freebsd-dev/share/man/man4/snp.4

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.\"
.\" $Id: snp.4,v 1.13 1997/03/21 20:13:26 mpp Exp $
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.\"
.Dd February 24, 1995
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.Dt SNP 4
.Os FreeBSD
.Sh NAME
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.Nm snp
.Nd tty snoop interface
.Sh SYNOPSIS
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.Fd #include <sys/snoop.h>
.Ft int
.Fn ioctl fd SNPSTTY &dev
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.Ft int
.Fn ioctl fd SNPGTTY &dev
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.Ft int
.Fn ioctl fd FIONREAD &result
.Sh DESCRIPTION
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/dev/snp? are snoop devices which allow user to attach to any tty
and watch activities on it.
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To associate a given
.Nm snp
device with a tty to be observed, open the
.Nm 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 -1, the user may detach
the snp device from a tty.
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.Pp
The SNPGTTY ioctl returns information about the current tty attached to
the open
.Nm snp
device.
.Pp
The FIONREAD ioctl returns a positive value equal to the number of characters
in a read buffer.
Special values defined are:
.Bl -tag -width SNP_TTYCLOSE
.It Dv SNP_OFLOW
device overflow occured, device detached.
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.It Dv SNP_TTYCLOSE
tty not attached.
.It Dv SNP_DETACH
.Nm snp
device has been detached by user or tty device has been closed
and detached.
.Sh SEE ALSO
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.Xr pty 4 ,
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.Xr sio 4 ,
.Xr watch 8
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.Sh RESTRICTIONS
Only the superuser may access the
.Nm snp
devices.
.Sh BUGS
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While in line mode, user input can't be seen.
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No signals may be sent to the observed tty.
.Sh AUTHORS
.An Ugen J.S. Antsilevich Aq ugen@NetVision.net.il
.Sh HISTORY
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The
.Nm snp
device first appeared in
.Fx 2.1 .