assign(C)

assign, deassign -- assign and deassign devices

Syntax

assign [ -u ] [ -v ] [ -d ] [ device ] ...

deassign [ -u ] [ -v ] [ device ] ...

Description

The assign command attempts to assign device to the current user. The device argument must be an assignable device that is not currently assigned. An assign command without an argument prints a list of assignable devices along with the name of the user to whom they are assigned.

The deassign command is used to ``deassign'' devices. Without any arguments, deassign will deassign all devices assigned to the user. With arguments, an attempt is made to deassign each device given as an argument.

With these commands you can exclusively use a device, such as a tape drive or floppy drive. This keeps other users from using the device. They have a similar effect to chown(C) and chmod(C), although they only act on devices in /dev. Other aspects are discussed further on.

Available options include:

-d: Performs the action of deassign. The -d option can be embedded in device names to assign some devices and deassign others.
-v: Gives verbose output.
-u: Suppresses assignment or deassignment, but performs error checking.

The assign command will not assign any assignable devices if it cannot assign all of them. deassign gives no diagnostic if the device cannot be deassigned. Devices can be automatically deassigned at logout, but this is not guaranteed. Device names can be just the beginning of the device required. For example,

assign fd

should be used to assign all floppy disk devices. Raw versions of device will also be assigned, for example, the raw floppy disk devices /dev/rfd? would be assigned in the above example.

Note that in many installations the assignable devices such as floppy disks have general read and write access, so the assign command may not be necessary. This is particularly true on single-user systems. Devices supposed to be assignable with this command should be owned by the user asg. The directory /dev should be owned by bin and have mode 755. The assign command (after checking for use by someone else) will then make the device owned by whoever invokes the command, without changing the access permissions. This allows the system administrator to set up individual devices that are freely available, assignable (owned by asg), or nonassignable and restricted (not owned by asg and with some restricted mode).

Note that the first time assign is invoked, it builds the assignable devices table /etc/atab. This table is used in subsequent invocations to save repeated searches of the /dev directory. If one of the devices in /dev is changed to be assignable or unassignable (that is, owned by asg), then /etc/atab should be removed (by the superuser) so that a correct list will be built the next time the command is invoked.

Exit values

Exit code 0 returned if successful, 1 if problems, 2 if device cannot be assigned.

Limitations

Although it should never happen, if assign is aborted before completion (via kill -9, a power failure, etc.), the lock file /dev/asglock may need to be removed by root.

Files

/etc/atab: table of assignable devices
/dev/asglock: file to prevent concurrent access