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MOUNT(2)		    BSD	System Calls Manual		      MOUNT(2)

     mount, nmount, unmount -- mount or	dismount a file	system

     Standard C	Library	(libc, -lc)

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

     mount(const char *type, const char	*dir, int flags, void *data);

     unmount(const char	*dir, int flags);

     #include <sys/uio.h>

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

     The mount() system	call grafts a file system object onto the system file
     tree at the point dir.  The argument data describes the file system ob-
     ject to be	mounted.  The argument type tells the kernel how to interpret
     data (See type below).  The contents of the file system become available
     through the new mount point dir.  Any files in dir	at the time of a suc-
     cessful mount are swept under the carpet so to speak, and are unavailable
     until the file system is unmounted.

     The nmount() system call behaves similarly	to mount(), except that	the
     mount options (file system	type name, device to mount, mount-point	name,
     etc.) are passed as an array of name-value	pairs in the array iov,	con-
     taining niov elements.  The following options are required	by all file
	   fstype     file system type name (e.g., "procfs")
	   fspath     mount point pathname (e.g., "/proc")

     Depending on the file system type,	other options may be recognized	or re-
     quired; for example, most disk-based file systems require a "from"	option
     containing	the pathname of	a special device in addition to	the options
     listed above.

     By	default	only the super-user may	call the mount() system	call.  This
     restriction can be	removed	by setting the vfs.usermount sysctl(8) vari-
     able to a non-zero	value.

     The following flags may be	specified to suppress default semantics	which
     affect file system	access.

     MNT_RDONLY	      The file system should be	treated	as read-only; even the
		      super-user may not write on it.  Specifying MNT_UPDATE
		      without this option will upgrade a read-only file	system
		      to read/write.

     MNT_NOEXEC	      Do not allow files to be executed	from the file system.

     MNT_NOSUID	      Do not honor setuid or setgid bits on files when execut-
		      ing them.	 This flag is set automatically	when the
		      caller is	not the	super-user.

     MNT_NOATIME      Disable update of	file access times.

     MNT_SNAPSHOT     Create a snapshot	of the file system.  This is currently
		      only supported on	UFS2 file systems, see mksnap_ffs(8)
		      for more information.

     MNT_SUIDDIR      Directories with the SUID	bit set	chown new files	to
		      their own	owner.	This flag requires the SUIDDIR option
		      to have been compiled into the kernel to have any	ef-
		      fect.  See the mount(8) and chmod(2) pages for more in-

     MNT_SYNCHRONOUS  All I/O to the file system should	be done	synchronously.

     MNT_ASYNC	      All I/O to the file system should	be done	asyn-

     MNT_FORCE	      Force a read-write mount even if the file	system appears
		      to be unclean.  Dangerous.  Together with	MNT_UPDATE and
		      MNT_RDONLY, specify that the file	system is to be
		      forcibly downgraded to a read-only mount even if some
		      files are	open for writing.

     MNT_NOCLUSTERR   Disable read clustering.

     MNT_NOCLUSTERW   Disable write clustering.

     The flag MNT_UPDATE indicates that	the mount command is being applied to
     an	already	mounted	file system.  This allows the mount flags to be
     changed without requiring that the	file system be unmounted and re-
     mounted.  Some file systems may not allow all flags to be changed.	 For
     example, many file	systems	will not allow a change	from read-write	to

     The flag MNT_RELOAD causes	the vfs	subsystem to update its	data struc-
     tures pertaining to the specified already mounted file system.

     The type argument names the file system.  The types of file systems known
     to	the system can be obtained with	lsvfs(1).

     The data argument is a pointer to a structure that	contains the type spe-
     cific arguments to	mount.	The format for these argument structures is
     described in the manual page for each file	system.	 By convention file
     system manual pages are named by prefixing	``mount_'' to the name of the
     file system as returned by	lsvfs(1).  Thus	the NFS	file system is de-
     scribed by	the mount_nfs(8) manual	page.  It should be noted that a man-
     ual page for default file systems,	known as UFS and UFS2, does not	exist.

     The unmount() system call disassociates the file system from the speci-
     fied mount	point dir.

     The flags argument	may include MNT_FORCE to specify that the file system
     should be forcibly	unmounted even if files	are still active.  Active spe-
     cial devices continue to work, but	any further accesses to	any other ac-
     tive files	result in errors even if the file system is later remounted.

     If	the MNT_BYFSID flag is specified, dir should instead be	a file system
     ID	encoded	as "FSID:val0:val1", where val0	and val1 are the contents of
     the fsid_t	val[] array in decimal.	 The file system that has the speci-
     fied file system ID will be unmounted.

     Upon successful completion, the value 0 is	returned; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the

     The mount() and nmount() system calls will	fail when one of the following

     [EPERM]		The caller is neither the super-user nor the owner of

     [ENAMETOOLONG]	A component of a pathname exceeded 255 characters, or
			the entire length of a path name exceeded 1023 charac-

     [ELOOP]		Too many symbolic links	were encountered in translat-
			ing a pathname.

     [ENOENT]		A component of dir does	not exist.

     [ENOTDIR]		A component of name is not a directory,	or a path pre-
			fix of special is not a	directory.

     [EBUSY]		Another	process	currently holds	a reference to dir.

     [EFAULT]		The dir	argument points	outside	the process's allo-
			cated address space.

     The following errors can occur for	a ufs file system mount:

     [ENODEV]		A component of ufs_args	fspec does not exist.

     [ENOTBLK]		The fspec argument is not a block device.

     [ENXIO]		The major device number	of fspec is out	of range (this
			indicates no device driver exists for the associated

     [EBUSY]		fspec is already mounted.

     [EMFILE]		No space remains in the	mount table.

     [EINVAL]		The super block	for the	file system had	a bad magic
			number or an out of range block	size.

     [ENOMEM]		Not enough memory was available	to read	the cylinder
			group information for the file system.

     [EIO]		An I/O error occurred while reading the	super block or
			cylinder group information.

     [EFAULT]		The fspec argument points outside the process's	allo-
			cated address space.

     The following errors can occur for	a nfs file system mount:

     [ETIMEDOUT]	Nfs timed out trying to	contact	the server.

     [EFAULT]		Some part of the information described by nfs_args
			points outside the process's allocated address space.

     The unmount() system call may fail	with one of the	following errors:

     [EPERM]		The caller is neither the super-user nor the user who
			issued the corresponding mount() call.

     [ENAMETOOLONG]	The length of the path name exceeded 1023 characters.

     [EINVAL]		The requested directory	is not in the mount table.

     [ENOENT]		The file system	ID specified using MNT_BYFSID was not
			found in the mount table.

     [EINVAL]		The file system	ID specified using MNT_BYFSID could
			not be decoded.

     [EINVAL]		The specified file system is the root file system.

     [EBUSY]		A process is holding a reference to a file located on
			the file system.

     [EIO]		An I/O error occurred while writing cached file	system

     [EFAULT]		The dir	argument points	outside	the process's allo-
			cated address space.

     A ufs mount can also fail if the maximum number of	file systems are cur-
     rently mounted.

     lsvfs(1), mksnap_ffs(8), mount(8),	umount(8)

     The mount() and unmount() functions appeared in Version 6 AT&T UNIX.

     Some of the error codes need translation to more obvious messages.

BSD			       February	23, 2005			   BSD


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