Performance monitoring

top - Interactive process monitoring tool

# top

lsof - List open files and sockets/pipes as well

# lsof

htop - Advanced interactive process monitoring tool

# htop

iotop - Display real time Disk I/O and process

# iotop

tcpdump - Network packet capture (Sniffer)

# tcpdump -n -i eth0 src host 10.1.1.1 and dst host 10.1.1.10 and port 80
# tcpdump -w - | tee capture.pcap | tcpdump -r -   (write to file and standard output the same time)

iptraf - Real time IP and network monitoring

# iptraf

Also check ntop, iftop, pftop, trafshow

vmstat - Display statistics of virtual memory, kernel, disks, process, I/O blocks and CPU activity

# vmstat
# vmstat -s  (other visualization)
# vmstat -S m (show MB instead of KB)

iostat - Display statistics of CPU, disk I/O and NFS

# iostat
# iostat -m   (show MB/sec instead of blocks/sec)
# iostat -n

Additional tools: iperf for traffic generation, and apache mod_status

And Collectl - Powerful and feature rich command line utility that monitors CPU, memory, disk and network