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How Should an Application's Logs Work?
emmjayell writes "You've been there, loaded up a new application (think server-based app like Apache or Samba ...), it's working okay for a few days or a few months, then the intermittent problems start. Usually it's the CEO or someone else of relative importance that is the first victim. You can't readily duplicate the problem, so you go to find out where the application put's it's logs - maybe it's in var/log/messages - maybe in it's own directory - sometimes it's right there and available in some administrative GUI. So what makes you happiest when diagnosing the problem? Do you want tools to access it? UI or command line? Do you want it formatted to use tools like cut and sed? Do you have any examples of an app that does a great job with system logging and diag logging? Background: My team is working on an application that is gearing up for a first release. We have a logging framework in place already (we are using Apache: logging.apache.org/) -- so that covers how we are logging, but not what we should log and how it should be laid out for optimal use."
JBoss 4. Even though I can't figure it the first time most time I look at it, the answer is always in the log.
Even though it is resource intensive, I prefer the developer log everything, and let me decide how verbose or terse I want the logs to be.
-- Bryan
Any kid of log is fine with me as long as it's there and it gives me some kind of insight into what's going wrong, e.g. "can't open this file," "that file's corrupt," "null pointer." Of course, text files are nice, because you can actually search through them.
Sadly, most applications for M$ operating systems usually just leave things like, "Error #543892157893421 occured." When you go to look up what error 84901257893423 is, no one in the world seems to have had it. Tech support proceeds to blame your hardware vendor, who blames your software vendor, ad nauseum. Seems like most applications for m$ operating systems just pull error numbers out of their asses.
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/registered user did
When from Where did What by Whom
When = ISO 8601 Timestamp (from)
Where = IP Adress / Name of computer...
Who = which Login
What requested file foo/bar?a=213b=dfg
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I say this as a sysadmin for a large number (several thousands) of servers. So many problems could be solved by Apache et al using, and modifying where necessary, the existing solutions. But they don't, they roll their own, and so we see problems.
I realize this is a sorta OT rant, but it's causing major problems for me at work and so I think it's justified. Stuff like rotatelog has functionality to tell Apache "dump your logs, I'm rotating the file!" (which by the way doesn't always work) which could be easily rolled into a single notification of the syslog daemon. But it isn't. For whatever perverse reason, Apache and many others decided to roll their own.
It pisses me the fuck off, having to deal with it. The greatest shortcoming by far of OSS is this insistency on reimplemtning proven, robust, existing solutions in favor of a trivial fix. This is a particularly egregious example, one the OSS world would be served well by acknowledging.
as I once said to a colleague. /var/log
/var/log/appname/* is good.
If you have simple logging needs, log via syslog and leave the details to the site.
For more complex needs, especially if you have several logs,
Obviously, the logs should be a text file. You ask if special tools should be provided. For text files we already have grep, sed, awk, perl.
The exception is if you are providing some kind of administrative GUI, say a web app. Logs that relate to specific functionality should be near the controls for that functionality. By using a GUI you are saying "I don't want to get my hands dirty" which, for time-pressed admins, is a perfectly legitimate approach for apps with complicated configuration architectures (Sendmail, WebShere 5). So the GUI should take away the complexity of having to know where the logs are. It should always be possible, though, to get at the text of the logs and run standard tools against them.
MHO.
Yours Sincerely, Michael.
My favorite logs are the ones where I get control over what events get logged and in what detail they get logged. There's no such thing as a one-size-fits-all software solution; why do we believe in one-size-fits-all logging?
The alternative is to log everything in great detail, but do so in such a way as to make it truly trivial for me to strip out everything except the specific events in which I'm interested, in the level of detail in which I'm interested.
is easily the best logging package.
Configurable log levels, and you can define your own appenders.
Eg, I typically configure an email appender for severe/fatal errors, so they come straight to my inbox. Often I know of problems before the users do as a result of this.
Also, something described in one the Pragmatic Series of books is an RSS appender - just point your RSS reader at the channel, and wait for any errors to occur.
Write to a god damned text file. Add a timestamp. Be verbose. Is it really that hard to figure out?
You've been there, sitting at a console peering at your application's newly created text log file after a crash. The question, naturally, turns to editors. Should you open it with vi? Maybe emacs? Is nano the tool you're looking for?
What editor makes you happiest when viewing log files? Do you enjoy navigating with intuitive kay combinations? Does syntax highlighting make your day? Do you have any examples of an editor that does a great job with system log files? Background: My team is new to the command-line, but we're gearing up for this brave new experience.
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I really don't much care where logs are kept or what particular format they are in. However, it's important that the man page tells me where the logs are, and clearly documents the format of the log files. What do flags mean? What do particular messages mean?
Also, formatting the logs in such a way that they can be quickly searched with grep or parsed by a simple script is most helpful. One of my favorite loggers does this:
This lets me see everything in chronological order, but I can quickly parse the log. Splitting on ':' will yeild the first two feilds consistently, and the first four chars are *always* the type of log message. So doing something like:
Lets me immediately see all the errors for a given day. The key to good logging is, IMO, making sure that the logs can be parsed effectively.
We may not imagine how our lives could be more frustrating and complex—but Congress can. – Cullen Hightower
Whatever your logging strategy, please remember to rotate your logfiles.
/var or your custom directory under /a
You'd be amazed how many Internet applications crash simply because the logs fill up the partition that hosts the application.
This problem was threefold, because:
1. The logfiles should never get that size
2. Logs should usually exist on a seperate partition like
3. People usually ignore the messages in a Production debug log
I run 12 moderate websites. We easily generate 5GB of logfiles a week (Rotated). It used to be 10GB, but then I switched off debug logging and fixed the most common errors.
When I started my current job 1 year ago, I deleted 40GB of logs which ran back to year 2000.
94% of Repubs and 21% of Dems voted to renew the Patriot Act
So, in order to make storage, analysis and reporting easy, your framework should attempt to coerce a consistent approach to the data logged - even the plaintext "human readable" data if you can. If you can do the same with metadata about the event (e.g. ID fields, links to online KBs etc), so much the better.
BB
MS requires that non-MS software sets bit 29 on all custom error codes, giving absurd decimal interpetations of these codes.
-mkb
It is nice to allow the end user to specify the verbosity of the log file - do you log each request, only failures, or every entrance/exit to a function? If the log is to assist in diagnosing the error, it is nice to be able to turn on extra information that would normally just quickly fill up disk space.
I agree with what others have said--I don't care about the format too much as long as it's text and has a timestamp in front.
/blah/blah" is infintely better since it lets you actually fix the error without looking something up on google. Speaking of that, if you *do* have some kind of strange error you are reporting and you know it's not going to make sense, at least make it long and unique so I *can* look it up on google. Terseness can be a good quality in a program, but it is *not* a good quality in an error log.
What really matters to me is that errors get logged nicely. "Error number #57575" or even "permission denied" doesn't help at all. It needs to be specific "permission denied while opening file
Just remember, the people installing your software and using probably don't the first thing about the way it works on the inside. You have to explain to them what went wrong and give them clues on how to fix it in a short error line.
Oh, it's also nice to have a link back to the original source line that caused the problem. In C, use __FILE__, __LINE__, and __func__ (if you have it) so that if I'm really stumped I can download your source, quickly find the error and start working backwards to find the cause. However, this could get confusing if there are a number of different versions of your code floating around, and it's not as important as the other things I mentioned.
-David
There. Now go play some cool javascript games!
To paraphrase an Apache (1.x) error I recently encountered, was: "The client was denied access by configuration rule.".
First of all: which rule did the denial? Second: does the program recall the file or line this rule was in or on? Simply having the text or location of a rule would be a huge help in debugging.
Related to logging, is program output. If you are writing tools that run at a Unix console, then someday you'll want to run them from scripts and use their output:
1. Use stdout and stderr appropriately: I should be able to run "foo > file" and see warnings on my console, but only get useful data in the file. Don't write messages to stdout if they aren't useful output. C++ has std::clog too. Don't make scripts use "grep -v" to remove random status messages or whatever.!
2. prefix your warnings/errors with the name of the program. So if a bunch of programs run in a script-- or in the background-- you can sort them out.
3. Indicate if something in an error or a warning.
4. Don't get too emotional, unless it's really neccesary:
Bad: WARNING! SOMETHING REALLY HORIBLE HAPPENED! AHH!!!
Good: fooprogram: Warning: Something really horrible happened!
Notice that you can use a ! at the end for emphasis, but it's not obnoxious.
Make reasonable suggestions if you think an error might be caused by user error:
fooprogram: Error: No status file found. (Use fooprogram -s to initialize.)
fooprogram: Error: No response from server at localhost:2323. Did you run it first?
(But try not to be too patronizing!)
5. Use error codes. (in exit() or return from main). Make an enum or #defines somewhere. Document them in the man page and/or --help output.
You know what logs I really like? The Windows 2000 system logs. All the services write in them, so there is never any hunting for files. They can have a lot of information packed into them, if the application takes some time to do it. They rotate automatically. They have severity icons so you know which ones are the errors and which are not. And they are all in a nice GUI list, so you don't need a command line PhD to view them. User friendly, indeed!
You're welcome. And thanks for the posted BONUS. The /. may not reflect it but you and I both know it's there.
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