Recipe 9.12. Finding Device Names for mount and fstab

9.12.1 Problem

You want to mount a storage disk, such as an IDE or SCSI hard drive, CD, DVD, USB storage device, or Zip disk. You don't know what device name to use—where do you look?

9.12.2 Solution

Use dmesg and fdisk. dmesg finds device names, and fdisk shows the partition numbers on hard drives. Referring to http://www.lanana.org/docs/device-list/devices.txt can be helpful as well, as it is the list of official /dev names. (If you have kernel sources installed, the devices.txt file may be present on your system in the /usr/src/* directory.)

This command searches dmesg for CD drives:

$ dmesg | grep -i cd

hdc: ATAPI CDROM, ATAPI CD/DVD-ROM DRIVE

hdc: ATAPI 40X CD-ROM DRIVE, 128K cache, UDMA (33)

A quick search in devices.txt reveals

Second IDE hard disk/CD-ROM interface

0 = /dev/hdc           Master: whole disk (or CD-ROM)

Ignore the 0 = part; your device name is /dev/hdc.

This is what CD drives using the IDE-SCSI subsystem look like:

$ dmesg | grep -i cd

hdb: TOSHIBA DVD-ROM SD-M1202, ATAPI CD/DVD-ROM drive

hdc: LITE-ON LTR-24102B, ATAPI CD/DVD-ROM drive

ide-cd: ignoring drive hdb

ide-cd: ignoring drive hdc

  Type:   CD-ROM             ANSI SCSI revision: 02

  Type:   CD-ROM             ANSI SCSI revision: 02

Attached scsi CD-ROM sr0 at scsi0, channel 0, id 0, lun 0

Attached scsi CD-ROM sr1 at scsi0, channel 0, id 1, lun 0

scd0: scsi3-mmc drive: 32x/32x cd/rw xa/form2 cdda tray

Uniform CD-ROM driver Revision: 3.12

scd1: scsi3-mmc drive: 131x/40x writer cd/rw xa/form2 cdda tray

So the drive names are /dev/scd0 and /dev/scd1.

With hard drives, you must select specific partitions, since each partition is a separate block device. fdisk -l displays all partitions on all detected hard drives:

# /sbin/fdisk -l

Disk /dev/hda: 20.5 GB, 20576747520 bytes

255 heads, 63 sectors/track, 2501 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

   

 Device    Boot  Start   End    Blocks  Id  System

/dev/hda1   *     1      893    7172991  7  HPFS/NTFS

/dev/hda2       894     1033    1124550  c  W95 FAT32 (LBA)

/dev/hda4      1034     2501   11791710  f  W95 Ext'd (LBA)

/dev/hda5      2437     2501     522081  82  Linux swap

/dev/hda6      1034     1670   5116639+  83  Linux

/dev/hda7      1671     2436   6152863+  83  Linux

   

Partition table entries are not in disk order

Copy the device name from the Device column exactly as it is shown.

This is what a USB pen drive looks like in dmesg:

hub.c: new USB device 00:1d.0-2.3, assigned address 5

usb.c: USB device 5 (vend/prod 0x1915/0x2220) is not claimed ...

SCSI device sda: 128000 512-byte hdwr sectors (66 MB)

sda: Write Protect is off

sda: sda1

Your device name is /dev/sda1.

This how fdisk sees USB drives:

# fdisk -l

Disk /dev/sda: 65 MB, 65536000 bytes

8 heads, 32 sectors/track, 500 cylinders

Units = cylinders of 256 * 512 = 131072 bytes

   

Device    Boot   Start   End    Blocks   Id  System

/dev/sda1  *     1       499     63856    6  FAT16

9.12.3 Discussion

All storage devices are block devices in /dev. /dev names them according to their physical connections. For example:

/dev/hda: Primary device on IDE0 (whole disk)
/dev/hdb: Secondary device on IDE0 (whole disk)
/dev/fd0: Floppy drive on controller 0, drive 0
/dev/fd1: Floppy drive on controller 0, drive 1
/dev/sda: First SCSI disk (whole disk)
/dev/sdb: Second SCSI disk (whole disk)

Storage devices on Linux follow this naming convention:

/dev/fd*: Floppy disks
/dev/hd*: IDE drives
/dev/sd*: SCSI drives
/dev/sd*: USB storage devices
/dev/hd*: IDE/Atapi CD/DVD-ROM drives
/dev/sd*: IDE/Atapi CD/DVD-R/RW drives
/dev/sd*, /dev/hd*, or /dev/XXXx4: Zip drives

IDE and USB devices that use the SCSI emulation subsystem are sometimes named /dev/sr*, which is symlinked to /dev/sd*.

If you have kernel sources installed, look for the devices.txt file to see the definitions of all those /dev names.

9.12.4 See Also

Chapter 5
Official list of /dev names (http://www.lanana.org/docs/device-list/devices.txt), or the devices.txt file in your system's /usr/src/* directory

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