mount(2)

NAME

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

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/param.h>
#include <sys/mount.h>
int
mount(const char *type, const char  *dir,  int  flags,  void
*data);
int
unmount(const char *dir, int flags);
#include <sys/uio.h>
int
nmount(struct iovec *iov, u_int niov, int flags);

DESCRIPTION

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
object 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 successful 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(), ex

cept 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 ar

ray iov, containing niov elements. The following options are required

by all file
systems:

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 rec

ognized or
required; for example, most disk-based file systems require

a ``from''
option containing the pathname of a special device in addi

tion 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) variable to a non-zero value.

The following flags may be specified to suppress default se

mantics 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-on

ly 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
effect. See the mount(8) and chmod(2)

pages for more
information.

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

chronously.

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 be

ing 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, many file systems will not allow a change from

read-write to
read-only.

The flag MNT_RELOAD causes the vfs subsystem to update its

data structures pertaining to the specified already mounted file sys

tem.

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 specific arguments to mount. The format for these argument

structures is
described in the manual page for each file system. By con

vention 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 sys

tem is
described by the mount_nfs(8) manual page. It should be

noted that a
manual page for default file systems, known as UFS and UFS2,

does not
exist.

The unmount() system call disassociates the file system from

the specified 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 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.

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 specified file system ID will be unmounted.

RETURN VALUES

The function returns the value 0 if successful; otherwise

the value -1 is
returned and the global variable errno is set to indicate

the error.

ERRORS

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

the following
occurs:

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

the owner of

dir.

[ENAMETOOLONG] A component of a pathname exceeded 255

characters, or

the entire length of a path name exceeded

1023 characters.

[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 refer

ence to dir.

[EFAULT] The dir argument points outside the pro

cess'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
hardware).

[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 serv

er.

[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

information.

[EFAULT] The dir argument points outside the pro

cess's allo

cated address space.

A ufs mount can also fail if the maximum number of file sys

tems are currently mounted.

SEE ALSO

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

HISTORY

The mount() and unmount() functions appeared in Version 6

AT&T UNIX.

BUGS

Some of the error codes need translation to more obvious

messages.

BSD February 23, 2005

BSD