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."

Comments

When Where Who What

[NoSuchGuy]

Maybe you want to know

When from Where did What by Whom

When = ISO 8601 Timestamp (from)
Where = IP Adress / Name of computer...
Who = which Login /registered user did
What requested file foo/bar?a=213b=dfg

syslog!

[Anonymous Coward]

The distressing part is that there's an answer: the syslog daemon, a quite capable application. The problem is that some prominent apps don't use it at all. This is in part due to the limitations of syslog, but the solution is not to reinvent the wheel, it's to modify the wheel so that it does as you wish. syslog doesn't have the facilities you want? Change it so it does. It doesn't deal with things like splitting logs for virtual (web) hosts? Change is so it does.

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.

Errors should be clear

[__david__]

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.

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 /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.

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