1.\" 2.\" $FreeBSD$ 3.\" 4.Dd February 24, 1995 5.Dt SNP 4 6.Os FreeBSD 7.Sh NAME 8.Nm snp 9.Nd tty snoop interface 10.Sh SYNOPSIS 11.Fd #include <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. 21 22To associate a given 23.Nm snp 24device with a tty to be observed, open the 25.Nm snp 26device and then use the SNPSTTY ioctl. 27The argument passed to the IOCTL is the address of a variable of type 28dev_t. 29By setting the value of the variable pointed to -1, the user may detach 30the snp device from a tty. 31.Pp 32The SNPGTTY ioctl returns information about the current tty attached to 33the open 34.Nm snp 35device. 36.Pp 37The FIONREAD ioctl returns a positive value equal to the number of characters 38in a read buffer. 39Special values defined are: 40.Bl -tag -width SNP_TTYCLOSE 41.It Dv SNP_OFLOW 42device overflow occured, device detached. 43.It Dv SNP_TTYCLOSE 44tty not attached. 45.It Dv SNP_DETACH 46.Nm snp 47device has been detached by user or tty device has been closed 48and detached. 49.Sh SEE ALSO 50.Xr pty 4 , 51.Xr sio 4 , 52.Xr watch 8 53.Sh RESTRICTIONS 54Only the superuser may access the 55.Nm snp 56devices. 57.Sh BUGS 58While in line mode, user input can't be seen. 59No signals may be sent to the observed tty. 60.Sh AUTHORS 61.An Ugen J.S. Antsilevich Aq ugen@NetVision.net.il 62.Sh HISTORY 63The 64.Nm snp 65device first appeared in 66.Fx 2.1 . 67