How to delete old Time Machine backup with tmutil command. (then start and show backup status)
# cat /etc/netatalk/AppleVolumes.default | grep "TimeMachine-for-mba1"
# tmutil destinationinfo
# tmutil listbackups
# tmutil delete <backup_target>
# for ((x=1; x<=3; x++)) ; do tmutil delete "`tmutil listbackups | head -1`" ; done
# tmutil startbackup
# tmutil status
# tmutil status | awk '/_raw_Percent/ {print $3}' | grep -o '[0-9].[0-9]\+' | awk '{print $1*100,"% backed up"}'