hdparm


SYNOPSIS
       hdparm [ flags ] [device] ..

DESCRIPTION
       hdparm  provides  a command line interface to various kernel interfaces
       supported by the Linux SATA/PATA/SAS "libata" subsystem and  the  older
       IDE driver subsystem.  Many newer (2008 and later) USB drive enclosures
       now also support "SAT" (SCSI-ATA Command Translation) and therefore may
       also  work  with  hdparm.   Eg.  recent WD "Passport" models and recent
       NexStar-3 enclosures.  Some options may work correctly  only  with  the
       latest kernels.

OPTIONS
       When  no flags are given, -acdgkmur is assumed.  For Get/Set options, a
       query without an optional parameter (e.g.  -d)  will  query  (get)  the
       device  state,  and  with  a  parameter (e.g., -d0) will set the device
       state.

       -a     Get/set sector count for filesystem (software) read-ahead.  This
              is  used  to  improve  performance  in sequential reads of large
              files, by prefetching additional blocks in anticipation of  them
              being  needed  by the running task.  Many IDE drives also have a
              separate  built-in  read-ahead  function,  which  augments  this
              filesystem (software) read-ahead function.

       -A     Get/set  the  IDE  drive's read-lookahead feature (usually ON by
              default).  Usage: -A0 (disable) or -A1 (enable).

       -b     Get/set bus state.

       -B     Query/set Advanced Power Management feature, if the  drive  sup-
              ports  it.  A  low value means aggressive power management and a
              high value means better performance.   Possible  settings  range
              from  values  1 through 127 (which permit spin-down), and values
              128 through 254 (which do not permit  spin-down).   The  highest
              degree  of power management is attained with a setting of 1, and
              the highest I/O performance with a setting of 254.  A  value  of
              255 tells hdparm to disable Advanced Power Management altogether
              on the drive (not all drives support disabling it, but most do).

       -c     Query/enable (E)IDE 32-bit I/O support.  A numeric parameter can
              be  used  to  enable/disable  32-bit I/O support: Currently sup-
              ported values include 0 to disable  32-bit  I/O  support,  1  to
              enable 32-bit data transfers, and 3 to enable 32-bit data trans-
              fers with a special sync sequence  required  by  many  chipsets.
              The  value  3  works  with  nearly  all 32-bit IDE chipsets, but
              incurs slightly more overhead.  Note  that  "32-bit"  refers  to
              data  transfers  across  a  PCI or VLB bus to the interface card
              only; all (E)IDE drives still have only a 16-bit connection over
              the ribbon cable from the interface card.

       -C     Check  the  current  IDE power mode status, which will always be
              one  of  unknown  (drive  does  not   support   this   command),
              formance, with fast I/O throughput and low CPU usage.  But there
              are at least a few configurations of  chipsets  and  drives  for
              which  DMA  does not make much of a difference, or may even slow
              things down (on really messed up hardware!).  Your  mileage  may
              vary.

       --dco-freeze
              DCO  stands  for Device Configuration Overlay, a way for vendors
              to selectively disable certain features of a drive.  The  --dco-
              freeze  flag  will  freeze/lock the current drive configuration,
              thereby preventing software (or malware) from changing  any  DCO
              settings until after the next power-on reset.

       --dco-identify
              Query  and  dump  information regarding drive configuration set-
              tings which can be disabled by  the  vendor  or  OEM  installer.
              These  settings  show  capabilities  of the drive which might be
              disabled by the vendor for "enhanced compatibility".  When  dis-
              abled,  they  are  otherwise  hidden and will not show in the -I
              identify output.  For example, system vendors sometimes  disable
              48_bit  addressing  on large drives, for compatibility (and loss
              of capacity) with a specific BIOS.  In such  cases,  --dco-iden-
              tify will show that the drive is 48_bit capable, but -I will not
              show it, and nor will the drive accept 48_bit commands.

       --dco-restore
              Reset all drive settings, features,  and  accessible  capacities
              back  to  factory  defaults and full capabilities.  This command
              will fail if DCO is frozen/locked, or  if  a  -Np  maximum  size
              restriction  has also been set.  This is EXTREMELY DANGEROUS and
              will very likely cause massive loss of data.  DO  NOT  USE  THIS
              COMMAND.

       --direct
              Use  the  kernel O_DIRECT flag when performing a -t timing test.
              This bypasses the page cache, causing the reads to  go  directly
              from the drive into hdparm's buffers, using so-called "raw" I/O.
              In many cases, this can produce results that appear much  faster
              than  the usual page cache method, giving a better indication of
              raw device and driver performance.

       --drq-hsm-error
              VERY DANGEROUS, DON'T EVEN THINK  ABOUT  USING  IT.   This  flag
              causes  hdparm  to  issue an IDENTIFY command to the kernel, but
              incorrectly marked as a "non-data" command.  This results in the
              drive  being  left  with  its DataReQust(DRQ) line "stuck" high.
              This confuses the kernel drivers, and may crash the system imme-
              diately  with  massive  data loss.  The option exists to help in
              testing and fortifying the  kernel  against  similar  real-world
              drive malfunctions.  VERY DANGEROUS, DO NOT USE!!

       -D     Enable/disable  the  on-drive defect management feature, whereby
              the drive firmware tries to automatically manage defective  sec-
              tors  by relocating them to "spare" sectors reserved by the fac-

       --fibmap
              When used, this must be the only flag given.  It requires a file
              path as a parameter, and will print out a  list  of  the  device
              extents  (sector  ranges) occupied by that file on disk.  Sector
              numbers are given as absolute LBA numbers, referenced from  sec-
              tor  0  of  the physical device (*not* the partition or filesys-
              tem).  This information can then be used for a variety  of  pur-
              poses,  such  as  examining the degree of fragmenation of larger
              files, or determining appropriate sectors to  deliberately  cor-
              rupt during fault-injection testing procedures.

       --fibmap-sector
              When used, this must be the only flag given.  It requires a file
              path followed by a sector number  as  parameters.   This  sector
              number  is  given  relative to the start of the file itself, not
              the device.  hdparm will scan the device extents occupied by the
              file,  and  print  out  the absolute LBA number of the requested
              sector of the file.  This LBA number is referenced from sector 0
              of  the physical device (not the partition or filesystem).  This
              LBA value can then be used for a variety of purposes,  including
              determining an appropriate sector to deliberately corrupt during
              fault-injection testing procedures.

       --fwdownload
              When used, this should be the only flag given.   It  requires  a
              file  path  immediately after the flag, indicating where the new
              drive firmware should be read from.  The contents of  this  file
              will  be  sent  to the drive using the (S)ATA DOWNLOAD MICROCODE
              command, using either transfer protocol 7 (entire file at once),
              or,  if  the  drive  supports it, transfer protocol 3 (segmented
              download).  This command is EXTREMELY DANGEROUS  and  HAS  NEVER
              BEEN PROVEN TO WORK and will probably destroy both the drive and
              all data on it.  DO NOT USE THIS COMMAND.

       -F     Flush the on-drive write cache  buffer  (older  drives  may  not
              implement this).

       -g     Display the drive geometry (cylinders, heads, sectors), the size
              (in sectors) of the device, and the starting offset (in sectors)
              of the device from the beginning of the drive.

       -h     Display terse usage information (help).

       -i     Display  the  identification info which the kernel drivers (IDE,
              libata) have stored from boot/configuration time.  This may dif-
              fer  from  the  current information obtainable directly from the
              drive itself with the -I flag.  The data returned may or may not
              be current, depending on activity since booting the system.  For
              a more detailed interpretation of the identification info, refer
              to  AT  Attachment  Interface  for  Disk Drives, ANSI ASC X3T9.2
              working draft, revision 4a, April 19/93, and later editions.

       -I     Request identification info directly from the  drive,  which  is
       --Istdin
              This  is  a  special variation on the -I option, which accepts a
              drive identification block as standard input instead of using  a
              /dev/hd*  parameter.   The  format of this block must be exactly
              the same as that found in the /proc/ide/*/hd*/identify  "files",
              or  that produced by the --Istdout option described below.  This
              variation is designed for  use  with  collected  "libraries"  of
              drive  identification information, and can also be used on ATAPI
              drives which may give media errors with the standard  mechanism.
              When --Istdin is used, it must be the *only* parameter given.

       --Istdout
              This option dumps the drive's identify data in hex to stdout, in
              a format similar to that from /proc/ide/*/identify, and suitable
              for later use with the --Istdin option.

       -k     Get/set  the  keep_settings_over_reset flag for the drive.  When
              this flag is set, the driver will preserve the -dmu options over
              a  soft  reset,  (as  done  during the error recovery sequence).
              This flag defaults to off, to prevent drive  reset  loops  which
              could  be  caused by combinations of -dmu settings.  The -k flag
              should therefore only be set after one has  achieved  confidence
              in  correct  system operation with a chosen set of configuration
              settings.  In practice, all that is typically necessary to  test
              a  configuration (prior to using -k) is to verify that the drive
              can be read/written, and that no error  logs  (kernel  messages)
              are  generated in the process (look in /var/adm/messages on most
              systems).

       -K     Set the drive's  keep_features_over_reset  flag.   Setting  this
              enables the drive to retain the settings for -APSWXZ over a soft
              reset (as done during the error  recovery  sequence).   Not  all
              drives support this feature.

       -L     Set  the drive's doorlock flag.  Setting this to 1 will lock the
              door mechanism of some removable hard drives (eg. Syquest,  ZIP,
              Jazz..),  and  setting  it  to 0 will unlock the door mechanism.
              Normally, Linux maintains the door locking  mechanism  automati-
              cally, depending on drive usage (locked whenever a filesystem is
              mounted).  But on system shutdown, this can be a nuisance if the
              root  partition is on a removable disk, since the root partition
              is left mounted (read-only) after shutdown.  So, by  using  this
              command  to  unlock  the  door  after  the  root  filesystem  is
              remounted read-only, one can then remove the cartridge from  the
              drive after shutdown.

       -m     Get/set  sector  count  for multiple sector I/O on the drive.  A
              setting of 0 disables this feature.  Multiple sector  mode  (aka
              IDE  Block  Mode),  is a feature of most modern IDE hard drives,
              permitting the transfer of multiple sectors per  I/O  interrupt,
              rather  than the usual one sector per interrupt.  When this fea-
              ture is enabled, it typically reduces operating system  overhead
              for  disk  I/O  by  30-50%.   On  many systems, it also provides
              increased data throughput of anywhere  from  5%  to  50%.   Some

       --make-bad-sector
              Deliberately create a bad sector (aka.  "media  error")  on  the
              disk.   EXCEPTIONALLY  DANGEROUS.   DO NOT USE THIS FLAG!!  This
              can be useful for testing of device/RAID error  recovery  mecha-
              nisms.  The sector number is given as a (base10) parameter after
              the flag.  Depending on the device, hdparm will  choose  one  of
              two  possible  ATA  commands  for  corrupting  the  sector.  The
              WRITE_LONG works on most drives, but only up to the 28-bit  sec-
              tor  boundary.   Some  very recent drives (2008) may support the
              new WRITE_UNCORRECTABLE_EXT command, which works for  any  LBA48
              sector.   If  available,  hdparm  will use that in preference to
              WRITE_LONG.  The WRITE_UNCORRECTABLE_EXT command itself presents
              a  choice  of how the new bad sector should behave.  By default,
              it will look like any other bad sector, and the drive  may  take
              some  time  to retry and fail on subsequent READs of the sector.
              However, if a single letter f is prepended immediately in  front
              of  the  first digit of the sector number parameter, then hdparm
              will issue a "flagged" WRITE_UNCORRECTABLE_EXT, which causes the
              drive  to  merely  flag the sector as bad (rather than genuinely
              corrupt it), and subsequent READs of the sector will fail  imme-
              diately (rather than after several retries).  Note also that the
              --repair-sector flag can be used to restore  (any)  bad  sectors
              when they are no longer needed, including sectors that were gen-
              uinely bad (the drive will likely remap those to a fresh area on
              the media).

       -M     Get/set Automatic Acoustic Management (AAM) setting. Most modern
              harddisk drives have the ability to speed down  the  head  move-
              ments  to  reduce  their  noise output.  The possible values are
              between 0 and 254. 128 is the most quiet (and therefore slowest)
              setting and 254 the fastest (and loudest). Some drives have only
              two levels (quiet / fast), while others may have different  lev-
              els  between  128 and 254.  At the moment, most drives only sup-
              port 3 options, off, quiet, and fast.  These have been  assigned
              the values 0, 128, and 254 at present, respectively, but integer
              space has been incorporated for future  expansion,  should  this
              change.

       -N     Get/set  max  visible  number of sectors, also known as the Host
              Protected Area setting.  Without a parameter,  -N  displays  the
              current  setting,  which  is  reported  as two values: the first
              gives the current max sectors setting, and the second shows  the
              native  (real)  hardware  limit  for  the  disk.  The difference
              between these two values indicates how many sectors of the  disk
              are currently hidden from the operating system, in the form of a
              Host Protected Area (HPA).  This area is often used by  computer
              makers  to hold diagnostic software, and/or a copy of the origi-
              nally provided  operating  system  for  recovery  purposes.   To
              change  the  current max (VERY DANGEROUS, DATA LOSS IS EXTREMELY
              LIKELY), a new value should be provided (in base10)  immediately
              following  the  -N  flag.  This value is specified as a count of
              sectors, rather than the "max  sector  address"  of  the  drive.
              Drives  have the concept of a temporary (volatile) setting which
              between them by the kernel.  So if it fails initially, just  try
              again.   Kernel  support  for -N is buggy for many adapter types
              across many kernel versions, in that an  incorrect  (too  small)
              max  size value is sometimes reported.  As of the 2.6.27 kernel,
              this does finally seem to be working on most hardware.

       -n     Get or set the "ignore write errors" flag in the driver.  Do NOT
              play with this without grokking the driver source code first.

       -p     Attempt to reprogram the IDE interface chipset for the specified
              PIO mode, or attempt to auto-tune for the "best" PIO  mode  sup-
              ported  by  the  drive.  This feature is supported in the kernel
              for only a few "known" chipsets, and even then  the  support  is
              iffy  at  best.   Some  IDE chipsets are unable to alter the PIO
              mode for a single drive, in which case this flag may  cause  the
              PIO  mode  for both drives to be set.  Many IDE chipsets support
              either fewer or more than the standard six (0 to 5)  PIO  modes,
              so  the  exact  speed  setting that is actually implemented will
              vary by chipset/driver sophistication.  Use  with  extreme  cau-
              tion!  This feature includes zero protection for the unwary, and
              an unsuccessful outcome may result in severe filesystem  corrup-
              tion!

       -P     Set  the  maximum sector count for the drive's internal prefetch
              mechanism.  Not all drives support  this  feature,  and  it  was
              dropped from the offical spec as of ATA-4.

       --prefer-ata12
              When  using the SAT (SCSI ATA Translation) protocol, hdparm nor-
              mally prefers to use the 16-byte command format whenever  possi-
              ble.   But  some  USB drive enclosures don't work correctly with
              16-byte commands.  This flag can be used to  force  use  of  the
              smaller  12-byte  command  format with such drives.  hdparm will
              still revert to 16-byte commands for things that cannot be  done
              with the 12-byte format (eg. sector accesses beyond 28-bits).

       -q     Handle the next flag quietly, suppressing normal output (but not
              error messages).  This is useful  for  reducing  screen  clutter
              when running from system startup scripts.  Not applicable to the
              -i or -v or -t or -T flags.

       -Q     Get or set the device's command queue_depth, if supported by the
              hardware.   This  only works with 2.6.xx (or later) kernels, and
              only with device and driver combinations which support  changing
              the  queue_depth.   For  SATA  disks, this is the Native Command
              Queuing (NCQ) queue depth.

       -r     Get/set read-only flag for the device.  When set,  Linux  disal-
              lows write operations on the device.

       --read-sector
              Reads  from  the specified sector number, and dumps the contents
              in hex to standard output.  The  sector  number  must  be  given
              (base10)  after  this  flag.  hdparm will issue a low-level read

       -s     Enable/disable  the power-on in standby feature, if supported by
              the drive.  VERY DANGEROUS.  Do not use  unless  you  are  abso-
              lutely  certain  that both the system BIOS (or firmware) and the
              operating system kernel (Linux >= 2.6.22)  support  probing  for
              drives  that  use this feature.  When enabled, the drive is pow-
              ered-up in the standby mode to allow the controller to  sequence
              the  spin-up of devices, reducing the instantaneous current draw
              burden when many drives share a power supply.  Primarily for use
              in  large RAID setups.  This feature is usually disabled and the
              drive is powered-up in the active mode  (see  -C  above).   Note
              that  a  drive may also allow enabling this feature by a jumper.
              Some SATA drives support the control of this feature by  pin  11
              of the SATA power connector. In these cases, this command may be
              unsupported or may have no effect.

       -S     Put the drive into idle  (low-power)  mode,  and  also  set  the
              standby (spindown) timeout for the drive.  This timeout value is
              used by the drive to determine how long to wait  (with  no  disk
              activity)  before  turning  off the spindle motor to save power.
              Under such circumstances, the drive may take as long as 30  sec-
              onds  to respond to a subsequent disk access, though most drives
              are much quicker.  The encoding of the timeout value is somewhat
              peculiar.   A  value  of zero means "timeouts are disabled": the
              device will not automatically enter standby mode.  Values from 1
              to  240 specify multiples of 5 seconds, yielding timeouts from 5
              seconds to 20 minutes.  Values from 241 to 251 specify from 1 to
              11 units of 30 minutes, yielding timeouts from 30 minutes to 5.5
              hours.  A value of 252 signifies a  timeout  of  21  minutes.  A
              value  of 253 sets a vendor-defined timeout period between 8 and
              12 hours, and the value 254 is reserved.  255 is interpreted  as
              21  minutes  plus  15  seconds.  Note that some older drives may
              have very different interpretations of these values.

       -T     Perform timings of cache reads for benchmark and comparison pur-
              poses.    For  meaningful  results,  this  operation  should  be
              repeated 2-3 times on an otherwise  inactive  system  (no  other
              active  processes)  with  at least a couple of megabytes of free
              memory.  This displays the speed of reading  directly  from  the
              Linux  buffer  cache  without  disk access.  This measurement is
              essentially an indication of the throughput  of  the  processor,
              cache, and memory of the system under test.

       -t     Perform  timings  of  device  reads for benchmark and comparison
              purposes.  For meaningful  results,  this  operation  should  be
              repeated  2-3  times  on  an otherwise inactive system (no other
              active processes) with at least a couple of  megabytes  of  free
              memory.   This  displays the speed of reading through the buffer
              cache to the disk without any prior caching of data.  This  mea-
              surement  is  an  indication  of  how fast the drive can sustain
              sequential data reads under Linux, without any filesystem  over-
              head.   To  ensure  accurate  measurements,  the buffer cache is
              flushed during the processing of -t using the BLKFLSBUF ioctl.

       -u     Get/set interrupt-unmask flag for the drive.   A  setting  of  1
       -U     Un-register an IDE interface (DANGEROUS).  The companion for the
              -R option.  Intended for use with hardware made specifically for
              hot-swapping  (very rare!).  Use with knowledge and extreme cau-
              tion as this can easily hang or damage your system.  The  hdparm
              source  distribution  includes  a  'contrib' directory with some
              user-donated scripts for  hot-swapping  on  the  UltraBay  of  a
              ThinkPad 600E.  Use at your own risk.

       -v     Display some basic settings, similar to -acdgkmur for IDE.  This
              is also the default behaviour when no flags are specified.

       --verbose
              Display extra diagnostics from some commands.

       -w     Perform a device reset (DANGEROUS).  Do NOT use this option.  It
              exists for unlikely situations where a reboot might otherwise be
              required to get a confused drive back into a useable state.

       --write-sector
              Writes zeros to the specified sector  number.   VERY  DANGEROUS.
              The  sector  number  must  be  given  (base10)  after this flag.
              hdparm will issue a low-level write  (completely  bypassing  the
              usual  block  layer read/write mechanisms) to the specified sec-
              tor.  This can be used to force a drive to repair a  bad  sector
              (media error).

       -W     Get/set the IDE/SATA drive's write-caching feature.

       -x     Tristate device for hotswap (DANGEROUS).

       -X     Set  the IDE transfer mode for (E)IDE/ATA drives.  This is typi-
              cally used in combination with -d1 when enabling DMA  to/from  a
              drive  on  a supported interface chipset, where -X mdma2 is used
              to select multiword DMA mode2 transfers and -X sdma1 is used  to
              select  simple mode 1 DMA transfers.  With systems which support
              UltraDMA burst timings, -X udma2  is  used  to  select  UltraDMA
              mode2 transfers (you'll need to prepare the chipset for UltraDMA
              beforehand).  Apart from that, use of this flag is seldom neces-
              sary  since  most/all modern IDE drives default to their fastest
              PIO transfer mode at power-on.  Fiddling with this can  be  both
              needless  and risky.  On drives which support alternate transfer
              modes, -X can be used to switch the  mode  of  the  drive  only.
              Prior to changing the transfer mode, the IDE interface should be
              jumpered or programmed (see -p flag) for the new mode setting to
              prevent  loss  and/or corruption of data.  Use this with extreme
              caution!  For the PIO (Programmed Input/Output)  transfer  modes
              used  by Linux, this value is simply the desired PIO mode number
              plus 8.  Thus, a value of 09 sets  PIO  mode1,  10  enables  PIO
              mode2,  and  11  selects  PIO  mode3.   Setting  00 restores the
              drive's "default" PIO mode, and 01 disables IORDY.   For  multi-
              word DMA, the value used is the desired DMA mode number plus 32.
              for UltraDMA, the value is the desired UltraDMA mode number plus
              64.

              device(s).

       -Z     Disable  the  automatic power-saving function of certain Seagate
              drives (ST3xxx models?), to prevent them  from  idling/spinning-
              down at inconvenient times.

       -H     Read  the  temperature  from some (mostly Hitachi) drives.  Also
              reports if the temperature is within operating  condition  range
              (this  may not be reliable). Does not cause the drive to spin up
              if idle.


       ATA Security Feature Set

       These switches are DANGEROUS to experiment with,  and  might  not  work
       with every kernel.  USE AT YOUR OWN RISK.

       --security-help
              Display terse usage info for all of the --security-* flags.

       --security-freeze
              Freeze the drive's security settings.  The drive does not accept
              any security commands until next power-on reset.  Use this func-
              tion in combination with --security-unlock to protect drive from
              any attempt to set a new password. Can be used standalone,  too.
              No other flags are permitted on the command line with this one.

       --security-unlock PWD
              Unlock  the  drive, using password PWD.  Password is given as an
              ASCII string and is padded with NULs to  reach  32  bytes.   The
              applicable  drive  password  is  selected with the --user-master
              switch.  No other flags are permitted on the command  line  with
              this one.  THIS FEATURE IS EXPERIMENTAL AND NOT WELL TESTED. USE
              AT YOUR OWN RISK.

       --security-set-pass PWD
              Lock the drive, using password PWD (Set  Password)  (DANGEROUS).
              Password  is given as an ASCII string and is padded with NULs to
              reach 32 bytes.  Use the special password NULL to set  an  empty
              password.   The  applicable  drive password is selected with the
              --user-master switch and the applicable security mode  with  the
              --security-mode  switch.   No  other  flags are permitted on the
              command line with this one.  THIS FEATURE  IS  EXPERIMENTAL  AND
              NOT WELL TESTED. USE AT YOUR OWN RISK.

       --security-disable PWD
              Disable drive locking, using password PWD.  Password is given as
              an ASCII string and is padded with NULs to reach 32 bytes.   The
              applicable  drive  password  is  selected with the --user-master
              switch.  No other flags are permitted on the command  line  with
              this one.  THIS FEATURE IS EXPERIMENTAL AND NOT WELL TESTED. USE
              AT YOUR OWN RISK.

       --security-erase PWD
              the  --user-master  switch.  No other flags are permitted on the
              command line with this one.  THIS FEATURE  IS  EXPERIMENTAL  AND
              NOT WELL TESTED. USE AT YOUR OWN RISK.

       --user-master USER
              Specifies  which  password (user/master) to select.  Defaults to
              master.  Only  useful  in  combination  with  --security-unlock,
              --security-set-pass,   --security-disable,  --security-erase  or
              --security-erase-enhanced.
                      u       user password
                      m       master password

              THIS FEATURE IS EXPERIMENTAL AND NOT WELL TESTED.  USE  AT  YOUR
              OWN RISK.

       --security-mode MODE
              Specifies  which  security mode (high/maximum) to set.  Defaults
              to high.  Only useful in combination with --security-set-pass.
                      h       high security
                      m       maximum security

              THIS FEATURE IS EXPERIMENTAL AND NOT WELL TESTED.  USE  AT  YOUR
              OWN RISK.

FILES
       /etc/hdparm.conf

BUGS
       As  noted  above, the -m sectcount and -u 1 options should be used with
       caution at first, preferably on a read-only  filesystem.   Most  drives
       work  well with these features, but a few drive/controller combinations
       are not 100% compatible.  Filesystem  corruption  may  result.   Backup
       everything before experimenting!

       Some  options (eg. -r for SCSI) may not work with old kernels as neces-
       sary ioctl()'s were not supported.

       Although this utility is intended primarily for use with SATA/IDE  hard
       disk devices, several of the options are also valid (and permitted) for
       use with SCSI hard disk devices and MFM/RLL hard disks with  XT  inter-
       faces.

       The  Linux  kernel  up until 2.6.12 (and probably later) doesn't handle
       the security unlock and disable commands gracefully and  will  segfault
       and  in  some  cases  even  panic.  The security commands however might
       indeed have been executed by the  drive.  This  poor  kernel  behaviour
       makes the PIO data security commands rather useless at the moment.

       Note  that  the  "security  erase" and "security disable" commands have
       been implemented as two consecutive PIO data commands and will not suc-
       ceed  on  a  locked drive because the second command will not be issued
       after the segfault.  See the code for hints how patch it to work around
       this  problem.  Despite  the segfault it is often still possible to run
       two instances of hdparm consecutively and issue the two necessary  com-

       PIO  data out security commands by Leonard den Ottolander , 2005.  Some
       other parts by Benjamin Benz and others.

SEE ALSO
       http://www.t13.org/ Technical Committee T13 AT  Attachment  (ATA/ATAPI)
       Interface.

       http://www.serialata.org/ Serial ATA International Organization.

       http://www.compactflash.org/ CompactFlash Association



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