This is ddrescue.info, produced by makeinfo version 4.13+ from ddrescue.texi. INFO-DIR-SECTION GNU Packages START-INFO-DIR-ENTRY * Ddrescue: (ddrescue). Data recovery tool END-INFO-DIR-ENTRY  File: ddrescue.info, Node: Top, Next: Introduction, Up: (dir) GNU ddrescue Manual ******************* This manual is for GNU ddrescue (version 1.25, 21 February 2020). * Menu: * Introduction:: Purpose and features of GNU ddrescue * Basic concepts:: Blocks, clusters, devices, files, sectors, etc * Important advice:: Read this or risk losing your data * Algorithm:: How ddrescue recovers the data * Output:: Meaning of ddrescue's screen output * Invoking ddrescue:: Command line interface * Mapfile structure:: Detailed format of the mapfile * Emergency save:: Saving the mapfile in case of trouble * Optical media:: Copying CD-ROMs and DVDs * Examples:: A small tutorial with examples * Direct disc access:: Bypassing the kernel cache * Command mode:: Copying parts of the input file on demand * Fill mode:: Selectively overwriting the output file * Generate mode:: Generating an approximate mapfile * Ddrescuelog:: Tool for ddrescue mapfiles * Invoking ddrescuelog:: Command line interface * Problems:: Reporting bugs * Concept index:: Index of concepts Copyright (C) 2004-2020 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute, and modify it.  File: ddrescue.info, Node: Introduction, Next: Basic concepts, Prev: Top, Up: Top 1 Introduction ************** GNU ddrescue is a data recovery tool. It copies data from one file or block device (hard disc, cdrom, etc) to another, trying to rescue the good parts first in case of read errors. The basic operation of ddrescue is fully automatic. That is, you don't have to wait for an error, stop the program, restart it from a new position, etc. If you use the mapfile feature of ddrescue, the data are rescued very efficiently, (only the blocks needed are read). Also you may interrupt the rescue at any time and resume it later at the same point. The mapfile is an essential part of ddrescue's effectiveness. Use it unless you know what you are doing. Ddrescue does not write zeros to the output when it finds bad sectors in the input, and does not truncate the output file if not asked to. So, every time you run it on the same output file, it tries to fill in the gaps without wiping out the data already rescued. Automatic merging of backups: If you have two or more damaged copies of a file, cdrom, etc, and run ddrescue on all of them, one at a time, with the same output file, you will probably obtain a complete and error-free file. This is so because the probability of having the same area damaged in all copies is low (if the errors are randomly located). Using the mapfile, only the blocks needed are read from the second and successive copies. Ddrescue recommends lzip for compression of backups because the lzip format is designed for long-term archiving and provides data recovery capabilities which nicely complement those of ddrescue. (Ddrescue fills unreadable sectors with data from other copies, while lziprecover corrects corrupt sectors with data from other copies). If the cause of file corruption is damaged media, the combination ddrescue + lziprecover is the best option for recovering data from multiple damaged copies. *Note lziprecover-example::. Because ddrescue needs to read and write at random places, it only works on seekable (random access) input and output files. If your system supports it, ddrescue can use direct disc access to read the input file, bypassing the kernel cache. Ddrescue also features a 'fill mode' able to selectively overwrite parts of the output file, which has a number of interesting uses like wiping data, marking bad areas, or even, in some cases, "repair" damaged sectors. One of the great strengths of ddrescue is that it is interface-agnostic, and so can be used for any kind of device supported by your kernel (ATA, SATA, SCSI, old MFM drives, floppy discs, or even flash media cards like SD).  File: ddrescue.info, Node: Basic concepts, Next: Important advice, Prev: Introduction, Up: Top 2 Basic concepts **************** Block Any amount of data. A block is described by its starting position and its size. The starting position (or beginning position) is the lowest position in the block. The end of the block is its starting position plus its size. Cluster Group of consecutive sectors read or written in one go. Device Piece of hardware containing data. Hard disc drives, cdrom drives, USB pendrives, are devices. /dev/hda, /dev/sdb, are device names. File Files are named units of data which are stored by the operating system for you to retrieve later by name. Devices and partitions are accessed by means of their associated file names. Partition Every part in which a device is divided. A partition normally contains a file system. /dev/hda1, /dev/sdb3, are partition names. Recoverable formats As ddrescue uses standard library functions to read data from the device being rescued, only mountable device formats can be rescued with ddrescue. CD-ROMs and DVDs can be rescued, "compact disc digital audio" CDs can't, "video CDs"[1] maybe. [1] http://en.wikipedia.org/wiki/Video_CD Rescue domain Block or set of blocks to be acted upon (rescued, listed, etc). You may define it with the options '--input-position', '--size', and '--domain-mapfile'. The rescue domain defaults to the whole input file or mapfile. If ddrescue can't determine the size of the input file, the rescue domain defaults to the maximum size of a block (at least 2^63 - 1 bytes, or 8 EiB minus 1 byte). Ddrescue will never try to read any data outside of the rescue domain except when unaligned direct disc access is requested (*note Direct disc access::). If it does, please, report it as a bug. The amount of data rescued, number of bad areas, etc, shown by ddrescue may vary or even become zero if you limit the rescue domain. Don't worry, they have not disappeared; they are simply out of the specified rescue domain. Sector Hardware block. Smallest accessible amount of data on a device.  File: ddrescue.info, Node: Important advice, Next: Algorithm, Prev: Basic concepts, Up: Top 3 Using ddrescue safely *********************** Ddrescue is like any other power tool. You need to understand what it does, and you need to understand some things about the machines it does those things to, in order to use it safely. Never try to rescue a r/w mounted partition. The resulting copy may be useless. It is best that the device or partition to be rescued is not mounted at all, not even read-only. Never try to repair a file system on a drive with I/O errors; you will probably lose even more data. If you use a device or a partition as destination, any data stored there will be overwritten. Some systems may change device names on reboot (e.g. udev enabled systems). If you reboot, check the device names before restarting ddrescue. If you interrupt the rescue and then reboot, any partially copied partitions should be hidden before allowing them to be touched by any operating system that tries to mount and "fix" the partitions it sees.  File: ddrescue.info, Node: Algorithm, Next: Output, Prev: Important advice, Up: Top 4 Algorithm *********** GNU ddrescue is not a derivative of dd, nor is related to dd in any way except in that both can be used for copying data from one device to another. The key difference is that ddrescue uses a sophisticated algorithm to copy data from failing drives causing them as little additional damage as possible. Versions of ddrescue prior to 1.19 used a divide-and-conquer strategy to rescue the difficult parts of the drive. But that caused a lot of head movement, which is bad for the drive. Therefore, newer versions try to minimize head movement to minimize drive damage. Ddrescue manages efficiently the status of the rescue in progress and tries to rescue the good parts first, scheduling reads inside bad (or slow) areas for later. This maximizes the amount of data that can be finally recovered from a failing drive. The standard dd utility can be used to save data from a failing drive, but it reads the data sequentially, which may wear out the drive without rescuing anything if the errors are at the beginning of the drive. Other programs read the data sequentially but switch to small size reads when they find errors. This is a bad idea because it means spending more time at error areas, damaging the surface, the heads, and the drive mechanics, instead of getting out of them as fast as possible. This behavior reduces the chances of rescuing the remaining good data. The algorithm of ddrescue is as follows (the user may interrupt the process at any point, but be aware that a bad drive can block ddrescue for a long time until the kernel gives up): 1) Optionally read a mapfile describing the status of a multi-part or previously interrupted rescue. If no mapfile is specified, or is empty, or does not exist, mark all the rescue domain as non-tried. 2) (First phase; Copying) Copying is done in up to five passes. The first pass reads the non-tried parts of the input file, marking the failed blocks as non-trimmed and skipping beyond them. The second pass delimits the blocks skipped by the first pass. The first two passes also skip beyond slow areas. The skipped areas are tried later in one or three additional passes (before trimming). The copying direction is reversed after each pass until all the rescue domain is tried. The third and fourth passes read the blocks skipped due to slow areas (if any) by the first two passes, in the same direction that each block was skipped. For each block, passes 2 to 4 skip the rest of the block after finding the first error in the block. The last pass is a sweeping pass, with skipping disabled. The purpose of the multiple passes is to delimit large bad areas fast, recover the most promising areas first, keep the mapfile small, and produce good starting points for trimming. Only non-tried areas are read in large blocks. Trimming, scraping, and retrying are done sector by sector. Each sector is tried at most two times; the first in this phase as part of a large block read, the second in one of the phases below as a single sector read. 3) (Second phase; Trimming) Trimming is done in one pass. For each non-trimmed block, read forwards one sector at a time from the leading edge of the block until a bad sector is found. Then read backwards one sector at a time from the trailing edge of the block until a bad sector is found. Then mark the bad sectors found (if any) as bad-sector, and mark the rest of the block as non-scraped without trying to read it. If any edge is already adjacent to a bad sector, it is considered as already trimmed and is not trimmed again. 4) (Third phase; Scraping) Scrape together the data not recovered by the copying or trimming phases. Scraping is done in one pass. Each non-scraped block is read forwards, one sector at a time. Any bad sectors found are marked as bad-sector. 5) (Fourth phase; Retrying) Optionally try to read again the bad sectors until the specified number of retry passes is reached. The direction is reversed after each pass. Every bad sector is tried only once in each pass. Ddrescue can't know if a bad sector is unrecoverable or if it will be eventually read after some retries. 6) Optionally write a mapfile for later use. When ddrescue finishes the steps above, any areas marked as bad-sector will remain untouched in the output file. If the output file is a regular file created by ddrescue, the areas marked as bad-sector will contain zeros. If it is a device or a previously existing file, the areas marked as bad-sector will still contain the data previously present there. The mapfile is periodically saved to disc, as well as when ddrescue finishes or is interrupted. A backup copy of the mapfile with the extension '.bak' is also periodically created (if possible). So in case of a crash you can resume the rescue with little recopying. The default interval between saves varies from 30 seconds to 5 minutes depending on mapfile size (larger mapfiles are saved at longer intervals), but may be overriden. *Note --mapfile-interval::. The same mapfile can be used for multiple commands that copy different areas of the input file, and for multiple recovery attempts over different subsets. See this example: Rescue the most important part of the disc first. ddrescue -i0 -s50MiB /dev/sdc hdimage mapfile ddrescue -i0 -s1MiB -d -r3 /dev/sdc hdimage mapfile Then rescue some key disc areas. ddrescue -i30GiB -s10GiB /dev/sdc hdimage mapfile ddrescue -i230GiB -s5GiB /dev/sdc hdimage mapfile Now rescue the rest (does not recopy what is already done). ddrescue /dev/sdc hdimage mapfile ddrescue -d -r3 /dev/sdc hdimage mapfile  File: ddrescue.info, Node: Output, Next: Invoking ddrescue, Prev: Algorithm, Up: Top 5 Meaning of ddrescue's screen output ************************************* The output of ddrescue looks like this: GNU ddrescue 1.25 Press Ctrl-C to interrupt Initial status (read from mapfile) rescued: 1665 MB, tried: 0 B, bad-sector: 0 B, bad areas: 0 Current status ipos: 2874 MB, non-trimmed: 0 B, current rate: 21479 kB/s opos: 2874 MB, non-scraped: 0 B, average rate: 21023 kB/s non-tried: 13603 MB, bad-sector: 0 B, error rate: 0 B/s rescued: 2401 MB, bad areas: 0, run time: 35s pct rescued: 15.00%, read errors: 0, remaining time: 10m slow reads: 5, time since last successful read: 0s Copying non-tried blocks... Pass 1 (forwards) The meaning of each field is as follows: 'ipos' Input position. The position in the input file where data are being currently read from. 'opos' Output position. The position in the output file where data are being currently written to. 'non-tried' Size of the part of the rescue domain pending to be tried. This is the sum of the sizes of all the non-tried blocks. 'rescued' Size of the part of the rescue domain already successfully recovered. This is the sum of the sizes of all the finished blocks. 'pct rescued' Percentage of the rescue domain that has been successfully recovered. 'slow reads' Number of times that the read rate fell below '--min-read-rate' during the first two passes of the copying phase. *Note --min-read-rate::. 'tried' Size of the part of the rescue domain already tried but not yet rescued. This is the sum of the sizes of all the non-trimmed, non-scraped, and bad-sector blocks. 'non-trimmed' Size of the part of the rescue domain pending to be trimmed. This is the sum of the sizes of all the non-trimmed blocks. 'non-scraped' Size of the part of the rescue domain pending to be scraped. This is the sum of the sizes of all the non-scraped blocks. 'bad-sector' Total error size. This is the size of the part of the rescue domain formed by known bad sectors. The total error size is the sum of the sizes of all the bad-sector blocks. It increases during the trimming and scraping phases, and may decrease during the retrying phase. A sector is not marked as bad-sector and considered part of a bad area until it has been tried individually instead of as part of a large block read. Note that as ddrescue retries the bad-sector blocks, the good data found may divide them into smaller blocks, decreasing the total error size but increasing the number of bad areas. 'bad areas' Number of separate bad-sector blocks inside the rescue domain. Non-trimmed and non-scraped blocks are not considered bad areas. *Note --max-bad-areas::. 'read errors' Number of failed read attempts. *Note --max-error-rate::. 'current rate' The read rate measured during the last second. 'average rate' The average read rate measured during the current run. 'error rate' The read error rate measured during the last second. 'run time' Time elapsed since the beginning of the current run. 'remaining time' Estimated remaining time to rescue all the data in the rescue domain. The remaining time is calculated using the average rate of the last 30 seconds and does not take into account that some parts of the rescue domain may be excluded from the rescue (for example with '--no-trim'), or that some areas may be unrecoverable. Therefore it may be very imprecise, may vary widely during the rescue, and may show a non-zero value at the end of the rescue. In particular it may go down to a few seconds at the end of the first pass, just to grow to hours or days in the following passes. Such is the nature of ddrescue; the good parts are usually recovered fast, while the rest may take a long time. 'time since last successful read' Time elapsed since the last successful read attempt.  File: ddrescue.info, Node: Invoking ddrescue, Next: Mapfile structure, Prev: Output, Up: Top 6 Invoking ddrescue ******************* The format for running ddrescue is: ddrescue [OPTIONS] INFILE OUTFILE [MAPFILE] INFILE and OUTFILE may be files, devices, or partitions. MAPFILE is a regular file and must be placed in an existing directory. If MAPFILE does not exist, ddrescue will create it. Be careful to not specify by mistake an old MAPFILE from an unrelated rescue. Ddrescue tries to create a backup copy of the mapfile, with the name MAPFILE.bak, every time it is going to overwrite a fsynced MAPFILE. *Note --mapfile-interval::. Always use a mapfile unless you know you won't need it. Without a mapfile, ddrescue can't resume a rescue, only reinitiate it. ddrescue supports the following options: '-h' '--help' Print an informative help message describing the options and exit. '-V' '--version' Print the version number of ddrescue on the standard output and exit. This version number should be included in all bug reports. '-a BYTES' '--min-read-rate=BYTES' Minimum read rate of good non-tried areas, in bytes per second. If the read rate falls below this value during the first two passes of the copying phase, ddrescue will skip ahead a variable amount depending on rate and error histories. The skipped blocks are tried in additional passes (before trimming). If BYTES is 0 (auto), the minimum read rate is recalculated every second as (average_rate / 10). '-A' '--try-again' Mark all non-trimmed and non-scraped blocks inside the rescue domain as non-tried before beginning the rescue. Try this if the drive stops responding and ddrescue immediately starts scraping failed blocks when restarted. If '--retrim' is also specified, mark all failed blocks inside the rescue domain as non-tried. '-b BYTES' '--sector-size=BYTES' Sector (hardware block) size of input device in bytes (usually 512 for hard discs and 3.5" floppies, 1024 for 5.25" floppies, and 2048 for cdroms). Defaults to 512. In rescue mode, any non-finished subsector that is found during the initial read of the mapfile will be joined to its corresponding sector (if it is also not finished), marking the whole sector with the less processed state, so as to make sure that sub-sector data will not be discarded from a successful read during the rescue. (A subsector is a block smaller than sector size). Subsector joining is performed in all the mapfile, not only in the rescue domain. '-B' '--binary-prefixes' Show units with binary prefixes (powers of 1024). SI prefixes (powers of 1000) are used by default. (See table below). '-c SECTORS' '--cluster-size=SECTORS' Number of sectors to copy at a time. Defaults to 64 KiB / sector_size. Try smaller values for slow drives. The number of sectors per track (18 or 9) is a good value for floppies. '-C' '--complete-only' Limit rescue domain to the blocks listed in the MAPFILE. Don't read new data beyond MAPFILE limits. This is useful when reading from devices of undefined size (like raw devices), when the drive returns an incorrect size, or when reading from a partial copy. It can only be used after a first rescue attempt, possibly limited with the option '--size', has produced a complete MAPFILE. '-d' '--idirect' Use direct disc access (*note Direct disc access::) to read from INFILE, bypassing the kernel cache. (Opens the file with the flag 'O_DIRECT'). Sector size must be correctly set for this to work. Not all systems support this. If your system does not support direct disc access, ddrescue will warn you. If the sector size is not correctly set, an unaligned read error will result and ddrescue will exit with status 1. '-D' '--odirect' Use direct disc access to write to OUTFILE, bypassing the kernel cache. (Opens the file with the flag 'O_DIRECT'). Sector size must be correctly set for this to work. Not all systems support this. If your system does not support direct disc access, ddrescue will warn you. If the sector size is not correctly set, a write error will result and no data will be rescued. Some OSs have a bug that prevents them from detecting write errors properly (or at all) on some devices if direct disc access is not used for OUTFILE. '-e [+]N' '--max-bad-areas=[+]N' Maximum number of bad areas allowed before giving up. Defaults to infinity. If N is preceded by '+' the number refers to new bad areas found in this run, not counting those already present in the MAPFILE. '-E BYTES' '--max-error-rate=BYTES' Maximum rate of read errors allowed before giving up, in bytes per second. Defaults to infinity. The rate being measured is that of actually failed reads, so ddrescue may exit because of this rate being exceeded even if the total error size (size of bad-sector areas) does not change because the areas being tried are being marked as non-trimmed or non-scraped, or are already marked as bad-sector. '-f' '--force' Force overwrite of OUTFILE. Needed when OUTFILE is not a regular file, but a device or partition. This option is just a safeguard to prevent the inadvertent destruction of partitions, and is ignored for regular files. '-F TYPES' '--fill-mode=TYPES' Fill the blocks in OUTFILE specified as any of TYPES in MAPFILE, with data read from INFILE. TYPES contains one or more of the status characters defined in the chapter Mapfile structure (*note Mapfile structure::) and an optional 'l' for sector location data. See the chapter Fill mode (*note Fill mode::) for a complete description of the fill mode. '-G' '--generate-mode' Generate an approximate MAPFILE from the INFILE and OUTFILE of the original rescue run. Note that you must keep the original offset between '--input-position' and '--output-position' of the original rescue run. See the chapter Generate mode (*note Generate mode::) for a complete description of the generate mode. '-H FILE' '--test-mode=FILE' Builds a map of good/bad blocks using the mapfile FILE and uses it to simulate read errors in INFILE. The blocks marked as finished in FILE will be read normally. All other block types will be considered read errors without even trying to read them from INFILE. The apparent size of INFILE is truncated to the extent of FILE. This mode is an aid in improving the algorithm of ddrescue and is also useful to verify that ddrescue produces accurate results in presence of read errors. Use '-' as FILE to read from standard input. '-i BYTES' '--input-position=BYTES' Starting position of the rescue domain in INFILE, in bytes. Defaults to 0. This is not the point from which ddrescue starts copying. (For example, if you pass the option '--reverse' to ddrescue, it starts copying from the end of the rescue domain). In fill mode it refers to a position in the INFILE of the original rescue run. See the chapter Fill mode (*note Fill mode::) for details. '-I' '--verify-input-size' Compare the size of INFILE with the size calculated from the list of blocks contained in the MAPFILE, and exit with status 1 if they differ. This is not enabled by default because the size of some devices can't be known in advance and because the size derived from the MAPFILE may be incomplete, for example after doing a partial rescue. '-J' '--verify-on-error' After every read error, read again the last good sector found and verify that it returns the same data. Exit with status 2 if the read fails or returns inconsistent data. Exit with status 1 if a read error happens before a good sector is found. This option performs one extra read after each error, wearing the drive faster. Use it only on drives that stop responding or return garbage data after finding errors. You may need to power cycle the drive before restarting ddrescue. '-K [INITIAL][,MAX]' '--skip-size=[INITIAL][,MAX]' Set limits to skip size during the copying phase. At least one of INITIAL or MAX must be specified. INITIAL is the size to skip on the first read error or slow read, in bytes. MAX is the maximum size to skip. The values given will be rounded to the next multiple of sector size. The skip size will be doubled for each read error or slow read until it reaches MAX or, if MAX is omitted, 1% of the size of INFILE, and will be reset to INITIAL when good data are found. Valid values range from 64 KiB to 1 EiB. INITIAL defaults to INFILE_SIZE / 100_000 with a minimum value of 64 KiB. An INITIAL value of 0 disables skipping entirely. If ddrescue is having difficulties skipping away from a large area with scattered errors, or if the device has large bad areas at regular intervals, you may increase the initial skip size with this option. Inversely, if ddrescue is skipping too much, leaving large non-tried areas behind each error (which will be read later in the usually slower backwards direction), you may reduce the maximum skip size, or disable skipping. '--skip-size' is independent from '--cluster-size'. The size to skip is calculated from the end of the block that just failed. '-L' '--loose-domain' Accept an incomplete synthetic (user fabricated) domain mapfile or test-mode mapfile, and fill the gaps in the list of data blocks with non-tried blocks. The blocks in the mapfile must be strictly ascending and non-overlapping, but they don't need to be contiguous. This option allows making quick edits to a mapfile without all the size calculations involved in making all data blocks contiguous again. '-m FILE' '--domain-mapfile=FILE' Restrict the rescue domain to the blocks marked as finished in the mapfile FILE. This is useful for merging partially recovered images of backups, or if the destination drive fails during the rescue. Use '-' as FILE to read the domain mapfile from standard input. Specialized tools like ddrutility or partclone can produce a domain mapfile listing all the used blocks in a partition, making the rescue more efficient. '-M' '--retrim' Mark all failed blocks inside the rescue domain as non-trimmed before beginning the rescue. The effect is similar to '--retry-passes=1', but the bad sectors are tried in a different order, making perhaps possible to rescue some of them. '-n' '--no-scrape' Skip the scraping phase. Avoids spending a lot of time trying to rescue the most difficult parts of the file. '-N' '--no-trim' Skip the trimming phase. Especially useful in the first parts of a multi-part rescue. '-o BYTES' '--output-position=BYTES' Starting position of the image of the rescue domain in OUTFILE, in bytes. Defaults to '--input-position'. The bytes below BYTES aren't touched if they exist and truncation is not requested. Else they are set to 0. '-O' '--reopen-on-error' Close INFILE and then reopen it after every read error encountered during the copying phase. If '--min-read-rate' is set, also close and reopen INFILE after every slow read encountered during the first two passes of the copying phase. Use this option if you notice a permanent drop in transfer rate after finding read errors or slow areas. But be warned that most probably the slowing-down is intentionally caused by the kernel in an attempt to increase the probability of reading data from the device. '-p' '--preallocate' Preallocate space on disc for OUTFILE. Only space for regular files can be preallocated. If preallocation succeeds, rescue will not fail due to lack of free space on disc. If ddrescue can't determine the size to preallocate, you may need to specify it with some combination of the options '--input-position', '--output-position', '--size', and '--domain-mapfile'. '-P[LINES]' '--data-preview[=LINES]' Show LINES lines of the latest data read in '16-byte hex + ASCII' format. Valid values for LINES range from 1 to 32. If LINES is omitted, a default value of 3 is used. '-q' '--quiet' Quiet operation. Suppress all messages. '-r N' '--retry-passes=N' Exit after the given number of retry passes. Defaults to 0. -1 means infinity. Every bad sector is tried only once in each pass. To retry bad sectors detected on a previous run, you must specify a non-zero number of retry passes. '-R' '--reverse' Reverse the direction of all passes (copying, trimming, scraping, and retrying). Every pass that is normally run forwards will now be run backwards, and vice versa. '--reverse' does not modify the size of the blocks copied during each phase, just the order in which they are tried. '-s BYTES' '--size=BYTES' Maximum size of the rescue domain in bytes. It limits the amount of input data to be copied. If ddrescue can't determine the size of the input file, you may need to specify it with this option. Note that this option does not specify the size of the resulting OUTFILE. For example, the following command creates an OUTFILE 300 bytes long, but only writes data on the last 200 bytes: ddrescue -i 100 -s 200 infile outfile mapfile '-S' '--sparse' Use sparse writes for OUTFILE. (The blocks of zeros are not actually allocated on disc). May save a lot of disc space in some cases. Not all systems support this. Only regular files can be sparse. '-t' '--truncate' Truncate OUTFILE to zero size before writing to it. Only works for regular files, not for drives or partitions. '-T INTERVAL' '--timeout=INTERVAL' Maximum time since last successful read allowed before giving up. Defaults to infinity. INTERVAL is an integer or rational number (like 1.5 or 1/2) optionally followed by one of 's', 'm', 'h', or 'd', meaning seconds, minutes, hours, and days respectively. If no unit is specified, it defaults to seconds. INTERVAL has a resolution of one second; fractions of a second are not allowed. '-u' '--unidirectional' Run all passes in the same direction. Forwards by default, or backwards if the option '--reverse' is also given. '-v' '--verbose' Verbose mode. Further -v's (up to 4) increase the verbosity level. Some large numbers in messages (like device sizes) are printed in groups of 3 digits separated by underscore characters to make them more readable. '-w' '--ignore-write-errors' Make fill mode ignore write errors. This is useful to avoid ddrescue exiting because of new bad sectors developing while wiping the good sectors of a failing drive. Fill mode normally writes to OUTFILE one cluster at a time. With this option, after the first write error is found in an area, the rest of that area is filled sector by sector. Note that in rescue mode a write error is fatal, which means that the rescue needs to be repeated or else OUTFILE needs to be copied to a third drive using MAPFILE as domain (*note --domain-mapfile::). '-x BYTES' '--extend-outfile=BYTES' Extend the size of OUTFILE to make it at least BYTES long. If the size of OUTFILE is already equal or longer than BYTES, then this option does nothing. Use this option to guarantee a minimum size for OUTFILE. Only regular files can be extended. '-X N' '--max-read-errors=N' Maximum number of read errors allowed before giving up. Defaults to infinity. Exit with status 1 if more than N read errors are encountered. '--max-read-errors=0' is similar but different to '--timeout=0', which waits until the screen status is refreshed (at least 1 second). If there is at least one successful read per second, '--timeout=0' does not make ddrescue to exit. '--max-read-errors=0' is also similar but different to '--max-bad-areas=+0', which exits when a new bad area is found. If the read errors are adjacent to existing bad areas, no new bad areas are produced (just enlarged), and '--max-bad-areas=+0' does not make ddrescue to exit. '-y' '--synchronous' Use synchronous writes for OUTFILE. (Issue a fsync call after every write). May be useful when forcing the drive to remap its bad sectors. '-Z BYTES' '--max-read-rate=BYTES' Maximum read rate, in bytes per second. If BYTES is too small, the actual read rate is rounded up to the equivalent of a whole number of cluster reads per second. Use this option to limit the bandwidth used by ddrescue, for example when recovering over a network. '--ask' Ask for user confirmation before starting the copy. If the first letter of the answer is 'y', ddrescue starts copying. Else it exits with status 1. If they can be obtained, ddrescue shows the model and serial number of the input and output devices. Ddrescue also shows the size in bytes of the corresponding file or device if it exists. The format used is [MODEL::SERIAL_NUMBER] (SIZE) '--command-mode' Read commands from the standard input and execute them, copying parts of the input file on demand. Command line arguments controling the display (like '--data-preview') or the automatic algorithm (like '--max-errors' or '--reverse') have no effect in command mode. *Note Command mode::, for a complete description of the command mode. '--cpass=RANGE' Select what pass(es) to run during the copying phase. Valid pass values range from 1 to 5. To run only the given pass(es), specify also '--no-trim' and '--no-scrape'. '--cpass=0' skips the copying phase entirely. Examples of RANGE Passes run 1 1 1,2,3 1, 2, 3 2-4 2, 3, 4 1,3-5 1, 3, 4, 5 1-3,5 1, 2, 3, 5 '--delay-slow=INTERVAL' Initial delay before ddrescue starts checking for slow reads. Defaults to 30 seconds. INTERVAL is formatted as in the option '--timeout' above. '--log-events=FILE' Log all significant events (start of each pass and end of run) in FILE. If FILE already exists, the new events are appended at the end of FILE. For each event a line is printed containing a time stamp, the percentage rescued, and a message describing the event. The 'end of run' line also contains the current position and status. If ddrescue exits because of an error or interruption, the cause is also logged in FILE. '--log-rates=FILE' Log rates and error sizes every second in FILE. If FILE already exists, it will be overwritten. Every time the screen is updated with new details, some of those details (time, input position, current and average rates, number of bad areas, and total error size) are written to FILE in a format usable by plotting utilities like gnuplot. This allows a posterior analysis of the drive to see if it has any weak zones (areas where the transfer rate drops well below the sustained average). '--log-reads=FILE' Log all read operations in FILE. If FILE already exists, it will be overwritten. Every read attempt and its result (position, size, copied size, and error size) is written to FILE. (The position written is always the beginning of the block tried, even if reading backwards). A line is also written at the beginning of each phase (copying, trimming, scraping, and retrying). Finally, a line with a time mark is written every second (unless the read takes more time). Use this option with caution because FILE may become very large very quickly. Use lzip to compress FILE if you need to store or transmit it. '--mapfile-interval=[SAVE_INTERVAL][,SYNC_INTERVAL]' Change the interval at which ddrescue saves and fsyncs the MAPFILE. At least one of SAVE_INTERVAL or SYNC_INTERVAL must be specified. A SAVE_INTERVAL of -1 chooses the default automatic interval (from 30 seconds to 5 minutes depending on mapfile size). A SAVE_INTERVAL of 0 saves the MAPFILE after every read (use with caution). SYNC_INTERVAL is the interval between fsync calls. Default SYNC_INTERVAL is 5 minutes. Minimum SYNC_INTERVAL is 5 seconds. SYNC_INTERVAL must be greater or equal than SAVE_INTERVAL. Intervals are formatted as in the option '--timeout' above. In practice, fsyncs are a subset of saves. I.e., some of the times when the MAPFILE is saved, it is also fsync'ed. Therefore, '--mapfile-interval=30,45' is really '--mapfile-interval=30,60'. The time needed to write the MAPFILE is excluded from the mapfile save and sync intervals. (Some mapfiles may take several seconds to write). '--max-slow-reads=N' Maximum number of slow reads allowed before giving up. Defaults to infinity. Exit with status 1 if more than N slow reads are encountered during the first two passes of the copying phase. Only works if a minimum read rate has been set with '--min-read-rate'. '--pause-on-error=INTERVAL' Time to wait after each read error or slow read. Defaults to 0. INTERVAL is formatted as in the option '--timeout' above. If INTERVAL begins with 's', the pause is simulated and INTERVAL can be smaller than one second; the time displayed is increased by INTERVAL but without performing any pause. Pause simulation can be useful in combination with '--test-mode' for testing purposes. '--pause-on-pass=INTERVAL' Time to wait between passes. Defaults to 0. INTERVAL is formatted as in the option '--timeout' above. '--reset-slow' Reset the slow reads counter every time the read rate reaches or surpasses '--min-read-rate'. With this option, ddrescue only exits after the read rate has remained below '--min-read-rate' for at least as many seconds as the argument given to '--max-slow-reads'. '--same-file' Allow INFILE and OUTFILE to be the same file or device. This may be used to test the writing ability of a drive. It may also be used to copy part of a file to another location inside or beyond the end of the same file by setting different values for '--input-position' and '--output-position'. If the data to be copied overlap with the destination, the right copying direction must be chosen to avoid overwriting the overlapping part before it is copied. Numbers given as arguments to options (positions, sizes, rates, etc) may be expressed as decimal, hexadecimal, or octal values (using the same syntax as integer constants in C++), and may be followed by a multiplier and an optional 'B' for "byte". The 's' multiplier may be appended to any of the other multipliers. For example, 'ks' means kilosectors (1000 * sector_size), and 'Kis' means kibisectors (1024 * sector_size). Table of SI and binary prefixes (unit multipliers): Prefix Value | Prefix Value s sectors | k kilobyte (10^3 = 1000) | Ki kibibyte (2^10 = 1024) M megabyte (10^6) | Mi mebibyte (2^20) G gigabyte (10^9) | Gi gibibyte (2^30) T terabyte (10^12) | Ti tebibyte (2^40) P petabyte (10^15) | Pi pebibyte (2^50) E exabyte (10^18) | Ei exbibyte (2^60) Z zettabyte (10^21) | Zi zebibyte (2^70) Y yottabyte (10^24) | Yi yobibyte (2^80) Exit status: 0 for a normal exit, 1 for environmental problems (file not found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or invalid input file, 3 for an internal consistency error (eg, bug) which caused ddrescue to panic. If ddrescue is interrupted by a signal, it updates MAPFILE and then terminates by raising the signal received.  File: ddrescue.info, Node: Mapfile structure, Next: Emergency save, Prev: Invoking ddrescue, Up: Top 7 Mapfile structure ******************* NOTE: In versions of ddrescue prior to 1.20 the mapfile was called 'logfile'. The format is the same; only the name has changed. The mapfile is a text file easy to read and edit. It is formed by three parts, the heading comments, the status line, and the list of data blocks. The character '#' at begin of line or after whitespace starts a comment that extends to the end of the line. The heading comments contain the version of ddrescue or ddrescuelog that created the mapfile, the command line used, and the time when the program started. If the mapfile was created by ddrescue it will also contain the current time when the mapfile was saved and a copy of the status message from the screen describing the operation being performed (copying, trimming, finished, etc). They are intended as information for the user. The first non-comment line is the status line. It contains a non-negative integer, a status character, and a positive decimal integer. The first integer is the position being tried in the input file. (The beginning of the block being tried in a forward pass or the end of the block in a backward pass). The status character is one of these: Character Meaning '?' copying non-tried blocks '*' trimming non-trimmed blocks '/' scraping non-scraped blocks '-' retrying bad sectors 'F' filling specified blocks 'G' generating approximate mapfile '+' finished Finally, the last integer is the number of the current pass in the current phase. The status line allows ddrescue to resume the copying phase instead of restarting it from pass 1. It also allows the retrying phase to resume in the same direction it was interrupted. The blocks in the list of data blocks must be contiguous and non-overlapping. Every line in the list of data blocks describes a block of data. It contains 2 non-negative integers and a status character. The first integer is the starting position of the block in the input file, the second integer is the size (in bytes) of the block. The status character is one of these: Character Meaning '?' non-tried block '*' failed block non-trimmed '/' failed block non-scraped '-' failed block bad-sector(s) '+' finished block And here is an example mapfile: # Mapfile. Created by GNU ddrescue version 1.25 # Command line: ddrescue -d -c18 /dev/fd0 fdimage mapfile # Start time: 2015-07-21 09:37:44 # Current time: 2015-07-21 09:38:19 # Copying non-tried blocks... Pass 1 (forwards) # current_pos current_status current_pass 0x00120000 ? 1 # pos size status 0x00000000 0x00117000 + 0x00117000 0x00000200 - 0x00117200 0x00001000 / 0x00118200 0x00007E00 * 0x00120000 0x00048000 ? If you edit the file, you may use decimal, hexadecimal, or octal values, using the same syntax as integer constants in C++, except for current_pass, which must be a decimal integer.  File: ddrescue.info, Node: Emergency save, Next: Optical media, Prev: Mapfile structure, Up: Top 8 Saving the mapfile in case of trouble *************************************** The mapfile is an essential part of ddrescue's effectiveness. Without a mapfile, ddrescue can't resume a rescue, only reinitiate it. Given that a difficult rescue may take days to complete, it would be a serious drawback if the mapfile were lost because of a solvable problem like a lack of space on the device the mapfile is written to. In case of trouble writing the mapfile, ddrescue will print a message like this: Error writing mapfile 'MAPFILE': No space left on device Fix the problem and press ENTER to retry, or E+ENTER for an emergency save and exit, or Q+ENTER to abort. You may try to fix the problem, for example deleting some files to make room for the mapfile, and press to retry. If the problem can't be fixed, you may press followed by to try an emergency save and exit. Ddrescue will try to write the mapfile to the file 'ddrescue.map' in the current directory or, if this fails, to '$HOME/ddrescue.map'. If the mapfile is written successfully, ddrescue will exit with status 1. Else it will print the above message again. Or you may press followed by to quit and exit with status 1. In this case the contents of the mapfile will be lost.  File: ddrescue.info, Node: Optical media, Next: Examples, Prev: Emergency save, Up: Top 9 Copying CD-ROMs and DVDs ************************** Ddrescue may be better than dd for copying recordable CD-ROMs because the two lead out sectors at the end of some of them may cause a read error that prevents the whole last record from being copied by dd, potentially losing data. Also dd may create an image larger than the original if the 'sync' conversion and a block size larger than the sector size are specified. In the special case of reading CD-ROMs (but not DVDs), the specialized tool dvdisaster may be a better option than ddrescue for recovering data because dvdisaster can read and analyze raw CD sectors, which ddrescue can't. Recordable CD and DVD media keep their data only for a finite time (typically for some years). After that time, data loss develops slowly with read errors growing from the outer media region towards the inside. It is a good idea to make two (or more) copies of every important CD-ROM/DVD you burn so that you can later recover them with ddrescue. If you have only one copy of a CD-ROM or DVD that fails when being copied, and if you have access to multiple optical media drives, you have a better chance of recovering the bad sectors since one drive may fail to read a particular sector, but another drive might be able to squeeze the data out of it, depending on the laser frequency and the sensitivity of the laser-sensor that reads the reflected laser light. Example 1: Rescue a CD-ROM in /dev/cdrom. ddrescue -n -b2048 /dev/cdrom cdimage mapfile ddrescue -d -r1 -b2048 /dev/cdrom cdimage mapfile (if bad-sector size is zero, cdimage now contains a complete image of the CD-ROM and you can write it to a blank CD-ROM) Example 2: Rescue a CD-ROM in /dev/cdrom from two copies. ddrescue -n -b2048 /dev/cdrom cdimage mapfile ddrescue -d -b2048 /dev/cdrom cdimage mapfile (insert second copy in the CD drive) ddrescue -d -r1 -b2048 /dev/cdrom cdimage mapfile (if bad-sector size is zero, cdimage now contains a complete image of the CD-ROM and you can write it to a blank CD-ROM) Example 3: Rescue a CD-ROM in /dev/cdrom using two CD drives from two different computers, writing the image into an USB drive mounted on /mnt/mem. ddrescue -n -b2048 /dev/cdrom /mnt/mem/cdimage /mnt/mem/mapfile ddrescue -d -r1 -b2048 /dev/cdrom /mnt/mem/cdimage /mnt/mem/mapfile (umount the USB drive and move both USB drive and CD-ROM to second computer) ddrescue -d -r1 -b2048 /dev/cdrom /mnt/mem/cdimage /mnt/mem/mapfile (if bad-sector size is zero, /mnt/mem/cdimage now contains a complete image of the CD-ROM and you can write it to a blank CD-ROM) Example 4: Merge the partially recovered images of 3 identical DVDs using their mapfiles as domain mapfiles. ddrescue -m mapfile1 dvdimage1 dvdimage mapfile ddrescue -m mapfile2 dvdimage2 dvdimage mapfile ddrescue -m mapfile3 dvdimage3 dvdimage mapfile (if bad-sector size is zero, dvdimage now contains a complete image of the DVD and you can write it to a blank DVD) Example 5: Rescue a lzip compressed backup from two copies on CD-ROM with error-checked merging of copies. *Note lziprecover manual: (lziprecover)Top, for details about lziprecover. ddrescue -d -r1 -b2048 /dev/cdrom cdimage1 mapfile1 mount -t iso9660 -o loop,ro cdimage1 /mnt/cdimage cp /mnt/cdimage/backup.tar.lz rescued1.tar.lz umount /mnt/cdimage (insert second copy in the CD drive) ddrescue -d -r1 -b2048 /dev/cdrom cdimage2 mapfile2 mount -t iso9660 -o loop,ro cdimage2 /mnt/cdimage cp /mnt/cdimage/backup.tar.lz rescued2.tar.lz umount /mnt/cdimage lziprecover -m -v -o backup.tar.lz rescued1.tar.lz rescued2.tar.lz Input files merged successfully. lziprecover -tv backup.tar.lz backup.tar.lz: ok  File: ddrescue.info, Node: Examples, Next: Direct disc access, Prev: Optical media, Up: Top 10 A small tutorial with examples ********************************* This tutorial is for those already able to use the dd command. If you don't know what dd is, better search the net for some introductory material about dd and GNU ddrescue first. A failing drive tends to develop more and more errors as time passes. Because of this, you should rescue the data from a drive as soon as you notice the first error. Be diligent because every time a physically damaged drive powers up and is able to output some data, it may be the very last time that it ever will. You should make a copy of the failing drive with ddrescue, and then try to repair the copy. If your data are really important, use the first copy as a master for a second copy, and try to repair the second copy. If something goes wrong, you have the master intact to try again. If you are trying to rescue a whole partition, first repair the copy with e2fsck or some other tool appropriate for the type of partition you are trying to rescue, then mount the repaired copy somewhere and try to recover the files in it. If the drive is so damaged that the file system in the rescued partition can't be repaired or mounted, you will have to browse the rescued data with an hex editor and extract the desired parts by hand, or use a file recovery tool like photorec. If the partition table is damaged, you may try to rescue the whole disc, then try to repair the partition table and the partitions on the copy. If the damaged drive is not listed in /dev, then you cannot rescue it. At least not with ddrescue. *Note Optical media::, for rescue examples of CD-ROMs and DVDs. Example 1: Fully automatic rescue of a whole disc with two ext2 partitions in /dev/sda to /dev/sdb. Note: you don't need to partition /dev/sdb beforehand, but if the partition table on /dev/sda is damaged, you'll need to recreate it somehow on /dev/sdb. ddrescue -f -r3 /dev/sda /dev/sdb mapfile fdisk /dev/sdb e2fsck -v -f /dev/sdb1 e2fsck -v -f /dev/sdb2 Example 2: Rescue an ext2 partition in /dev/sda2 to /dev/sdb2. Note: you need to create the sdb2 partition with fdisk first. sdb2 should be of appropriate type and size. ddrescue -f -n /dev/sda2 /dev/sdb2 mapfile ddrescue -d -f -r3 /dev/sda2 /dev/sdb2 mapfile e2fsck -v -f /dev/sdb2 mount -t ext2 -o ro /dev/sdb2 /mnt (read rescued files from /mnt) Example 3: While rescuing the whole drive /dev/sda to /dev/sdb, /dev/sda freezes up at position 12345678. ddrescue -f /dev/sda /dev/sdb mapfile # /dev/sda freezes here (restart /dev/sda or reboot computer) (restart copy at a safe distance from the troubled sector) ddrescue -f -i 12350000 /dev/sda /dev/sdb mapfile (then copy backwards down to the troubled sector) ddrescue -f -R /dev/sda /dev/sdb mapfile Example 4: While rescuing the whole drive /dev/sda to /dev/sdb, /dev/sdb fails and you have to rescue data to a third drive, /dev/sdc. ddrescue -f -n /dev/sda /dev/sdb mapfile1 # /dev/sdb fails here ddrescue -f -m mapfile1 /dev/sdb /dev/sdc mapfile2 ddrescue -f -n /dev/sda /dev/sdc mapfile2 ddrescue -d -f -r3 /dev/sda /dev/sdc mapfile2 Example 5: While rescuing a partition in /dev/sda1 to the file hdimage, /dev/sda1 stops responding and begins returning read errors, causing ddrescue to mark the rest of the partition as non-scraped. ddrescue -n /dev/sda1 hdimage mapfile # /dev/sda1 fails here (restart /dev/sda or reboot computer) ddrescue -n -A -i -O /dev/sda1 hdimage mapfile (if /dev/sda1 fails again, restart /dev/sda or reboot computer and then repeat the above command as many times as needed until it succeeds. is the position where the drive stopped responding) ddrescue -d -r3 /dev/sda1 hdimage mapfile Example 6: While rescuing a partition in /dev/sda1 to the file hdimage, sda1 disappears from /dev. ddrescue -n /dev/sda1 hdimage mapfile # /dev/sda1 fails here (restart /dev/sda or reboot computer and then repeat the above command as many times as needed until it succeeds) ddrescue -d -r3 /dev/sda1 hdimage mapfile Example 7: While rescuing a partition in /dev/sda1 to the file hdimage, the partition table of /dev/sda becomes unreadable and the OS no longer shows sda1 in /dev. The solution is to shift the mapfile and read the rest of the partition sda1 from /dev/sda. Note: you need to know the offset of the partition sda1 in the drive sda and the size of sda1. ddrescue /dev/sda1 hdimage mapfile # partition table fails here ddrescuelog --shift -o mapfile > shifted_mapfile ddrescue -i -o0 -s /dev/sda hdimage shifted_mapfile Example 8: After rescuing a partition in /dev/sda1 to the file hdimage, expand hdimage to copy the whole drive in /dev/sda without recopying the already copied partition /dev/sda1. The solution is to shift the mapfile, move the data of sda1 to its final position in hdimage, and then read the rest of the data from /dev/sda. Note: you need to know the offset of the partition sda1 in the drive sda and the size of sda1. ddrescue /dev/sda1 hdimage mapfile # rescue partition ddrescuelog --shift -o mapfile > shifted_mapfile ddrescue --same-file -o -s --reverse hdimage hdimage ddrescue /dev/sda hdimage shifted_mapfile # rescue rest of drive  File: ddrescue.info, Node: Direct disc access, Next: Command mode, Prev: Examples, Up: Top 11 Direct disc access ********************* If you notice that the positions and sizes in MAPFILE are always multiples of the sector size, maybe your kernel is caching the disc accesses and grouping them. In this case you may want to use direct disc access for INFILE, or read from a raw device, to bypass the kernel cache and rescue more of your data. NOTE! Sector size must be correctly set with the option '--sector-size' for direct disc access to work. NOTE: Direct disc access can copy arbitrary domains by reading whole sectors and then writing only the requested part. This is the only case where ddrescue will try to read data outside of the rescue domain. Try the option '--idirect' first. If direct disc access is not available in your system, try raw devices. Read your system documentation to find how to bind a raw device to a regular block device. Some OSs provide raw access through especial device names, like /dev/rdisk. Ddrescue aligns its I/O buffer to the sector size so that it can be used for direct disc access or to read from raw devices. For efficiency reasons, also aligns it to the memory page size if page size is a multiple of sector size. On some systems, ddrescue can't determine the size of a raw device, so an explicit '--size' or '--complete-only' option may be needed. Using direct disc access, or reading from a raw device, may be slower or faster than normal cached reading depending on your OS and hardware. In case it is slower you may want to make a first pass using normal cached reads and use direct disc access, or a raw device, only to recover the good sectors inside the failed blocks. Example 1: using direct disc access. ddrescue -f -n /dev/sdb1 /dev/sdc1 mapfile ddrescue -d -f -r3 /dev/sdb1 /dev/sdc1 mapfile e2fsck -v -f /dev/sdc1 mount -t ext2 -o ro /dev/sdc1 /mnt Example 2: using a raw device. raw /dev/raw/raw1 /dev/sdb1 ddrescue -f -n /dev/sdb1 /dev/sdc1 mapfile ddrescue -C -f -r3 /dev/raw/raw1 /dev/sdc1 mapfile raw /dev/raw/raw1 0 0 e2fsck -v -f /dev/sdc1 mount -t ext2 -o ro /dev/sdc1 /mnt  File: ddrescue.info, Node: Command mode, Next: Fill mode, Prev: Direct disc access, Up: Top 12 Copying parts of the input file on demand ******************************************** The command mode of ddrescue implements a scripting interface similar to the one of ed. *Note ed manual: (ed)Top. In this mode commands are read from the standard input and executed to copy parts of the input file to the output file, retrieve information from the mapfile, or write the mapfile to disc. Ddrescue's responses are written to standard output. "done\n" for a successfully executed command, "error\n" for a failed command (for example because of wrong arguments), and "error: ERROR MESSAGE\n" for serious or fatal errors like write errors. If end-of-file is detected on standard input, ddrescue discards any partial command being read and executes the 'f' (finish) command. All ddrescue commands are single characters, though some require additonal parameters separated by spaces. Only one command is allowed per line. Ddrescue recognizes the following commands: 'c POS SIZE' Copy command. Copies a block of data from INFILE to OUTFILE and updates the internal copy of the mapfile. The areas already marked as finished in the mapfile are not copied again. 'f' Finish command. Compacts the internal copy of the mapfile and writes it to MAPFILE (if it was specified in the command line). Then prints "done\n" to standard output and quits. On startup, the mapfile is first compacted and then split following the rescue domain borders. The finish command compacts the mapfile again before exiting. If writing MAPFILE to disc fails, a non-interactive emergency save is tried before exiting. *Note Emergency save::. 'q' Quit command. Exits ddrescue. Does not update the mapfile. 's POS SIZE' Status command. Writes to standard output one or more lines in mapfile format (*note Mapfile structure::), showing the status of the areas included in the block requested. A line consisting of the string "done" marks the end of the list. 'u' Update mapfile command. Writes the internal copy of the mapfile to MAPFILE (if it was specified in the command line). If update mapfile fails, you may try to fix the problem, for example deleting some files to make room for MAPFILE, before trying to update it again.  File: ddrescue.info, Node: Fill mode, Next: Generate mode, Prev: Command mode, Up: Top 13 Fill mode ************ When ddrescue is invoked with the option '--fill-mode' it operates in "fill mode", which is different from the default "rescue mode". That is, in "fill mode" ddrescue does not rescue anything. It only fills with data read from INFILE the blocks of OUTFILE whose status character from MAPFILE coincides with one of the type characters specified in the argument to '--fill-mode'. If the argument to '--fill-mode' contains an 'l', ddrescue will write location data (position, sector number, and status) into each sector filled. With bad sectors filled in this way, it should be possible to retry the recovery of important files, as the location of the error is known by looking into the unfinished copy of the file. In fill mode INFILE does not need to be seekable and it may be of any size. If it is too small, the data will be duplicated as many times as necessary to fill the input buffer. If it is too big, only the data needed to fill the input buffer will be read. Then the same data will be written to every cluster or sector to be filled. Note that in fill mode INFILE is always read from position 0. If you specify a '--input-position', it refers to the original INFILE from which MAPFILE was built, and is only used to calculate the offset between input and output positions. Note also that when filling the INFILE of the original rescue run you should not set '--output-position', whereas when filling the OUTFILE of the original rescue run you should keep the original offset between '--input-position' and '--output-position'. The option '--fill-mode' implies '--complete-only'. In fill mode MAPFILE is updated to allow resumability when interrupted or in case of a crash, but as nothing is being rescued MAPFILE is not destroyed. The status line is the only part of MAPFILE that is modified. The fill mode has a number of uses. See the following examples: Example 1: Mark parts of the rescued copy to allow finding them when examined in an hex editor. For example, the following command line fills all blocks marked as '-' (bad-sector) with copies of the string 'BAD-SECTOR ': ddrescue --fill-mode=- <(printf "BAD-SECTOR ") outfile mapfile Example 2: Wipe only the good sectors, leaving the bad sectors alone. This way, the drive will still test bad (i.e., with unreadable sectors). This is the fastest way of wiping a failing drive, and is especially useful when sending the drive back to the manufacturer for warranty replacement. ddrescue --fill-mode=+ --force /dev/zero bad_drive mapfile Example 3: Force the drive to remap the bad sectors, making it usable again. If the drive has only a few bad sectors, and they are not caused by drive age, you can probably just rewrite those sectors, and the drive will reallocate them automatically to new "spare" sectors that it keeps for just this purpose. WARNING! This may not work on your drive. ddrescue --fill-mode=- -f --synchronous /dev/zero bad_drive mapfile Fill mode can also help you to figure out, independently of the file system used, what files are partially or entirely in the bad areas of the disc. Just follow these steps: 1) Copy the damaged drive with ddrescue until finished. Don't use sparse writes. This yields a mapfile containing only finished ('+') and bad-sector ('-') blocks. 2) Fill the bad-sector blocks of the copied drive or image file with a string not present in any file, for example "DEADBEEF". Use '--fill-mode=l-' if you want location data. 3) Mount the copied drive (or the image file, via loopback device) read-only. 4) Grep for the fill string in all the files. Those files containing the string reside (at least partially) in damaged disc areas. Note that if all the damaged areas are in unused space, grep will not find the string in any file, which means that no files are damaged. 5) Take note of the location data of any important files that you want to retry. 6) Unmount the copied drive or image file. 7) Retry the sectors belonging to the important files until they are rescued or until it is clear that they can't be rescued. 8) Optionally fill the bad-sector blocks of the copied drive or image file with zeros to restore the disc image. Example 4: Figure out what files are in the bad areas of the disc. ddrescue -b2048 /dev/cdrom cdimage mapfile printf "DEADBEEF" > tmpfile ddrescue --fill-mode=l- tmpfile cdimage mapfile rm tmpfile mount -t iso9660 -o loop,ro cdimage /mnt/cdimage find /mnt/cdimage -type f -exec grep -l "DEADBEEF" '{}' ';' (note that my_thesis.txt has a bad sector at pos 0x12345000) umount /mnt/cdimage ddrescue -b2048 -i0x12345000 -s2048 -dr9 /dev/cdrom cdimage mapfile ddrescue --fill-mode=- /dev/zero cdimage mapfile mount -t iso9660 -o loop,ro cdimage /mnt/cdimage cp -a /mnt/cdimage/my_thesis.txt /safe/place/my_thesis.txt  File: ddrescue.info, Node: Generate mode, Next: Ddrescuelog, Prev: Fill mode, Up: Top 14 Generate mode **************** When ddrescue is invoked with the option '--generate-mode' it operates in "generate mode", which is different from the default "rescue mode". That is, in "generate mode" ddrescue does not rescue anything. It only tries to generate a MAPFILE for later use. So you didn't read the manual and started ddrescue without a MAPFILE. Now, two days later, your computer crashed and you can't know how much data ddrescue managed to save. And even worse, you can't resume the rescue; you have to restart it from the very beginning. Or maybe you started copying a drive with 'dd conv=noerror,sync' and are now in the same situation described above. In this case, note that you can't use a copy made by dd unless it was invoked with the 'sync' conversion argument. Don't despair (yet). Ddrescue can in some cases generate an approximate MAPFILE, from INFILE and the (partial) copy in OUTFILE, that is almost as good as an exact MAPFILE. It makes this by simply assuming that sectors containing all zeros were not rescued. However, if the destination of the copy was a drive or a partition, (or an existing regular file and truncation was not requested), most probably you will need to restart ddrescue from the very beginning. (This time with a MAPFILE, of course). The reason is that old data may be present in the drive that have not been overwritten yet, and may be thus non-tried but non-zero. For example, if you first tried one of these commands: ddrescue infile outfile or dd if=infile of=outfile conv=noerror,sync then you can generate an approximate mapfile with this command: ddrescue --generate-mode infile outfile mapfile Note that you must keep the original offset between '--input-position' and '--output-position' of the original rescue run.  File: ddrescue.info, Node: Ddrescuelog, Next: Invoking ddrescuelog, Prev: Generate mode, Up: Top 15 Ddrescuelog ************** Ddrescuelog is a tool that manipulates ddrescue mapfiles, shows mapfile contents, converts mapfiles to/from other formats, compares mapfiles, tests rescue status, and can delete a mapfile if the rescue is done. Ddrescuelog operations can be restricted to one or several parts of the mapfile if the domain setting options are used. When performing logic operations (AND, OR, XOR) on mapfiles of different extension, only the blocks present in both files are processed. Here are some examples of how to use ddrescuelog, alone or in combination with other tools. Example 1: Delete the mapfile if the rescue is finished (all data have been recovered without errors left). ddrescue -f /dev/sda /dev/sdb mapfile ddrescuelog -d mapfile Example 2: Rescue two ext2 partitions in /dev/sda to /dev/sdb and repair the file systems using badblock lists generated with ddrescuelog. File system block size is 4096. Note: you do need to partition /dev/sdb beforehand. fdisk /dev/sdb # partition /dev/sdb ddrescue -f /dev/sda1 /dev/sdb1 mapfile1 ddrescue -f /dev/sda2 /dev/sdb2 mapfile2 ddrescuelog -l- -b4096 mapfile1 > badblocks1 ddrescuelog -l- -b4096 mapfile2 > badblocks2 e2fsck -v -f -L badblocks1 /dev/sdb1 e2fsck -v -f -L badblocks2 /dev/sdb2 Example 3: Rescue a whole disc with two ext2 partitions in /dev/sda to /dev/sdb and repair the file systems using badblock lists generated with ddrescuelog. Disc sector size is 512, file system block size is 4096. Arguments to options '-i' and '-s' are the starting positions and sizes of the partitions being rescued. Note: you don't need to partition /dev/sdb beforehand, but if the partition table on /dev/sda is damaged, you'll need to recreate it somehow on /dev/sdb. ddrescue -f /dev/sda /dev/sdb mapfile fdisk /dev/sdb # get partition sizes ddrescuelog -l- -b512 -i63s -o0 -s767457s -b4096 mapfile > badblocks1 ddrescuelog -l- -b512 -i767520s -o0 -s96520s -b4096 mapfile > badblocks2 e2fsck -v -f -L badblocks1 /dev/sdb1 e2fsck -v -f -L badblocks2 /dev/sdb2  File: ddrescue.info, Node: Invoking ddrescuelog, Next: Problems, Prev: Ddrescuelog, Up: Top 16 Invoking ddrescuelog *********************** The format for running ddrescuelog is: ddrescuelog [OPTIONS] MAPFILE Use '-' as MAPFILE to read the mapfile from standard input (also in the options taking a mapfile argument) or to write the mapfile created by '--create-mapfile' to standard output. Ddrescuelog supports the following options: '-h' '--help' Print an informative help message describing the options and exit. '-V' '--version' Print the version number of ddrescuelog on the standard output and exit. This version number should be included in all bug reports. '-a OLD_TYPES,NEW_TYPES' '--change-types=OLD_TYPES,NEW_TYPES' Change the status of every block in the rescue domain from one type in OLD_TYPES to the corresponding type in NEW_TYPES, much like the command 'tr' does, and write the resulting mapfile to standard output. OLD_TYPES and NEW_TYPES are strings of block status characters as defined in the chapter Mapfile structure (*note Mapfile structure::). Blocks whose status is not in OLD_TYPES are left unchanged. If NEW_TYPES is shorter than OLD_TYPES the last type of NEW_TYPES is repeated as many times as necessary. '-A' '--annotate-mapfile' Add comments containing the human-readable positions and sizes of the blocks in MAPFILE which are included in the rescue domain, and write the resulting mapfile to standard output. '-b BYTES' '--block-size=BYTES' Block size used by ddrescuelog. Depending on the requested operation it may be the sector size of the input device, the block size of the rescued file system, etc. Defaults to 512. '-B' '--binary-prefixes' Show units with binary prefixes (powers of 1024). SI prefixes (powers of 1000) are used by default. (See table above, *note Invoking ddrescue::). '-c[TYPE1TYPE2]' '--create-mapfile[=TYPE1TYPE2]' Create a MAPFILE from a list of block numbers read from standard input. Only blocks included in the rescue domain will be added to MAPFILE. TYPE1 and TYPE2 are block status characters as defined in the chapter Mapfile structure (*note Mapfile structure::). TYPE1 sets the type for blocks included in the list, while TYPE2 sets the type for the rest of MAPFILE. If not specified, TYPE1 defaults to '+' and TYPE2 defaults to '-'. '-C[TYPE]' '--complete-mapfile[=TYPE]' Complete a synthetic (user fabricated) MAPFILE by filling the gaps with blocks of type TYPE, and write the completed mapfile to standard output. TYPE is one of the block status characters defined in the chapter Mapfile structure (*note Mapfile structure::). If TYPE is not specified, the gaps are filled with non-tried blocks. All gaps in MAPFILE are filled. Domain options are ignored. '-d' '--delete-if-done' Delete the given MAPFILE if all the blocks in the rescue domain have been successfully recovered. The exit status is 0 if MAPFILE could be deleted, 1 otherwise. '-D' '--done-status' Test if all the blocks in the rescue domain have been successfully recovered. The exit status is 0 if all tested blocks are finished, 1 otherwise. '-f' '--force' Force overwrite of MAPFILE. '-i BYTES' '--input-position=BYTES' Starting position of the rescue domain, in bytes. Defaults to 0. It refers to a position in the original INFILE. '-l TYPES' '--list-blocks=TYPES' Print on standard output the block numbers of the blocks specified as any of TYPES in MAPFILE and included in the rescue domain. TYPES contains one or more of the block status characters defined in the chapter Mapfile structure (*note Mapfile structure::). The list format is one block number per line in decimal, like the output of the badblocks program, so that it can be used as input for e2fsck or other similar filesystem repairing tool. '-L' '--loose-domain' Accept an incomplete synthetic (user fabricated) domain mapfile or compare-as-domain mapfile, and fill the gaps in the list of data blocks with non-tried blocks. The blocks in the mapfile must be strictly ascending and non-overlapping, but they don't need to be contiguous. This option allows making quick edits to a mapfile without all the size calculations involved in making all data blocks contiguous again. '-m FILE' '--domain-mapfile=FILE' Restrict the rescue domain to the blocks marked as finished in the mapfile FILE. '-n' '--invert-mapfile' Invert the types of the blocks in MAPFILE which are included in the rescue domain, and write the resulting mapfile to standard output. Finished blocks ('+') are changed to bad-sector ('-'), all other types are changed to finished. '--invert-mapfile' is equivalent to '--change-types=?*/-+,++++-' '-o BYTES' '--output-position=BYTES' Starting position of the image of the rescue domain in the original OUTFILE, in bytes. Is used by the option '--list-blocks'. Defaults to '--input-position'. '-p FILE' '--compare-mapfile=FILE' Compare the types of the blocks included in the rescue domain. The exit status is 0 if all the blocks tested are the same in both FILE and MAPFILE, 1 otherwise. '-P FILE' '--compare-as-domain=FILE' Compare only the blocks marked as finished in the rescue domain. The exit status is 0 if all the blocks tested are the same in both FILE and MAPFILE, 1 otherwise. Two files comparing equal with this option are equivalent when used as domain mapfiles. '-q' '--quiet' Quiet operation. Suppress all messages. '-s BYTES' '--size=BYTES' Maximum size of the rescue domain in bytes. It refers to a size in the original INFILE. '-t' '--show-status' Print a summary of the contents of each MAPFILE to the standard output. This option allows more than one MAPFILE. If the domain setting options are used, the summary can be restricted to one or several parts of MAPFILE. '-v' '--verbose' Verbose mode. Further -v's (up to 4) increase the verbosity level. '-x FILE' '--xor-mapfile=FILE' Perform a logical XOR (exclusive OR) operation between the finished blocks in FILE and those in MAPFILE, and write the resulting mapfile to standard output. In other words, in the resulting mapfile a block is only shown as finished if it was finished in either of the two input mapfiles but not in both. '-y FILE' '--and-mapfile=FILE' Perform a logical AND operation between the finished blocks in FILE and those in MAPFILE, and write the resulting mapfile to standard output. In other words, in the resulting mapfile a block is only shown as finished if it was finished in both input mapfiles. '-z FILE' '--or-mapfile=FILE' Perform a logical OR operation between the finished blocks in FILE and those in MAPFILE, and write the resulting mapfile to standard output. In other words, in the resulting mapfile a block is shown as finished if it was finished in either of the two input mapfiles. '--shift' Shift the positions of all the blocks in MAPFILE by the offset ('--output-position' - '--input-position'), and write the resulting mapfile to standard output. Either '--input-position' or '--output-position' must be 0. If the offset is positive, a non-tried block is inserted before the first block. Any blocks beyond the end of the rescue domain are removed before performing the shift. Exit status: 0 for a normal exit, 1 for environmental problems (file not found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or invalid input file, 3 for an internal consistency error (eg, bug) which caused ddrescuelog to panic.  File: ddrescue.info, Node: Problems, Next: Concept index, Prev: Invoking ddrescuelog, Up: Top 17 Reporting bugs ***************** There are probably bugs in ddrescue. There are certainly errors and omissions in this manual. If you report them, they will get fixed. If you don't, no one will ever know about them and they will remain unfixed for all eternity, if not longer. If you find a bug in GNU ddrescue, please send electronic mail to . Include the version number, which you can find by running 'ddrescue --version'.  File: ddrescue.info, Node: Concept index, Prev: Problems, Up: Top Concept index ************* [index] * Menu: * algorithm: Algorithm. (line 6) * basic concepts: Basic concepts. (line 6) * bugs: Problems. (line 6) * command mode: Command mode. (line 6) * ddrescuelog: Ddrescuelog. (line 6) * direct disc access: Direct disc access. (line 6) * emergency save: Emergency save. (line 6) * examples: Examples. (line 6) * fill Mode: Fill mode. (line 6) * generate Mode: Generate mode. (line 6) * getting help: Problems. (line 6) * introduction: Introduction. (line 6) * invoking ddrescue: Invoking ddrescue. (line 6) * invoking ddrescuelog: Invoking ddrescuelog. (line 6) * mapfile structure: Mapfile structure. (line 6) * optical media: Optical media. (line 6) * options: Invoking ddrescue. (line 6) * output: Output. (line 6) * raw devices: Direct disc access. (line 6) * usage: Invoking ddrescue. (line 6) * using ddrescue safely: Important advice. (line 6) * version: Invoking ddrescue. (line 6)  Tag Table: Node: Top201 Node: Introduction1568 Node: Basic concepts4275 Node: Important advice6533 Node: Algorithm7610 Node: Output13378 Node: Invoking ddrescue17669 Ref: --min-read-rate18751 Ref: --max-bad-areas22186 Ref: --max-error-rate22445 Ref: --domain-mapfile27749 Ref: --mapfile-interval37953 Node: Mapfile structure42154 Node: Emergency save45335 Node: Optical media46792 Ref: lziprecover-example49999 Node: Examples50776 Node: Direct disc access56384 Node: Command mode58610 Node: Fill mode61030 Node: Generate mode66054 Node: Ddrescuelog67972 Node: Invoking ddrescuelog70266 Node: Problems78200 Node: Concept index78757  End Tag Table  Local Variables: coding: iso-8859-15 End: