Administering filesystems

About mounting DOS filesystems

In addition to manipulating DOS files with the DOS utilities provided with the operating system, you can mount a DOS filesystem and access its files freely while still operating from your UNIX system.

NOTE: The ability to mount DOS filesystems is available, regardless of whether you have a DOS emulator program installed.

When you mount a DOS filesystem, you can edit, examine, or copy DOS data and text files, without first copying them into the UNIX filesystem. However, you cannot execute DOS files and applications from a mounted DOS filesystem. To do this, you must run NeTraverse Merge or boot DOS from a DOS partition.

If you use the DOS utilities on a mounted DOS filesystem, you see this error:

   dosdir: FAT not recognized on /dev/dsk/0sC

In addition, you cannot create DOS filesystems using the mkfs(ADM) command. The DOS mounting feature is intended for existing DOS filesystems (on a floppy disk or on an existing DOS partition).

The UNIX operating system handles mounted DOS filesystems, without actually changing the files, by superimposing certain qualities of UNIX system filesystems on the DOS filesystem. UNIX filesystems are highly structured and operate in a multiuser environment. Thus, many UNIX filesystem concepts do not apply to DOS, including:

file ownership
access permissions
special files (pipes, device files, and so forth)
links

To make DOS files readily accessible, the UNIX system superimposes access permissions and file ownership on the DOS filesystem when you mount it. See ``DOS filesystems and access permissions''.

Because no changes are made to the DOS files, the carriage return character (^M) is visible when you edit a DOS file on a UNIX system. (UNIX systems use only a newline character; DOS uses both a carriage return and a newline.) To switch the end-of-line from DOS format to UNIX system format, use dtox(C). To switch back to UNIX system format, use xtod(C). See ``Displaying a DOS file'' and ``Converting DOS files to and from UNIX system file format''.

DOS filesystems and access permissions

Only root and users with filesystem authorization can mount filesystems, including DOS filesystems.

A user's access to a mounted DOS filesystem is determined by the permissions and ownership that root places on the filesystem.

When DOS files are mounted on a UNIX system:

The permissions and ownership of the filesystem are determined by the permissions of the mount point.
For example, if root creates a mount point /x with permissions of 0777, all users can read or write the contents of the filesystem. If the mount point is owned by root, all files in the DOS filesystem and any created by other users are owned by root.
The permissions for regular files on the mounted DOS filesystem are set to either 0777 (for readable/writable files) or 0555 for read-only files.
The permissions are based on the umask(C) of the creator when a user creates a file on a mounted DOS filesystem.
For example, if a user's umask is 0022, all files created by that user have permissions of 0644.
Files in a DOS filesystem cannot have multiple links.
NOTE: ``.'' and ``..'' are special cases; on a mounted DOS filesystem, they are not links as they are on a UNIX system.
Features such as locking govern how different users can access a file simultaneously on UNIX systems. These features operate identically on a mounted DOS filesystem. Two users can edit the same file and write to it as permitted by the locking mechanism used.

DOS filesystem limitations

The following limitations apply when accessing files on a mounted DOS filesystem:

The rules for filenames and filename conversion follow the guidelines listed in the doscmd(C) manual page. In addition, the standard DOS restrictions on illegal characters apply. However, you can use wildcards to match DOS files, just as you do on a UNIX system.
Timestamps differ between DOS and UNIX systems.
When mounted from the UNIX system partition, the UNIX DOS filesystem driver records the creation, modification, and access times of files in GMT (Greenwich Mean Time) and then converts them to the appropriate local time. DOS timestamps are recorded in the local time.
Thus, in time zones other than GMT, when you access a file created in the DOS filesystem while mounted on the UNIX system, the timestamp will be wrong because DOS assumes that the timestamp was recorded in the local time. If you mount the DOS filesystem under the UNIX system and access a file created under DOS, the timestamp will also be wrong because the UNIX system assumes the timestamp was recorded in GMT and converts it to the local time.
You cannot use the Backup Manager or the backup(ADM) utility to make backups of a mounted DOS filesystem. However, you can use DOS utilities and other copy programs such as tar(C) to create backups.