snp(4)

NAME

snp - tty snoop interface

SYNOPSIS

#include <sys/snoop.h>
int
ioctl(fd, SNPSTTY, &dev);
int
ioctl(fd, SNPGTTY, &dev);
int
ioctl(fd, FIONREAD, &result);

DESCRIPTION

/dev/snp? are snoop devices which allow users to attach to

any tty and
watch activities on it. The kernel must be compiled with

device snp, or
the snp module must be loaded, for these devices to be

available.

To associate a given snp device with a tty to be observed,

open the snp
device and a tty device, and then issue the SNPSTTY ioctl on

snp device.
The argument passed to the ioctl(2) is the address of a

variable of type
int, holding the file descriptor of a tty device. To detach

the snp
device from a tty use a pointer to a value of -1.

The SNPGTTY ioctl returns information about the current tty

attached to
the open snp device.

The FIONREAD ioctl returns a positive value equal to the

number of characters in a read buffer. Special values defined are:

SNP_OFLOW device overflow occurred, device detached.

SNP_TTYCLOSE tty not attached.

SNP_DETACH snp device has been detached by user or

tty device has

been closed and detached.

SEE ALSO

pty(4), sio(4), kldload(8), watch(8)

HISTORY

The snp device first appeared in FreeBSD 2.1.

AUTHORS

Ugen J.S. Antsilevich <ugen@NetVision.net.il>

BUGS

Caveat emptor! This manual page is horribly stale and wild

ly inaccurate
in some places.

While in line mode, user input cannot be seen. No signals

may be sent to
the observed tty.

BSD September 18, 2005

BSD