.\"
.\"----------------------------------------------------------------------------
.\""THE BEER-WARE LICENSE" (Revision 42):
.\"<phk@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
.\"can do whatever you want with this stuff. If we meet some day, and you think
.\"this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
.\"----------------------------------------------------------------------------
.\"
.\"$Id: jail.2,v 1.1 1999/04/28 11:38:35 phk Exp $
.\"
.\"
.Dd April 28, 1999
.Dt JAIL 2
.Os FreeBSD 4.0
.Sh NAME
.Nm jail
.Nd Imprison current process and future decendants.
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/jail.h>
.Ft int
.Fn jail "struct jail *jail"
.Sh DESCRIPTION
The
.Nm
system call sets up a jail and locks the current process in it.
.Pp
The argument is a pointer to a structure describing the prison:
.Bd -literal -offset indent
struct jail {
        char *path;
        char *hostname;
        u_int32_t ip_number;
};
.Ed
.Pp
The
.Dq Li path
pointer should be set to the directory which is to be the root of the
prison.
.Pp
The
.Dq Li hostname
pointer can be set the hostname of the prison.  This can be changed
from the inside of the prison.
.Pp
The
.Dq Li ip_number
can be set to the IP number assigned to the prison.
.Sh PRISON ?
Once a process has been put in a prison, it and its decendants cannot escape
the prison.  It is not possible to add a process to a preexisting prison.
.Pp
Inside the prison, the concept of "superuser" is very diluted, in general
it can be assumed that nothing can be mangled from inside a prison, that
doesn't exist inside that prison (ie: the directory tree below
.Dq Li path .
.Pp
All IP activity will be forced to happen to/from the IP number specified,
which should be an alias on one of the systems interfaces.
.Pp
It is possible to identify a process as jailed by examining
.Dq Li /proc/<pid>/status :
it will show a field near the end of the line, either as
a single hyphen for a process at large, or the hostname currently
set for the prison for jailed processes.
.Sh ERRORS
.Fn Jail
calls
.Xr chroot 2
internally, so the it can fail for all the same reasons.
Please consult the
.Xr chroot 2
manual page for details.
.Sh SEE ALSO
.Xr chroot 2
.Xr chdir 2
.Sh HISTORY
The
.Fn jail
function call appeared in
.Fx 4.0 .
.Pp
The jail feature was written by Poul-Henning Kamp for
R&D Associates
.Dq Li http://www.rndassociates.com/
who contributed it to FreeBSD.