The mount() function requests that a removable file system contained on the block special file identified by spec be mounted on the directory identified by dir. The spec and dir arguments are pointers to path names.

After a successful call to mount(), all references to the file dir refer to the root directory on the mounted file system. The mounted file system is inserted into the kernel list of all mounted file systems. This list can be examined through the mounted file system table (see mnttab(4)).

The fstype argument is the file system type name. Standard file system names are defined with the prefix MNTTYPE_ in <sys/mntent.h>.

The dataptr argument is 0 if no file system-specific data is to be passed; otherwise it points to an area of size datalen that contains the file system-specific data for this mount and the MS_DATA flag should be set.

If the MS_OPTIONSTR flag is set, then optptr points to a buffer containing the list of options to be used for this mount. The optlen argument specifies the length of the buffer. On completion of the mount() call, the options in effect for the mounted file system are returned in this buffer. If MS_OPTIONSTR is not specified, then the options for this mount will not appear in the mounted file systems table.

The mflag argument is constructed by a bitwise-inclusive-OR of flags from the following list, defined in <sys/mount.h>.

MS_DATA

The dataptr and datalen arguments describe a block of file system-specific binary data at address dataptr of length datalen. This is interpreted by file system-specific code within the operating system and its format depends on the file system type. If a particular file system type does not require this data, dataptr and datalen should both be 0.

MS_GLOBAL

Mount a file system globally if the system is configured and booted as part of a cluster (see clinfo(1M)).

MS_NOSUID

Prevent programs that are marked set-user-ID or set-group-ID from executing (see chmod(1)). It also causes open(2) to return ENXIO when attempting to open block or character special files.

MS_OPTIONSTR

The optptr and optlen arguments describe a character buffer at address optptr of size optlen. When calling mount(), the character buffer should contain a null-terminated string of options to be passed to the file system-specific code within the operating system. On a successful return, the file system-specific code will return the list of options recognized. Unrecognized options are ignored. The format of the string is a list of option names separated by commas. Options that have values (rather than binary options such as suid or nosuid), are separated by "=" such as dev=2c4046c. Standard option names are defined in <sys/mntent.h>. Only strings defined in the "C" locale are supported. The maximum length option string that can be passed to or returned from a mount() call is defined by the MAX_MNTOPT_STR constant. The buffer should be long enough to contain more options than were passed in, as the state of any default options that were not passed in the input option string may also be returned in the recognized options list that is returned.

MS_OVERLAY

Allow the file system to be mounted over an existing file system mounted on dir, making the underlying file system inaccessible. If a mount is attempted on a pre-existing mount point without setting this flag, the mount will fail.

MS_RDONLY

Mount the file system for reading only. This flag should also be specified for file systems that are incapable of writing (for example, CDROM). Without this flag, writing is permitted according to individual file accessibility.

MS_REMOUNT

Remount a read-only file system as read-write.

Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error.

The mount() function will fail if:

EBUSY

The dir argument is currently mounted on, is someone's current working directory, or is otherwise busy; the device associated with spec is currently mounted; or there are no more mount table entries.

EFAULT

The spec, dir, fstype, dataptr, or optptr argument points outside the allocated address space of the process.

EINVAL

The super block has an invalid magic number or the fstype is invalid.

ELOOP

Too many symbolic links were encountered in translating spec or dir.

ENAMETOOLONG

The length of the path argument exceeds PATH_MAX, or the length of a path component exceeds NAME_MAX while _POSIX_NO_TRUNC is in effect.

ENOENT

None of the named files exists or is a null pathname.

ENOLINK

The path argument points to a remote machine and the link to that machine is no longer active.

ENOSPC

The file system state in the super-block is not FsOKAY and mflag requests write permission.

ENOTBLK

The spec argument is not a block special device.

ENOTDIR

The dir argument is not a directory, or a component of a path prefix is not a directory.

ENOTSUP

A global mount is attempted (the MS_GLOBAL flag is set in mflag) on a machine which is not booted as a cluster or a local mount is attempted and dir is within a globally mounted file system.

ENXIO

The device associated with spec does not exist.

EOVERFLOW

The length of the option string to be returned in the optptr argument exceeds the size of the buffer specified by optlen.

EPERM

The effective user ID is not superuser.

EREMOTE

The spec argument is remote and cannot be mounted.

EROFS

The spec argument is write protected and mflag requests write permission.

The mount() function can be invoked only by processes with superuser privileges.

mount(1M), umount(2), mnttab(4)

MS_OPTIONSTR-type option strings should be used.

Some flag bits set file system options that can also be passed in an option string. Options are first set from the option string with the last setting of an option in the string determining the value to be set by the option string. Any options controlled by flags are then applied, overriding any value set by the option string.