NAME
mount,
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,
size_t data_len);
int
unmount(
const
char *dir,
int
flags);
DESCRIPTION
The
mount() function 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, and
is
data_len bytes long. 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 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.
-
-
MNT_UNION
- Union with underlying file system instead of obscuring
it.
-
-
MNT_HIDDEN
- Cause the df(1)
program, and perhaps others, to, by default, exclude this file system from
its output.
-
-
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 executing
them.
-
-
MNT_NODEV
- Do not interpret special files on the file system.
-
-
MNT_NOCOREDUMP
- Do not allow programs to dump core files on the file
system.
-
-
MNT_NOATIME
- Never update access time in the file system.
-
-
MNT_RELATIME
- Update access time on write and change. This helps programs
that verify that the file has been read after written to work.
-
-
MNT_NODEVMTIME
- Never update modification time of device files.
-
-
MNT_SYMPERM
- Recognize the permission of symbolic link when reading or
traversing.
-
-
MNT_SYNCHRONOUS
- All I/O to the file system should be done synchronously.
This will slow I/O performance considerably, but enhances overall file
system reliability.
-
-
MNT_ASYNC
- All I/O to the file system should be done asynchronously.
This vastly improves I/O throughput, but at a cost of making the file
system likely to be completely unrecoverable should the system crash while
unwritten data is pending in kernel buffers.
-
-
MNT_LOG
- Use a file system journal.
MNT_LOG
causes a journal (or log) to be created in the file system, creating a
record of meta-data writes to be performed, allowing the actual writes to
be deferred. This improves performance in most cases.
-
-
- MNT_EXTATTR
- Enable extended attributes, if the file system supports
them and does not enable them by default. Currently this is only the case
for UFS1.
The
MNT_UPDATE
,
MNT_RELOAD
, and
MNT_GETARGS
flags indicate that the mount command is
being applied to an already mounted file system. The
MNT_UPDATE
flag allows the mount flags to be changed
without requiring that the file system be unmounted and remounted. A
conversion from read-write to read-only will fail if any files are currently
open for writing on the file system, unless the
MNT_FORCE
flag is also applied. Some file systems may
not allow all flags to be changed. For example, some file systems will not
allow a change from read-write to read-only. The
MNT_RELOAD
flag causes kernel file system data to be
reloaded from the file system device. It is only permitted on file systems
mounted read-only. Its purpose is to notify the system that the file system
data has been modified by some external process. The
MNT_GETARGS
flag does not alter any of the mounted
file system's properties, but returns the file system-specific arguments for
the currently mounted file system.
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>, and those supported
by the current running kernel obtained using
sysctl(8) to obtain the node
vfs.generic.fstypes.
data is a pointer to a structure
that contains the type specific arguments to mount. Some of the currently
supported types of file systems and their type specific data are:
MOUNT_FFS
struct ufs_args {
char *fspec; /* block special file to mount */
};
MOUNT_NFS
struct nfs_args {
int version; /* args structure version */
struct sockaddr *addr; /* file server address */
int addrlen; /* length of address */
int sotype; /* Socket type */
int proto; /* and Protocol */
u_char *fh; /* File handle to be mounted */
int fhsize; /* Size, in bytes, of fh */
int flags; /* flags */
int wsize; /* write size in bytes */
int rsize; /* read size in bytes */
int readdirsize; /* readdir size in bytes */
int timeo; /* initial timeout in .1 secs */
int retrans; /* times to retry send */
int maxgrouplist; /* Max. size of group list */
int readahead; /* # of blocks to readahead */
int leaseterm; /* Term (sec) of lease */
int deadthresh; /* Retrans threshold */
char *hostname; /* server's name */
};
MOUNT_MFS
struct mfs_args {
char *fspec; /* name to export for statfs */
struct export_args30 pad; /* unused */
caddr_t base; /* base of file system in mem */
u_long size; /* size of file system */
};
The
unmount() function call disassociates the file system from
the specified mount point
dir.
The
flags argument may specify
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.
RETURN VALUES
mount() returns the value 0 if the mount was successful, the
number of bytes written to
data for
MNT_GETARGS
, otherwise -1 is returned and the variable
errno is set to indicate the error.
unmount() returns the value 0 if the unmount succeeded;
otherwise -1 is returned and the variable
errno is set
to indicate the error.
ERRORS
mount() will fail when one of the following occurs:
-
-
- [
EBUSY
]
- Another process currently holds a reference to
dir, or for an update from read-write to read-only
there are files on the file system open for writes.
-
-
- [
EFAULT
]
- dir points outside the process's
allocated address space.
-
-
- [
ELOOP
]
- Too many symbolic links were encountered in translating a
pathname.
-
-
- [
ENAMETOOLONG
]
- A component of a pathname exceeded
{
NAME_MAX
} characters, or an entire path name
exceeded {PATH_MAX
} characters.
-
-
- [
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.
-
-
- [
EPERM
]
- The caller is not the super-user, and ordinary user mounts
are not permitted or this particular request violates the rules.
The following errors can occur for a
ufs file system mount:
-
-
- [
EBUSY
]
- Fspec is already mounted.
-
-
- [
EFAULT
]
- Fspec points outside the process's
allocated address space.
-
-
- [
EINVAL
]
- The super block for the file system had a bad magic number
or an out of range block size.
-
-
- [
EIO
]
- An I/O error occurred while reading the super block or
cylinder group information.
-
-
- [
EMFILE
]
- No space remains in the mount table.
-
-
- [
ENODEV
]
- A component of ufs_args fspec does
not exist.
-
-
- [
ENOMEM
]
- Not enough memory was available to read the cylinder group
information for the file system.
-
-
- [
ENOTBLK
]
- Fspec 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).
The following errors can occur for a
nfs file system mount:
-
-
- [
EFAULT
]
- Some part of the information described by nfs_args points
outside the process's allocated address space.
-
-
- [
ETIMEDOUT
]
- Nfs timed out trying to contact the
server.
The following errors can occur for a
mfs file system mount:
-
-
- [
EFAULT
]
- Name points outside the process's
allocated address space.
-
-
- [
EINVAL
]
- The super block for the file system had a bad magic number
or an out of range block size.
-
-
- [
EIO
]
- A paging error occurred while reading the super block or
cylinder group information.
-
-
- [
EMFILE
]
- No space remains in the mount table.
-
-
- [
ENOMEM
]
- Not enough memory was available to read the cylinder group
information for the file system.
unmount() may fail with one of the following errors:
-
-
- [
EBUSY
]
- A process is holding a reference to a file located on the
file system.
-
-
- [
EFAULT
]
- dir points outside the process's
allocated address space.
-
-
- [
EINVAL
]
- The requested directory is not in the mount table.
-
-
- [
EIO
]
- An I/O error occurred while writing cached file system
information.
-
-
- [
ELOOP
]
- Too many symbolic links were encountered in translating the
pathname.
-
-
- [
ENAMETOOLONG
]
- A component of a pathname exceeded
{
NAME_MAX
} characters, or an entire path name
exceeded {PATH_MAX
} characters.
-
-
- [
ENOTDIR
]
- A component of the path is not a directory.
-
-
- [
EPERM
]
- The caller is not the super-user.
A
ufs or
mfs mount can also fail if the
maximum number of file systems are currently mounted.
SEE ALSO
df(1),
getvfsstat(2),
nfssvc(2),
getmntinfo(3),
symlink(7),
mount(8),
sysctl(8),
umount(8)
HISTORY
The
mount() and
umount() (now
unmount()) function calls were all present in
Version 6 AT&T UNIX.
Prior to
NetBSD 4.0 the
mount call was
used to export NFS file systems. This is now done through
nfssvc().
The
data_len
argument was added for
NetBSD 5.0.
BUGS
Some of the error codes need translation to more obvious messages.
Far more file systems are supported than those those listed.