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67 lines
1.5 KiB
Groff
67 lines
1.5 KiB
Groff
.\"
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.\" $Id: snp.4,v 1.13 1997/03/21 20:13:26 mpp Exp $
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.\"
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.Dd February 24, 1995
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.Dt SNP 4
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.Os FreeBSD
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.Sh NAME
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.Nm snp
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.Nd tty snoop interface
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.Sh SYNOPSIS
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.Fd #include <sys/snoop.h>
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.Ft int
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.Fn ioctl fd SNPSTTY &dev
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.Ft int
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.Fn ioctl fd SNPGTTY &dev
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.Ft int
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.Fn ioctl fd FIONREAD &result
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.Sh DESCRIPTION
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/dev/snp? are snoop devices which allow user to attach to any tty
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and watch activities on it.
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To associate a given
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.Nm snp
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device with a tty to be observed, open the
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.Nm snp
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device and then use the SNPSTTY ioctl.
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The argument passed to the IOCTL is the address of a variable of type
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dev_t.
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By setting the value of the variable pointed to -1, the user may detach
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the snp device from a tty.
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.Pp
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The SNPGTTY ioctl returns information about the current tty attached to
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the open
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.Nm snp
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device.
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.Pp
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The FIONREAD ioctl returns a positive value equal to the number of characters
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in a read buffer.
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Special values defined are:
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.Bl -tag -width SNP_TTYCLOSE
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.It Dv SNP_OFLOW
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device overflow occured, device detached.
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.It Dv SNP_TTYCLOSE
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tty not attached.
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.It Dv SNP_DETACH
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.Nm snp
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device has been detached by user or tty device has been closed
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and detached.
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.Sh SEE ALSO
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.Xr pty 4 ,
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.Xr sio 4 ,
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.Xr watch 8
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.Sh RESTRICTIONS
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Only the superuser may access the
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.Nm snp
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devices.
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.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.
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.Sh AUTHORS
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.An Ugen J.S. Antsilevich Aq ugen@NetVision.net.il
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.Sh HISTORY
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The
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.Nm snp
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device first appeared in
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.Fx 2.1 .
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