MOUNT(2)                    BSD System Calls Manual                   MOUNT(2)

NAME
     mount, fmount, 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
     fmount(const char *type, int fd, 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.

     MNT_CPROTECT     Enable data protection on the filesystem if the filesys-
                      tem is configured for it.

     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 fmount() function call is equivalent to the mount() function call,
     except in the use of the second argument.  It takes an open file descrip-
     tor representing mount point instead of the string literal containing
     full path to the mount point in the filesystem hierarchy.

     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 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() and fmount() return the value 0 if the mount was successful,
     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() and fmount() 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.

     unmount 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 ALSO
     mount(8), unmount(8), open(2)

BUGS
     Some of the error codes need translation to more obvious messages.

HISTORY
     mount() and unmount() function calls appeared in Version 6 AT&T UNIX.
     fmount() function call first appeared in macOS version 10.13.

4th Berkeley Distribution      December 11, 1993     4th Berkeley Distribution