Chapter 29 Accessing Devices (Overview)

This chapter provides information about how to access the devices on a system.

This is a list of the overview information in this chapter.

• Accessing Devices

• Logical Disk Device Names

• Logical Tape Device Names

• Logical Removable Media Device Names

For overview information about configuring devices, see Chapter 26, Managing Devices (Tasks).

Accessing Devices

You need to know how to specify device names when using commands to manage disks, file systems, and other devices. In most cases, you can use logical device names to represent devices that are connected to the system. Both logical and physical device names are represented on the system by logical and physical device files.

How Device Information Is Created

When a system is booted for the first time, a device hierarchy is created to represent all the devices connected to the system. The kernel uses the device hierarchy information to associate drivers with their appropriate devices, and provides a set of pointers to the drivers that perform specific operations. For more information on device hierarchy, see OpenBoot 3.x Command Reference Manual.

How Devices Are Managed

The devfsadm command manages the special device files in the /dev and /devices directories. By default, the devfsadm command attempts to load every driver in the system and attach to all possible device instances. Then, devfsadm creates the device files in the /devices directory and the logical links in the /dev directory. In addition to managing the /dev and /devices directories, the devfsadm command also maintains the path_to_inst(4) instance database.

Both reconfiguration boot processing and updating the /dev and /devices directories in response to dynamic reconfiguration events is handled by devfsadmd, the daemon version of the devfsadm command. This daemon is started from the /etc/rc* scripts when a system is booted.

Since the devfsadmd daemon automatically detects device configuration changes generated by any reconfiguration event, there is no need to run this command interactively.

For more information, see devfsadm(1M).

Device Naming Conventions

Devices are referenced in three ways in the Solaris environment.

• Physical device name – Represents the full device pathname in the device information hierarchy. Physical device names are displayed by using the following commands:

  • dmesg

  • format

  • sysdef

  • prtconf

  Physical device files are found in the /devices directory.

• Instance name – Represents the kernel's abbreviation name for every possible device on the system. For example, sd0 and sd1 represent the instance names of two disk devices. Instance names are mapped in the /etc/path_to_inst file and are displayed by using the following commands:

  • dmesg

  • sysdef

  • prtconf

• Logical device name – Used with most file system commands to refer to devices. For a list of file commands that use logical device names, see Table 29–1. Logical device files in the /dev directory are symbolically linked to physical device files in the /devices directory.

Logical Disk Device Names

Logical device names are used to access disk devices when you:

• Add a new disk to the system

• Move a disk from one system to another system

• Access or mount a file system residing on a local disk

• Back up a local file system

Many administration commands take arguments that refer to a disk slice or file system.

Refer to a disk device by specifying the subdirectory to which it is symbolically linked, either /dev/dsk or /dev/rdsk, followed by a string identifying the particular controller, disk, and slice.

Figure 29–1 Logical Device Names

Specifying the Disk Subdirectory

Disk and file administration commands require the use of either a raw (or character) device interface, or a block device interface. The distinction is made by how data is read from the device.

Raw device interfaces transfer only small amounts of data at a time. Block device interfaces include a buffer from which large blocks of data are read at once.

Different commands require different interfaces.

• When a command requires the raw device interface, specify the /dev/rdsk subdirectory. (The “r” in rdsk stands for “raw.”)

• When a command requires the block device interface, specify the /dev/dsk subdirectory.

• When you are not sure whether a command requires use of /dev/dsk or /dev/rdsk, check the man page for that command.

The following table shows which interface is required for some commonly used disk and file system commands.

Table 29–1 Device Interface Type Required by Some Frequently Used Commands

Command	Interface Type	Example of Use
df(1M)	Block	df /dev/dsk/c0t3d0s6
fsck(1M)	Raw	fsck -p /dev/rdsk/c0t0d0s0
mount(1M)	Block	mount /dev/dsk/c1t0d0s7 /export/home
newfs(1M)	Raw	newfs /dev/rdsk/c0t0d1s1
prtvtoc(1M)	Raw	prtvtoc /dev/rdsk/c0t0d0s2

Specifying the Slice

The string that you use to identify a specific slice on a specific disk depends on the controller type, either direct or bus-oriented. The following table describes the different types of direct or bus-oriented controllers on different platforms.

Table 29–2 Controller Types

Direct controllers	Bus-Oriented Controllers
IDE (IA)	SCSI (SPARC/IA)
	FCAL (SPARC)
	ATA (SPARC/IA)

The conventions for both types of controllers are explained in the following subsections.

---

Note –

Controller numbers are assigned automatically at system initialization. The numbers are strictly logical and imply no direct mapping to physical controllers.

---

x86: Disks With Direct Controllers

To specify a slice on a disk with an IDE controller on an IA based system, follow the naming convention shown in the following figure.

Figure 29–2 IA: Disks with Direct Controllers

To indicate the entire Solaris fdisk partition, specify slice 2 (s2).

If you have only one controller on your system, w is usually 0.

SPARC: Disks With Bus-Oriented Controllers

To specify a slice on a disk with a bus-oriented controller, SCSI for instance, on a SPARC based system, follow the naming convention shown in the following figure.

Figure 29–3 SPARC: Disks With Bus-Oriented Controllers

On a SPARC based system with directly connected disks such as the IDE disks on a Ultra10, the naming convention is the same as that for systems with bus-oriented controllers.

If you have only one controller on your system, w is usually 0.

For SCSI controllers, x is the target address set by the switch on the back of the unit, and y is the logical unit number (LUN) of the drive attached to the target. If the disk has an embedded controller, y is usually 0.

To indicate the whole disk, specify slice 2 (s2).

x86: Disks With SCSI Controllers

To specify a slice on a disk with a SCSI controller on an IA based system, follow the naming convention shown in the following figure.

Figure 29–4 IA: Disks with SCSI Controllers

If you have only one controller on your system, v is usually 0.

For SCSI controllers, w is the target address set by the switch on the back of the unit, and x is the logical unit number (LUN) of the drive attached to the target. If the disk has an embedded controller, x is usually 0.

To indicate the entire Solaris fdisk partition, specify slice 2 (s2).

Logical Tape Device Names

Logical tape device files are found in the /dev/rmt/* directory as symbolic links from the /devices directory.

Figure 29–5 Logical Tape Device Names

The first tape device connected to the system is 0 (/dev/rmt/0). Tape density values (l, m, h, c, and u) are described in Chapter 51, Managing Tape Drives (Tasks).

Logical Removable Media Device Names

Since removable media is managed by volume management (vold), the logical device name is usually not used unless you want to mount the media manually.

The logical device name that represents the removable media devices on a system are described in Chapter 18, Accessing Removable Media (Tasks).