Show HN: Nerdlog – Fast, multi-host TUI log viewer with timeline histogram

by dimonomid • 1 year ago

134 56 1 year ago

For more background and technical details, I wrote this up as well: https://dmitryfrank.com/projects/nerdlog/article

Zopieux• 1 year ago

journalctl is mentioned once in the landing page and it seems to imply that journalctl is not supported per se, as logs need to be stored plaintext to legacy syslog (?).

I do not want to store plaintext logs and use ancient workarounds like logrotate. journald itself has the built-in ability to receive logs from remote hosts (journald remote & gateway) and search them using --merge.

tstack2• 1 year ago

The article makes it sound like it uses various command-line tools (bash/awk/head/tail) to process the logs. So, I imagine it's not a huge leap to extend support to using journalctl to do that work instead.

mamcx• 1 year ago

One small hitch I found is that this kind of tools are fixes in what to process, so for example I can't use them for structured logging. If it has an escape hatch where I can supply my own pipe (for example `process = 'vector ....'`) then it will be enough.

dimonomid23• 1 year ago

That's true, as of today nerdlog doesn't use journalctl, and needs plain log files. There were a few reasons of that, primarily related to the sheer amount of logs that we were dealing with.

As mentioned in the article, my original use case was: having a fleet of hosts, each printing pretty sizeable amount of logs, e.g. having more than 1-2GB log file on every host on a single day was pretty common. My biggest problem with journalctl is that, during some intensive spikes of logs, it might drop logs; we were definitely observing this behavior that some messages are clearly missing from the journalctl output, but when we check the plain log files, the messages are there. I don't remember details now, but I've read about some kind of ratelimiting / buffer overflow going on there (and somehow the part which writes to the files enjoys not having these limits, or at least having more permissive limits). So that's the primary one; I definitely didn't want to deal with missing logs. Somehow, old school technology like plain log files keeps being more reliable.

Second, at least back then, journalctl was noticeably slower than simply using tail+head hacks to "select" the requested time range.

Third, having a dependency like journalctl it's just harder to test than plain log files.

Lastly, I wanted to be able to use any log files, not necessarily controlled by journalctl.

I think adding support for journalctl should be possible, but I still do have doubts on whether it's worth it. You mention that you don't want to store plaintext logs and using logrotate, but is it painful to simply install rsyslog? I think it takes care of all this without us having to worry about it.

whalesalad• 1 year ago

can't you just read from stdin?

i use lnav in this way all the time: journalctl -f -u service | lnav

this is the ethos of unix tooling

lenova8• 1 year ago

I appreciate this response, and want to say I really like your tool's UI over something like lazyjournal. But like the above commentor, I would love to see journald support as well, just because it's the default these days on the distros I use, and seems like the direction the Linux system industry has headed in.

tstack2• 1 year ago

Nice work! The TUI looks really sharp and I like the histogram on top. Going to play with this today.

TIL awk patterns can be more than just regexes and can be combined with boolean operators. I've written a bit of awk and never realized this.

philsnow• 1 year ago

There's a ton of overlap between "powerful stuff that's easy to write in (g)awk" and "powerful stuff that's trivial to write in perl", but I find awk to be succinct without losing readability.

esafak• 1 year ago

Looks nice. You might want to get help from the community to get it packaged for major linux distros, if you want more users.

dimonomid23• 1 year ago

Thanks, and yeah getting distro packages would be dope. Hopefully, some day.

tomerbd• 1 year ago

Can i view logs from aws cloudwatch?

mdaniel2• 1 year ago

You'll go broke doing that, as those API calls are not free. Best to configure cloudwatch to dump into some sane place (S3, SigNoz, whatever) so you only pay the api call once and not every time for interactive viewing

I went spelunking around in the codebase trying to get the actual answer to your question and it seems it's like many things: theoretically yes with enough energy expended but by default it seems to be ssh-ing into the target hosts and running a pseudo agent over its own protocol back through ssh. So, "no"

openWrangler• 1 year ago

Seconded - it sounds like compatibility isn't there yet with AWS, but it would be great if there was a way to use nerdlog with other OSS dashboard tools like Signoz or Coroot like you mentioned. Still a really interesting graylog altnerative.

knowitnone• 1 year ago

Nice. I needed this a few years ago. No license file?

dimonomid23• 1 year ago

Yeah right, my bad, and thanks for reminding me. Just added one (the BSD 2-clause).

adityavinodh• 1 year ago

Looks great! Was just looking for something like this.

ryanhecht2• 1 year ago

I definitely intend on playing around with this later! I see that [gzipped log archives aren't supported](https://dmitryfrank.com/projects/nerdlog/article#depends_on_...), minimizing the use case for me personally. You've at least thought enough about that to bring it up as a limitation you think people will call attention to -- any plans to eventually support it?

dimonomid23• 1 year ago

Thanks for the feedback!

Yeah it would be great, and I do want to support it, especially if the demand is popular. In fact, even if you ungzip them manually, as of today nerdlog doesn't support more than 2 files in a logstream, which needs to be fixed first.

Specifically about supporting gzipped logs though, the UX I'm thinking about is like this: if the requested time range goes beyond the earliest available ungzipped file, then warn the user that we'll have to ungzip the next file (that warning can be turned off in options though, but by default I don't want to just ungzip it silently, because it can consume a signficant amount of disk space). So if the user agrees, nerdlog ungzips it and places somewhere under tmp. It'll never delete it manually though, relying on the regular OS means of cleaning up /tmp, and will keep using it as long as it's available.

Does it make sense?

ryanhecht2• 1 year ago

Definitely makes sense!

In fact, even if you ungzip them manually, as of today nerdlog doesn't support more than 2 files in a logstream

Ah, interesting! I read the limitation as "we don't support zipped files," not "we only support two files!"

Best of luck, this is neat!

nodesocket• 1 year ago

Very nice work. Anyway to specify a group of log files in the config that are shared across many hosts? For example:

  log_files:
    mygroup:
      - /var/log/syslog
      - /var/log/foo
      - /var/log/bar
  log_streams:
    myhost-01:
      hostname: actualhost1.com
      port: 1234
      user: myuser
      log_files: mygroup
    myhost-02:
      hostname: actualhost2.com
      port: 7890
      user: myuser
      log_files: mygroup
    myhost-03:
      hostname: actualhost3.com
      port: 8888
      user: myuser
      log_files: mygroup

dimonomid23• 1 year ago

Thanks. And no, as of today, there's no way to define a group like that. Might be a viable idea though.

However, before we go there, I want to double check that we're on the same page: this `log_files` field specifies only files _in the same logstream_; meaning, these files need to have consecutive logs. So for example, it can be ["/var/log/syslog", "/var/log/syslog.1"], or it can be ["/var/log/auth.log", "/var/log/auth.log.1"], but it can NOT be something like ["/var/log/syslog", "/var/log/auth.log"].

mdaniel2• 1 year ago

At the very grave risk of scope creep, I'll point out that the GP's yaml is very close to an Ansible inventory file so rather than just making up a new structure one could leverage any existing muscle memory (and create helpful defaults for folks who have not yet seen Ansible but have seen your tool)

https://docs.ansible.com/ansible/11/collections/ansible/buil...

e.g.

  all:
    children:
      mygroup:
        hosts:
          myhost-01:
            hostname: actualhost1.com
            port: 1234
            user: myuser
          myhost-02:
            hostname: actualhost2.com
            port: 7890
            user: myuser
          myhost-03:
            hostname: actualhost3.com
            port: 8888
            user: myuser
        vars:
          files:
          - /var/log/syslog
          - /var/log/foo
          - /var/log/bar

That first "children" key is because in ansible's world one can have "vars" and "hosts" that exist at the very top, too; the top-level "vars" would propagate down to all hosts which one can view as "not necessary" in the GP's example, or "useful" if those files are always the same for every single host in the whole collection. Same-same for the "user:" but I wasn't trying to get bogged down in the DRY for this exercise

piterrro• 1 year ago

This is a really cool project — love the simplicity and the TUI approach, especially with the timeline histogram and remote-first design. I had similar pain points at my end when dealing with logs across many hosts, which led to building Logdy[1] — a tool with a slightly different philosophy.

Logdy is more web-based and focuses on live tailing, structured log search, and quick filtering across multiple sources, also without requiring a centralized server. Not trying to compare directly, but if you're exploring this space, you might find it useful as a complementary approach or for different scenarios. Although we need to work more on adding ability to query multiple hosts.

Anyway, kudos on nerdlog—always great to see lean tools in the logging space that don’t require spinning up half a dozen services.

[1] https://logdy.dev

johnisgood6• 1 year ago

This looks good. Any way to use date/time in RFC 3339 format without changing the source code?

Does this work with runit (Void Linux)?

dimonomid23• 1 year ago

Re: the date/time format, I was thinking about implementing support for an option like timefmt, so you'd be able to do :set timefmt=2006-01-02T15:04:05Z07:00 , but postponed for now.

That's not hard to implement, however to make it persistent requires implementing some config / scriptability, which is a whole other thing and requires more thought.

Re: runit, I never tested it, but after looking around briefly, it sounds like there is no unified log file, and not even unified log format? I mean it's possible to make it work, treating every log file as a separate logstream, but I've no idea what these logs look like and whether supporting the formats would be easy.

johnisgood6• 1 year ago

Void Linux uses svlogtail for viewing logs.

It is a simple script: https://github.com/void-linux/socklog-void/blob/master/svlog...

I think everything is in /var/log/socklog/everything/current, so this could be considered united.

Before you add the timefmt, it may be better to add a configuration file if one does not already exist, but it seems like it does? You already have ~/.config/nerdlog/logstreams.yaml, so might as well have config.yaml?

For more about logging on Void: https://docs.voidlinux.org/config/services/logging.html

dloss• 1 year ago

Very nice! Added to my little list of log viewers at https://github.com/dloss/klp#alternative-tools

dimonomid23• 1 year ago

Thanks, appreciate that!

Show HN: Nerdlog – Fast, multi-host TUI log viewer with timeline histogram

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