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JAIL(2)			  FreeBSD System Calls Manual		       JAIL(2)

     jail, jail_attach -- imprison current process and future descendants

     Standard C	Library	(libc, -lc)

     #include <sys/param.h>
     #include <sys/jail.h>

     jail(struct jail *jail);

     jail_attach(int jid);

     The jail()	system call sets up a jail and locks the current process in

     The argument is a pointer to a structure describing the prison:

	   struct jail {
		   u_int32_t	   version;
		   char		   *path;
		   char		   *hostname;
		   char		   *jailname;
		   unsigned int	   ip4s;
		   unsigned int	   ip6s;
		   struct in_addr  *ip4;
		   struct in6_addr *ip6;

     ``version'' defines the version of	the API	in use.	 JAIL_API_VERSION is
     defined for the current version.

     The ``path'' pointer should be set	to the directory which is to be	the
     root of the prison.

     The ``hostname'' pointer can be set to the	hostname of the	prison.	 This
     can be changed from the inside of the prison.

     The ``jailname'' pointer is an optional name that can be assigned to the
     jail for example for managment purposes.

     The ``ip4s'' and ``ip6s'' give the	numbers	of IPv4	and IPv6 addresses
     that will be passed via their respective pointers.

     The ``ip4'' and ``ip6'' pointers can be set to an arrays of IPv4 and IPv6
     addresses to be assigned to the prison, or	NULL if	none.  IPv4 addresses
     must be in	network	byte order.

     The jail_attach() system call attaches the	current	process	to an existing
     jail, identified by jid.

     If	successful, jail() returns a non-negative integer, termed the jail
     identifier	(JID).	It returns -1 on failure, and sets errno to indicate
     the error.

     The jail_attach() function	returns	the value 0 if successful; otherwise
     the value -1 is returned and the global variable errno is set to indicate
     the error.

     Once a process has	been put in a prison, it and its descendants cannot
     escape the	prison.

     Inside the	prison,	the concept of ``superuser'' is	very diluted.  In gen-
     eral, it can be assumed that nothing can be mangled from inside a prison
     which does	not exist entirely inside that prison.	For instance the
     directory tree below ``path'' can be manipulated all the ways a root can
     normally do it, including ``rm -rf	/*'' but new device special nodes can-
     not be created because they reference shared resources (the device	driv-
     ers in the	kernel).  The effective	``securelevel''	for a process is the
     greater of	the global ``securelevel'' or, if present, the per-jail

     All IP activity will be forced to happen to/from the IP number specified,
     which should be an	alias on one of	the network interfaces.	 All connec-
     tions to/from the loopback	address	( for IPv4, ::1 for IPv6)
     will be changed to	be to/from the primary address of the jail for the
     given address family.

     It	is possible to identify	a process as jailed by examining
     ``/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 cur-
     rently set	for the	prison for jailed processes.

     The jail()	system call will fail if:

     [EINVAL]		The version number of the argument is not correct.

     Further jail() calls chroot(2) internally,	so it can fail for all the
     same reasons.  Please consult the chroot(2) manual	page for details.

     chdir(2), chroot(2)

     The jail()	system call appeared in	FreeBSD	4.0.  The jail_attach()	system
     call appeared in FreeBSD 5.1.

     The jail feature was written by Poul-Henning Kamp for R&D Associates
     ``'' who contributed it to FreeBSD.

FreeBSD	7.2			January	6, 2009			   FreeBSD 7.2


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