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MOUNT(2) FreeBSD System Calls Manual MOUNT(2)
NAME
mount, nmount, unmount -- mount or dismount a file system
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include
#include
int
mount(const char *type, const char *dir, int flags, void *data);
int
unmount(const char *dir, int flags);
#include
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 inter-
pret 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(), 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
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 recognized or
required; 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
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 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, 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 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
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 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
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 speci-
fied file system ID will be unmounted.
RETURN VALUES
Upon successful completion, the value 0 is returned; 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 charac-
ters.
[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
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 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
information.
[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.
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.
FreeBSD 6.1 February 23, 2005 FreeBSD 6.1
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