This command is very hot, these commands I do almost every day in order to monitor the linux box that serves as Nat servers, proxy servers, caching only dns, dhcp server and router static.
# df -h
to view the free hdd space
# top
to see the utility processor and memory
# arp -v
to see the number of users connected
# /etc/rc.d/rc.bind restart
to restart the dns caching
# /usr/local/lusca/squid -k reconfgure
to reload the modified proxy server settings
# iptraf -g
to see network utilization