How to view a log file realtime (similar to "tail -f") via web

Question

I have a server that runs a number of tasks. Each task has a log file. I have a webserver that lets you see these log files, but it just copies the contents of the file to the browser and the user has to press F5 over & over...

Is there a way to produce a clean scrolling "live" view for a specified log? Similar to "tail -f" in the terminal window.

Answer 1

That's possible, but possibly quite impractical if the logs are filling rapidly. This would require

• a script that keeps track of a log file.
  • It could check if the file has changed after the last check and possibly how much it has increased.
  • Then it should get the data from the end of the file: the increased bytes or sufficient amount of lines to compare what's new. That depends on whether it's ok to skip some lines here and there or not, and might be a lot trickier than just tail -f.
  • A constantly running tail -f might be a source for the script, but that might be a bad design: the buffer might get huge, or be flushed by other users.
  • The script would output the file in e.g. JSON format.
• a JavaScript that
  • calls the previous script regularly and
  • adds the new lines into an element on the web page.
  • Possibly adding the lines above the previous lines would be better suitable for web?

There might be such work or part of it done, if you Google for log, tail & AJAX. I don't know of the quality of those projects, and most seem quite old and unmanaged.

Answer 2

What you are looking for is a real-time logs browser which is a piece of a simple software that either listens to files with logs or STDIN and prints it to the UI. Depending on the problem you're trying to solve there are a couple of tools that could be used for that purpose. I'm the most advanced on the market currently would be Logdy since you just download a precompiled binary, it can run with ANY input like:

$ tail -f file.log | logdy 

Run it and you'll get all of the contents streamed to a Web UI. It also supports listening to multiple files and can even open a port and listen on TCP socket, check the docs and blog for more use cases.

There are also other similar tools like:

• log.io
• goaccess.io
• klogg
• lnav