SNP(4)

NAME
snp - tty snoop interface

SYNOPSIS
#include <sys/ioctl.h>
#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 user to attach to any tty and watch activities on it. 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. By setting the value of the variable pointed to to -1, the user may detach the snp device from a tty.

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

RESTRICTIONS
Only the superuser may access the snp devices.

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

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

HISTORY
The snp device first appeared in FreeBSD 2.1.