Tuesday, August 26, 2008


No, this is not a misspelling for ROTFL, but rather a variant of RTFM. It stands for Read The F...riendly Log. It's a troubleshooting technique that is very basic, yet surprisingly overlooked. I use it all the time, and I just want to draw attention to it in case you find yourself stumped by a problem that seems mysterious.

Here are some recent examples from my work.

Apache wouldn't start properly

A 'ps -def | grep http' would show only the main httpd process, with no worker processes. The Apache error log showed these lines:

Digest: generating secret for digest authentication

A google search for this line revealed this article:


It turns out the randomness/entropy on that box had been exhausted. I grabbed the rng-tools tar.gz from sourceforge, compiled and installed it, then ran

rngd -r /dev/urandom

...and apache started its worker processes instantly.

Cannot create InnoDB tables in MySQL

Here, all it took was to read the MySQL error log in /var/lib/mysql. It's very friendly indeed, and tells you exactly what to do!

InnoDB: Error: data file ./ibdata1 is of a different size
InnoDB: 2176 pages (rounded down to MB)
InnoDB: than specified in the .cnf file 128000 pages!
InnoDB: Could not open or create data files.
InnoDB: If you tried to add new data files, and it failed here,
InnoDB: you should now edit innodb_data_file_path in my.cnf back
InnoDB: to what it was, and remove the new ibdata files InnoDB created
InnoDB: in this failed attempt. InnoDB only wrote those files full of
InnoDB: zeros, but did not yet use them in any way. But be careful: do not
InnoDB: remove old data files which contain your precious data!

Windows-based Web sites are displaying errors

Many times I've seen Windows/IIS based Web sites displaying cryptical errors such as:

Server Error in '/' Application.
Runtime Error

The IIS logs are much less friendly in terms of useful information than the Apache logs. However, the Event Viewer is a good source of information. In a recent case, inspecting the Event Viewer told us that the account used to connect from the Web server to the DB server had expired, so re-enabling it was all it took to fix the issue.

In conclusion -- RTFL and google it! You'll be surprised how large of a percentage of issues you can solve this way.


fumanchu said...

And the corollary--design new systems to log enough information to be nicely googlable. ;)

Michele Smith said...

Good reminder... I use them both. I also attach copies of them to my defect reports.

Srikanth said...

True, I learned this the hard way. But RTFL certainly enforces the habit. Thanks for the wonderful blog posts.