MOUNT(2) BSD Programmer's Manual MOUNT(2)
NAME
mount, unmount - mount or dismount a filesystem
SYNOPSIS
#include <sys/mount.h>
int
mount(int type, const char *dir, int flags, caddrt 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 successful 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.
M_RDONLY The file system should be treated as read-only; Even the
super-user may not write on it.
M_NOEXEC Do not allow files to be executed from the file system.
M_NOSUID Do not honor setuid or setgid bits on files when executing
them.
M_NODEV Do not interpret special files on the file system.
M_SYNCHRONOUS All I/O to the file system should be done synchronously.
The flag 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.
The type argument defines the type of the file system. The types of file
systems known to the system are defined in <sys/mount.h>. 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 spe-
cific data are:
MOUNT_UFS
struct ufs_args {
char *fspec; /* Block special file to mount */
int exflags; /* export related flags */
uid_t exroot; /* mapping for root uid */
};
MOUNT_NFS
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 0.1 secs */
int retrans; /* times to retry send */
char *hostname; /* server's name */
};
MOUNT_MFS
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 */
};
The umount() function call disassociates the filesystem from the speci-
fied mount point dir.
The flags argument may have one of the following values:
MNT_NOFORCE The unmount should fail if any files are active on the
file system.
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 remount-
ed.
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 re-
turned and the variable errno is set to indicate the error.
ERRORS
Mount() will fail when one of the following occurs:
[EPERM] The caller is not the super-user.
[ENAMETOOLONG]
A component of a pathname exceeded 255 characters, or the en-
tire length of a path name exceeded 1023 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.
The following errors can occur for a ufs file system mount:
[ENODEV] A component of ufs_args fspec does not exist.
[ENOTBLK] Fspec is not a block device.
[ENXIO] The major device number of fspec is out of range (this indi-
cates 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 in-
formation for the file system.
[EIO] An I/O error occurred while reading the super block or cylin-
der group information.
[EFAULT] Fspec points outside the process's allocated 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 out-
side the process's allocated address space.
The following errors can occur for a mfs file system mount:
[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 in-
formation for the file system.
[EIO] An paging error occurred while reading the super block or
cylinder group information.
[EFAULT] Name 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.
[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 255 characters, or an en-
tire path name exceeded 1023 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 file
system.
[EIO] An I/O error occurred while writing cached file system infor-
mation.
[EFAULT] Dir points outside the process's allocated address space.
A ufs or mfs mount can also fail if the maximum number of filesystems are
currently mounted.
SEE ALSO
mount(8), umount(8), mfs(8)
BUGS
Some of the error codes need translation to more obvious messages.
HISTORY
Mount() and umount() function calls appeared in Version 6 AT&T UNIX.
4th Berkeley Distribution March 26, 1993 4