7.1 Device Special File Names and Locations

7.1 Device Special File Names and Locations

In Tru64 UNIX prior to version 5.0, all devices were located in the /dev subdirectory. In version 5.0 and above, this has changed; to the casual observer, though, it will look the same. It bears mentioning up front that the device special file naming convention for storage devices has changed. Gone is the bus-target-lun (b-t-l) mnemonic for disks and cdrom devices; gone is the cryptic tape device naming convention. Table 7-1 shows the device special file naming changes.

Table 7-1: Device Special File Naming

Device Special File Naming
Version 4 and below						Version 5.0 and above
	directory(/dev)	base name	LUN[*]	instance	partition or density	directory(/devices)	base name	instance	partition or density
CDROM	.	rz	[a-h]	[n]	[ac]	./disk	cdrom	[n]	[ac]	block
		rrz	[a-h]	[n]	[ac]	./rdisk		[n]	[ac]	character
Disk	.	rz	[a-h]	[n]	[a-h]	./disk	dsk	[n]	[a-h]	block
		rrz	[a-h]	[n]	[a-h]	./rdisk		[n]	[a-h]	character
Tape	.	rmt	[a-h]	[n]	[almh]	./tape	tape	[n]	_d[0-7]	rewind
		nrmt	[a-h]	[n]	[almh]	./ntape		[n]	_d[0-7]	no rewind
CCL	.	rz	[a-h]	[n]	c	./cport	scp	[n]
Changer	.	mc	[a-h]	[n]	[a-h]	./changer	mc	[n]
LSM	./rvol/dg	user-defined volume name				./vol/dg	user-defined volume name			block
	./rvol/dg					./rvol/dg				character
[*]- if LUN 0, this field is optional [n]= device number

Why did the b-t-l naming convention get replaced? First, to enable Tru64 UNIX to support multiple paths to a device, and second, to enable every member in a cluster to see the same device by the same device special file name regardless of its physical location. How is this accomplished? We will answer that question in the next section.

Another fundamental change that has occurred is the location of the device special files. Storage devices have been relocated to the /devices directory tree. The /dev file is now a CDSL pointing to a member-specific /dev directory and contains member-specific devices (e.g., the console, keyboard, mouse, pseudo terminals, etc.). Figure 7-1 shows the device directory hierarchy.

Figure 7-1: Device Directory Hierarchy

Let's explore the hierarchy. First, what are the device files in the root (/) directory?

 # file /dev* /dev: symbolic link to cluster/members/{memb}/dev /devices:       directory 

Notice that /dev is now a CDSL, whereas /devices is actually a cluster-common directory. If we look more closely at what is in /devices we see that the storage device directories are located there. This is done because storage devices are shared in a cluster.

 # file /devices/* /devices/changer:          directory /devices/cport:   directory /devices/disk:    directory /devices/dmapi:   directory /devices/ntape:   directory /devices/rdisk:   directory /devices/rvol:    directory /devices/tape:    directory /devices/vol:     directory 

Although the directory hierarchy has changed, it looks the same. That is to say we can still cd(1) to /dev, and all devices, including the storage device directories, are there. However, the storage device directories are actually symbolic links to the /devices directory.

 # find /dev/ -type l -ls | awk '{ print $11,$12,$13 }' /dev/none -> ../devices/none /dev/cport -> ../../../../devices/cport /dev/disk -> ../../../../devices/disk /dev/rdisk -> ../../../../devices/rdisk /dev/tape -> ../../../../devices/tape /dev/ntape -> ../../../../devices/ntape /dev/changer -> ../../../../devices/changer /dev/dmapi -> ../../../../devices/dmapi /dev/vol -> ../../../../devices/vol /dev/rvol -> ../../../../devices/rvol