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In most cases you will need root permission to be able to capture packets on an interface. Using tcpdump (with root) to capture the packets and saving them to a file to analyze with Wireshark (using a regular account) is recommended over using Wireshark with a root account to capture packets on an "untrusted" interface. See the Wireshark security advisories for reasons why.

See the list of interfaces on which tcpdump can listen:

tcpdump -D
Listen on interface eth0:

tcpdump -i eth0
Listen on any available interface (cannot be done in promiscuous mode. Requires Linux kernel 2.2 or greater):

tcpdump -i any
Be verbose while capturing packets:

tcpdump -v
Be more verbose while capturing packets:

tcpdump -vv
Be very verbose while capturing packets:

tcpdump -vvv
Be verbose and print the data of each packet in both hex and ASCII, excluding the link level header:

tcpdump -v -X
Be verbose and print the data of each packet in both hex and ASCII, also including the link level header:

tcpdump -v -XX
Be less verbose (than the default) while capturing packets:

tcpdump -q
Limit the capture to 100 packets:

tcpdump -c 100
Record the packet capture to a file called capture.cap:

tcpdump -w capture.cap
Record the packet capture to a file called capture.cap but display on-screen how many packets have been captured in real-time:

tcpdump -v -w capture.cap
Display the packets of a file called capture.cap:

tcpdump -r capture.cap
Display the packets using maximum detail of a file called capture.cap:

tcpdump -vvv -r capture.cap
Display IP addresses and port numbers instead of domain and service names when capturing packets (note: on some systems you need to specify -nn to display port numbers):

tcpdump -n
Capture any packets where the destination host is 192.168.1.1. Display IP addresses and port numbers:

tcpdump -n dst host 192.168.1.1
Capture any packets where the source host is 192.168.1.1. Display IP addresses and port numbers:

tcpdump -n src host 192.168.1.1
Capture any packets where the source or destination host is 192.168.1.1. Display IP addresses and port numbers:

tcpdump -n host 192.168.1.1
Capture any packets where the destination network is 192.168.1.0/24. Display IP addresses and port numbers:

tcpdump -n dst net 192.168.1.0/24
Capture any packets where the source network is 192.168.1.0/24. Display IP addresses and port numbers:

tcpdump -n src net 192.168.1.0/24
Capture any packets where the source or destination network is 192.168.1.0/24. Display IP addresses and port numbers:

tcpdump -n net 192.168.1.0/24
Capture any packets where the destination port is 23. Display IP addresses and port numbers:

tcpdump -n dst port 23
Capture any packets where the destination port is is between 1 and 1023 inclusive. Display IP addresses and port numbers:

tcpdump -n dst portrange 1-1023
Capture only TCP packets where the destination port is is between 1 and 1023 inclusive. Display IP addresses and port numbers:

tcpdump -n tcp dst portrange 1-1023
Capture only UDP packets where the destination port is is between 1 and 1023 inclusive. Display IP addresses and port numbers:

tcpdump -n udp dst portrange 1-1023
Capture any packets with destination IP 192.168.1.1 and destination port 23. Display IP addresses and port numbers:

tcpdump -n "dst host 192.168.1.1 and dst port 23"
Capture any packets with destination IP 192.168.1.1 and destination port 80 or 443. Display IP addresses and port numbers:

tcpdump -n "dst host 192.168.1.1 and (dst port 80 or dst port 443)"
Capture any ICMP packets:

tcpdump -v icmp
Capture any ARP packets:

tcpdump -v arp
Capture either ICMP or ARP packets:

tcpdump -v "icmp or arp"
Capture any packets that are broadcast or multicast:

tcpdump -n "broadcast or multicast"
Capture 500 bytes of data for each packet rather than the default of 68 bytes:

tcpdump -s 500
Capture all bytes of data within the packet:

tcpdump -s 0