#Dev dd sex code
The first 440 bytes contain the bootstrap code (boot loader).The MBR is stored in the the first 512 bytes of the disk. You can also use a backup to copy the same partition layout to numerous drives.
If one wants to replace offset 0x123AB of a file with the FF C0 14 hexadecimal sequence, this can be done with the command line: # printf '\xff\xc0\x14' | dd seek=$((0x123AB)) conv=notrunc bs=1 of= /path/to/file Backup and restore MBRīefore making changes to a disk, you may want to backup the partition table and partition scheme of the drive. # cat /path/to/* | gunzip -c | dd of=/dev/sda When the image has been split, use the following instead:
For large disks, this can potentially save hours.
#Dev dd sex install
In order to leverage multicore compression and create a disk image more quickly, one could for instance install the pigz package, and simply replace the gzip -c command above with pigz -c. Tip: gzip is only able to compress data using a single CPU core, which leads to a data throughput considerably lower than the write speeds on modern storage. The most important of which is the cylinder size. # dd if=/dev/sda conv=sync,noerror bs=64K | gzip -c | ssh dd of=įinally, save extra information about the drive geometry necessary in order to interpret the partition table stored within the image. If there is not enough disk space locally, you may send the image through ssh: # dd if=/dev/sda conv=sync,noerror bs=64K | gzip -c | split -a3 -b2G - /path/to/ when the resulting files will be stored on a FAT32 file system) split the disk image into multiple parts (see also split(1)): # dd if=/dev/sda conv=sync,noerror bs=64K | gzip -c > /path/to/ Then mount the external hard drive and backup the drive: See fdisk#Backup and restore partition table or gdisk#Backup and restore partition table.īoot from a live medium and make sure no partitions are mounted from the source hard drive. To notify of changes without rebooting, use a utility like partprobe (part of GNU Parted). Partition table changes from dd are not registered by the kernel.For swap partitions, use mkswap /dev/sd XY instead. To regain unique UUIDs of an ext2/3/4 filesystem, use tune2fs /dev/sd XY -U random on every partition.a single 512-byte read error will mess up the whole 64 KiB output block. But keep in mind that read errors on the source disk will end up as block errors on the destination disk, i.e. For example, changing bs from 512 to 64K changed copying speed from 35 MB/s to 120 MB/s on a simple Celeron 2.7 GHz system. If you are positive that your disk does not contain any errors, you could proceed using a larger block size, which will increase the speed of your copying several fold. This means, for a disk, that effectively the whole 1 MiB would become messed up because of a single 512 byte read error in the beginning of the read: 12ERROR89 would become 128900000 instead of 120000089. dd will, according to documentation, fill up the OBS to IBS size after completing its read, which means adding zeroes at the end of the block. Many people seem to think that dd will "fill up read errors with zeroes" if you use the noerror,sync options, but this is not what happens. But if a read error occurs, things will go wrong. Normally, if your block size is, say, 1 MiB, dd will read 1024×1024 bytes and write as many bytes. When you set bs, you effectively set both IBS and OBS. The dd utility technically has an "input block size" (IBS) and an "output block size" (OBS). Note: The block size you specify influences how read errors are handled. status=progress shows periodic transfer statistics which can be used to estimate when the operation may be complete.sync fills input blocks with zeroes if there were any read errors, so data offsets stay in sync.Default behavior for dd is to halt at any error. noerror instructs dd to continue operation, ignoring all read errors.See and for details and to figure out the best bs value for your use case. Also, please read the warning below, because there is more to this than just "block sizes" -it also influences how read errors propagate. Defaults to 512 bytes, which is the "classic" block size for hard drives since the early 1980s, but is not the most convenient. This will clone the entire drive, including the MBR (and therefore bootloader), all partitions, UUIDs, and data. # dd if=/dev/sda of=/dev/sdb bs=64K conv=noerror,sync status=progress Cloning an entire hard diskįrom physical disk /dev/sda to physical disk /dev/sdb: Note: Be careful that if the output partition of= ( sdb1 in the example) does not exist, dd will create a file with this name and will start filling up your root file system.
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