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MOUNT_MSDOS(8) System Manager's Manual MOUNT_MSDOS(8)

mount_msdosmount an MS-DOS file system

mount_msdos [-9ls] [-g group] [-m mask] [-o options] [-u user] special node

The mount_msdos command attaches the MS-DOS file system residing on the device special to the global file system namespace at the location indicated by node. This command is invoked by mount(8) when using the syntax

mount [options] -t msdos special node

The special device must correspond to a partition registered in the disklabel(5).

This command is normally executed by mount(8) at boot time, but can be used by any user to mount an MS-DOS file system on any directory that they own (provided, of course, that they have appropriate access to the device that contains the file system).

The options are as follows:

Ignore the special Windows 95/98 directory entries even if deleting or renaming a file. This forces -s.
Specifies the group name or GID of the root inode of the file system. Defaults to the mount point's GID.
Force listing and generation of Windows 95/98 long filenames and separate creation/modification/access dates.

This is the default.

Specify the maximum permissions for files and directories in the file system. Only the nine low-order bits of mask are used.
Use the specified mount options, as described in mount(8).
Force behaviour to ignore and not generate Windows 95/98 long filenames.
Specifies the user name or UID of the root inode of the file system. Defaults to the mount point's UID.

File permissions for FAT file systems are imitated, since the file system has no real concept of permissions. The default mask is taken from the directory on which the file system is being mounted, except when the -m option is used. FAT does have a “read only” mode, in which the writable bit is unset. If such files are found, they are marked non-writable; it can be set using chmod -w or unset using chmod +w.

File modes work the same way for directories. However a directory will inherit the executable bit if it is readable. See chmod(1) for more information about octal file modes.

chmod(1), mount(2), disklabel(5), fstab(5), disklabel(8), mount(8), umount(8)

The mount_msdos utility first appeared in NetBSD 0.9. Its predecessor, the mount_pcfs utility, appeared in NetBSD 0.8, and was abandoned in favor of the more aptly named mount_msdos.

The original code was written by Paul Popelka <> as a patch to 386BSD-0.1 in November 1992. The current version is based on code written by Christopher G. Demetriou <> in April 1994.

The maximum file size supported by the MS-DOS file system is one byte less than 4GB. This is a FAT file system limitation, documented by Microsoft in Knowledge Base article 314463.

The MS-DOS file system (even with long filenames) does not support filenames with trailing dots or spaces. Any such characters will be silently removed before the directory entry is written. This too is a FAT file system limitation.

The use of the -9 flag could result in damaged file systems, albeit the damage is in part taken care of by procedures similar to the ones used in Windows 95/98.

Note that Windows 95/98 handles only access dates, but not access times.

August 20, 2022 OpenBSD-7.3