In Linux or UNIX log files are located in /usr/local/var/log/CouchDB/couch.log . This log FILE location can be SET in the default.ini file.default.ini file is located in /etc/CouchDB/path.
If the user has installed from the SOURCE and the user is RUNNING the CouchDB in the dev mode, then the location of the log files will be:- YOUR_CouchDB_SOURCE_DIRECTORY/tmp/log/couch.log