vhangup.2

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)vhangup.2	8.2	1/28/91
.TH vhangup 2
.SH Name
vhangup \- virtually hang up the current control terminal
.SH Syntax
.B void vhangup\|(\|)
.SH Description
.NXR "vhangup system call"
.NXR "terminal" "revoking access"
The
.PN vhangup
system call initializes a terminal line. 
For example, the 
.PN init 
command uses
.PN vhangup
to ensure that 
the previous user's processes cannot access the
terminal anymore.
.PP
First,
.PN vhangup
searches the system tables for references to the current
terminal (the control terminal
of the invoking process) and revokes access permissions
on each instance of the terminal that it finds.
.PP
The
.PN vhangup
system call
also removes all references to the inode that corresponds to the
control terminal. 
The
.PN vhangup 
system call
then invokes the kernel's device close routine to turn
the terminal off.
Finally,
.PN vhangup
sends a hangup signal (SIGHUP) to the process group
of the control terminal.  For further information, see
.MS tty 4
for a description of process groups.
.PP
When
.PN vhangup
finishes, a terminal line is 
initialized; no other processes refer to this line.
The only way for other processes to access 
the control terminal is through the special file,
.PN /dev/tty .
All other requests will yield I/O errors (EBADF).
.SH See Also
init(8)