Logging in YaCy

Every YaCy instance keeps a log of it's operation.

To take a look into a log is useful for debugging, when hunting an error, inefficiency or just for... train-spotting.

Seak peek into log is in the web UI /ViewLog_p.html. You can filter the entries based on regular-expression. And as you know, a fragment of log is shown live at the Status page (/Status.html).


Real log is located in file DATA/LOG/yacy00.log. You can watch it live by common unix tools like tail.

tail has a parameter -F, which allows to monitor logfile live:

`tail -F DATA/LOG/yacy00.log`

You can use grep to filter out only lines you wanna see:

`tail -F DATA/LOG/yacy00.log | grep CRAWLER`

or to hide the lines you don't want to read ('negative' grep):

`tail -F DATA/LOG/yacy00.log | grep -v CRAWLER`

You can also use some colorizer like ccze to increase the readability of logs.

Logs are rotated after filling, which can be very fast, last log is yacy00.log and tails parameter -F helps you to keep a track of actual file.

Queries searched by your instance are logged anonymously in DATA/LOG/queries.log with timestamps. Currently, there is a certain delay after which entry appears in the queries.log.


You can set the verbosity of logging in DATA/LOG/yacy.logging file, for example when you hunt a bug or, on the other side, you want to unclutter the logfile and show only information useful for you.

For each component of YaCy, eg. CRAWLER, NETWORK, etc. you can set a level of details logged:

For example NETWORK.level = WARNING set in yacy.logging will not show the regular p2p network traffic, only the warnings, in the logs.

Technically, ConcurrentLog class is used for logging in YaCy java source code.