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NAME

     jail, jail_get, jail_set, jail_remove, jail_attach -- create and manage
     system jails

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

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

     int
     jail(struct jail *jail);

     int
     jail_attach(int jid);

     int
     jail_remove(int jid);

     #include <sys/uio.h>

     int
     jail_get(struct iovec *iov, u_int niov, int flags);

     int
     jail_set(struct iovec *iov, u_int niov, int flags);

DESCRIPTION

     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;
                   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.

     This is equivalent to the jail_set() system call (see below), with the
     parameters path, host.hostname, name, ip4.addr, and ip6.addr, and with
     the JAIL_ATTACH flag.

     The jail_set() system call creates a new jail, or modifies an existing
     one, and optionally locks the current process in it.  Jail parameters are
     passed as an array of name-value pairs in the array iov, containing niov
     elements.  Parameter names are a null-terminated string, and values may
     be strings, integers, or other arbitrary data.  Some parameters are
     boolean, and do not have a value (their length is zero) but are set by
     the name alone with or without a ``no'' prefix, e.g.  persist or
     nopersist.  Any parameters not set will be given default values,
     generally based on the current environment.

     Jails have a set of core parameters, and modules can add their own jail
     parameters.  The current set of available parameters, and their formats,
     can be retrieved via the security.jail.param sysctl MIB entry.  Notable
     parameters include those mentioned in the jail() description above, as
     well as jid and name, which identify the jail being created or modified.
     See jail(8) for more information on the core jail parameters.

     The flags arguments consists of one or more of the following flags:

     JAIL_CREATE
             Create a new jail.  If a jid or name parameters exists, they must
             not refer to an existing jail.

     JAIL_UPDATE
             Modify an existing jail.  One of the jid or name parameters must
             exist, and must refer to an existing jail.  If both JAIL_CREATE
             and JAIL_UPDATE are set, a jail will be created if it does not
             yet exist, and modified if it does exist.

     JAIL_ATTACH
             In addition to creating or modifying the jail, attach the current
             process to it, as with the jail_attach() system call.

     JAIL_DYING
             Allow setting a jail that is in the process of being removed.

     The jail_get() system call retrieves jail parameters, using the same
     name-value list as jail_set() in the iov and niov arguments.  The jail to
     read can be specified by either jid or name by including those parameters
     in the list.  If they are included but are not intended to be the search
     key, they should be cleared (zero and the empty string respectively).

     The special parameter lastjid can be used to retrieve a list of all
     jails.  It will fetch the jail with the jid above and closest to the
     passed value.  The first jail (usually but not always jid 1) can be found
     by passing a lastjid of zero.

     The flags arguments consists of one or more following flags:

     JAIL_DYING
             Allow getting a jail that is in the process of being removed.

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

     The jail_remove() system call removes the jail identified by jid.  It
     will kill all processes belonging to the jail, and remove any children of
     that jail.

RETURN VALUES

     If successful, jail(), jail_set(), and jail_get() return a non-negative
     integer, termed the jail identifier (JID).  They return -1 on failure,
     and set errno to indicate the error.

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

PRISON?

     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
     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).  The effective ``securelevel'' for a process is
     the greater of the global ``securelevel'' or, if present, the per-jail
     ``securelevel''.

     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
     connections to/from the loopback address (127.0.0.1 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 name currently
     set for the prison for jailed processes.

ERRORS

     The jail() system call will fail if:

     [EPERM]            This process is not allowed to create a jail, either
                        because it is not the super-user, or because it would
                        exceed the jail's children.max limit.

     [EFAULT]           jail points to an address outside the allocated
                        address space of the process.

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

     [EAGAIN]           No free JID could be found.

     The jail_set() system call will fail if:

     [EPERM]            This process is not allowed to create a jail, either
                        because it is not the super-user, or because it would
                        exceed the jail's children.max limit.

     [EPERM]            A jail parameter was set to a less restrictive value
                        then the current environment.

     [EFAULT]           Iov, or one of the addresses contained within it,
                        points to an address outside the allocated address
                        space of the process.

     [ENOENT]           The jail referred to by a jid or name parameter does
                        not exist, and the JAIL_CREATE flag is not set.

     [ENOENT]           The jail referred to by a jid is not accessible by the
                        process, because the process is in a different jail.

     [EEXIST]           The jail referred to by a jid or name parameter
                        exists, and the JAIL_UPDATE flag is not set.

     [EINVAL]           A supplied parameter is the wrong size.

     [EINVAL]           A supplied parameter is out of range.

     [EINVAL]           A supplied string parameter is not null-terminated.

     [EINVAL]           A supplied parameter name does not match any known
                        parameters.

     [EINVAL]           One of the JAIL_CREATE or JAIL_UPDATE flags is not
                        set.

     [ENAMETOOLONG]     A supplied string parameter is longer than allowed.

     [EAGAIN]           There are no jail IDs left.

     The jail_get() system call will fail if:

     [EFAULT]           Iov, or one of the addresses contained within it,
                        points to an address outside the allocated address
                        space of the process.

     [ENOENT]           The jail referred to by a jid or name parameter does
                        not exist.

     [ENOENT]           The jail referred to by a jid is not accessible by the
                        process, because the process is in a different jail.

     [ENOENT]           The lastjid parameter is greater than the highest
                        current jail ID.

     [EINVAL]           A supplied parameter is the wrong size.

     [EINVAL]           A supplied parameter name does not match any known
                        parameters.

     The jail_attach() and jail_remove() system calls will fail if:

     [EINVAL]           The jail specified by jid does not exist.

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

SEE ALSO

     chdir(2), chroot(2), jail(8)

HISTORY

     The jail() system call appeared in FreeBSD 4.0.  The jail_attach() system
     call appeared in FreeBSD 5.1.  The jail_set(), jail_get(), and
     jail_remove() system calls appeared in FreeBSD 8.0.

AUTHORS

     The jail feature was written by Poul-Henning Kamp for R&D Associates
     ``http://www.rndassociates.com/'' who contributed it to FreeBSD.
     James Gritton added the extensible jail parameters and hierarchical
     jails.