ttcp man page

ttcp — test TCP and UDP performance


ttcp -t [-u] [-s] [-p port] [-l buflen] [-b size] [-n numbufs] [-A align] [-O offset] [-f format] [-D] [-v] host
ttcp -r [-u] [-s] [-p port] [-l buflen] [-b size] [-A align] [-O offset] [-f format] [-B] [-T] [-v]


Ttcp times the transmission and reception of data between two systems using  the UDP or TCP protocols. It differs from common “blast” tests, which tend to measure the remote inetd as much as the network performance, and which usually do not allow  measurements at the remote end of a UDP transmission.

For testing, the transmitter should be started with -t and -s after the receiver has been started with -r and -s. Tests lasting at least tens of seconds should be used to obtain accurate measurements. Graphical presentations of throughput versus buffer size for buffers ranging from tens of bytes to several “pages” can illuminate bottlenecks.

Ttcp can also be used as a “network pipe” for moving directory hierarchies between systems when routing problems exist or when the use of other mechanisms is undesirable. For example, on the destination machine, use:

ttcp -r -B | tar xvpf -

and on the source machine:

tar cf - directory | ttcp -t dest_machine

Additional intermediate machines can be included by:

ttcp -r | ttcp -t next_machine



Transmit mode.  Transmit data presented on standard input.


Receive mode. Send received data to standard output.


Use UDP instead of TCP.


If transmitting, source a data pattern to network; if receiving, sink (discard) the data. Without the -s option, the default is to transmit data from stdin or print the received data to stdout.

-l length

Length of buffers in bytes (default 8192). For UDP, this value is the number of data bytes in each packet. The system limits the maximum UDP packet length. This limit can be  changed with the -b option.

-b size

Set size of socket buffer.  The default varies from system to system. This parameter affects the maximum UDP packet length. It may not be possible to set this parameter on some systems (for example, 4.2BSD).

-n numbufs

Number of source buffers transmitted (default 2048).

-p port

Port number to send to or listen on (default 2000). On some systems, this port may be allocated to another network daemon.


If transmitting using TCP, do not buffer data when sending (sets the TCP_NODELAY socket option). It may not be possible to set this parameter on some systems (for example, 4.2BSD).


When receiving data, output only full blocks,  using the block size specified by -l. This option is useful for programs, such as tar(1), that require complete blocks.

-A align

Align the start of buffers to this modulus (default 16384).

-O offset

Align the start of buffers to this offset (default 0). For example, “-A8192 -O1” causes buffers to start at the second byte of an 8192-byte page.

-f format

Specify, using one of the following characters,  the format of the throughput rates as  kilobits/sec ('k'), kilobytes/sec ('K'),  megabits/sec ('m'), megabytes/sec ('M'),  gigabits/sec ('g'), or gigabytes/sec ('G'). The default is 'K'.


“Touch” the data as they are read in order to measure cache effects.


Verbose: print more statistics.


Debug: set the SO_DEBUG socket option.

See Also

ping(1M), traceroute(1M), netsnoop(1M)