Working with DOS

Using mounted DOS filesystems

In addition to using the DOS utilities, you can mount a DOS filesystem (including those on floppy disks) and access its files directly while still operating from the SCO OpenServer system. A general description of mounting filesystems is given in ``Mounting a filesystem''.

NOTE: You must add support for DOS filesystems to the kernel before you can mount DOS filesystems. See ``Adding support for different filesystem types'' for more information.

This means that you can edit DOS files in place, without first copying them into the UNIX filesystem. The SCO OpenServer system deals with DOS files by superimposing certain qualities of UNIX filesystems over the DOS filesystem without changing the actual files. UNIX filesystems are highly structured and operate in a multiuser environment. In order to make DOS files readily accessible, access permissions and file ownership are superimposed on the DOS filesystem when mounted.

Normally, only the system administrator can mount a filesystem. Access by users is governed by the permissions and ownership that your system administrator places on the DOS filesystem. The system administrator must either mount the DOS filesystem or set up the system so that users can use the mnt(C) command. The filesystem must also be mountable. Such systems have an entry in /etc/default/filesys that contains the command mount=yes. See ``Mounting a filesystem'' for details of /etc/default/filesys and how to check its contents.

You can mount DOS filesystems from the Filesystem Manager after adding them to the mount configuration, as described in ``Adding and removing mount configuration''. You must use the device names shown in ``DOS device names'' or create the nodes described in ``Accessing DOS partitions on a second disk'' For information on the behavior of DOS filesystems, see ``About mounting DOS filesystems''.

You can also mount these partitions manually using the mount(ADM) command. The form for a DOS filesystem mount command is:

mount -r -f DOS /dev/dsk/xsy /mountpoint

where:

x: is the hard disk number
y: is the drive letter (for example, C:, D:)
mountpoint: is the name of the directory in the root filesystem where the DOS filesystem is to be mounted.

The -r flag mounts the filesystem read-only, an optional precaution that will prevent damage to the DOS filesystem (which is not as robust as other filesystems.

DOS automatically calls the primary DOS drive, on the first disk, C:. If you have a primary DOS partition on the second disk this becomes D:, automatically, and logical drives on extended partitions are named in order (for example disk0 Primary C: EXT E: F: G: H:, disk1 Primary D: EXT I: J:). ``DOS device names'' lists these device names under DOS and SCO OpenServer.

DOS device names

DOS C: D: E: F: G: H: I: J:

UNIX 0sC 1sC 0sD 0sE 0sF 0sG 1sD 1sE

NOTE: When using mount, you must give the specific hard disk and partition numbers (wildcards are not allowed).

The major restriction with mounting a DOS floppy or a DOS partition is that DOS applications (for example, your DOS word processing package) cannot be executed under this arrangement.

If you need to use your DOS applications, you (or your system administrator) need to do one of the following:

Boot the system as a DOS system (only your system administrator can do this).
Make the DOS partition the active partition, so that the computer boots DOS by default (only your system administrator can do this).
Run NeTraverse Merge from the UNIX partition. (Ask your system administrator if you have this application on your system.)

DOS utilities cannot be used on a mounted DOS filesystem.

Because of the limitations discussed earlier, DOS does not recognize permissions or ownership. When mounted from the UNIX partition, DOS files behave as follows:

The permissions and ownership of the filesystem are governed by the mount point. For example, if root creates a mount point /X with permissions of 777, all users can read or write the contents of the filesystem. If root creates a mount point with permissions of 700, only root can read or write the contents of the filesystem.
The ownership of regular files is governed by the mount point. If the mount point is owned by root, all files within the DOS filesystem and any created by other users are all owned by root.
DOS does not distinguish between users, therefore files can be either readable/writable for everyone, or read-only for everyone. The permissions for regular files are either 0777 for readable/writable files or 0555 for read-only files. When a file is created, the permissions are based on the umask of the creator, but may not be the same as they would be in a normal filesystem. If the umask allows anyone to write to the file, then the permissions are set to 777; if no one can write to the file, the permissions are set to 555. See umask(C) for details.