path: root/lib/libc/sys/mount.2

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.\"     @(#)mount.2	8.3 (Berkeley) 5/24/95
.\" $FreeBSD$
.\"
.Dd May 24, 1995
.Dt MOUNT 2
.Os
.Sh NAME
.Nm mount ,
.Nm unmount
.Nd mount or dismount a filesystem
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <sys/mount.h>
.Ft int
.Fn mount "const char *type" "const char *dir" "int flags" "void *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 MNT_SYNCHRONOUS
.It Dv MNT_RDONLY
The filesystem 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 filesystem to read/write.
.It Dv MNT_NOEXEC
Do not allow files to be executed from the filesystem.
.It Dv MNT_NOSUID
Do not honor setuid or setgid bits on files when executing them.
.It Dv MNT_NOATIME
Disable update of file access times.
.It Dv MNT_NODEV
Do not interpret special files on the filesystem.
.It Dv MNT_SUIDDIR
Directories with the SUID bit set chown new files to their own owner.
.It Dv MNT_SYNCHRONOUS
All I/O to the filesystem should be done synchronously.
.It Dv MNT_ASYNC
All I/O to the filesystem should be done asynchronously.
.It Dv MNT_FORCE
Force a read-write mount even if the filesystem appears to be unclean.
Dangerous.
.It Dv MNT_NOCLUSTERR
Disable read clustering.
.It Dv MNT_NOCLUSTERW
Disable write clustering.
.El
.Pp
The flag
.Dv MNT_UPDATE
indicates that the mount command is being applied 
to an already mounted filesystem.
This allows the mount flags to be changed without requiring
that the filesystem be unmounted and remounted.
Some filesystems may not allow all flags to be changed.
For example,
many filesystems will not allow a change from read-write to read-only.
.Pp
The flag
.Dv MNT_RELOAD
causes the vfs subsystem to update its data structures pertaining to
the specified already mounted filesystem.
.Pp
The
.Fa type
argument names the filesystem.
The types of filesystems known to the system can be obtained with
.Xr lsvfs 1 .
.Pp
.Fa Data
is a pointer to a structure that contains the type
specific arguments to mount.
The format for these argument structures is described in the
manual page for each filesystem.
By convention filesystem manual pages are named
by prefixing ``mount_'' to the name of the filesystem as returned by
.Xr lsvfs 1 .
Thus the
.Nm NFS
filesystem is described by the
.Xr mount_nfs 8
manual page.
.Pp
The
.Fn unmount
function call disassociates the filesystem from the specified
mount point
.Fa dir .
.Pp
The
.Fa flags
argument may specify
.Dv MNT_FORCE
to specify that the filesystem should be forcibly unmounted or made read-only
(if MNT_UPDATE and MNT_RDONLY are also specified)
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 filesystem is later remounted.
.Pp
The
.Dv MNT_SUIDDIR
option requires the SUIDDIR option to have been compiled into the kernel
to have any effect.
See the
.Xr mount 8 
and
.Xr chmod 2
pages for more information.
.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
The
.Fn unmount
function 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
The
.Fn mount
function will fail when one of the following occurs:
.Bl -tag -width Er
.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 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
filesystem mount:
.Bl -tag -width Er
.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 filesystem 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 filesystem.
.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
filesystem mount:
.Bl -tag -width Er
.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
.Fn unmount
function may fail with one of the following errors:
.Bl -tag -width Er
.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 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 filesystem.
.It Bq Er EIO
An I/O error occurred while writing cached filesystem information.
.It Bq Er EFAULT
.Fa Dir
points outside the process's allocated address space.
.El
.Pp
A
.Em ufs
mount can also fail if the maximum number of filesystems are currently
mounted.
.Sh SEE ALSO
.Xr lsvfs 1 ,
.Xr mount 8 ,
.Xr umount 8
.Sh BUGS
Some of the error codes need translation to more obvious messages.
.Sh HISTORY
.Fn Mount
and
.Fn unmount
function calls appeared in
.At v6 .