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by knute
Tue May 26, 2020 2:34 pm
Forum: General discussion
Topic: UFW is blocking my ftp traffic.
Replies: 17
Views: 1120

Re: UFW is blocking my ftp traffic.

In debian I entered: sudo ufw default deny . I don't know if that blocks outgoing or not but it is not required and if it blocks outgoing you are going to have all sorts of issues. And ftp uploading and downloading just works. As you now know there are two types of FTP, passive and active. I have f...
by knute
Fri May 22, 2020 9:30 pm
Forum: Beginners
Topic: Socket communication among multiple Raspberry Pis
Replies: 3
Views: 229

Re: Socket communication among multiple Raspberry Pis

thesisPi20 wrote:
Fri May 22, 2020 6:15 pm
Hi all,

As the title says, I need to create a system with multiple Raspberry Pis that the Pis can send simple socket messages among them. Do you have any suggestion how I can start this?
Are you talking messages as in data acq/dist or text messages for humans?
by knute
Fri May 22, 2020 2:54 pm
Forum: General discussion
Topic: UFW is blocking my ftp traffic.
Replies: 17
Views: 1120

Re: UFW is blocking my ftp traffic.

You don't want to open a port range. You want the firewall to take care of it for you. What you need to do is add the following to the end of /etc/ufw/before.rules: *raw :PREROUTING ACCEPT [0:0] -A PREROUTING -p tcp --dport 21 -j CT --helper ftp COMMIT That will make inbound passive FTP work. You on...
by knute
Thu May 21, 2020 6:35 pm
Forum: General discussion
Topic: UFW is blocking my ftp traffic.
Replies: 17
Views: 1120

Re: UFW is blocking my ftp traffic.

Well I have a couple of questions: Are there more rules in UFW than you posted? Are your problems with outgoing FTP or incoming? And a couple of observations: Your rules seem too complex for a simple installation. There is a fault in UFW that prevents inbound passive FTP from working correctly. If t...
by knute
Tue May 19, 2020 1:41 am
Forum: Java
Topic: Running multithreaded application on RPi
Replies: 5
Views: 1119

Re: Running multithreaded application on RPi

Did you get it running? If not, post your code and I'll take a look.
by knute
Thu Apr 16, 2020 2:11 am
Forum: Java
Topic: Remote Java IDE for Raspberry Zero, where to start?
Replies: 3
Views: 996

Re: Remote Java IDE for Raspberry Zero, where to start?

For embedded Java take a look at bell-sw.com. For IDEs you are on your own :-).
by knute
Fri Apr 10, 2020 1:33 am
Forum: Graphics, sound and multimedia
Topic: Turn the pi into a webcam
Replies: 1
Views: 277

Re: Turn the pi into a webcam

Take a look at my website, pi.knutejohnson.com, there is a complete set of instructions to operate the camera and serve the image with apache.
by knute
Tue Apr 07, 2020 2:00 am
Forum: Java
Topic: How to use ArrayList in multi-threaded environment?
Replies: 3
Views: 741

Re: How to use ArrayList in multi-threaded environment?

I have been found it is hard to use ArrayList in the multithreaded environment. I want a solution to use ArrayList in a multithreaded environment. There are many ways but it depends a lot on what your use case is. Here is the quote from the docs: "Note that this implementation is not synchronized. ...
by knute
Tue Apr 07, 2020 1:50 am
Forum: Java
Topic: How to use ArrayList in multi-threaded environment?
Replies: 3
Views: 741

Re: How to use ArrayList in multi-threaded environment?

See post below.
by knute
Mon Mar 30, 2020 6:30 pm
Forum: Java
Topic: Pi Zero w and Java
Replies: 2
Views: 2997

Re: Pi Zero w and Java

There is a problem with Pi 0s and 1s with newer Javas. There are four openjdks available in the repository, 8, 9, 10 and 11. 8, 9 and 10 will run on a Pi 0 if you install openjdk-?-jre-zero and use the -zero command line option. openjdk-8 also appears to run without that on a Pi 0. There is no openj...
by knute
Mon Mar 23, 2020 8:31 pm
Forum: Português
Topic: GUI
Replies: 1
Views: 439

Re: GUI

Não sei qual software foi usado para esse gráfico, mas esse tipo de coisa é muito fácil de fazer em Java.
by knute
Wed Mar 04, 2020 10:47 pm
Forum: Beginners
Topic: Will a real time clock be found/configured on a new OS install?
Replies: 6
Views: 450

Re: Will a real time clock be found/configured on a new OS install?

DougieLawson wrote:
Mon Mar 02, 2020 5:58 pm
Add

Code: Select all

 dtoverlay=i2c-rtc,ds3231
to /boot/config.txt and your RTC will be recognised when you poweroff, connect it and reboot.
Dougie do you still need to kill off the fake-hwclock and modify /lib/udev/hwclock-set?
by knute
Fri Feb 21, 2020 9:04 pm
Forum: Raspberry Pi OS
Topic: Apache2 & CGI Setup
Replies: 4
Views: 863

Re: Apache2 & CGI Setup

So enabling CGI is very simple with current apache. You don't need to edit ANY files. Just run the command: sudo a2enmod cgid Next put your CGI files in the /usr/lib/cgi-bin directory. They need to be executable by www-data. That's it! I would guess that your 500 error is caused by some permission p...
by knute
Thu Feb 13, 2020 3:42 am
Forum: Networking and servers
Topic: Hosting Multiple Websites on RPi 4 - Help Needed
Replies: 3
Views: 930

Re: Hosting Multiple Websites on RPi 4 - Help Needed

I have website1.com inside of "/var/www/website1.com/public_html/index.php" and I have website2.com inside of "/var/www/website2.com/public_html/index.php" "<VirtualHost *:80> ServerAdmin admin@Website1.com ServerName Website1.com ServerAlias www.Website1.com DocumentRoot /var/www/Website1/public_h...
by knute
Sun Feb 09, 2020 3:02 am
Forum: Networking and servers
Topic: Can't ssh into raspberry pi from internet unless 0.0.0.0 Listen address is in sshd_config
Replies: 22
Views: 1993

Re: Can't ssh into raspberry pi from internet unless 0.0.0.0 Listen address is in sshd_config

Two NICs? /etc/hosts has no 205. address?

You don't need the two Port ### lines if you have the ListenAddress lines with the same ports. I want to see ip a too.
by knute
Fri Feb 07, 2020 3:54 pm
Forum: Java
Topic: Terminal printing over JavaFX application
Replies: 4
Views: 4377

Re: Terminal printing over JavaFX application

Post an SSCCE and I'll look at the problem for you.
by knute
Thu Feb 06, 2020 2:11 am
Forum: Advanced users
Topic: USB WiFi hangs intermittently
Replies: 0
Views: 235

USB WiFi hangs intermittently

I've got a Pi2B with a USB WiFi dongle that hangs up every now and then. I originally thought it was the Pi dying but the WiFi dongle goes deaf. If I pull it out of it's socket and put it back my Pi is back up and running just fine. Is there a way to power cycle the USB ports with software so I can ...
by knute
Thu Feb 06, 2020 1:57 am
Forum: Troubleshooting
Topic: RPi4 - serious (UDP) network issues
Replies: 22
Views: 2916

Re: RPi4 - serious (UDP) network issues

Anyhow. Which buffers did you change to what size? We've got about 200 NUCs running Xubuntu 18.04. We send them a lot of UDP datagrams. For those we created a file 80-sysctl.conf in /etc/sysctl.d. In that we put: net.core.rmem_max=4194304 This improved the lost packet situation for us. I've seen fo...
by knute
Wed Feb 05, 2020 3:49 pm
Forum: Beginners
Topic: Building a small Raspberry Pi phone
Replies: 10
Views: 1972

Re: Building a small Raspberry Pi phone

AJ Hunter wrote:
Wed Feb 05, 2020 10:20 am
Well i am basically going for a VoIP solution
Take a look at the intercom code I wrote for the Pi, http://knutejohnson/pi. It is basically VoIP. You could cludge up an old phone handset with a USB mic and speaker.
by knute
Wed Feb 05, 2020 3:39 pm
Forum: Troubleshooting
Topic: RPi4 - serious (UDP) network issues
Replies: 22
Views: 2916

Re: RPi4 - serious (UDP) network issues

Don't know if this will help you but we found that increasing the receive buffer size significantly reduced the number of lost UDP packets.
by knute
Wed Feb 05, 2020 3:30 pm
Forum: Java
Topic: Install OpenJFX 13 on Raspberry Pi 3B and Raspbian
Replies: 5
Views: 1846

Re: Install OpenJFX 13 on Raspberry Pi 3B and Raspbian

I'm sorry, I really don't know anything about Maven or even what it does.
by knute
Tue Feb 04, 2020 10:06 pm
Forum: Java
Topic: How to install jre / jdk on RPi zero
Replies: 2
Views: 1537

Re: How to install jre / jdk on RPi zero

That problem had me going for some time. The OpenJDK 11 in the repository won't run on a Pi 0 or 1. I think you can still install JDK 8 from the repository and get it to work but the best answer is to download the Zulu OpenJDK for Arm from azul.com. Azul has both a JDK 8 and JDK 11 available for the...
by knute
Tue Feb 04, 2020 7:21 pm
Forum: Java
Topic: Install OpenJFX 13 on Raspberry Pi 3B and Raspbian
Replies: 5
Views: 1846

Re: Install OpenJFX 13 on Raspberry Pi 3B and Raspbian

You can't get it from the repository but you can download it from https://gluonhq.com/products/javafx/ or you can get a complete JDK from BellSoft, https://bell-sw.com/ with their version of JavaFX. They have three versions available, I like the full version that includes JavaFX and the DeviceIO API...
by knute
Thu Jan 30, 2020 9:06 pm
Forum: Troubleshooting
Topic: Apache Update
Replies: 3
Views: 711

Re: Apache Update

creative-2008 wrote:
Thu Jan 30, 2020 8:56 pm
What am I missing? Is it that I don't have the latest version of Raspbian, and I can't update Apache without updating that first.
Most likely. My Raspbian Buster is up to date and I have apache version 2.4.38.
by knute
Tue Jan 28, 2020 10:21 pm
Forum: Raspberry Pi OS
Topic: Apache2 website permissions???
Replies: 4
Views: 421

Re: Apache2 website permissions???

The permissions for apache can drive you crazy. The thing to remember is that apache runs as www-data and needs to be able to read HTML files. They can be owned by anybody as long as they are readable by www-data. Usually this means world readable. The directory /var/www/html is owned by root and of...

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