TOP

The top program provides a dynamic real-time view of a running system. It can display system summary information as well as a list of tasks currently being managed by the Linux kernel. The types of system summary information shown and the types, order and size of information displayed for tasks are all user configurable and that configuration can be made persistent across restarts.

HTOP

htop is an interactive system-monitor process-viewer and process-manager. It is designed as an alternative to the Unix program top. It shows a frequently updated list of the processes running on a computer, normally ordered by the amount of CPU usage. Unlike top, htop provides a full list of processes running, instead of the top resource-consuming processes. Htop uses color and gives visual information about processor, swap and memory status.

IOTOP (Linux only, top on BSD has this included)

iotop watches I/O usage information output by the Linux kernel (requires 2.6.20 or later) and displays a table of current I/O usage by processes or threads on the system.

IFTOP

iftop listens to network traffic on a named interface, or on the first interface it can find which looks like an external interface if none is specified, and displays a table of current bandwidth usage by pairs of hosts. iftop must be run with sufficient permissions to monitor all network traffic on the interface; see pcap(3) for more information, but on most systems this means that it must be run as root.

GLANCES

Glances is a free (LGPL) curses-based monitoring tool which aims to present a maximum of information in a minimum of space, ideally to fit in a classical 80×24 terminal. Glances can adapt dynamicaly the displayed information depending on the terminal size.

NLOAD

nload is a console application which monitors network traffic and bandwidth usage in real time. It visualizes the in- and outgoing traffic using two graphs and provides additional info like the total amount of transfered data and min/max network usage.

NCDU

ncdu (NCurses Disk Usage) is a curses-based version of the well-known 'du', and provides a fast way to see what directories are using your disk space.

IPTRAF (Linux only)

iptraf is an ncurses-based IP LAN monitor that generates various network statistics including TCP info, UDP counts, ICMP and OSPF information, Ethernet load info, node stats, IP checksum errors, and others.

LFTP

lftp is a file transfer program that allows sophisticated ftp, http and other connections to other hosts. If siteis specified then lftp will connect to that site otherwise a connection has to be established with the open command.

lftp can handle several file access methods – ftp, ftps, http, https, hftp, fish, sftp and file (https and ftps are only available when lftp is compiled with GNU TLS or OpenSSL library). You can specify the method to use in 'open URL' command, e.g. 'open http://www.us.kernel.org/pub/linux'. hftp is ftp-over-http-proxy protocol. It can be used automatically instead of ftp if ftp:proxy is set to 'http://proxy[:port]'. Fish is a protocol working over an ssh connection to a unix account. SFtp is a protocol implemented in ssh2 as sftp subsystem.

TCPDUMP

Tcpdump prints out a description of the contents of packets on a network interface that match the boolean expression. It can also be run with the -w flag, which causes it to save the packet data to a file for later analysis, and/or with the -r flag, which causes it to read from a saved packet file rather than to read packets from a network interface. In all cases, only packets that match expression will be processed by tcpdump.

NETSTAT

Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships

LSOF

Lsof lists on its standard output file information about files opened by processes 

W

w displays information about the users currently on the machine, and their processes. The header shows, in this order, the current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.

NETHOGS

NetHogs is an open source command line program (similar to Linux top command) that is used for monitor real time network traffic bandwidth used by each process or application.