The information on this page is provided for compatibility with
applications built on previous releases.
See the
sd01(HW)
manual page for a description of the Release 6 interface, which also
supports the functionality described on this page.
Block special files allow access to hard disks via
the operating system's buffer cache mechanism.
Block-buffered access to the primary hard disk
is provided through the following block special files:
hd00, hd01 through
hd04, hd0a, hd0d,
boot, swap, and root.
hd00 refers to the entire physical disk;
hd01 through hd04
refer to
fdisk(ADM)
partitions.
boot refers to the boot filesystem (mounted as /stand),
swap to the swap area, and
root to the root filesystem (mounted as /).
Block-buffered access to a secondary hard disk
is provided through the special files:
hd10, hd11 through hd14, and hd1a.
Character special files follow the same naming
convention as the block special files except that
the character special file is prefaced with an ``r''
(for ``raw'' or character device).
For example, the character special file referring to
the entire physical primary disk is /dev/rhd00.
Device names such as /dev/hd01 and
/dev/rhd01 follow the XENIX® naming convention.
Equivalent UNIX® system devices are found in
the /dev/dsk (block) and
/dev/rdsk (raw) directories.
XENIX devices extend only
to the primary and secondary hard disks; beyond this, UNIX system
devices must be used.
``Minor device bits''
shows the third and fourth device nodes (/dev/dsk/2s0
and /dev/dsk/3s0). Following this scheme, disk five
would correspond to /dev/dsk/4s0, disk six to
/dev/dsk/5s0, and so on for the physical disk devices.
The following table shows
both XENIX and UNIX system devices
for the primary and secondary hard disks:
Block and character device filenames for hard disks
Primary disk
Secondary disk
Partition
/dev/hd00
/dev/dsk/0s0
/dev/hd10
/dev/dsk/1s0
entire disk
/dev/rhd00
/dev/rdsk/0s0
/dev/rhd10
/dev/rdsk/1s0
/dev/hd01
/dev/dsk/0s1
/dev/hd11
/dev/dsk/1s1
first partition
/dev/rhd01
/dev/rdsk/0s1
/dev/rhd11
/dev/rdsk/1s1
/dev/hd02
/dev/dsk/0s2
/dev/hd12
/dev/dsk/1s2
second partition
/dev/rhd02
/dev/rdsk/0s2
/dev/rhd12
/dev/rdsk/1s2
/dev/hd03
/dev/dsk/0s3
/dev/hd13
/dev/dsk/1s3
third partition
/dev/rhd03
/dev/rdsk/0s3
/dev/rhd13
/dev/rdsk/1s3
/dev/hd04
/dev/dsk/0s4
/dev/hd14
/dev/dsk/1s4
fourth partition
/dev/rhd04
/dev/rdsk/0s4
/dev/rhd14
/dev/rdsk/1s4
/dev/hd0a
/dev/dsk/0sa
active partition
/dev/rhd0a
/dev/rdsk/0sa
/dev/hd0d
/dev/dsk/0sd
/dev/hd1d
/dev/dsk/1sd
DOS partition
/dev/rhd0d
/dev/rdsk/0sd
/dev/rhd1d
/dev/rdsk/1sd
Minor device numbering scheme
The scheme of the minor device number bit representation
for hard disks is show in the following table:
Hard disk minor device bit representation
Bits
7
6
5
4
3
2
1
0
Description
X
X
-
-
-
-
-
-
disk # (0-3)
-
-
X
X
X
-
-
-
partition # (1-4)
-
-
-
-
-
X
X
X
division # (0-6)
-
-
X
X
X
1
1
1
whole partition
-
-
0
0
0
0
0
0
whole physical disk
-
-
1
0
1
-
-
-
active partition
-
-
1
1
0
-
-
-
DOS partition
-
-
1
1
0
X
X
X
DOS drive (C-J)
Because some SCSI controllers support large numbers of physical
drives, an extended minor device numbering scheme is provided for those
devices requiring more than 256 minor numbers.
Each driver that uses extended minor numbers has a base major number
which is used to refer to the driver through the extended minor numbers.
The driver has a normal entry in the
mdevice(F)
table for the
base major number, plus one additional entry for each group of 256 minor
devices that the driver uses.
Additional entries are identified by the ``M'' flag in the driver's device
characteristics field. The ``M'' flag indicates that the entry corresponds
to a virtual major number that points to a device driver that uses
extended minor numbers.
Therefore a large array of disks may sometimes have two
(or more) major numbers; the first will correspond to minor numbers 0
through 255, the second to minor devices 256 through 511, and so on.
See
scsidisk(HW)
for other information that is specific to SCSI hard disks.
The following table lists the minor device number definitions for the
hard disk special files, along with examples. Note that block and
character special devices share the same minor device number.
The minor device bits for DOS disk special files are listed in a separate
table.
Minor device bits
Disk
Partition
Division
Block interface
Description
7 6
5 4 3
2 1 0
device name
0 0
0 0 0
0 0 0
/dev/hd00
whole PD 0 (primary)
/dev/dsk/0s0
0 0
0 0 1
1 1 1
/dev/hd01
PD 0, whole FP 1
0 0
0 1 0
1 1 1
/dev/hd02
PD 0, whole FP 2
0 0
0 1 1
1 1 1
/dev/hd03
PD 0, whole FP 3
0 0
1 0 0
1 1 1
/dev/hd04
PD 0, whole FP 4
0 0
1 0 1
1 1 1
/dev/hd0a
PD 0, whole active FP
0 0
1 0 1
0 0 0
/dev/boot
PD 0, active partition, DP 0
0 0
1 0 1
0 0 1
/dev/swap
PD 0, active partition, DP 1
0 0
1 0 1
0 1 0
/dev/root
PD 0, active partition, DP 2
0 0
1 0 1
0 1 1
/dev/u
PD 0, active partition, DP 3
0 0
1 0 1
1 1 0
/dev/recover
PD 0, active partition, DP 6
0 1
0 0 0
0 0 0
/dev/hd10
whole PD 1 (secondary)
/dev/dsk/1s0
0 1
0 0 1
1 1 1
/dev/hd11
PD 1, whole FP 1
0 1
0 1 0
1 1 1
/dev/hd12
PD 1, whole FP 2
0 1
0 1 1
1 1 1
/dev/hd13
PD 1, whole FP 3
0 1
1 0 0
1 1 1
/dev/hd14
PD 1, whole FP 4
0 1
1 0 1
1 1 1
/dev/hd1a
PD 1, whole active FP
0 1
1 0 1
0 0 0
/dev/u0
PD 1, active partition, DP 0
0 1
1 0 1
0 0 1
/dev/u1
PD 1, active partition, DP 1
0 1
1 0 1
0 1 0
/dev/u2
PD 1, active partition, DP 2
1 0
0 0 0
0 0 0
/dev/dsk/2s0
whole PD 2
1 0
0 0 1
1 1 1
/dev/dsk/2s1
PD 2, whole FP 1
1 0
0 1 0
1 1 1
/dev/dsk/2s2
PD 2, whole FP 2
1 0
0 1 1
1 1 1
/dev/dsk/2s3
PD 2, whole FP 3
1 0
1 0 0
1 1 1
/dev/dsk/2s4
PD 2, whole FP 4
1 0
1 0 1
1 1 1
/dev/dsk/2sa
PD 2, whole active FP
1 1
0 0 0
0 0 0
/dev/dsk/3s0
whole PD 3
1 1
0 0 1
1 1 1
/dev/dsk/3s1
PD 3, whole FP 1
1 1
0 1 0
1 1 1
/dev/dsk/3s2
PD 3, whole FP 2
1 1
0 1 1
1 1 1
/dev/dsk/3s3
PD 3, whole FP 3
1 1
1 0 0
1 1 1
/dev/dsk/3s4
PD 3, whole FP 4
1 1
1 0 1
1 1 1
/dev/dsk/3sa
PD 3, whole active FP
Key
FP = fdisk partition
PD = physical drive
DP = division (divvy partition)
= user-defined name
The device files u and u[0-2] are optional
filesystem names; these nodes are not present unless created
by the system administrator.
On the first disk, hd00
denotes the entire disk and is used to access the master
boot block, which includes the fdisk partition table.
For the second disk, hd10
denotes the entire disk and is used to access its fdisk partition table.
DOS minor device bits
Disk
Partition
Division
Device special
Description
7 6
5 4 3
2 1 0
file name
0 0
1 1 0
0 0 0
/dev/dsk/0sC
PD 0, PDP, logical drive C
0 0
1 1 0
0 0 1
/dev/dsk/0sD
PD 0, EDP, logical drive D
0 0
1 1 0
0 1 0
/dev/dsk/0sE
PD 0, EDP, logical drive E
0 0
1 1 0
0 1 1
/dev/dsk/0sF
PD 0, EDP, logical drive F
0 0
1 1 0
1 0 0
/dev/dsk/0sG
PD 0, EDP, logical drive G
0 0
1 1 0
1 0 1
/dev/dsk/0sH
PD 0, EDP, logical drive H
0 0
1 1 0
1 1 0
/dev/dsk/0sI
PD 0, EDP, logical drive I
0 0
1 1 0
1 1 1
/dev/dsk/0sJ
PD 0, EDP, logical drive J
0 1
1 1 0
0 0 0
/dev/dsk/1sC
PD 1, PDP, logical drive C
0 1
1 1 0
0 0 1
/dev/dsk/1sD
PD 1, EDP, logical drive D
0 1
1 1 0
0 1 0
/dev/dsk/1sE
PD 1, EDP, logical drive E
0 1
1 1 0
0 1 1
/dev/dsk/1sF
PD 1, EDP, logical drive F
0 1
1 1 0
1 0 0
/dev/dsk/1sG
PD 1, EDP, logical drive G
0 1
1 1 0
1 0 1
/dev/dsk/1sH
PD 1, EDP, logical drive H
0 1
1 1 0
1 1 0
/dev/dsk/1sI
PD 1, EDP, logical drive I
0 1
1 1 0
1 1 1
/dev/dsk/1sJ
PD 1, EDP, logical drive J
1 0
1 1 0
0 0 0
/dev/dsk/2sC
PD 2, PDP, logical drive C
1 0
1 1 0
0 0 1
/dev/dsk/2sD
PD 2, EDP, logical drive D
1 0
1 1 0
0 1 0
/dev/dsk/2sE
PD 2, EDP, logical drive E
1 0
1 1 0
0 1 1
/dev/dsk/2sF
PD 2, EDP, logical drive F
1 0
1 1 0
1 0 0
/dev/dsk/2sG
PD 2, EDP, logical drive G
1 0
1 1 0
1 0 1
/dev/dsk/2sH
PD 2, EDP, logical drive H
1 0
1 1 0
1 1 0
/dev/dsk/2sI
PD 2, EDP, logical drive I
1 0
1 1 0
1 1 1
/dev/dsk/2sJ
PD 2, EDP, logical drive J
1 1
1 1 0
0 0 0
/dev/dsk/3sC
PD 3, PDP, logical drive C
1 1
1 1 0
0 0 1
/dev/dsk/3sD
PD 3, EDP, logical drive D
1 1
1 1 0
0 1 0
/dev/dsk/3sE
PD 3, EDP, logical drive E
1 1
1 1 0
0 1 1
/dev/dsk/3sF
PD 3, EDP, logical drive F
1 1
1 1 0
1 0 0
/dev/dsk/3sG
PD 3, EDP, logical drive G
1 1
1 1 0
1 0 1
/dev/dsk/3sH
PD 3, EDP, logical drive H
1 1
1 1 0
1 1 0
/dev/dsk/3sI
PD 3, EDP, logical drive I
1 1
1 1 0
1 1 1
/dev/dsk/3sJ
PD 3, EDP, logical drive J
Key
PDP = primary DOS partition
EDP = extended DOS partition
Bits 5, 4, and 3 are set to ``110'' to signify that a partition
is a DOS partition. The division number indexes the primary or
extended logical DOS partitions in the order that they were created
on the disk using fdisk.
The device file /dev/hd0d (first DOS partition)
is linked to /dev/dsk/0sC for backwards compatibility.
To access DOS partitions, specify
letters such as ``C:'' or ``D:'' to indicate first or second
partitions.
The file /etc/default/msdos
contains lines that assign a letter abbreviation for
the DOS device name.
Refer to
doscmd(C).
An existing XENIX filesystem may be mounted on a UNIX system provided that a special
device file is created in the /dev directory by adding device
node entries to the file /etc/conf/node.d/hd and then running the
idmknod(ADM)
command.
The major and minor device numbers that must be specified for the
XENIX device file are calculated in exactly the same way as for a UNIX
system.
For example, to create character and block special files for the
XENIX /u filesystem in division 2 of partition 3 on
physical drive 0, follow these steps:
Log in as root.
Calculate the minor number for the device.
Bits 7 and 6 of the minor device number specify the physical drive number;
bit 5 is set to 0 (zero); bits 4 and 3 specify the partition;
and bits 2, 1, and 0 specify the division.
In this case, the minor device bit representation would be
``00011010''.
This corresponds to a minor number of 26.
Add the following entries to /etc/conf/node.d/hd for the block and
character device files:
hd dsk/0s3x b 26 sysinfo sysinfo 600
hd rdsk/0s3x c 26 sysinfo sysinfo 600
The naming convention for hard disk device files has been adapted
by adding ``x'' to mean ``XENIX filesystem''.
Create the new device nodes using the command:
/etc/conf/bin/idmknod -s
Use the Filesystem Manager
to mount the XENIX filesystem on a suitable mount point
such as /x.
Supported ioctls
The esdi, st506, ida, omti,
wd1010, and Sdsk drivers support the following
ioctl(S)
commands, as well as the ioctl commands for
asynchronous I/O described on
aio(HW).
These ioctls and the structures they use are
defined in <sys/dio.h>.
Each ioctl command is performed on the partition indicated by the
file descriptor passed to
ioctl(S).
WARNING:DIOWPART, DWVDT, and DIOWDISK
overwrite existing disk information.
Data on the affected partition may be destroyed.
DIOGETP
Return disk parameters in the struct dparam pointed to
by arg.
[EFAULT] is set in errno if
an invalid pointer was passed.
DIORPART
Return the division table for the partition.
arg points to a struct partable in which
the information is returned.
The following errno values are possible, in addition to those
described on the
ioctl(S)
manual page:
[ENXIO]
The operating system on the partition is neither UNIX nor XENIX.
[EFAULT]
No division table can be found for the partition,
or an invalid pointer was passed.
DIOWPART
Write the division table from the struct partable pointed
to by arg to the partition.
Possible errno values include:
[ENXIO]
The operating system on the partition is neither
UNIX nor XENIX, or the maximum amount of 4 virtual
XENIX devices or 4 UNIX partitions per physical device has been reached.
This limit is imposed by the PC BIOS.
[EFAULT]
An invalid pointer was passed.
DIOBITP
Return the number of bits used for each portion of the minor device
in the struct dbitparams pointed to by arg.
[EFAULT] is set in errno if an invalid pointer
was passed.
DIORVDT
Return the partition table of the physical drive in the
struct vdtab pointed to by arg.
[EFAULT] is set in errno if an invalid pointer was
passed.
DIOWVDT
Set the partition table of the physical drive to the struct vdtab
pointed to by arg.
Possible errno values include:
[EFAULT]
An invalid pointer was passed.
[ENXIO]
Either the masterboot disk table or the division table could not be read.
DIOSDISK
Return the number of entries in the masterboot disk table in
arg, which should be a short.
[EFAULT] is set in errno if there is a problem
transferring data.
DIORDISK
Return a masterboot disk table entry in the array of 8 longs pointed to
by arg.
[EFAULT] is set in errno if an invalid pointer was
passed.
DIOWDISK
Write a masterboot disk table entry.
Not supported by the omti driver.
Possible values for errno are:
[ENXIO]
The masterboot disk table could not be read, or the operating system is
SCO UNIX 3.2.0 or earlier.
[EFAULT]
An invalid pointer was passed.
DIODKTYPE
Return the disk layout to which the driver is currently configured in
arg, which should be a short.
arg will be 1 if the disk layout mode is SCO UNIX 3.2.0,
or 0 otherwise.
DIOFORCE22
Force the driver into SCO UNIX 3.2.0 disk layout mode.
[EFAULT] is set in errno if problems occurred.
Diagnostics
The following error messages may be displayed on the console.
See
messages(M)
for general information about kernel error messages,
including a list of generic device driver errors.
esdi -- ESDI hard disk driver
WARNING: esdi: adapter reset failed
The adapter could not be reset.
WARNING: esdi: adapter reset failed - no status bsr
The adapter could not be reset; the BSR
status register contained the value bsr.
WARNING: esdi: adapter reset command failed
Reset failed because an interrupt was present.
WARNING: esdi: error parking heads for drive n
An error occurred while parking the disk drive heads.
WARNING: esdi: esdiattention timeout - stat = n
The routine esdiattention in the driver timed out after requesting
attention.
WARNING: esdi: get drive attention error
Could not get drive attention while testing the configuration.
WARNING: esdi: get drive command error
An error was detected in the command block sent to the controller
on testing the configuration.
WARNING: esdi: get drive configuration failed
The drive configuration test failed.
WARNING: esdi: get drive interrupt bit not set
The drive configuration test failed because the drive interrupt status
was not available.
WARNING: esdi: get drive no status block
The drive configuration test failed because the drive status block
was not available.
WARNING: esdi: no controller installed
An ESDI controller could not be found.
WARNING: esdi: no drive n
A drive could not be opened because the physical device corresponding to the
minor device number was not present.
WARNING: esdi: on fixed disk dev=major/minor block=n
esdi: cmd=command, isr=completion_status, sir=error_code
DMA error still present after four retries.
WARNING: esdi: Reset failed isr=completion status
esdi: status=n
The completion status after a reset still reported an error.
WARNING: esdi: timeout parking heads for drive n
A timeout occurred on parking the disk drive heads.
hd -- root hard disk driver
NOTICE: hd: Invalid hard disk partition sector on device major/minor
The root hard disk partition information could not be read on opening the drive.
WARNING: hd: multiple root disk controllers
More than one disk controller was found to be present; boot-time
loading of a valid driver using the hd=driver
keyword will override this error.
WARNING: hd: no controller
No disk controller was found.
WARNING: hd: no root disk controller
The root disk controller was not found on system initialization.
WARNING: Ignoring "hd=name" : Unknown driver
The hard disk device driver name
specified in the bootstring could not be found.
PANIC: hd: devsw error
The driver was not found.
PANIC: hd: intsw error
The interrupt handler routine could not be patched.
PANIC: hd: multiple controllers
More than one disk controller was found to be present on booting up; boot-time
loading of a valid driver using the hd=driver
keyword will override this error.
ida -- Compaq EISA disk drive array (DISCO) driver
CONFIG: ida#: Vectors for controller in slot m differ (kernel=o, system=p)
The EISA configuration interrupt vector does not match that in
sdevice(F).
NOTICE: ida#: n abort errors on dev major/minor unit m, block=n cmd=0xo status=0xp
Reports the number of abort errors.
NOTICE: ida#: n bad command lists on dev major/minor unit m, block=n cmd=0xo status=0xp
Reports the number of bad command lists.
NOTICE: ida#: n bad requests on dev major/minor unit m, block=n cmd=0xo
status=0xp
Reports the number of bad requests.
NOTICE: ida#: n recoverable errors on dev major/minor unit m, block=n cmd=0xo status=0xp
Reports the number of recoverable errors.
WARNING: ida: Cannot allocate nk, IDA disabled
Not enough memory was available to allocate to command blocks.
WARNING: ida: Only first six of n Disc Array Controllers supported
A maximum of six drive controllers can be attached.
WARNING: ida#: m non-recoverable errors on dev major/minor unit n, block=o cmd=0xp status=0xq
Reports the number of non-recoverable errors.
WARNING: ida#: m unknown errors on dev major/minor unit n, block=o cmd=0xp status=0xq
Reports the number of unknown errors.
WARNING: ida#: No queued requests
No request blocks were found for processing on update.
WARNING: ida#: Spurious interrupt
No command was pending when an interrupt was received.
WARNING: ida#: Unknown cmd=0xm on dev major/minor unit n, offset=0xo status=0xp
An unknown command was received.
PANIC: ida - ran out of cmdlist
No more command blocks were available.
omti -- OMTI disk driver
WARNING: omti: already busy
omtistart had already been called on a busy drive.
WARNING: omti: C_D bit stuck off
The controller failed to indicate its readiness for a command.
WARNING: omti: cannot enter command phase
The controller failed to accept the selected command.
WARNING: omti: colliding polling routines
A re-entrant call to omtipoll has been detected.
WARNING: omti: command setup failed
The controller failed to accept the setup command.
WARNING: omti: controller configured for no drive n
An open on a drive failed to identify the disk type.
WARNING: omti: error during OMTI_SENSE
An interrupt was received during an OMTI sense command.
WARNING: omti: error on fixed disk (minor minor), block=m
omti: Error Type n, Code o, Unit p
omti: Sector = q, Cylinder/head = r/s,
omti: msg
The OMTI sense error message msg provides more information
about the error.
The following are possible drive errors:
Cartridge Changed
Drive Not Selected/Not Ready
Multiple Drives Selected
No error or no sense information
No Index
No Seek/Command Complete
No Track zero or Cylinder zero found
Seek/Command in progress
Write/Drive Fault
The following are possible data errors:
Alternate of Bad Track Already Assigned
Bad Track Encountered
Correctable ECC
Data Address Mark Not Found
Error with unknown type and code
ID Address Mark Not Found
ID CRC
Illegal Access To An Alternated Track/Unable to Read the Alternate Track Address
Illegal Alternate Track Address
Illegal Disk Address
Illegal Interleave Factor
No Alternate Track Found
Sector Not Found
Seek Error
Sequence/DMA
Uncorrectable Data ECC
Unknown Error
Write Protected
The following are possible command errors:
Illegal Function for Drive Type
Invalid Command
Volume Overflow
The following are possible diagnostic errors:
EPROM Checksum/Internal Diagnostic error
RAM error
WARNING: omti: initialization failure
An error occurred during initialization.
WARNING: omti: non-omti interrupt (status)
The controller did not signal an interrupt when one was received.
WARNING: omti: OMTI_BUSY bit still stuck on
The controller failed to obey the reset command.
WARNING: omti: sense command setup failed
The controller failed to accept the setup command.
WARNING: omti: still busy
The controller is still busy after generating an interrupt.
WARNING: omti: timed out
An expected interrupt did not arrive.
WARNING: omti: unexpected interrupt (status)
No command was pending when an interrupt was received.
WARNING: omti: unknown command(n)
omtistart encountered an unrecognized command.
WARNING: omti: unloading all requests
The driver is preparing for manual reset because the programmed reset
did not work.
WARNING: unexpected end of data phase
Abnormal termination of a data read.
WARNING: Please use sfmt to modify disk parameters
Attempt to write the disk characteristics directly using the DIOWDISKioctl call.
st506 -- ST506 fixed disk adapter driver
This driver supports the ST506, the Adaptec 2610 and 2620, and the
IBM 50-021, 50-031,
60-041, and 80-041.
WARNING: st506: Invalid fixed disk parameter table on dev major/minor
The disk information had been corrupted.
WARNING: st506: Error on fixed disk dev major/minor block=n
st506: isr=status, ASR BUSY after reset
A reset failed on the adapter status register.
WARNING: st506: Error on fixed disk dev major/minor block=n
st506: isr=status, ASR_BUSY set, command aborted
A command was aborted because the adapter is busy.
WARNING: st506: Error on fixed disk dev major/minor block=n
st506: isr=status, CCB error, sector=m, cylinder/head=n/o
An error occurred with a command control block.
WARNING: st506: isr=status, error parking heads for drive n
An error occurred while parking the disk drive heads.
WARNING: st506: Error on fixed disk dev major/minor block=n
st506: isr=status, initialization error, sending CSB
The error occurred while sending the command specify block.
WARNING: st506: Error on fixed disk dev major/minor block=n
st506: isr=status, reading SSB
The sense summary block could not be read.
WARNING: st506: Error on fixed disk dev major/minor block=n
st506: isr=status, sending data (possible bad track)
drive=m, sector=n, cylinder/head=o/p
A possibly defective track was found on the disk.
WARNING: st506: Error on fixed disk dev major/minor block=n
st506: isr=status, spurious interrupt
WARNING: st506: Error on fixed disk dev major/minor block=n
st506: isr=status, spurious interrupt during unknown state
No command was pending when an interrupt was received.
WARNING: st506: Error on fixed disk dev major/minor block=n
st506: isr=status, timeout, ASR BUSY waiting to read SSB
A command timed out because the adapter was busy waiting to read the sense
summary block.
wd -- Western Digital 1010 disk controller driver
This driver is also used for the IBM 35SX, 40SX,
L40SX, and for the TA Walkstation 386.
WARNING: wd#: Error on fixed disk dev major/minor, block=m, cmd=0xn
status=0xerror, sector=o, cylinder/head=p/q
Reports an error detected while accessing the disk.
