You are using Collectd 4, which is deprecated by CGP. Graphs like df and interfaces may be incomplete.
FreeSun-Gaswerksiedlung-4

ping

"-l" "0" "-w" "800" "-h" "350" "-t" "Ping latency on FreeSun-Gaswerksiedlung-4" "-v" "Milliseconds" "-s" "e-86400" "DEF:min_8f3d7fc7_raw=rrd.php?path=FreeSun-Gaswerksiedlung-4%2Fping%2Fping-ping.berlin.freifunk.net.rrd:value:MIN" "DEF:avg_8f3d7fc7_raw=rrd.php?path=FreeSun-Gaswerksiedlung-4%2Fping%2Fping-ping.berlin.freifunk.net.rrd:value:AVERAGE" "DEF:max_8f3d7fc7_raw=rrd.php?path=FreeSun-Gaswerksiedlung-4%2Fping%2Fping-ping.berlin.freifunk.net.rrd:value:MAX" "CDEF:min_8f3d7fc7=min_8f3d7fc7_raw,1,*" "CDEF:avg_8f3d7fc7=avg_8f3d7fc7_raw,1,*" "CDEF:max_8f3d7fc7=max_8f3d7fc7_raw,1,*" "LINE1:avg_8f3d7fc7#ff0000:ping.berlin.freifunk.net" "GPRINT:min_8f3d7fc7:MIN:%5.1lf Min," "GPRINT:avg_8f3d7fc7:AVERAGE:%5.1lf Avg," "GPRINT:max_8f3d7fc7:MAX:%5.1lf Max," "GPRINT:avg_8f3d7fc7:LAST:%5.1lf Last\l"