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

     jail - Imprison current process and future decendants.

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

     jail(struct jail *jail);

     The jail system call sets up a jail and locks the current process in it.

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

           struct jail {
                   u_int32_t       version;
                   char            *path;
                   char            *hostname;
                   u_int32_t       ip_number;

     ``version'' defines the version of the API in use.  It should be set to
     zero at this time.

     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 ``ip_number'' can be set to the IP number assigned to the 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

     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 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
     cannot be created because they reference shared resources (the device
     drivers in the kernel).

     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.

     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
     currently set for the prison for jailed processes.

     jail() will fail if:

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

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

     chdir(2), chroot(2)

     The jail() function call appeared in FreeBSD 4.0.

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

FreeBSD 4.0                     April 28, 1999                     FreeBSD 4.0


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