Note: this is the Legacy v2 Wiki. The new V3 Wiki can be found at the Servarr Wiki.
Sonarr's AppData folder contains the databases for logs and general app information (series, episodes, history, most settings), log files and the config file that contains settings required to start the web server. This path is listed on the System Status page in Sonarr, but if you are unable to access it, here are some common locations for it:
Windows
C:\ProgramData\NzbDrone
C:\ProgramData\Sonarr
Linux
/home/$USER/.config/NzbDrone (~$USER/.config/NzbDrone)
/home/$USER/.config/Sonarr (~$USER/.config/Sonarr)
/var/lib/sonarr
OS X
/Users/$USER/.config/NzbDrone (~/.config/NzbDrone)
Synology
/usr/local/nzbdrone/var/.config/NzbDrone
/volume1/@appstore/nzbdrone/var/.config/NzbDrone
QNAP
/share/MD0_DATA/homes/admin/.config/NzbDrone
/share/CACHEDEV1_DATA/SONARR_CONFIG
Argument
The -data argument forces the location of the AppData folder, so your startup command may be forcing a specific location. This is especially useful when trying to run multiple instances.
user@host ~ $ ps aux | grep -i sonarr
sonarr 15522 28.3 1.5 3596376 1037600 ? Ssl Nov11 291:03 /usr/bin/mono --debug /usr/lib/sonarr/Sonarr.exe -nobrowser -data=/var/lib/sonarr
user@host ~ $ sudo systemctl cat sonarr
...
ExecStart=/usr/bin/mono --debug /usr/lib/sonarr/Sonarr.exe -nobrowser -data=/var/lib/sonarr
...