MOUNT(2) BSD System Calls Manual MOUNT(2)NAME
mount, unmount — mount or dismount a filesystem
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);
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.
By default only the super-user may call the mount() function. This
restriction can be removed by setting the sysctl vfs.usermount to a non-
zero value.
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. Specifying MNT_UPDATE
without this option will upgrade a read-only filesystem
to read/write.
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. This flag is set automatically when the call‐
er is not the super-user.
MNT_NOATIME Disable update of file access times.
MNT_NODEV Do not interpret special files on the filesystem. This
flag is set automatically when the caller is not the
super-user.
MNT_SUIDDIR Directories with the SUID bit set chown new files to
their own owner.
MNT_SYNCHRONOUS All I/O to the filesystem should be done synchronously.
MNT_ASYNC All I/O to the filesystem should be done asynchronously.
MNT_FORCE Force a read-write mount even if the filesystem appears
to be unclean. Dangerous.
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 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, many
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 names the filesystem. The types of filesystems known
to the system can be obtained with lsvfs(1).
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. By convention filesystem manual
pages are named by prefixing ``mount_'' to the name of the filesystem as
returned by lsvfs(1). Thus the NFS filesystem is described by the
mount_nfs(8) manual page.
The unmount() 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 or made read-only (if MNT_UPDATE and
MNT_RDONLY are also specified) 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 filesystem is later remounted.
The MNT_SUIDDIR option 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.
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() function will fail when one of the following occurs:
[EPERM] The caller is neither the super-user nor the owner of
dir, or dir belongs to a filesystem that does not sup‐
port stacked mounts.
[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] Dir points outside the process's allocated address
space.
The following errors can occur for a ufs filesystem 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
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 filesystem 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 filesystem.
[EIO] An I/O error occurred while reading the super block or
cylinder group information.
[EFAULT] Fspec points outside the process's allocated address
space.
The following errors can occur for a nfs filesystem 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 following errors can occur for a mfs filesystem mount:
[EMFILE] No space remains in the mount table.
[EINVAL] The super block for the filesystem 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 filesystem.
[EIO] A paging error occurred while reading the super block
or cylinder group information.
[EFAULT] Name points outside the process's allocated address
space.
The unmount() function may fail with one of the following errors:
[EPERM] The caller is neither the super-user nor the user who
issued the corresponding mount(2) call.
[ENOTDIR] A component of the path is not a directory.
[ENAMETOOLONG] A component of a pathname exceeded 255 characters, or
an entire path name exceeded 1023 characters.
[ELOOP] Too many symbolic links were encountered in translat‐
ing 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.
A ufs or mfs mount can also fail if the maximum number of filesystems are
currently mounted.
SEE ALSOlsvfs(1), mountctl(2), mfs(8), mount(8), sysctl(8), umount(8)HISTORYMount() and unmount() function calls appeared in Version 6 AT&T UNIX.
BUGS
Some of the error codes need translation to more obvious messages.
BSD May 24, 1995 BSD
