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SNP(4)                 FreeBSD Kernel Interfaces Manual                 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 device 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)

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.

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

HISTORY
     The snp device first appeared in FreeBSD 2.1.

FreeBSD 11.0-PRERELEASE        February 24, 1995       FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | BUGS | AUTHORS | HISTORY

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