1.\" 2.\" $FreeBSD$ 3.\" 4.Dd February 24, 1995 5.Dt SNP 4 6.Os 7.Sh NAME 8.Nm snp 9.Nd tty snoop interface 10.Sh SYNOPSIS 11.In sys/snoop.h 12.Ft int 13.Fn ioctl fd SNPSTTY &dev 14.Ft int 15.Fn ioctl fd SNPGTTY &dev 16.Ft int 17.Fn ioctl fd FIONREAD &result 18.Sh DESCRIPTION 19/dev/snp? are snoop devices which allow user to attach to any tty 20and watch activities on it. 21The kernel must be compiled with 22.Cd "device snp" , 23or the 24.Nm 25device must be loaded, 26for these devices to be available. 27.Pp 28To associate a given 29.Nm 30device with a tty to be observed, open the 31.Nm 32device and then use the SNPSTTY ioctl. 33The argument passed to the IOCTL is the address of a variable of type 34dev_t. 35By setting the value of the variable pointed to -1, the user may detach 36the snp device from a tty. 37.Pp 38The SNPGTTY ioctl returns information about the current tty attached to 39the open 40.Nm 41device. 42.Pp 43The FIONREAD ioctl returns a positive value equal to the number of characters 44in a read buffer. 45Special values defined are: 46.Bl -tag -width SNP_TTYCLOSE 47.It Dv SNP_OFLOW 48device overflow occurred, device detached. 49.It Dv SNP_TTYCLOSE 50tty not attached. 51.It Dv SNP_DETACH 52.Nm 53device has been detached by user or tty device has been closed 54and detached. 55.El 56.Sh SEE ALSO 57.Xr pty 4 , 58.Xr sio 4 , 59.Xr kldload 8 , 60.Xr watch 8 61.Sh BUGS 62Caveat emptor! 63This manual page is horribly stale and wildly inaccurate in some places. 64.Pp 65While in line mode, user input can't be seen. 66No signals may be sent to the observed tty. 67.Sh AUTHORS 68.An Ugen J.S. Antsilevich Aq ugen@NetVision.net.il 69.Sh HISTORY 70The 71.Nm 72device first appeared in 73.Fx 2.1 . 74