added a yacy logging guide

docs/docs.md

@@ -13,6 +13,7 @@
 ## Operation
 * [Setting the ranking rules](operation/ranking.md)
 * [YaCy config settings](operation/yacy_conf.md)
+* [Logging in YaCy](operation/logging.md)
 
 ## Developers
 * [How to contribute](contribute.md)

docs/faq.md

@@ -144,13 +144,23 @@ Alternatively, another way to do this is through the configuration file httpProx
 
 ### Something seems not to be working properly ; what should I do?
 
-YaCy is still undergoing development, so one should opt for a stable version for use. The latest stable version can be downloaded from the [YaCy homepage](https://yacy.net). If you are experiencing a strange behaviour of YaCy then you should search the [community forum](https://community.searchlab.eu/) for known issues. If the issue is unknown, then you can ask for help on the forum (and provide the YaCy version, details on the occurrence of the issue, and if possible an excerpt from the log file in order to help fix the bug) or [start an issue](https://github.com/yacy/yacy_search_server/issues/) on github.
+YaCy is still undergoing development, so one should opt for a stable version
+for use.  The latest stable version can be downloaded from the [YaCy
+homepage](https://yacy.net).  If you are experiencing a strange behaviour of
+YaCy then you should search the [community
+forum](https://community.searchlab.eu/) for known issues.  If the issue is
+unknown, then you can ask for help on the forum (and provide the YaCy
+version, details on the occurrence of the issue, and if possible an excerpt
+from the [log file](operation/logging.md) in order to help fix the bug) or [start an
+issue](https://github.com/yacy/yacy_search_server/issues/) on github.
+
 
 First thing to see while experiencing some errors, is the log located at `DATA/LOG/yacy00.log`. You can monitor it live using `tail` command. While it flips around when certain size is reached, it's better to use -F option:
 ```
 tail -F DATA/LOG/yacy00.log
 ```
-You can also filter lines by using `grep` command (eg. `tail -F DATA/LOG/yacy00.log | grep DHT` to show only DHT lines) or -v parameter of grep to ignore some lines (eg. `tail -F DATA/LOG/yacy00.log | grep -v DHT` to ignore DHT lines).
+See more about setting and using the [yacy log](operation/logging.md).
+
 
 ### YaCy is running terribly slow; what should I do? 
 As an indexing and search host, YaCy is quite resource hungry. It's written in Java. Fast disks (SSD or RAID) and plenty of RAM will help. 

docs/operation/logging.md

@@ -0,0 +1,71 @@
+# 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`).
+
+## Logfiles
+
+Real log is located in file `DATA/LOG/yacy00.log`. You can watch it live by
+common unix tools like
+[tail](https://www.man7.org/linux/man-pages/man1/tail.1.html).
+
+`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](https://github.com/cornet/ccze)
+to increase the readability of logs.
+
+Logs are rotated after filling, which can be very fast, last log is
+`yacy00.log` and `tail`s 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.
+
+## Verbosity
+
+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:
+
+ - `OFF` - no output at all
+
+ - `SEVERE` - system-level error, internal cause, critical and not fixable (i.e. inconsistency)
+
+ - `WARNING` - uncritical service failure, may require user activity (i.e. input required, wrong authorization)
+
+ - `INFO` - regular action information (i.e. any httpd request URL)
+
+ - `CONFIG` - regular system status information (i.e. start-up messages)
+
+ - `FINE` - in-function status debug output
+
+ - `FINER` - more details in debug output
+
+ - `FINEST` - even more details in debug output
+
+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](https://yacy.net/api/javadoc/net/yacy/cora/util/ConcurrentLog.html)
+class is used for logging in YaCy java source code.