1.\" 2.\" $Id$ 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/ioctl.h> 13.Fd #include <sys/snoop.h> 14.Ft int 15.Fn ioctl fd SNPSTTY &dev 16.Ft int 17.Fn ioctl fd SNPGTTY &dev 18.Ft int 19.Fn ioctl fd FIONREAD &result 20.Sh DESCRIPTION 21/dev/snp? are snoop devices which allow user to attach to any tty 22and watch activities on it. 23 24To associate a given 25.Nm snp 26device with a tty to be observed, open the 27.Nm snp 28device and then use the SNPSTTY ioctl. 29The argument passed to the IOCTL is the address of a variable of type 30dev_t. 31By setting the value of the variable pointed to -1, the user may detach 32the snp device from a tty. 33.Pp 34The SNPGTTY ioctl returns information about the current tty attached to 35the open 36.Nm snp 37device. 38.Pp 39The FIONREAD ioctl returns a positive value equal to the number of characters 40in a read buffer. 41Special values defined are: 42.Bl -tag -width SNP_TTYCLOSE 43.It Dv SNP_OFLOW 44device overflow occured, device detached. 45.It Dv SNP_TTYCLOSE 46tty not attached. 47.It Dv SNP_DETACH 48.Nm snp 49device has been detached by user or tty device has been closed 50and detached. 51.Sh SEE ALSO 52.Xr pty 4 , 53.Xr sio 4 , 54.Xr watch 8 55.Sh RESTRICTIONS 56Only the superuser may access the 57.Nm snp 58devices. 59.Sh BUGS 60While in line mode, user input can't be seen. 61No signals may be sent to the observed tty. 62.Sh AUTHOR 63Ugen J.S. Antsilevich <ugen@NetVision.net.il> 64.Sh HISTORY 65The 66.Nm snp 67device first appeared in FreeBSD 2.1. 68