lofs(7FS)							   File Systems 							 lofs(7FS)

NAME

       lofs - loopback virtual file system

SYNOPSIS

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

       int mount (const char* dir, const char* virtual, int mflag, lofs, NULL, 0);

DESCRIPTION

       The  loopback  file  system  device  allows new, virtual file systems to be created, which provide access to existing files using alternate
       pathnames. Once the virtual file system is created, other file systems can be mounted within it, without affecting the original	file  sys-
       tem.  However,  file systems which are subsequently mounted onto the original file system are visible to the virtual file system, unless or
       until the corresponding mount point in the virtual file system is covered by a file system mounted there.

       virtual is the mount point for the virtual file system. dir is the pathname of the existing file system. mflag specifies the mount options;
       the   MS_DATA  bit  in  mflag must be set. If the MS_RDONLY bit in  mflag is not set, accesses to the loop back file system are the same as
       for the underlying file system. Otherwise, all accesses in the loopback file system will be  read-only.	All  other  mount(2)  options  are
       inherited from the underlying file systems.

       A  loopback  mount  of '/' onto /tmp/newroot allows the entire file system hierarchy to appear as if it were duplicated under /tmp/newroot,
       including any file systems mounted from remote NFS servers. All files would then be accessible either from a pathname relative  to  '/'	or
       from a pathname relative to /tmp/newroot until such time as a file system is mounted in /tmp/newroot, or any of its subdirectories.

       Loopback  mounts  of  '/'  can  be  performed in conjunction with the chroot(2) system call, to provide a complete virtual file system to a
       process or family of processes.

       Recursive traversal of loopback mount points is not allowed. After the loopback mount of /tmp/newroot,  the  file  /tmp/newroot/tmp/newroot
       does  not  contain  yet	another file system hierarchy; rather, it appears just as /tmp/newroot did before the loopback mount was performed
       (for example, as an empty directory).

   Examples
       lofs file systems are mounted using:

	 mount -F lofs /tmp /mnt

SEE ALSO

       lofiadm(1M), mount(1M), chroot(2), mount(2), sysfs(2), vfstab(4), lofi(7D)

NOTES

       All access to entries in lofs mounted file systems map to their underlying file system. If a mount point  is  made  available  in  multiple
       locations  via  lofs  and is busy in any of those locations, an attempt to mount a file system at that mount point fails unless the overlay
       flag is specified. See mount(1M). Examples of a mount point being busy within a lofs mount include having a file system mounted on it or it
       being a processes' current working directory.

WARNINGS

       Because	of  the  potential  for  confusing  users  and	applications,  you should use loopback mounts with care. A loopback mount entry in
       /etc/vfstab must be placed after the mount points of both directories it depends on.  This is most easily accomplished by  making the loop-
       back mount entry the last in  /etc/vfstab.

SunOS 5.11							    10 Apr 2001 							 lofs(7FS)