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 then use the SNPSTTY ioctl. The argument passed to the ioctl is the address of a variable of type dev_t. To detach the snp device from a tty use a pointer to a value of (dev_t)-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 wildly inaccurate in some places.

While in line mode, user input can't be seen. No signals may be sent to the observed tty.