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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 wildly inaccurate
     in some places.

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