MOUNT(2) BSD System Calls Manual MOUNT(2)NAME
mount, unmount — mount or dismount a filesystem
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);
DESCRIPTION
The mount() function grafts a filesystem object onto the system file tree
at the point dir. The argument data describes the filesystem object to
be mounted. The argument type tells the kernel how to interpret data
(See type below). The contents of the filesystem 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 filesystem is unmounted.
The following flags may be specified to suppress default semantics which
affect filesystem access.
MNT_RDONLY The filesystem should be treated as read-only; Even the
super-user may not write on it.
MNT_NOEXEC Do not allow files to be executed from the filesystem.
MNT_NOSUID Do not honor setuid or setgid bits on files when execut‐
ing them.
MNT_NODEV Do not interpret special files on the filesystem.
MNT_UNION Union with underlying filesystem instead of obscuring
it.
MNT_SYNCHRONOUS All I/O to the filesystem should be done synchronously.
The flag 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, most
filesystems 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 filesystem.
The type argument defines the type of the filesystem.
Data is a pointer to a structure that contains the type specific argu‐
ments to mount. The format for these argument structures is described in
the manual page for each filesystem.
The umount() function call disassociates the filesystem from the speci‐
fied mount point dir.
The flags argument may specify MNT_FORCE to specify that the filesystem
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 filesystem is later remounted.
RETURN VALUES
The mount() returns the value 0 if the mount was successful, otherwise -1
is returned and the variable errno is set to indicate the error.
Umount returns the value 0 if the umount succeeded; otherwise -1 is
returned and the variable errno is set to indicate the error.
ERRORSMount() will fail when one of the following occurs:
[EPERM] The caller is not the super-user, and the device-node and
the mountpoint do not have adequate ownership and permis‐
sions.
[ENAMETOOLONG] A component of a pathname exceeded {NAME_MAX} characters,
or an entire path name exceeded {PATH_MAX} characters.
[ELOOP] Too many symbolic links were encountered in translating a
pathname.
[ENOENT] A component of dir does not exist.
[ENOTDIR] A component of name is not a directory, or a path prefix
of special is not a directory.
[EINVAL] A pathname contains a character with the high-order bit
set.
[EBUSY] Another process currently holds a reference to dir.
[EFAULT] Dir points outside the process's allocated address space.
Umount may fail with one of the following errors:
[EPERM] The caller is not the super-user, and the mount() was not
done by the user.
[ENOTDIR] A component of the path is not a directory.
[EINVAL] The pathname contains a character with the high-order bit
set.
[ENAMETOOLONG] A component of a pathname exceeded {NAME_MAX} characters,
or an entire path name exceeded {PATH_MAX} characters.
[ELOOP] Too many symbolic links were encountered in translating
the pathname.
[EINVAL] The requested directory is not in the mount table.
[EBUSY] A process is holding a reference to a file located on the
filesystem.
[EIO] An I/O error occurred while writing cached filesystem
information.
[EFAULT] Dir points outside the process's allocated address space.
SEE ALSOmount(8), umount(8)BUGS
Some of the error codes need translation to more obvious messages.
HISTORYMount() and umount() function calls appeared in Version 6 AT&T UNIX.
4th Berkeley Distribution December 11, 1993 4th Berkeley Distribution
