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NAME

      jail, jail_attach - imprison current process and future descendants

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);

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;
                    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.
 
      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.

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 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 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.
 
      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.

ERRORS

      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)

HISTORY

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

AUTHORS

      The jail feature was written by Poul-Henning Kamp for R&D Associates
      “http://www.rndassociates.com/” who contributed it to FreeBSD.