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.\" Copyright (c) 1980, 1989 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.man%
.\"
.\"     @(#)mount.2	6.11 (Berkeley) %G%
.\"
.Dd 
.Dt MOUNT 2
.Os BSD 4
.Sh NAME
.Nm mount ,
.Nm unmount
.Nd mount or dismount a filesystem
.Sh SYNOPSIS
.Fd #include <sys/mount.h>
.Ft int
.Fn mount "int type" "const char *dir" "int flags" "caddr_t data"
.Ft int
.Fn unmount "const char *dir" "int flags"
.Sh DESCRIPTION
The
.Fn mount
function grafts
a filesystem object onto the system file tree
at the point
.Ar dir .
The argument
.Ar data
describes the filesystem object to be mounted.
The argument
.Ar type
tells the kernel how to interpret
.Ar data
(See
.Ar type
below).
The contents of the filesystem
become available through the new mount point
.Ar dir .
Any files in
.Ar dir
at the time
of a successful mount are swept under the carpet so to speak, and
are unavailable until the filesystem is unmounted.
.Pp
The following
.Ar flags
may be specified to
suppress default semantics which affect filesystem access.
.Bl -tag -width M_SYNCHRONOUS
.It Dv M_RDONLY
The file system should be treated as read-only;
Even the super-user may not write on it.
.It Dv M_NOEXEC
Do not allow files to be executed from the file system.
.It Dv M_NOSUID
Do not honor setuid or setgid bits on files when executing them.
.It Dv M_NODEV
Do not interpret special files on the file system.
.It Dv M_SYNCHRONOUS
All I/O to the file system should be done synchronously.
.El
.Pp
The flag
.Dv M_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 remounted.
Some file systems may not allow all flags to be changed.
For example,
most file systems will not allow a change from read-write to read-only.
.Pp
The
.Fa type
argument defines the type of the file system.
The types of file systems known to the system are defined in
.Aq Pa sys/mount.h .
.Fa Data
is a pointer to a structure that contains the type
specific arguments to mount.
The currently supported types of file systems and
their type specific data are:
.Pp
.Dv MOUNT_UFS
.Bd -literal -compact -offset indent
struct ufs_args {
	char	*fspec;	/* Block special file to mount */
	int	exflags;	/* export related flags */
	uid_t	exroot;	/* mapping for root uid */
};
.Ed
.Pp
.Dv MOUNT_NFS
.Bd -literal -compact -offset indent
struct nfs_args {
	struct	sockaddr_in *addr;	/* file server address */
	nfsv2fh_t	*fh;	/* File handle to be mounted */
	int	flags;	/* flags */
	int	wsize;	/* write size in bytes */
	int	rsize;	/* read size in bytes */
	int	timeo;	/* initial timeout in 0.1 secs */
	int	retrans;	/* times to retry send */
	char	*hostname;	/* server's name */
};
.Ed
.Pp
.Dv MOUNT_MFS
.Bd -literal -compact -offset indent
struct mfs_args {
	char	*name;	/* name of backing process */
	caddr_t	base;	/* base address of the file system */
	u_long	size;	/* size of the file system */
};
.Ed
.Pp
The
.Fn umount
function call disassociates the filesystem from the specified
mount point
.Fa dir .
.Pp
The
.Fa flags
argument may have one of the following values:
.Bl -tag -width  M_SYNCHRONOUS
.It Dv MNT_NOFORCE
The unmount should fail if any files are active on the file system.
.It Dv MNT_FORCE
The file system should be forcibly unmounted even if files are
still active.
Active special devices continue to work,
but any further accesses to any other active files result in errors
even if the file system is later remounted.
.El
.Sh RETURN VALUES
The
.Fn mount
returns the value 0 if the mount was successful, otherwise -1 is returned
and the variable
.Va errno
is set to indicate the error.
.Pp
.Nm Umount
returns the value 0 if the umount succeeded; otherwise -1 is returned
and the variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn Mount
will fail when one of the following occurs:
.Bl -tag -width [ENOTBLK]
.It Bq Er EPERM
The caller is not the super-user.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or the entire length of a path name exceeded 1023 characters.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating a pathname.
.It Bq Er ENOENT
A component of
.Fa dir
does not exist.
.It Bq Er ENOTDIR
A component of
.Ar name
is not a directory,
or a path prefix of
.Ar special
is not a directory.
.It Bq Er EINVAL
A pathname contains a character with the high-order bit set.
.It Bq Er EBUSY
Another process currently holds a reference to
.Fa dir .
.It Bq Er EFAULT
.Fa Dir
points outside the process's allocated address space.
.El
.Pp
The following errors can occur for a
.Em ufs
file system mount:
.Bl -tag -width [ENOTBLK]
.It Bq Er ENODEV
A component of ufs_args
.Ar fspec
does not exist.
.It Bq Er ENOTBLK
.Ar Fspec
is not a block device.
.It Bq Er ENXIO
The major device number of 
.Ar fspec
is out of range (this indicates no device driver exists
for the associated hardware).
.It Bq Er EBUSY
.Ar Fspec
is already mounted.
.It Bq Er EMFILE
No space remains in the mount table.
.It Bq Er EINVAL
The super block for the file system had a bad magic
number or an out of range block size.
.It Bq Er ENOMEM
Not enough memory was available to read the cylinder
group information for the file system.
.It Bq Er EIO
An I/O error occurred while reading the super block or
cylinder group information.
.It Bq Er EFAULT
.Ar Fspec
points outside the process's allocated address space.
.El
.Pp
The following errors can occur for a
.Em nfs
file system mount:
.Bl -tag -width [ENOTBLK]
.It Bq Er ETIMEDOUT
.Em Nfs
timed out trying to contact the server.
.It Bq Er EFAULT
Some part of the information described by nfs_args
points outside the process's allocated address space.
.El
.Pp
The following errors can occur for a
.Em mfs
file system mount:
.Bl -tag -width [ENOTBLK]
.It Bq Er EMFILE
No space remains in the mount table.
.It Bq Er EINVAL
The super block for the file system had a bad magic
number or an out of range block size.
.It Bq Er ENOMEM
Not enough memory was available to read the cylinder
group information for the file system.
.It Bq Er EIO
An paging error occurred while reading the super block or
cylinder group information.
.It Bq Er EFAULT
.Em Name
points outside the process's allocated address space.
.El
.Pp
.Em Umount
may fail with one of the following errors:
.Bl -tag -width [ENOTBLK]
.It Bq Er EPERM
The caller is not the super-user.
.It Bq Er ENOTDIR
A component of the path is not a directory.
.It Bq Er EINVAL
The pathname contains a character with the high-order bit set.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EINVAL
The requested directory is not in the mount table.
.It Bq Er EBUSY
A process is holding a reference to a file located
on the file system.
.It Bq Er EIO
An I/O error occurred while writing cached file system information.
.It Bq Er EFAULT
.Fa Dir
points outside the process's allocated address space.
.El
.Pp
A
.Em ufs
or
.Em mfs
mount can also fail if the maximum number of filesystems are currently
mounted.
.Sh SEE ALSO
.Xr mount 8 ,
.Xr umount 8 ,
.Xr mfs 8
.Sh BUGS
Some of the error codes need translation to more obvious messages.
.Sh HISTORY
.Fn Mount
and
.Fn umount
function calls appeared in Version 6 AT&T UNIX.