 2>&1
pkill -9 -f LED
$HOME/shineLED.sh
epochsOld=$epochs
fi
[[ $DEBUG -eq 1 ]] && echo No action taken. Continue to listen
fi
done
#!/usr/bin/bash
HOME=/home/pi
sleeptime=5
cd $HOME
# loop over all mp3 files in home directory
ls -1 record*mp3|while read line;do
echo working on $line at $(date)
video=$(echo ${line}|sed 's/mp3/flv/')
echo creating flv video file $video
# create the video first
./mp32flv.sh $line
echo move $line to mp3 directory
[[ -d mp3s ]] || mkdir mp3s
mv $line mp3s
echo mv flv to upload directory
[[ -d 00uploads ]] || mkdir 00uploads
mv $video 00uploads
echo start the upload
./auto-upload.sh
echo get the url to this video on YouTube
url=$(cat clipboard|xargs -0 echo)
echo test that it worked
if [[ ! "$url" =~ "http" ]]; then
echo FAIL. Try once again
./auto-upload.sh
fi
echo send mail to Drj
./announceit.sh
echo move video $video to flvs directory
mv ./00uploads/$video flvs
echo sleep for a bit before starting the next one
sleep $sleeptime
done
echo All done with processing at $(date)
#!/bin/sh
# DrJ 8/30/2021
# https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi
# put LED into GPIO mode
echo gpio | sudo tee /sys/class/leds/led1/trigger > /dev/null
# flash the bright RED PWR (power) LED quickly to signal whatever
while /bin/true; do
echo 0|sudo tee /sys/class/leds/led1/brightness > /dev/null
sleep 0.5
echo 1|sudo tee /sys/class/leds/led1/brightness > /dev/null
sleep 0.5
done
#!/bin/sh
# DrJ 8/30/2021
# https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi
# put LED into GPIO mode
echo gpio | sudo tee /sys/class/leds/led1/trigger > /dev/null
# turn on the bright RED PWR (power) LED
echo 1|sudo tee /sys/class/leds/led1/brightness > /dev/null
#!/bin/sh
# DrJ 8/30/2021
# https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi
# put LED into GPIO mode
echo gpio | sudo tee /sys/class/leds/led1/trigger > /dev/null
# flash the bright RED PWR (power) LED quickly to signal whatever
while /bin/true; do
echo 0|sudo tee /sys/class/leds/led1/brightness > /dev/null
sleep 3
echo 1|sudo tee /sys/class/leds/led1/brightness > /dev/null
sleep 0.35
echo 0|sudo tee /sys/class/leds/led1/brightness > /dev/null
sleep 0.35
echo 1|sudo tee /sys/class/leds/led1/brightness > /dev/null
sleep 0.35
done
The recordswitch.sh script waits for input from the remote controller. It is programmed to kick off ffmpegwireless9.sh if the ENTER button is pushed, or process.sh if the UPLOAD button is pushed.
For testing purposes you may want to run process.sh by hand, i.e., ./process.sh, while you are viewing the display using a VNC viewer alongside the terminal screen.
The scripts are quite verbose and give lots of helpful output in their log files.
Upgrading from Raspberry Pi Lite to Raspberry Pi Desktop
Unfortunately the plugin I use inserts a blank line at the top. Those should all be removed.
After getting all the script, make them all executable in one go with a command such as chmod +x *sh
To read the input from the remote controller you need to set up evread.py and there may be some python work to do. This post has those details.
The chromium bowser needs to be run by hand one time over your VNC viewer. Its size has to be shrunk to 50% by running CTRL SHIFT – about four times. You need to log in to your YouTube or Gmail account so it remembers your credentials. And you need to og through the motions of uploading a video so it knows to use the 00uploads directory next time.
Don’t run a recording and an upload at the same time. I think the CPU would be taxed so I did not test that out. But you can record one day – even multiple recordings, and upload them a day or days later. That should work OK. It just processes the files one at a time, hopefully (untested).
announceit.sh is pretty dodgy. You have to understand SMTP mail somewhat to have a spitting chance for that to work. Fortunately I was an SMTP admin previously. So my ISP, Optimum, has a filter in place which prevents ordinary residential customers from sending out normal email to arbitrary SMTP addresses. However, to my surprise, they do run a mail relay server which you can connect to on the standard tcp port 25. I don’t really want to give it away but you can find it with the appropriate Internet search. I assume it is only for Optimum customers. Perhaps your ISP has something similar. So after you install exim4, you can configure a “smarthost” with the command dpkg-reconfigure exim4-config. But, again, you have to know a bit what you are doing. Suffice it to say that I got mine to work.
But for everyone else who can’t figure that out, just comment out this line in process.sh ./announceit.sh. put a # character in the front of the line to do that.
I have really only tested recordings of up to 45 minutes. I think an hour should be fine. I would suggest to break it up for longer.
The files can take a lot of space so you may need to clean up older files if you are a frequent user.
I’ve had about one failure during the upload out of about seven tests. So reliability is pretty good, but probably not perfect.
Why not just livestream? True, it’s sooo much easier. And I’ve covered how to do that previously.But, maybe it’s my WiFi, but its reliability was closer to 50% in my actual experience. I needed greater reliability and turns out I didn’t need the live aspect of the whole thing, just the recording for later critiqueing.
The recording approach I’ve taken uses ffmpeg to directly produce a mp3 file – it’s more compact than a WAV file. In and of itself the mp3 file may be useful to you, to, e.g., include as an attachment in email or whatever. For instance for a single song. All the mp3s are finally stored in a folder called mp3s, and all the videos are finally stored in a folder called flvs.
About that upload
The upload itself is super awesome to watch. I captured an actual automated upload with the script running on the right and the X Window display on the left in this YouTube video.
Somehow I managed to use some of these tools the other day and my mp3s ended up sounding like Alvin and the Chipmunks! I wondered if there was a way to recover them. I found there is, though I had to develop it a bit. It uses the new-ish rubberband filter of ffmpeg. I call this tiny script dechipmunk.sh:
In my case I had to slow things down and lower the pitch by the same factor: one third, hence the 0.3333.
How to pass multiple options to an ffmpeg filter
In doing the above I had to work out the syntax for passing more than one option to the new rubberband filter of ffmpeg. I wanted to specify both the pitch and the tempo options. So you see from above they had to be separated with a colon and the whole filter expression enclosed in quotes. Hence the funny-looking
“rubberband=pitch=0.3333:tempo=0.3333”
Future development
Well, I’m thinking of removing the chit-chat from the recording in an automated fashion. That may mean applying machine learning, or maybe something simpler if someone has covered this territory before for the RPi. But it might be a good excuse to do a shallow dive into machine learning.
Conclusion
I’m sure this method of YouTube upload is very flaky and will probably only work once or twice, if at all. But at least in my trials, it did work a few times. So perhaps it could be hardened and made more error-correcting. There are a lot of moving parts for it all to work. But it’s definitely cool to watch it go when it is working!
This post promises more than it actually delivers, ha, ha. It is squarely aimed at the more mid to advanced RPi enthusiast. Most who read this will get discouraged and look for another solution. I did the same in fact and I will review my failures with alternatives.
The essence of this aproach is screen automation with a very nice tool called xdotool. For me it works. It will definitely, 100% require some tweaks for anyone else. This is not run a few installs, copy this code and you’re good to go. But if you have the patience, you wil be rewarded with either fully or at least semi-automated video uploads to YouTube from your Raspberry Pi.
One caveat. Please obey YouTube’s terms of service. In other words, don’t abuse this! As soon as someone starts using this method in an aggressive or abusive fashion, we will all lose this capability. They have crack security experts and could squelch this approach in a heartbeat.
I actually don’t have all the peices in place for myself, but I have enough cool stuff that I wanted to begin to share my findings.
One beautiful thing about what I’m going to show is that you get to see the cursor moving about the screen in response to your automated commands – you see exactly what it;s doing, which screens it’s clicking through, etc. So if there’s an issue – say YouTube changes its layout – you’ll most likely be able to know how to adapt.
What’s wrong with using YouTube’s api?
Plenty. It used to be feasible. It certainly would make all our lives a lot easier. But YouTube is not a charity. They have squeezed out the little guy by making the barrier to entry so high that it’s really only available to highly determined IT folks. It’s just too difficult to figure out all the neeed screens, etc, and all the help guides refer to older api versions where things were different. YouTube clamped down in July 2020 on who or what can use their api. There’s a lot of old HowTos pre-dating that that will just lead you to dead-ends. So, go ahead, I dare you to stop reading this and use the api and report back. Maybe yuo manage to create a project, great, and an api key, great, and even to assign your api key the correct YouTube specific permissions – all great, and associate crednetials – super, and finally borrow someone’s code to upload a video – been there, done that. That video will be listed private. So then you try to root around to see what you have to do to make it public. Ah, a project review. Great. You were only in test mode. So no your confronted with this form. If they cared about the little guy there would be a radio button – “I only wish to upload a few videos a week for a small cadre of users, spare me the bureaucracy,” and that’d be it. But, no… Are you applying for a quota? Huh? I just want to upload a video and have it marked as unlisted. Some users remarked they filled out the form, never got their project reviewed and never heard back. Maybe they’re the exception, I don’t know. It’s just over the top for me so I give up.
OK. So, maybe YoutubeUploader?
Nope. Doesn’t work. It’s based on the old stuff.
OK. What about that guy’s api-less Node.js uploader?
Maybe. I could not get it to work on RPi. But I didn’t try super hard. I just like rolling my own, frankly. My approach is much more transparent. At least this approach inspired me to imagine the approach I am about to share. Because I believe the Node.js guy is just doing screen scraping but you can’t even see the screens.
Or simply do a Livestream?
Agreed. Livestreaming is quite straightforward by comparison with what I developed. My blog post about one click livestreaming covers it. But I have not had good results with reliability. As often as it works, it doesn’t work. With this new approach I’m going to try to create separate steps so that if anything goes wrong, an individual step can be re-run. Another advantage of separating steps is that a recording can be done “in the field” and without WiFi access. Remember an RPi 3 works great for hours with a decent portable USB battery that’s normally used for phones. Then the resulting recording can be converted to video and uploaded once the RPi is back to its usual WiFi SSID.
Preliminary upload, October 2021
In the video below the right screen is a terminal window showing what the script is doing. It needs some tweaking, and the YouTube window gets stuck so it’s not showing some of the screens. But it’s already totally awesome – and it worked!
@reboot sleep 15; /home/pi/recordswitch.sh > recordswitch.log 2>&1
# launch vnc server on display 1
@reboot sleep 65;x0vncserver -localhost no -passwordfile ~/.vnc/passwd -display :0 > x0vncserver.log 2>&1
Work with chromium the first time by hand. As I recall you should:
Create a directory like 00uploads – so it appears highest in the list
put a single video in 00uploads
Do an upload by hand (to help chromium remember to choose this upload directory)
launch chromium browser
log into your YouTube account at https://studio.youtube.com
shrink the browser until its size is 50% (Ctrl-Shift – about four times)
Don’t add other tabs and stuff to Chromium
Then subsequent launches of chromium should remember a bunch of these settings, specifically, your login info, the shrunken size, the upload directory, and maybe the (lack of) other tabs.
The beauty of this approach is that it is more transparent than the alternatives. You see exactly what your program is doing. You can issue the xdotool commands by hand to, e.g., change up the coordinates a little bit. Or even enter a video title.
So getting back to the idea, the automation idea is to finish a video somehow, then move it to the 00uploads dircetory, invoke this uploader program, then either move it to a uploaded directory or some such.
Imagine the versatility if I used my remote controller for RPi to map one button for audio recording, and a second button for automating video upload! Well, when I find the time that’s what I plan to do. I will make a separate post where the recording and uploading are shown – more or less the culmination of all the pieces.
Oh, and back to the idea again, I wanted to share the unlisted link with band members. So, you see how it is basically in the result of xsel -b since xsel copied the clipboard which contained the YouTube URL for this video we just uploaded? I have to fix up the parsing because some junk characters are getting included, but I plan to email that link to myself first, where I will do a brief manual check, and then forward it to the rest of the band. so, again, it’s really cool that we could even think to pull that off with this simplistic approach.
Techniques developed for this project
Lots.
I “discovered” – in the sense that Columbus discovered America – xdotool as an amazing X Windows screen automation tool. I knew of autohotkey for Windows so inquired what was like it for X Windows. I further learned that xdotool is generally broken when it comes to use with traditional VNC servers such as the native tightvncserver. It simply doesn’t work. But Tiger VNC is a scraping server so it like shares your console screen and makes it available via VNC protocol. That’s required because to develop this approach you have to see what you’re doing. All those coordinates? it comes from experimentation.
I also learned how to embed a YouTube video in my blog post. In fact this is the very first video I made for a blog post. So I did a screen recording for the first time with screen recorder for Windows.
I landed on the idea of a side-by-side video showing my terminal running the automated script in one window and the effect it is having on the chromium browser in the other window running on the RPi.
I put a wrapper around xdotool to make things cleaner. (But it’s not done yet.)
I changed to two-factor authentication to see if it made a difference. It did not. It still remembers the authentication, thankfully, at least for a few days. I wonder for how long though. Hmm.
Kiosk mode. By launching chromium with kiosk mode it not only gives us more screen real estate to work in, it in principle should also permit you to interact with chromium in a regular fashion and still have it come up in a known, fixed position, which is an absolute requirement of this approach. All the buttons have to have the same coordinates from invocation to invocation.
I also developed ffmpeg-based converters which take wav files and converts them to mp3’s (a nice compact format. wav files are space hogs), and another which takes mp3 files and adds a gray screen and converts them to flv ([Adobe] Flash Video, I guess – a compact video file format which YouTube accepts).
I also learned the ffmpeg command to tell exactly how long a recording is.
I also learned how to turn off blocking in ffmpeg so that its constantly writing packets and thus not losing audio data at the end when stopped.
I came up with the idea of randomizing the sleep time between clicks to make it seem more human-like.
And mostly for the purpose of demonstrations, though it also greatly helps in debugging, I introduced around two seconds of sleep both before and after a command is issued. That really makes things a lot clearer.
The results of the clipboard, xsel -b, contains null bytes. I had trouble parsing it to pull out just the url, but finally landed on using xargs -0 which is designed to parse null-delimited strings. And it worked! This was a late edition and did not make it into the video, but is in the provided script above towards the bottom.
ffmpeg chokes on too-complicated filenames. Who knew? I had files containing colon (:) and dash (-) characters which work perfectly fine in linux, but ffmpeg was interpreting part of the filename as a command-line argument it appeared. The way out of that mess was to introduce file: in front of the filename.
I’ll probably put my ffmpeg tricks into my next post because I want to keep this one lean and focused on this one upload automation topic.
Suppose, hypothetically, that you had super admin access to a CMA in SmartConsole v 80.40, but lacked ssh or GUI access to firewalls within that CMA? What could you do? Can you run commands in a pinch? Yes. You can. Here are some concrete examples.
Caveats
In the servers section of the domain you can right-click and choose “Run one-time script.” That’s great, but I think there are limits. It will time out a script that takes too long. IDK, maybe 10 seconds or so is the maximum time allowed. The returned text gets truncated if it’s too long. 15 lines of text is OK. 200 is not. Somewhere inbetween those two is the limit.
Running clish commands
clish commands can indeed be run this way. I was interested in examining a few routes on a firewall with many static routes. I ran:
clish -sc “set route-redistribution to bgp-as 38002.48928 from static-route 197.6.75.0/24 on”
Run a PING (best to restrict the number of ping packets)
ping -c3 1.1.1.1
Show a part of configuration, e.g., BGP stuff
clish -c “show configuration”|grep bgp|head -15
Show cluster IPs
cphaprob -vs all -a -m if|grep 10.182.136
Learn the name of the switch and switch port an interface is connected to (Cisco switches only)
This is a really awesome trick. And it works. Maybe it relies on something clled CDP. Not sure. But you run it and it will tell you the hostname of the switch and the port, e.g., eth1/5.
tcpdump -vnni eth1-08 -s 1500 -c 1 ‘(ether[12:2]=0x88cc or ether[20:2]=0x2000) and not tcp and not udp and not icmp’
The interface name eth1-08 above is just an example.
Better still, it will even tell you the management IP of the switch! That output will appear like this:
Management Addresses (0x16), value length: 13 bytes: IPv4 (1) 10.122.37.81
This command is general-putpose and works with any device with any OS, assuming you can run a packet trace with tcpdump or equivalent. Very cool.
Conclusion
Real firewall admins I know fail to realize that even when they lack shell access to a firewall they can pretty issue any command they need if they use the one-time script option in SmartConsole. It just helps to follow along the lines of the examples above – limiting output, etc. Even clish config changes can be made! A common reason to be in this situation is to learn someone changed a password or cleaned up old accounts.
As a bonus I show how to identify the name of the switch a firewall is connected to as well as the switch port and management IP of that switch. The general-purpose command works on any OS.
I’ve been reliable running ISC’s BIND server for eons. Recently I had a problem getting my slave servers updated after a change to the primary master. What was going on there?
The details
This was truly a team effort. I saw that the zone file had differing serial numbers on the master versus the slave servers. My attempts to update via an rndc refresh zone was having no effect.
So I tried a zone transfer by hand: dig axfr drjohnstechtalk.com @50.17.188.196
That timed out!
Yet, regular dns qeuries went through fine: dig ns drjohnstechtakl.com @50.17.188.196
I thought about it and remembered zone transfers use TCP whereas standard queries use UDP. So I tried a TCP-based simple query: dig +tcp ns drjohnstechtalk.com @50.17.188.196. It timed out!
So of course one suspects the firewall, which is reasonable enough. And when I looked at the firewal I found some funny drops, though i cuoldn’t line them up exactly with my failed tests. But I’m not a firewall expert; I just muddle through.
The next day someone from the DNS group asked how local queries behaved? Hmm. never tried that. So I tried it: dig +tcp ns drjohnstechtalk.com @localhost. That timed out as well! That was a brilliant suggestion as we now could eliminate the firewall and all that complexity from the equation. Because I had tried to do packet traces on two different machines at the same time and line up the results. It wasn’t easy.
The whole issue was very concerning to us because we feared our secondaries would be unable to pudate their slave zones and ultimately time them out. The result would be devastating.
We have support, fortunately. A company that hearkens frmo the good old days, with real subject matter experts. But they’re extremely busy. We did not get a suggestion for a couple weeks. But eventually we did. They had seen this once before.
named time to respond to TCP-based queries
The above graph is from a Zabbix monitor showing how long it takes that dns server to respond to that simple query. 6 s is a time-out. I actually set dig to timeout at 2 s, but in wall-clock time it actually takes 6 s.
The fix
We removed this line from the options block of named.conf:
keep-response-order {any; };
The info fmo the experts is that most likely that was configured as a workaround to CVE-2019-6477 but that issue was fixed since 9.15.6.
Conclusion
We encountered the named daemon in a situation where it was unable to respond to TCP-based DNS queries and hence unable to do zone transfers. So although most queries use UDP, this was a serious issue for us and prevented zones from being updated on all authoritative nameservers.
As is the case with so many modern IT problems, the effect was not black or white. Failures were intermittent, and then permanent. A restart fixed ths issue (forgot to mention so far!). But we involved an expert to find the root cause and it was the presence of a single configuration line in our named.conf. After removing that all was good.
Add a file to the staging area – must be done or won’t be saved in next commit
git add temp.txt or git add -A (add everything at once)
My working style is to change one to three files, and only add those.
Suppose you run git add, then change the file again, and then run git commit: what version will you push? The original! Run git add, etc all over again to pick up the latest changes. And note that your git adds can be run over the course of time – not all at once!
Create a snapshot of the changes and save to git directory??
Note that any committed changes won’t make their way to the remote repo
git commit –m “Message to go with the commit here”
Nota bene: git does not allow to add empty folders! If you try, you’ll simply see: nothing to commit, working tree clean
Put some “junk file” like .gitkeep in your empty folder for git add/git commit to work.
Set user-specific values
git config –global user.email youremail
Displays the list of changed files together with the files that are yet to be staged or committed
git status
Undo that git add you just did
git status to see what’s going on. Then
git restore –staged filename
and then another git status to see that that worked.
Send local commits to the master branch of the remote repository
(Replace <master> with the branch where you want to push your changes when you’re not intending to push to the master branch)
git push origin <master>
For real basic setups like mine, where I work on branch master, it suffices to simply do git push
Merge all the changes present in the remote repository to the local working directory
git pull
Create branches and helps you to navigate between them
git checkout -b <branch-name>
Switch from one branch to another
git checkout <branch-name>
View all remote repositories
git remote -v
Connect the local repository to a remote server
git remote add origin <host-or-remoteURL>
Delete connection to a specified remote repository
git remote rm <name-of-the-repository>
List, create, or delete branches
git branch
Delete a branch
git -d <branch-name>
Merge a branch into the active one
git merge <branch-name>
List file conflicts
git diff –base <file-name>
View conflicts between branches before a merge
git diff <source-branch> <target-branch>
List all conflicts
git diff
Mark certain commits, i.e., v1.0
git tag <commitID>
View repository’s commit history, etc
git log, e.g., git log –oneline
Reset index?? and working directory to last git commit
git reset –hard HEAD
Remove files from the index?? and working directory
git rm filename.txt
Revert (undo) changes from a commit as per hash shown by git log –oneline
git revert <hash>
Temporarily save the changes not ready to be committed??
git stash
View info about any git object
git show
Fetch all objects from the remote repository that don’t currently reside in the local working directory
git fetch origin
View a tree object??
git ls-tree HEAD
Search everywhere
git grep <string>
Clean unneeded files and optimize local repository
git gc
Create zip or tar file of a repository
Git archive –format=tar master
Delete objects without incoming pointers??
git prune
Identify corrupted objects
git fsck
Merge conflicts
Today I got this error during my usual git pull:
error: Pulling is not possible because you have unmerged files.
hint: Fix them up in the work tree, and then use 'git add/rm '
hint: as appropriate to mark resolution and make a commit.
fatal: Exiting because of an unresolved conflict.
I did not wish to waste too much time. I tried a few things (git status, etc), none of which worked. As it is a small repository without much at stake and I know which files I changed, I simply deleted the clone and re-cloned the repo, put back the newer versions of the changed files, did a usual git add and git commit and git push. All was good. Not too much time wasted in becoming a gitmaster, a fate I wish to avoid.
Ignore a file
Put the unqualified name of the file in .gitignore at same level as .git. It will not be added to the project. Use this for keeping passwords secret.
Test a command
Most commands have a –dry-run option which prevents it from taking any action. Useful for debugging.
Here I’ve combined work I’ve done previously into one single useful application: I can initiate the live streaming of our band practice on YouTube with the click of a single button on a remote control, and stop it with another click.
Equipment
Raspberry Pi 3 or 4 with Raspberry Pi OS, e.g., Raspbian Lite is just fine
Logitech webcam or USB microphone
USB extender (my setup needed this, others may not)
Universal USB-based remote control – see references for a known good one
Method 1
In this method I rapidly blink the onboard red power (PWR) LED of the RPi while streaming is active. Outside of those times it is a solid red. This is my preferred mode – it’s a very visible sign that things are working. I am very excited about this approach.
#!/bin/sh
# DrJ 8/30/2021
# https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi
# put LED into GPIO mode
echo gpio | sudo tee /sys/class/leds/led1/trigger > /dev/null
# flash the bright RED PWR (power) LED quickly to signal whatever
while /bin/true; do
echo 0|sudo tee /sys/class/leds/led1/brightness > /dev/null
sleep 0.5
echo 1|sudo tee /sys/class/leds/led1/brightness > /dev/null
sleep 0.5
done
#!/bin/sh
# DrJ 8/30/2021
# https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi
# put LED into GPIO mode
echo gpio | sudo tee /sys/class/leds/led1/trigger > /dev/null
# turn on the bright RED PWR (power) LED
echo 1|sudo tee /sys/class/leds/led1/brightness > /dev/null
#!/bin/bash
# DrJ 8/2021
# Control the livestream of audio to youtube
# works in conjunction with an attached keyboard
# I use bash interpreter to give me access to RegEx matching
HOME=/home/pi
log=$HOME/audiocontrol.log
program=continuousaudio.sh
##program=tst.sh # testing
PGM=$HOME/$program
# de-press ENTER button produces this:
match="1, 28, 0"
epochsOld=0
cutoff=3 # seconds
DEBUG=1
ledtime=10
#
echo "$0 starting monitoring at "$(date)
# Note the use of script -q -c to avoid line buffering of the evread output
script -q -c $HOME/evread.py /dev/null|while read line; do
[[ $DEBUG -eq 1 ]] && echo line is $line
# seconds since the epoch
epochs=$(date +%s)
elapsed=$((epochs-$epochsOld))
if [[ $elapsed -gt $cutoff ]]; then
if [[ "$line" =~ $match ]]; then
echo "#################"
echo We caught this inpupt: $line at $(date)
# see if we are already running continuousaudio or not
pgrep -f $program>/dev/null
# 0 means it's been found
if [ $? -eq 0 ]; then
# kill it
echo KILLING $program
pkill -9 -f $program; pkill -9 ffmpeg
pkill -9 -f blinkLED
echo Shine the PWR LED
$HOME/shineLED.sh
else
# start it
echo Blinking PWR LED
$HOME/blinkLED.sh &
echo STARTING $PGM
$PGM > $PGM.log.$(date +%m-%d-%y:%H:%M) 2>&1 &
fi
epochsOld=$epochs
fi
[[ $DEBUG -eq 1 ]] && echo No action taken. Continue to listen
fi
done
The crontab entry and the referenced files are the same as in Method 2.
Method 2
In method 2 I flash the built-in LED on the webcam for a few seconds before starting the audio, and again when the streaming has terminated – as visible signal that the button press registered.
#!/bin/bash
# DrJ 8/2021
# Control the livestream of audio to youtube
# works in conjunction with an attached keyboard
# I use bash interpreter to give me access to RegEx matching
HOME=/home/pi
log=$HOME/audiocontrol.log
program=continuousaudio.sh
##program=tst.sh # testing
PGM=$HOME/$program
# de-press ENTER button produces this:
match="1, 28, 0"
epochsOld=0
cutoff=3 # seconds
DEBUG=1
ledtime=10
#
echo "$0 starting monitoring at "$(date)
# Note the use of script -q -c to avoid line buffering of the evread output
script -q -c $HOME/evread.py /dev/null|while read line; do
[[ $DEBUG -eq 1 ]] && echo line is $line
# seconds since the epoch
epochs=$(date +%s)
elapsed=$((epochs-$epochsOld))
if [[ $elapsed -gt $cutoff ]]; then
if [[ "$line" =~ $match ]]; then
echo "#################"
echo We caught this inpupt: $line at $(date)
# see if we are already running continuousaudio or not
pgrep -f $program>/dev/null
# 0 means it's been found
if [ $? -eq 0 ]; then
# kill it
echo KILLING $program
pkill -9 -f $program; pkill -9 ffmpeg
sleep 1
echo turn on led for a few seconds
$HOME/videotst.sh &
sleep $ledtime
pkill -9 ffmpeg
else
# start it
echo turn on led for a few seconds
$HOME/videotst.sh &
sleep $ledtime
pkill -9 ffmpeg
sleep 1
echo STARTING $PGM
$PGM &
fi
epochsOld=$epochs
fi
[[ $DEBUG -eq 1 ]] && echo No action taken. Continue to listen
fi
done
I press the Enter button once on the remote to begin the livestream to YouTube. I press it a second time to stop.
By extension this could also control other programs as well (like the photo frame). And other keys could be mapped to other functions. Record-only, don’t livestream, anyone?
I want to do these things because it’s a little tight in the room where I want to livestream – hard to get around. So this keeps me from having to squeeze past other people to access the RPi to for instance power cycle it. In my previous treatment, I had livestreaming start up as soon as the RPi booted up, which means it would only stop when it was similarly powered off, which I found somewhat limiting.
The purpose of videotst.sh in Method 2
videotst.sh serves almost no purpose whatsoever! It can simply be commented out. It’s somewhat specific to my webcam.
You see, I wanted to get some feedback that when I pressed the ENTER button the remote control the RPi had read that and was trying to start the livestream. I thought of flashing one of the built-in LEDs on the RPi. I still need to look into that.
With the robotics team we had soldered on an external LED onto one of the GPIO pins, but that’s way too much trouble.
So what videotst.sh does for me is to engage the webcam, specifically its video component, throwing away the actual video but with the net result that the webcam’s built-in green LED illuminates for a few seconds! That lets me know, “Yeah, your button press was registered and we’re beginning to start the livestream.” You see, because when you run ffmpegwireless6.sh with this webcam, it’s all about the audio. It only uses the audio of the webcam and thus the green “in use” LED never illuminates, unfortunately, while it is livestreaming the pure audio stream. So, similarly, when you press ENTER a second time to stop the stream I illuminate the webcam’s LED for a few seconds by using videotst.sh once again.
Techniques developed for this project
evread.py does some nasty buffering of its output, meaning, although it dos read the key presses on the remote, it holds the results “close to its chest,” and then spits them out, all at once, when the buffer is full. Well, that totally defeats the purpose needed here where I want to know if there’s been a single click. After some insightful Internet searches (note that I did not use Google as a verb, a practice I carry into my personal communication) I discovered the program script, which, when armed with the arguments -q -c, allows you to unbuffer the output of a program! And, it actually works. Cool.
And I made the command decision to “eat” the input. You see the timer of 3 seconds in broadcastswitch.sh? After you’ve done any button press it throws away any further button presses for the next three seconds. I just think that’ll reduce the misfires. In fact, I might take up the practice of double-clicking the ENTER button just to be sure I actually pressed it.
I’m using the double bracket notation more in my bash scripts. It permits use of a RegEx comparison operator. =~. I love regular expressions. More the perl style, PCRE, while this uses extended regular expressions, ERE. But I suppose those are good as well.
Getting control over the power LED was a nice coup. I’m only disappointed that you cannot control its brightness. In the dark it throws off quite a bit of light. But you cannot.
The green LED does not seem nearly as bright so I chose not to play with it. What I don’t want is to have to strain to see whether the thing is livestreaming or not.
Of course getting the whole remote control thing to work at all is another great advancement.
Techniques still to be developed
I still might investigate using voice-driven commands in place of a remote. Obviously, that’s a big nut to crack. Even if I managed to turn it on, turning it off while ffmpeg has commandeered the audio channel is even harder. I wonder if ffmpeg can split the audio stream so another process can be run alongside it to listen for voice commands? Or if an upstream process in front of ffmpeg could be used for that purpose? Or simply run with two microphones (seems wasteful of material)?? Needs research.
Suppose you want to take this on the road? Internet service can be unreliable after all. It’s well known you can power the RPi 3 for many hours with a small portable battery. So how about mapping a second button on the remote to a record-only mode (using the arecord utility, for instance)?? Then you can upload the audio at a time of you convenience. That’s something I can definitely program if I find I need it.
Lingering Problems with this approach
Despite all the care I’ve taken with the continuousaudio.sh script, still, there are times when YouTube does not show that a livestream is going on. I have no idea why at this point. If I knew the cause, I’d have fixed it!
As the livestream aspect of this is actual immaterial to me, I will probably switch to a pure recording mode where I upload in a later step – perhaps all done by the remote control for pure convenience.
Since this blog post has become popular, I may keep it preserved as is and start a new one for this recording approach as some people may genuinely be interested in the livestream aspect.
A very rough estimate of the failure rate is maybe as high as 50% but probably no lower than 25%. So, not great odds if you’re relying on success.
There’s another issue which I consider more minor. The beginning of the stream always sounds like a tape played on fast forward for a few seconds. The end also cut off a few seconds early I think.
Conclusion
We have presented a novel approach to livestreaming on a Raspberry Pi 3 using a remote control for added convenience. All the techniques were home-developed at drjohnstechtalk.com. The materials don’t cost much and it really does work.
I have always been somewhat agog at the idea of limiting bandwidth on my linux servers. Users complain about slow web sites and you want to try it for yourself, slowing your connection down to meet the parameters of their slower connection. More recently I happened on librespeed, an alternative to speedtest.net, where you can run both server and client. But in order to avoid transferring too much data and monopolizing the whole line, I wanted to actually put in some bandwidth throttling. I began an exploration of available methods to achieve this and found some satisfactory approaches that are readily available on Redhat-type linuxes.
bandwidth throttling, bandwidth rate limiting, bandwidth classes – these are all synonyms for what is most commonly called traffic shaping.
What doesn’t work so well
I think it’s important to start with the walls that I hit.
Cgroup
I stumbled on cgroups first. The man page starts in a promising way
cgroup - control group based traffic control filter
Then after you research it you see that support was enabled for cgroups in linux kernels already long ago. And there is version 1 and 2. And only version 1 supports bandwidth limits. But if you’re just a mid-level linux person such as myself, it is confusing and unclear how to take advantage of cgroup. My current conclusion is that it is more a subsystem designed for use by systemctl. In fact if you’ve ever looked at a status, for instance of crond, you see a mention of a cgroup:
sudo systemctl status crond
? crond.service - Command Scheduler
Loaded: loaded (/usr/lib/systemd/system/crond.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2021-08-09 15:44:24 EDT; 5 days ago
Main PID: 1193 (crond)
Tasks: 1 (limit: 11278)
Memory: 2.1M
CGroup: /system.slice/crond.service
mq1193 /usr/sbin/crond -n
I don’t claim to know what it all means, but there it is. Some nice abilities to schedule and allocate finite resources, at a very high level.
So I get the impression that no one really uses cgroups to do traffic shaping.
apache web server to the rescue – not
Since I was mostly interested in my librespeed server and controlling its bandwidth during testing, I wondered if the apache web server has this capability built-in. Essentially, it does! There is the module mod_ratelimit. So, quest over, and let the implementation begin! Except not so fast. In fact I did enable that module. And I set it up on my librespeed server. It kind of works, but mostly, not really, and nothing like its documented design.
That’s their example section. I have no interest in such low limits and tried various values from 4000 to 12000. I only got two different actual rates from librespeed out of all those various configurations. I could either get 83 Mbps or around 162 Mbps. And that’s it. Merely having any statement whatsoever starts limiting to one of these strange values. With the statement commented out I was getting around 300 Mbps. So I got rate-limiting, but not what I was seeking and with almost no control.
So the apache config approach was a bust for me.
Trickle
There are some linux programs that are perhaps promoted too heavily? Within a minute of posting my first draft of this someone comes along and suggests trickle. Well, on CentOS yum search trickle gives no results. My other OS was SLES v 15 and I similarly got no results. So I’m not enamored with trickle.
tc – now that looks promising
Then I discovered tc – traffic control. That sounds like just the thing. I had to search around a bit on one of my OSes to find the appropriate package, but I found it. On CentOS/Redhat/Fedora the package is iproute-tc. On SLES v15 it was iproute2. On FreeBSD I haven’t figured it out yet.
But it looks unwieldy to use, frankly. Not, as they say, user-friendly.
tcconfig + tc – perfect together
Then I stumbled onto tcconfig, a python wrapper for tc that provides convenient utilities and examples. It’s available, assuming you’ve already installed python, through pip or pip3, depending on how you’ve installed python. Something like
$ sudo pip3 install tcconfig
I love the available settings for tcset – just the kinds of things I would have dreamed up on my own. I wanted to limit download speeds, and only on the web server running on port 443, and noly from a specific subnet. You can do all that! My tcset command went something like this:
More importantly – does it work? Yes, it works beautifully. I run a librespeed cli with three concurrent streams against my AWS server thusly configured and I get around 149 Mbps. Every time.
Note that things are opposite of what you first think of. When I want to restrict download speeds from a server but am imposing traffic shaping on the server (as opposed to on the client machine), from its perspective that is upload traffic! And port 443 is the source port, not the destination port!
Raspberry Pi example
I’m going to try regular librespeed tests on my home RPi which is cabled to my router to do the Internet monitoring. So I’m trying
Despite the strange delay-distro appearing in the tcshow output, the results are perfect. Here are my librespeed results, running against my own private AWS server:
Time is Sat 21 Aug 16:17:23 EDT 2021
Ping: 20 ms Jitter: 1 ms
Download rate: 100.01 Mbps
Upload rate: 9.48 Mbps
!
Problems creep in on RPi
I swear I had it all working. This blog post is the proof. Now I’ve rebooted my RPi and that tcset command above gives the result Illegal instruction. Still trying to figure that one out!
March, 2022 update. My RPi had other issues. I’ve re-imaged the micro SD card and all is good once again. I set traffic shaping policies as shown in this post.
Conclusion about tcconfig
It’s clear tcset is just giving you a nice interface to tc, but sometimes that’s all you need to not sweat the details and start getting productive.
Possible issue – missing kernel module
On one of my servers (the CentOS 8 one), I had to do a
$ sudo yum install kernel-modules-extra
$ sudo modprobe sch_netem
before I could get tcconfig to really work.
To do list
Make the tc settings permanent.
Verify tc + tcconfig work on a Raspberry Pi. (tc is definitely available for RPi.)
Conclusion
We have found a pretty nice and effective way to do traffic shaping on linux systems. The best tool is tc and the best wrapper for it is tcconfig.
References and related
Librespeed is a great speedtest.net alternative for hard-code linux types who love command line and being in full control of both ends of a speed test. I describe it here.
Power cycling one’s cable modem automatically via an attached RPi. I refer to this blog post specifically because I intend to expand that RPi to also do periodic, automated speedtesting of my home braodband connection, with traffic shaping in place if all goes well (as it seems to thus far).
Bandwidth management and “queueing discipline” in all its gory detail is explained in this post, including example raw tc commands. I haven’t digested it yet but it may represent a way for me to get my RPi working again without a re-image: http://www.fifi.org/doc/HOWTO/en-html/Adv-Routing-HOWTO-9.html
I was building some infrastucture around automated speedtest.net tests using speedtest-cli. I noticed the assigned servers keep changing, some servers are categorized as malicious sources, some time out if tested on the hour and half-hour, and results are inconsistent depending on which server you get.
So, I saw that the speedtest-cli (linux command-line python script) has a switch for a “mini” server. When I investigated that seemed the answer to the problem – you can set up your own mini server and use that for yuor tests. I.e., control both ends of the test. great.
The speedtest.net mini server was discontinued in 2017! There’s some commercial replacement. So I thought. Forget that. I was disillusioned and then happened upon a breath of fresh air – an open source alternative to speedtest.net. Enter, librespeed.
Some details
librespeed has a command-line program whih is an obvious rip-off of speedtest-cli. In fact it is called librespeed-cli and has many similar switches.
There is also a server setup. Really, just a few files you can put on any apache + php web server. There is a web GUI as well, but in fact I am not even that interested in that. And you don’t need to set it up at all.
What I like is that with the appropriate switches supplied to librespeed-cli, I can have it run against my own librespeed server. In some testing configurations I was getting 500 Mbps downloads. Under less favorable circumstances, much less.
Testing, testing, testing
I tested between Europe and the US. I tested through a proxy. I tested from the Azure cloud to an Amazon AWS server. I tested with a single cpu linux server (good old drjohnstechtakl.com) either as server, or as the client. This was all possible because I had full control over both ends.
Some tips
Play with the speedtest-cli switches. See what works for you. librespeed-cli -h will shows you all the options.
Increasing the stream count can compensate for slower PING times (assuming both ends have a fast connection)
It does support proxy, but
Downloads don’t really work through proxy if the server is only running http
Counterintuitively, the cpu burden is on the client, not the server! My servers didn’t show the slightest bit of resource usage.
Corollary to 5. My 4-cpu client to 1-cpu server test was much faster than the other way around where server and client roles were reversed.
Most things aren’t sensitive to upload speeds anyway so seriously consider suppressing that test with the appropriate switch. Your tests will also run a lot faster (18 seconds versus 40 seconds).
Worried about consuming too much bandwidth and transferring too much data? I also developed a solution for that (will be my next blog post)
So I am running a librespeed server on my little VM on Amazon AWS but I can’t make it public for fear of getting overrun.
ISPs that have excellent interconnects such as the various cloud providers are probably going to give the best results
It is not true your web server needs write access to its directory in my experience. As long as you don’t care about sharing telemetry data and all that.
To emphasize, they supply the speedtest-cli binary, pre-built, for a whole slew of OSes. You do not and should not compile it yourself. For a standard linux VM you will want the binary called librespeed-cli_1.0.9_linux_386.tar.gz
Example files
The point of these files is to test librespeed-cli, from the directory where you copied it to, against your own librespeed server.
#!/bin/sh
# see ./librespeed-cli -help for all the options
./librespeed-cli --local-json json-ns6 --server 864 --simple --no-upload --no-icmp --ipv4 --concurrent 4 --skip-cert-verify
Purpose: are we getting good speeds?
My purpose in what I am constructing is to verify we are getting good download speeds. I am not trying to hit it out of the park. That consumes (read, wastes) a lot of resources. I am targeting to prove we can achieve about 150 Mbps downloads. I don’t know anyone who can point to 150 Mbps and honestly say that’s insufficient for them. For some setups that may take four simultaneous streams, for others six. But it is definitely achievable. By not going crazy we are saving a lot of data transfers. AWS charges me for my network usage. So a six stream download test at 150 Mbps (Megabits per second) consumes about 325 MBytes download data. If you’re not being careful with your switches, you can easily nudge that up to 1 GB downloads for a single test.
My librespeed client to server tests ran overnight alongside my old approach using speedtest. The speedtest results are all over the place, with a bunch of zeroes for whatever reason, as is typical, while librespeed – and mind you this is from a client in the US, going through a proxy, to a server in Europe – produced much more consistent results. In one case where the normal value was 130 mbps, it dipped down to 110 mbps.
Testing it out at home
Test from a home PC against my own librespeed server
I made my test URL on my AWS server private, but a public one is available at https://librespeed.de/
There were two final issues with speedtest that were the straws that broke the camel’s back, and they are closely related.
When you resolve www.speedtest.net it hits a Content Distribution Network (CDN), and the returned results vary. For instance right now we get:
;; QUESTION SECTION:
;www.speedtest.net. IN A
;; ANSWER SECTION:
www.speedtest.net. 4301 IN CNAME zd.map.fastly.net.
zd.map.fastly.net. 9 IN A 151.101.66.219
zd.map.fastly.net. 9 IN A 151.101.194.219
zd.map.fastly.net. 9 IN A 151.101.2.219
zd.map.fastly.net. 9 IN A 151.101.130.219
Note that you can also run speedtest-cli with the –list switch to get a list of speedtest servers. So in my case I found some servers which procuced good results. There was one where I even know the guy who runs the ISP and know he does an excellent job. His speedtest server is 15 miles away. But, in its infinite wisdom, speedtest sometimes thinks my server is in Lousiana, and other times thinks it’s in New Jersey! So the returned server list is completely different for the two cases. And, even though each server gets assigned a unique number, and you can specify that number with the –server switch, it won’t run the test if that particular server wasn’t proposed to you in its initial listing. (It always makes a server listing call whether you specified –list or not, for its own purposes as to which servers to use.)
I tried to use some of tricks to override this behaviour, but short of re-writing the whole thing, it was not going to work. I imagined I could force speedtest-cli to always use a particular IP address, overwriting the return from the fastly results, but getting that to work through proxy was not feasible. On the other hand if you suck it up and accept their randomly assigned server, you have to put up with a lot of garbage results.
So set up your own server, right? The –mini switch seems built to accommodate that. But the mini server was discontinued in 2017. The commercial replacement seemed to have some limits. So it’s dead end upon dead end with speedtest.net.
Conclusion
An open source alternative to speedtest.net’s speedtest-cli has been identified and tested, both server and client. It is librespeed. It gives you a lot more control than speedtest, if that is your thing and you know a smidgeon of linux.
librespeed server: https://github.com/librespeed/speedtest . You basically can git clone it (just a bunch of js and php files) from: https://github.com/librespeed/speedtest.git
If, in spite of every positive thing I’ve had to say about librespeed, you still want to try the more commercial speedtest-cli, here is that link: https://www.speedtest.net/apps/cli
In this context a lot of people feel iperf is also worth exploring. I think it is a built-in linux command.
Say you want to check if a tcp port is open from your standard-issue Windows 10 PC. Can you? Yes you can. I will share a way that requires the fewest keystrokes.
A use case
We wanted to know if an issue with a network drive mapping was a network issue. The suggestion is to connect to port 445 on the remote server.
That’s for the working case. If it can’t establish the connection it will take awhile and the last line will be False.
What you can type to minimize keystrokes is
test-n <TAB> in place of test-netconnection. It will be expanded to the full thing.
Conclusion
On linux you have tools like nc (netcat), nmap, scapy and even telnet, that we network engineers have used for ages. On Windows the options may be more limited, but this is one good way to know of. In the past I had written about portqry as a similar tool for Windows, but it requires an install. This test-netconnection needs nothing installed.
