I’m trying to do something real simple, but nothing is working.
Trying to see a container log. I have a simple program the just sends a string to stdout. From what I read Docker uses stdout and stderr to send to the logs. I’ll run the program then jump over to a terminal and use docker logs -f . Nothing shows up.
while (1)
{
fprintf( stdout, “Hello all\r\n”);
fflush(stdout);
sleep(1);
}
I did something simular in torizon os 5 and I recall seeing on the log anything I used printf on. is Torison OS 6 different? How can I write to the log from c code?
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To address your issue with container logging in Torizon OS, let’s break it down into two parts:
1. Viewing Container Logs
Your C code snippet should indeed send output to stdout, which Docker captures and makes available via docker logs. Here are a few steps to troubleshoot why docker logs -f isn’t showing your output:
Ensure the Container is Running: Make sure your container is actually running. You can check this with docker ps.
Check the Container ID: Ensure you are using the correct container ID or name with the docker logs command.
Verify the Logging Driver: By default, Docker uses the json-file logging driver, which should capture stdout and stderr. You can verify this by running:
Run a Simple Test: Try running a simple container to see if logging works:
docker run --rm -it busybox sh -c 'while true; do echo "Hello all"; sleep 1; done'
Then, in another terminal, run:
docker logs -f <container_id>
This should show the “Hello all” messages.
2. Enabling Container Monitoring with Fluent Bit
To enable container monitoring with Fluent Bit in Torizon OS, follow these steps:
Enable Fluent Bit: Ensure Fluent Bit is enabled on your Torizon OS device. This is typically done by provisioning the device to Torizon Cloud, which creates the /etc/fluent-bit/enabled file.
Configure Docker to Use Fluentd Logging Driver:
Edit your Docker Compose file to use the Fluentd logging driver. Here is an example:
Ensure Fluent Bit is configured to accept logs from Docker. Add the following to your /etc/fluent-bit/fluent-bit.conf:
[INPUT]
Name forward
Listen 0.0.0.0
Port 24224
[OUTPUT]
Name stdout
Match *
Restart Fluent Bit:
systemctl restart fluent-bit
Run Your Container:
Start your container with the updated Docker Compose file.
Check Fluent Bit Output:
Open a terminal and run:
journalctl -u fluent-bit -f
This should show the logs being forwarded from Docker to Fluent Bit.
Missing Documentation Link
Regarding the missing link in the “Enabling Container Monitoring” section, it seems there might be an issue with the documentation. You can refer to the official Docker documentation for configuring logging drivers in Docker Compose files: Docker Logging Drivers.
By following these steps, you should be able to see your container logs and configure Fluent Bit for container monitoring in Torizon OS. If you continue to face issues, please provide more details, and we can further troubleshoot.
Please, also check if these links can help you solve your problem:
If I run a simple container like so on the device:
docker run --rm -it torizon/debian:3-bookworm
Then in that container I install vim-tiny build-essential. I create a source file with the following contents:
#include <stdio.h>
#include <unistd.h>
int main() {
while (1)
{
fprintf(stdout, "Hello all\r\n");
fflush(stdout);
sleep(1);
}
}
If I compile this and execute it while monitoring the docker logs in a different terminal I can see the output:
torizon@verdin-imx8mp-06849059:~$ docker logs -f 7
Hello all
Hello all
Hello all
Hello all
Hello all
So as shown, it does work.
Now you mentioned you were using the VSCode extension. So I created a fresh project and used the same code as above and started the debug process. Here as you said docker logs is now empty and the output is seen in the debug window on VSCode. I believe this is because when running in debug mode, the stdout gets redirected to the debug console for debugging purposes. Therefore the container logs won’t see it.
If you instead run your container application in release mode, then the output is sent to stdout and seen in the container logs as expected.
Yeah, that did it. Anyway to tell it not to redirect. I want to debug, but have that stdout on the terminal, not on the debug console.
After briefly discussing with our IDE extension team, the short answer is that there doesn’t seem to be a way to do this. At least not without also breaking the debug in the process.
When the extension runs in debug mode, it runs first an sshd to connect the remote debugger. The data, including the application output, is under this sshd connection and will be seen only in the output of the VSCode debugger or, gdb in this case.
Theoretically if you were to break this redirection of the application data to gdb. Then, I imagine gdb wouldn’t be able to debug the application properly, which defeats the purpose of the debug mode.
I believe your goal is to parse the output from your application and feed it to fluent-bit correct?
You’ll probably need to do this in two-stages then:
The first stage would be to debug your application as normal, until the output is what you want it to be.
Then the second stage is to just run your application normally without the debugger, and start developing the data flow from your application to fluent-bit.
