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
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.
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.
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
!
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).
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 Amazno 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.
References and related
Just to do your own test with your browser the way you do with speedtest.net: https://librespeed.de/
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
Say you want to check if a tcp port is open frmo yuor 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.
I am kind of annoyed that my simple problem with a Dyson Animal vacuum cleaner took way more Internet research than should have been the case to resolve. I hope to spare someone else that grief.
The details
Actually this is a friend’s vacuum cleaner. I don’t think it would have played out this way had I been the exclusive user of it. She noted that it stops and starts. It goes for a few seconds and stops. Then you can start it up for a few more seconds. And so on.
More clues
This model shows the charge remaining on the battery. Still two bars out of three, so that’s good. It’s been properly charged. After examining it I get the gut feeling that the brush motor shouldn’t draw all that much power.
We also note that when the long tube is removed and its just acting as a short hand-held device, it doesn’t stop.
After doing some Internet research (not finding an exact hit for this model), I am inspired to take things apart and check all the filters. On other models the filters can do you in. This one has been very lightly used to date and so the filters are remarkably clean. No filter issue.
The solution
So I check the brush and that area. It is simply clogged with gray dirt. I begin to clear it out with my fingers – seems no easy way to do it – until all the gray dirt is gone from the brush area where it goes up into the tube.
The results
The results are in. Works like a champ now!
Comment
I am more used to a more obscure brand of vacuum cleaner, Miele. It has a simple orange status thing that visibly shows you when it can’t suck in dirt or what not due to a full bag, a clog, whatever. In addition you can pretty much hear the pitch of the motor’w whine increase when there’s a clog. With the Dyson I didn’t notice that pitch change, nor was there any indicator of a cloged system. So Dyson’s design is faulty.
Conclusion
A Dyson Animal vacuum cleaner was only running for a few seconds at a time. After a few more seconds it could run again. The power level showed two of three led bars. The filters were all clean, but the brush head was clogged with dirt. Cleaning that out fixed everything nicely.
Dyson’s design has to be faulted for not making this clogged situation more evident. Strange, coming from a company which obviously prides itself on its innovative design.
I’m imagining a scenario where yuo are in a world where a private pki reigns. In that case you want to just make sure lftp knows where to find the private root CA and possibly the intermediate CA.
So of interest here is that it involved a 64×64 LED matrix display, and a “hat” sold by Adafruit to supposedly make things easier to connect.
Now I am not a hardware guy and never pretended to be. When we realized that it required soldering, I bought those supplies but I didn’t want to be the one to mess things up so he volunteered for that. And yes, it was a mess.
Equipment
See later on in the post for the equipment we used.
The story continues
Who knew that gold on the PCB could be ruined so easily after you’ve changed your mind about a soldered joint and decided to undo what you’ve done? The experience pretty much validated my whole approach to staying away from soldering. So we ruined that hat and had to order another one. While we waited for it I developed a certain strtategy to deal with the shortcomings of the partially destroyed hat. See the section at the bottom entitled Recipe for a broken hat.
Comments on the project
I don’t think the guy did a good job. Details left out where needed, extra stuff added. For instance you don’t need to order that Firebeetle – it’s never used! Also, I’ve been told that his python isn’t very good either. But in general we followed his skimpy instructions. So we ordered the LED matrix from DFRobot, not Adafruit, and I think it’s different. In our case we did indeed follow the project suggestion to wire the 2×8 pin as shown in their (DFRobot’s) picture, leaving out the white wire. Once we soldered the white wire to the hat’s gpio pin 24, we were really in business. What we did not need to do is to solder pin E to either pin 8 or 16. (This is something you apparently need to do for the Adafruit LED.) In our testing it didn’t seem to matter whether or not those connections were made so we left it out on our second hat.
You think he might have mentioned just how much soldering is involed. Let’s see you have 2×20 connector, a 2×8 connector plus a single gpio connection = 57 pins to solder. Yuck.
What we got to work
Deploying images on these LED displays is cool. You just kind of have to see it. It’s hard to describe why. The picture below does not do it justice. Think stadium scoreboard.
In rpi-rgb-led-matrix/utils directory we followed the steps in the README.md file to compile the LED viewer:
#!/bin/sh
# invert images because the sound stuff is otherwise upside-down
sudo led-image-viewer –led-pixel-mapper=”U-mapper;Rotate:180″ –led-gpio-mapping=adafruit-hat –led-cols=64 –led-rows=64 /home/pi/walk-in-the-woods.jpg
Walk in the woods
Do we have flicker? Just a tiny bit. You wouldn’t notice it unless yuo were staring at it for a few seconds, and even then it’s just isolated to a small section of the display. Probably shoddy soldering – we are total amateurs.
Tip for your images
Consider that you only have 64 x 64 pixles to work with. So crop your pictures beforehand to focus on the most interesting aspect – people if there are people in the picture (like we’ve done in the above image), specifically faces if there are faces. Otherwise everything will just look like blurs and blobs. You yourself do not have to resize your pictures down to 64 x 64 – the led software will do the resizing. So just focus on cropping down to a square-sized part of the picture you want to draw attention to.
Real-time audio
So my friend got a USB microphone. I developed the following script to make the python example work with real-time sounds – music playing, conversatiom, whatever. It’s really cool – just the slightest lag. But, yes, the LEDs bounce up in response to louder sounds.
So in the directory rpi-rgb-led-matrix/bindings/python/samples I created the script drjexample.sh.
#!/bin/sh
# DrJ 6/21
# make the LED react to live sounds by use of a USB microphone
# I am too lazy to look up how to make the python program read from STDIN so I will just
# make the equivalent thing by creating test.wav as a nmed pipe. It's an old linux trick.
rm test.wav; mkfifo test.wav
# background the python program. It will patiently wait for input
sudo python spectrum_matrix.py &
# Now run ffmpeg
# see my own post, https://drjohnstechtalk.com/blog/2019/04/live-stream-to-youtube-from-a-raspberry-pi-webcam/
ffmpeg \
-thread_queue_size 4096 \
-f alsa -i plughw:1,0 \
-ac 2 \
-y \
test.wav
So note that by having inverted the image (180 degree rotation) we have the sounds bars and images both in the same direction so we can switch between the two modes.
I believe to get the python bindings to work we needed to install some additional python libraries, but that part is kind of a blur now. I think what should work is to follow the directions in the README.md file in the directory rpi-rgb-led-matrix/bindings/python, namely
sudo apt-get update && sudo apt-get install python2.7-dev python-pillow -y make build-python sudo make install-python
Hopefully that takes care of it. For sure you need numpy.
Future project ideas
How about a board that normally plays a slideshow, but when the ambient sound reaches a certain level – presumably because music is playing – it switches to real-time sound bar mode?? We think it’s doable.
Recipe for a broken hat
For the LED matrix display we got the DFRobot one since that’s what was linked to in the project guide. But the thing is, the reviewer’s write-up is incomplete so what you need to do involves a little guesswork.
At the end of the day all we could salvage while we wait for a new Adafruit hat to come in is the top fourth of the display! The band below it is either blank, or if we push on the cables a certain way, an unreliable duplicate of the top fourth.
The next band suffers from a different problem. Its blue is non-functional. So it’s no good…
And the last band rarely comes on at all.
OK? So we’re down to a 16 x 64 pixel useable area.
But despite all those problems, it’s still kind of cool, I have to admit! I know at work we have these digital sign boards and this reminds me of that. So first thing I did was to create a custom banner – scrolling text.
I call this display program drjexample2.sh. I put it in the directory rpi-rgb-led-matrix/examples-api-use
But that requires the existence of a ppm file containing the text I wanted to scroll, since I was working by example. So to create that custom PPM file I created this python script.
Once I discovered the problem with the bands – by way of running all the demos and experimenting with the arguments a bit – I noticed this directory: rpi-rgb-led-matrix/utils. I perked right up because it held out the promise of displaying jpeg images. Anyone who has seen any of my posts know that I am constantly putting out raspberry pi based photo displays in one form or another. For instance see https://drjohnstechtalk.com/blog/2021/01/raspberry-pi-photo-frame-using-the-pictures-on-your-google-drive-ii/
But see how cool it is? No? It’s a sleeping, recumbent baby. It’s like the further away from it you get, the clearer it becomes. Trust me in person it does look good. And it feels like creating one of those bright LED displays they use in ballparks.
But this same picture also shows the banding problem.
To get the picture displayed I first cropped it to make it wide and short. I wisely chose a picture which was amenable to that approach. I created this display script:
It went kind of slowly on my RPi 3, but it worked without incident. When I initially ran the led-image-viewer nothing displayed. So the script above shows the results of my experimentation which seems appropriate for our particular matrix display.
How did we get here?
Just to mention it, we followed the general instructions in that project. So I guess no need to repeat the recipe here.
Slideshow
You know I’m not going to let an opportunity to create a slideshow go to waste. So i created a second appropriately horizontal image which I might effectively show in my narrow available band of 16 x 64 pixels. just to share the little script, it is here:
My friend ordered all the stuff listed on the DFRobot project page, including their 64×64 LED matrix. Probably a mistake. They basically don’t document it and refer you to Adafruit, where they deal with a 64×64 LED matrix – their own – which may or may not have the same characteristics, leaving you somewhat in limbo. Next time I would order from Adafruit.
As mentioned above that gold foil on printed circuit boards really does come off pretty easily, and then you’re hosed. Because of the lack of technical specs we were never really sure if we needed to solder the E contact to 8 or to 16 and destroyed all those terminals in the process of backing out.
I actually created custom ppm files of solid colors, red, blue, green, white, so that I could prove my suspicions about the third band. Red and green display fine, blue not at all. White displays as yellow.
Viewed close up, the LED matrix doesn’t look like much, and of course I was close up when I was working with it. But when I stepped back I realized how beautiful a brightly illuminated picture of a baby can be! The pixels merge and your mind fills in the spaces between I guess.
The original idea was to tackle sound but I got stuck on the ability to use it as a photo frame (you know me). But he wants to return to sound which I am dreading….
Testing audio
In our first tests. the audio example wasn’t working. But now it seems to be. The project guy’s python code is named spectrum_matrix.py if I recall correctly. It goes into rpi-rgb-led-matrix/bindings/python/samples. And as he says, you run it from that directory as
$ sudo python spectrum_matrix.py
But, his link to test.wav is dead – yet another deficiency in his write-up. At least in my testing not every possible WAV file may work. This one, moo sounds, does however. http://soundbible.com/grab.php?id=1778&type=wav So, it plays for a few seconds – I can hear it through earphones – and the LEDs kind of go up and down. We recorded a wav file and found that that does not work. The error reads like this:
Home directory not accessible: Permission denied
W: [pulseaudio] core-util.c: Failed to open configuration file '/root/.config/pulse//daemon.conf': Permission denied
W: [pulseaudio] daemon-conf.c: Failed to open configuration file: Permission denied
Traceback (most recent call last):
File "spectrum_matrix.py.orig", line 56, in
matrix = calculate_levels(data,chunk,sample_rate)
File "spectrum_matrix.py.orig", line 49, in calculate_levels
power = np.reshape(power,(64,chunk/64))
File "/usr/lib/python2.7/dist-packages/numpy/core/fromnumeric.py", line 292, in reshape
return _wrapfunc(a, 'reshape', newshape, order=order)
File "/usr/lib/python2.7/dist-packages/numpy/core/fromnumeric.py", line 56, in _wrapfunc
return getattr(obj, method)(*args, **kwds)
ValueError: cannot reshape array of size 2048 into shape (64,64)
Note that I had renamed the original spectrum_matrix.py to spectrum_matrix.py.orig because we started messing with it. Actually, I pretty much get the same error on the file that works; it’s just that I get it at the end of the LED show, not immediately.
Superficially, the two files differ somewhat in their recording format:
I played the voice.wav on a Windows PC – it played just fine. Just a little soft.
So what’s the essential difference between the two files? Well, something that jumps out is that the one is mono, the other stereo. Can we somehow test for that? Yes! I made the simplest possible conversion af a mono to a stereo file with the following ffmpeg command:
I copy converted.wav to test.wav and re-run spectrum_matrix.py. This time it works!
Not sure how my friend produced his wave file. But I want to make one on my own. He had plugged a USB microphone into the RPi. I have done research somewhat related to this – publishing a livestream to Youtube, audio only, video grayed out. That’s in this post: https://drjohnstechtalk.com/blog/2019/04/live-stream-to-youtube-from-a-raspberry-pi-webcam/ So I am not afraid to se ffmpeg any longer. So I created this tiny script, record.sh, with my desired arguments:
My friend wants the LED to respond to live input such as his stereo at home. Being a terrible python programmer but at least middling linux techie, I see a way to accomplish it without his having to touch the sample program by employing an old Unix trick: named pipes. So I create this script, drjexample.sh which combines all the knowledge we gained above into one simple script:
#!/bin/sh
# DrJ 6/21
# make the LED react to live sounds by use of a USB microphone
# I am too lazy to look up how to make the python program read from STDIN so i will just
# make the equivalent thing by creating test.wav as a nmed pipe. It's an old linux trick.
rm test.wav; mkfifo test.wav
# background the python program. It will patiently wait for input
sudo python spectrum_matrix.py &
# Now run ffmpeg
# see my own post, https://drjohnstechtalk.com/blog/2019/04/live-stream-to-youtube-from-a-raspberry-pi-webcam/
ffmpeg \
-thread_queue_size 4096 \
-f alsa -i plughw:1,0 \
-ac 2 \
-y \
test.wav
So a named pipe is just that. Instead of the pipe character we know and love, you coordinate process output from the first process with process input of the second process by way of this special file. The operating system does all the hard work. But it works just as though you had used the | character.
Best of all, this script actually works, to wit, the LED is now responding to live input. I see it jump when I say test into the microphone. Unknown to me is if it will play for extended periods of time – it would be easy for one process to output faster than the other can input for instance, so a backlog builds up. The responsiveness is good, I would guess around no more than 200 ms lag.
Equipment
We used the equipment from this post, except the Firebeetle. You know, that’s just another reason I consider that post to be a sloppy effort. Who lists a piece of equipment that they don’t use?? And again, next time I would rather search for an LED display from Adafruit. We use an RPi 3 and installed the image on a micro SD card with the new-ish Raspberry Pi imager, which works just great:Introducing Raspberry Pi Imager, our new imaging utility – Raspberry Pi
Oh, plus the soldering iron and solder. And a multi-colored ribbon cable with female couplers at one end and a 2×8 connector on the other. Not sure if that came with the LED or not since I didn’t order it.
Our power supply is about 5 amps and plugs into the hat. We do not need power for the RPi.
