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

exec

"-l" "0" "-w" "800" "-h" "350" "-t" "exec gauge (dnsmasq)" "-s" "e-86400" "DEF:min_421aa68_raw=rrd.php?path=mela-core-erx%2Fexec-dnsmasq%2Fgauge-dhcp-leases.rrd:value:MIN" "DEF:avg_421aa68_raw=rrd.php?path=mela-core-erx%2Fexec-dnsmasq%2Fgauge-dhcp-leases.rrd:value:AVERAGE" "DEF:max_421aa68_raw=rrd.php?path=mela-core-erx%2Fexec-dnsmasq%2Fgauge-dhcp-leases.rrd:value:MAX" "CDEF:min_421aa68=min_421aa68_raw,1,*" "CDEF:avg_421aa68=avg_421aa68_raw,1,*" "CDEF:max_421aa68=max_421aa68_raw,1,*" "LINE1:avg_421aa68#ff0000:dhcp-leases" "GPRINT:min_421aa68:MIN:%5.1lf%s Min," "GPRINT:avg_421aa68:AVERAGE:%5.1lf%s Avg," "GPRINT:max_421aa68:MAX:%5.1lf%s Max," "GPRINT:avg_421aa68:LAST:%5.1lf%s Last\l"