GNU ddrescue

https://www.gnu.org/software/ddrescue/manual/
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GNU ddrescue is a data recovery tool that copies data from one file or block device to another,...
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### Direct disc access with raw device (Example 1 alternative)

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Alternative to --idirect: bind a raw device with the raw command, use -C for raw access, then unbind the raw device. Requires sector size set correctly and may need --size or --complete-only if the raw device size cannot be determined.

```shell
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
```

--------------------------------

### Direct disc access with --idirect (Example 1)

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

First pass uses normal cached reads (-n), second pass uses direct disc access (-d) with -r3 to recover good sectors inside failed blocks. Then checks and mounts the rescued filesystem.

```shell
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 ddrescue mapfile

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Shows the format of a ddrescue mapfile, including heading comments, status line, and data block list. The status line contains the current position, status character, and current pass. Data block lines contain position, size, and status character.

```plaintext
     # Mapfile. Created by GNU ddrescue version 1.30
     # 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  ?
```

--------------------------------

### Rescue and recover a partition with ddrescue and lziprecover

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Shows a complete workflow: rescue a partition with ddrescue, mount the image, copy a backup file, verify it with lzip, and repair it with lziprecover using a reference file. The output shows a decoder error and the successful reproduction of the bad area.

```shell
ddrescue -b4096 -r10 /dev/sdc1 hdimage mapfile
mount -o loop,ro hdimage /mnt/hdimage
cp /mnt/hdimage/backup.tar.lz backup.tar.lz
umount /mnt/hdimage
lzip -t backup.tar.lz
  backup.tar.lz: Decoder error at pos 1_020_530
lziprecover -vv -e --reference-file=old_backup.tar backup.tar.lz
Reproducing bad area in member 1 of 1
  (begin = 1_019_904, size = 4096, value = 0x00)
  (master mpos = 1_019_903, dpos = 5_857_954)
warning: old_backup.tar: Partial match found at offset 5_743_778, len 9546
Reference data may be mixed with other data.
Trying level -9
  Reproducing position 1_015_808
Member reproduced successfully.
Copy of input file reproduced successfully.
```

--------------------------------

### Rescue partition and rest of drive with --same-file

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Rescue a partition, shift the mapfile, then use --same-file to copy the partition image within the same file, and finally rescue the rest of the drive.

```shell
ddrescue /dev/sda1 hdimage mapfile             # rescue partition
ddrescuelog --shift -o<offset> mapfile > shifted_mapfile
ddrescue --same-file -o<offset> -s<size> --reverse hdimage hdimage
ddrescue /dev/sda hdimage shifted_mapfile      # rescue rest of drive
```

--------------------------------

### ddrescue and ddrescuelog: Single disk rescue with partition badblocks

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Rescue a whole disk, then use ddrescuelog with sector offsets to generate badblocks lists for each partition and run e2fsck.

```shell
     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

```

--------------------------------

### Basic ddrescue copy with fdisk and e2fsck

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Copy a failing drive /dev/sda to /dev/sdb using ddrescue with -f and -r3, then repair the partition table with fdisk and check the filesystems with e2fsck.

```shell
ddrescue -f -r3 /dev/sda /dev/sdb mapfile
fdisk /dev/sdb
e2fsck -v -f /dev/sdb1
e2fsck -v -f /dev/sdb2
```

--------------------------------

### Rescue a partition with ddrescue and mount

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Rescue a single partition /dev/sda2 to /dev/sdb2 using a two-pass ddrescue approach, then check the filesystem and mount it read-only to recover files.

```shell
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)
```

--------------------------------

### Resume after drive freeze with -n and -d -r3

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

When /dev/sda1 fails during a copy, restart the drive and repeat the command until it succeeds, then finish with direct access and retries.

```shell
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
```

--------------------------------

### ddrescuelog: Basic invocation format

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

The general command-line format for running ddrescuelog with options and a mapfile argument.

```shell
     ddrescuelog [options] mapfile

```

--------------------------------

### ddrescue and ddrescuelog: Partition rescue with badblocks for e2fsck

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Rescue two partitions separately, generate badblocks lists with ddrescuelog, and feed them to e2fsck to mark bad sectors.

```shell
     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

```

--------------------------------

### Recover a file from damaged CD-ROM using lziprecover

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Complete workflow to rescue a specific file (backup.tar.lz) from two copies of a damaged CD-ROM. It rescues each CD image, mounts it, copies the file, then uses lziprecover to merge the two rescued files and verify the result. The expected output 'Input files merged successfully.' and 'backup.tar.lz: ok' are shown.

```shell
     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 -v -m -o backup.tar.lz rescued1.tar.lz rescued2.tar.lz
       Input files merged successfully.
     lziprecover -tv backup.tar.lz
       backup.tar.lz: ok

```

--------------------------------

### Resume after drive freeze with -A and -O

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

When /dev/sda1 fails during a copy, restart the drive and resume with -A and -O at the position where it stopped, then finish with direct access and retries.

```shell
ddrescue -n /dev/sda1 hdimage mapfile          # /dev/sda1 fails here
  (restart /dev/sda or reboot computer)
ddrescue -n -A -i<pos> -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. <pos> is the position where the drive stopped responding)
ddrescue -d -r3 /dev/sda1 hdimage mapfile
```

--------------------------------

### Recover from destination drive failure with mapfile

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

When /dev/sdb fails during a copy, use the mapfile to continue copying from the failed destination to a new drive /dev/sdc, then finish the rescue with retries.

```shell
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
```

--------------------------------

### Recover files from rescued image with lziprecover

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Rescue a partition with ddrescue, mount the image, copy the photos and FEC files, then use lziprecover with --fec-file to repair damaged files.

```shell
ddrescue -b4096 -r10 /dev/sdc1 hdimage mapfile
mount -o loop,ro hdimage /mnt/hdimage
cp -a /mnt/hdimage/photos photos
cp -a /mnt/hdimage/photos-fec photos-fec
umount /mnt/hdimage
lziprecover -v -Fr --fec-file=photos-fec/ photos/*
  (Check and rename repaired files. They are named photos/*_fixed)
```

--------------------------------

### Initial rescue commands without mapfile

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Commands that may be used without a mapfile, leading to the need for generate mode. The dd command requires the 'sync' conversion argument for generate mode to work.

```shell
ddrescue infile outfile
or
dd if=infile of=outfile conv=noerror,sync
```

--------------------------------

### Repair damaged lzip backup with lziprecover

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Rescue a backup.tar.lz file, verify it with lzip, and use lziprecover --dump=tdata to extract and repair the damaged data using FEC.

```shell
ddrescue -b4096 -r10 /dev/sdc1 hdimage mapfile
mount -o loop,ro hdimage /mnt/hdimage
cp /mnt/hdimage/backup.tar.lz backup.tar.lz
umount /mnt/hdimage
lzip -t backup.tar.lz
  backup.tar.lz: Decoder error at pos 1_020_530
lziprecover --dump=tdata backup.tar.lz | \
  lziprecover -v -Fr --fec-file=- backup.tar.lz
```

--------------------------------

### ddrescue command syntax

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Shows the general command-line format for ddrescue. infile and outfile may be files, devices, or partitions; mapfile is a regular file that ddrescue creates if it does not exist. Always use a mapfile to allow resuming a rescue.

```bash
ddrescue [options] infile outfile [mapfile]
```

--------------------------------

### Rescue CD-ROM using USB drive and two computers

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Two-pass ddrescue sequence storing the image and mapfile on a USB drive mounted at /mnt/mem. After the first pass, the USB drive and CD-ROM are moved to a second computer, then the second pass is run there. If the bad-sector size is zero, the image is complete.

```shell
     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)

```

--------------------------------

### Rescue whole drive after partition table failure

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

When the partition table fails during a partition rescue, use ddrescuelog to shift the mapfile and then rescue the whole drive with the shifted mapfile.

```shell
ddrescue /dev/sda1 hdimage mapfile       # partition table fails here
ddrescuelog --shift -o<offset> mapfile > shifted_mapfile
ddrescue -i<offset> -o0 -s<size> /dev/sda hdimage shifted_mapfile
```

--------------------------------

### Rescue key disc areas with ddrescue mapfile

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Rescues two specific areas of the disc (30GiB offset with 10GiB size, and 230GiB offset with 5GiB size) using the same mapfile, continuing the multi-command rescue workflow.

```shell
     ddrescue -i30GiB -s10GiB /dev/sdc hdimage mapfile
     ddrescue -i230GiB -s5GiB /dev/sdc hdimage mapfile

```

--------------------------------

### Fill non-finished areas with 'NON-RESCUED-SECTOR' string

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

Fills all non-finished areas in the destination file with copies of the string 'NON-RESCUED-SECTOR '. Uses --fill-mode='?*/-' to specify the type characters for non-finished areas.

```bash
ddrescue --fill-mode='?*/-' <(printf "NON-RESCUED-SECTOR ") outfile mapfile
```

--------------------------------

### Rescue most important part of disc first with ddrescue mapfile

Source: https://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html

First command copies the first 50MiB without direct disc access. Second command retries the same area with direct access and up to 3 retry passes, using the same mapfile to avoid recopying.

```shell
     ddrescue -i0 -s50MiB /dev/sdc hdimage mapfile
     ddrescue -i0 -s1MiB -d -r3 /dev/sdc hdimage mapfile

```
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