I'm trying to read the NTP status on red hat linux server, but I'm getting socket timeout receive error
java.net.SocketTimeoutException: Receive timed out
This code works when run against a system using ntpd but not for chronyd?
I expect it's a configuration issue? I've run chronyc tracker and all looks good.
Any ideas as to why this isn't working?
Chrony is a NTP v4 server, which is backwards compatible with a NTP v3 client at best. The code we are using to query the server follows the NTP v2 protocol, which is why it does not work.
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Newbie in the community, here. First of all, thanks for all the help in all these years i've been working on embedded development :D
I have a problem with an Atmel AT91RM9200 ARM microprocessor, connected via RMII to a Mikrel KSZ8863 ethernet physical interface. The ARM is loaded with U-Boot 1.1.2, which loads the Linux Kernel v2.4.27.
I manually added the code to interface U-Boot with the KSZ.
The problem is:
Using U-Boot, if I try to download something from my TFTP server (located in the same network), the connection sometimes has so many timeouts that the download fails, and sometimes has just 2 or 3 timeouts.
I checked the U-Boot FAQ page, and the most probable reason for the timeouts is a wrong speed configuration, which I double checked.
What could be the reason for the unreliability of my connection?
Thanks,
Loranzp.
Setup a minimalist network consistent of TFTP server, client and Sniffer (Wireshark in promiscuous mode) (if you use a switch it must have a repeater port where to connect the sniffer PC)
Next run traffic captures and analyze when and how the timeouts occur.
Consider:
TFTP BlockSize too big leading to mishandled IP fragmentation.
Server provides the packets too fast after REQ or ACK
Not correctly handling block number roll-over (only when handling big files)
etc
i use a Mac from programming in C through Xcode. The version is macOS Mojave 10.14.
The code i'm using has a client who asks for time and a server who replies giving him the current time printed through a UDP connection.
I use client 127.0.0.1 to launch client.
The code works perfectly on linux, but on Mac it just starts loading and never stop.
These are the codes.
UDP Client
https://github.com/lufth/UDPClientServer/blob/master/clientUDP
UDP Server
https://github.com/lufth/UDPClientServer/blob/master/serverUDP
In Mac OS, there are several security features in place which is different from a linux machine. Maybe you could check to ensure if your program is not hindered by these 2 security features
Code Signing
Sandbox
For the sandbox, you may check if your UDP client / server executable is attempting to read/write to a location which is outside its allowed locations.
Alternatively, you may also try to run your server and client as root too
sudo java client.java 1111
The address_len parameter to recvfrom is an in/out parameter, but in your server you are passing a pointer to an uninitialized variable, len.
(Also, it is probably a good idea to give your C source files names ending in .c.)
I am currently working on a embedded c project using mqtt 3.1.1 and mosquitto broker 1.4.3. the issue I have is when the client board is publishing and subscribed to the same topic, after a random number of messages the client is blocked and the connection gets timed-out.
I am trying to send a string message, 25 bytes, over 3G network. Using QOS2 on both pub & sub, I have tried different settings on the client for keepalive (15s <-> 120s) and have a delay between each message (2000ms <-> 300000ms), on the broker I have tried different settings also, but nothing seem to work, is it possible to send messages using QOS2 over a 3G network or am I expecting too much?
We want to guarantee the transfer of some data that is critical so if this is not possible on mqtt is there a better alternative?
A keepalive of 120ms sounds bogus.
Keepalive is there for the broker to detect that a client may have gone missing, without having to wait for the TCP connection to time out. You would typically use a keepalive in the range of seconds, if not minutes.
With a keepalive of 120ms, you have to send a PING packet at least every 100ms or so (or do any other MQTT exchange in that time frame), so it might explain why you are introducing so much latency in your scenario – and probably killing your 3G data plan too ;-)
I suggest you start using a keep-alive of 30s to see if that improves things.
I have a small server program in C which prints a message to the client. This program uses UDP Port for communication.
My question is: Is there a way or application by which I can test the functionality of my program from my windows machine. Example, if I type in some command, I can see the response from my program on my computer.
telnet xx.xx.xx.xx. PortNum, I believe telnet wpuld not work.
Not aware of any existing tools. I assume your server receives a message from the client and sends a response message back. If this is correct, create a basic client program which sends a message (sendto()) and then calls recvfrom() (default is blocking mode on my platform), then print the response message received. This works well for me. Don't have time to ferret around for an example (which is on linux) but you should be able to use an example udp client for windows from the web, I imagine. Let me know if you would like my client program as a template.
I think you may want to use netcat; if it's installed on your machine, it's typically executed by "nc"
netcat can connect to or listen on tcp or udp ports; -u is udp.
nc -u host port # connect to a udp port
nc -u -l 127.0.0.1 1026 # listen on port 1026, in udp mode.
etc.
I'm running a game website where users connect using an Adobe Flash client to a C server running on a Fedora Linux box.
Often users complain about disconnects. Usually they're "Connection reset by peer"-disconnects.
Is there any way to make the connection more stable or does it all depend on the route from the user host to my server?
One thing I tried is to make it more stable by sending PING in clear text every other minute to avoid timeout problems.
Anyone got more ideas?
You are not exhausting the number of socket/memory use/cpu that the server process is given on the server, are you?
Do check with ulimit.
Also, if possible try to trace the error message in the source code (when a RST packet is sent--), i.e. when a send() or accept() returns an error value. In such cases print a debug message into the logs; if you really fancy debugging it do a simulation of the server:
run it into debug mode on a separate machine (possibly a clone of the server)
simulate thousands of connection (or find a network harnessing program)
backtrace the call and/or sniff the connection
where are you running the server?
at home? at work? at a hosting facility?
this will make a very big difference.
Can you design your app to connect to two sockets on the server and then load balance or make it active/passive (or active/active)?
You can use SO_KEEPALIVE TCP socket option.