Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
lofs(7FS)			 File Systems			     lofs(7FS)

       lofs - loopback virtual file system

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

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

       The loopback file system	device allows new, virtual file	systems	to  be
       created,	 which	provide	access to existing files using alternate path-
       names. Once the virtual file system is created, other file systems  can
       be  mounted within it, without affecting	the original file system. How-
       ever, 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  op-
       tions;  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 loop-
       back file system	will be	read-only. All other mount(2) options are  in-
       herited 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,  in-
       cluding	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  ch-
       root(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 exam-
       ple, as an empty	directory).

       lofs file systems are mounted using:

       mount -F	lofs /tmp /mnt

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

       Loopback	 mounts	 must  be  used	with care; the potential for confusing
       users and applications is enormous. A loopback mount entry in  /etc/vf-
       stab  must  be placed after the mount points of both directories	it de-
       pends on.  This is most easily accomplished  by	 making	 the  loopback
       mount entry the last in	/etc/vfstab.

SunOS 5.10			  10 Apr 2001			     lofs(7FS)


Want to link to this manual page? Use this URL:

home | help