> Linux Man Page: "hdparm"


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hdparm - get/set hard disk parameters


hdparm [ flags ] [device] ..


hdparm provides a command line interface to various hard disk ioctls supported by the Linux SATA/PATA/SAS “libata” subsystem and the older IDE driver subsystem. Some options may work correctly only with the latest kernels.


When no flags are given, -acdgkmur is assumed.

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.

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

Get/set bus state.

Set Advanced Power Management feature, if the drive supports it. A low value means aggressive power management and a high value means better performance. A value of 255 will disable apm on the drive.

Query/enable (E)IDE 32-bit I/O support. A numeric parameter can be used to enable/disable 32-bit I/O support: Currently supported values include 0 to disable 32-bit I/O support, 1 to enable 32-bit data transfers, and 3 to enable 32-bit data transfers 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.

Check the current IDE power mode status, which will always be one of unknown (drive does not support this command), active/idle (normal operation), standby (low power mode, drive has spun down), or sleeping (lowest power mode, drive is completely shut down). The -S, -y, -Y, and -Z flags can be used to manipulate the IDE power modes.

Disable/enable the “using_dma” flag for this drive. This option now works with most combinations of drives and PCI interfaces which support DMA and which are known to the kernel IDE driver. It is also a good idea to use the appropriate -X option in combination with -d1 to ensure that the drive itself is programmed for the correct DMA mode, although most BIOSs should do this for you at boot time. Using DMA nearly always gives the best performance, 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.

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‚Äôs 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.

VERY DANGEROUS, DON‚ÄôT 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 immediately 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!!

Enable/disable the on-drive defect management feature, whereby the drive firmware tries to automatically manage defective sectors by relocating them to “spare” sectors reserved by the factory for such. Control of this feature via the -D flag is not supported for most modern drives since ATA-4; thus this command may fail.

Set cdrom speed. This is NOT necessary for regular operation, as the drive will automatically switch speeds on its own. But if you want to play with it, just supply a speed number after the option, usually a number like 2 or 4.

Sync and flush the buffer cache for the device on exit. This operation is also performed as part of the -t and -T timings.

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

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.

Display terse usage information (help).

Display the identification info that was obtained from the drive at boot time, if available. This is a feature of modern IDE drives, and may not be supported by older devices. The data returned may or may not be current, depending on activity since booting the system. However, the current multiple sector mode count is always shown. 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).

Request identification info directly from the drive, which is displayed in a new expanded format with considerably more detail than with the older -i flag.

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.

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.

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).

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.

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 automatically, 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 removeable 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.

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 feature 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 drives, however (most notably the WD Caviar series), seem to run slower with multiple mode enabled. Your mileage may vary. Most drives support the minimum settings of 2, 4, 8, or 16 (sectors). Larger settings may also be possible, depending on the drive. A setting of 16 or 32 seems optimal on many systems. Western Digital recommends lower settings of 4 to 8 on many of their drives, due tiny (32kB) drive buffers and non-optimized buffering algorithms. The -i flag can be used to find the maximum setting supported by an installed drive (look for MaxMultSect in the output). Some drives claim to support multiple mode, but lose data at some settings. Under rare circumstances, such failures can result in massive filesystem corruption.

Get/set Automatic Acoustic Management (AAM) setting. Most modern harddisk drives have the ability to speed down the head movements 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 levels between 128 and 254. At the moment, most drives only support 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.

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

Attempt to reprogram the IDE interface chipset for the specified PIO mode, or attempt to auto-tune for the “best” PIO mode supported 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!

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.

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.

Set tagged queue depth (1 or greater), or turn tagged queuing off (0). This only works with the newer 2.5.xx (or later) kernels, and only with the few drives that currently support it.

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

Register an IDE interface (DANGEROUS). See the -U option for more information.

Enable/disable the power-on in standby feature, if supported by the drive. VERY DANGEROUS. Do not use unless you are absolutely 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 powered-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.

Set the standby (spindown) timeout for the drive. This 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 seconds 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.

Perform timings of cache 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 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.

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 measurement is an indication of how fast the drive can sustain sequential data reads under Linux, without any filesystem overhead. To ensure accurate measurements, the buffer cache is flushed during the processing of -t using the BLKFLSBUF ioctl.

Get/set interrupt-unmask flag for the drive. A setting of 1 permits the driver to unmask other interrupts during processing of a disk interrupt, which greatly improves Linux¬´s responsiveness and eliminates “serial port overrun” errors. Use this feature with caution: some drive/controller combinations do not tolerate the increased I/O latencies possible when this feature is enabled, resulting in massive filesystem corruption. In particular, CMD-640B and RZ1000 (E)IDE interfaces can be unreliable (due to a hardware flaw) when this option is used with kernel versions earlier than 2.0.13. Disabling the IDE prefetch feature of these interfaces (usually a BIOS/CMOS setting) provides a safe fix for the problem for use with earlier kernels.

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 caution 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.

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

Display extra diagnostics from some commands.

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.

Get/set the IDE/SATA drive¬´s write-caching feature.

Tristate device for hotswap (DANGEROUS).

Set the IDE transfer mode for newer (E)IDE/ATA drives. This is typically 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 multiword DMA, the value used is the desired DMA mode number plus 32. for UltraDMA, the value is the desired UltraDMA mode number plus 64.

Force an IDE drive to immediately enter the low power consumption standby mode, usually causing it to spin down. The current power mode status can be checked using the -C flag.

Force an IDE drive to immediately enter the lowest power consumption sleep mode, causing it to shut down completely. A hard or soft reset is required before the drive can be accessed again (the Linux IDE driver will automatically handle issuing a reset if/when needed). The current power mode status can be checked using the -C flag.

Force a kernel re-read of the partition table of the specified device(s).

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

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.

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

Freeze the drive¬´s security settings. The drive does not accept any security commands until next power-on reset. Use this function in combination with --security-unlock to protect drive from any attempt to set a new password. Can be used standalone, too.

--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. 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. The applicable drive password is selected with the --user-master switch and the applicable security mode with the --security-mode switch. 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. THIS FEATURE IS EXPERIMENTAL AND NOT WELL TESTED. USE AT YOUR OWN RISK.

--security-erase PWD
Erase (locked) drive, using password PWD (DANGEROUS). 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. THIS FEATURE IS EXPERIMENTAL AND NOT WELL TESTED. USE AT YOUR OWN RISK.

--security-erase-enhanced PWD
Enhanced erase (locked) drive, using password PWD (DANGEROUS). 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. 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.
user password
master password


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



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 necessary ioctl()¬´s were not supported.

Although this utility is intended primarily for use with (E)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 interfaces.

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 succeed 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 commands that way.


hdparm has been written by Mark Lord <>, the original primary developer and maintainer of the (E)IDE driver for Linux, with suggestions from many netfolk.

The disable Seagate auto-powersaving code is courtesy of Tomi Leppikangas(

Security freeze command by Benjamin Benz <>, 2005.

PIO data out security commands by Leonard den Ottolander <leonard den ottolander nl>, 2005. Parts by Benjamin Benz <> and others.

See Also Technical Committee T13 AT Attachment (ATA/ATAPI) Interface. Serial ATA International Organization. CompactFlash Association

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