Overview

btop    # Interactive resource monitor (sysutils/btop)

Network traffic per interface

systat -ifs
netstat -bdhi
iostat

Disk device

gstat
iostat

Continuous collection

The commands above are snapshots; for continuous collection telegraf (net-mgmt/telegraf) gathers system metrics and ships them to a time-series database such as InfluxDB. Inputs and the output are selected in /usr/local/etc/telegraf.conf:

telegraf_enable="YES"