NGHOOK(8) BSD System Manager’s Manual NGHOOK(8)


nghook — connect to a netgraph(4) node


nghook [−adlnSs] [−m msg] path [hookname]
nghook −e
[−n] [−m msg] path hookname program [args ...]


The nghook utility creates a ng_socket(4) socket type node and connects it to hook hookname of the node found at path. If hookname is omitted, ’’debug’’ is assumed.

If the −e option is given, the third argument is interpreted as the path to a program, and this program is executed with the remaining arguments as its arguments. Before executing, the program Netgraph messages (specified by the −m option) are sent to the node. The program is executed with its standard input (unless closed by −n) and output connected to the hook.

If the −e option is not given, all data written to standard input is sent to the node, and all data received from the node is relayed to standard output. Messages specified with −m are sent to the node before the loop is entered. The nghook utility exits when EOF is detected on standard input in this case.

The options are as follows:


Output each packet read in human-readable decoded ASCII form instead of raw binary.


Increase the debugging verbosity level.


Execute the program specified by the third argument.


Loops all received data back to the hook in addition to writing it to standard output.

−m msg

Before executing the program (in −e mode) send the given ASCII control message to the node. This option may be given more than once.


Do not attempt to read any data from standard input. The nghook utility will continue reading from the node until stopped by a signal.


Use file descriptor 0 for output instead of the default 1.


Use file descriptor 1 for input instead of the default 0.


Although all input is read in unbuffered mode, there is no way to control the packetization of the input.

If the node sends a response to a message (specified by −m), this response is lost.


netgraph(3), netgraph(4), ngctl(8)


The netgraph system was designed and first implemented at Whistle Communications, Inc. in a version of FreeBSD 2.2 customized for the Whistle InterJet.


Archie Cobbs <archie [AT]>

BSD October 24, 2003 BSD