1.\" 2.\" $Id: snp.4,v 1.11 1997/02/22 13:24:43 peter Exp $ 3.\" $Source: /home/ncvs/src/share/man/man4/snp.4,v $ 4.\" 5.Dd February 24, 1995 6.Dt SNP 4 7.Os FreeBSD 8.Sh NAME 9.Nm snp 10.Nd tty snoop interface 11.Sh SYNOPSIS 12.Fd #include <sys/snoop.h> 13.Ft int 14.Fn ioctl fd SNPSTTY &dev 15.Ft int 16.Fn ioctl fd SNPGTTY &dev 17.Ft int 18.Fn ioctl fd FIONREAD &result 19.Sh DESCRIPTION 20/dev/snp? are snoop devices which allow user to attach to any tty 21and watch activities on it. 22 23To associate a given 24.Nm snp 25device with a tty to be observed, open the 26.Nm snp 27device and then use the SNPSTTY ioctl. 28The argument passed to the IOCTL is the address of a variable of type 29dev_t. 30By setting the value of the variable pointed to -1, the user may detach 31the snp device from a tty. 32.Pp 33The SNPGTTY ioctl returns information about the current tty attached to 34the open 35.Nm snp 36device. 37.Pp 38The FIONREAD ioctl returns a positive value equal to the number of characters 39in a read buffer. 40Special values defined are: 41.Bl -tag -width SNP_TTYCLOSE 42.It Dv SNP_OFLOW 43device overflow occured, device detached. 44.It Dv SNP_TTYCLOSE 45tty not attached. 46.It Dv SNP_DETACH 47.Nm snp 48device has been detached by user or tty device has been closed 49and detached. 50.Sh SEE ALSO 51.Xr pty 4 , 52.Xr sio 4 , 53.Xr watch 8 54.Sh RESTRICTIONS 55Only the superuser may access the 56.Nm snp 57devices. 58.Sh BUGS 59While in line mode, user input can't be seen. 60No signals may be sent to the observed tty. 61.Sh AUTHOR 62Ugen J.S. Antsilevich <ugen@NetVision.net.il> 63.Sh HISTORY 64The 65.Nm snp 66device first appeared in FreeBSD 2.1. 67