> For the complete documentation index, see [llms.txt](https://evansastre.gitbook.io/srvops/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://evansastre.gitbook.io/srvops/linux/linux-fundamental/disk-management-1/dd.md). # dd ``` # dd [bs=][cbs=][conv=][count=][ibs=][if=][obs=][of=][seek=][skip=][--help][--version] # Dd can read data from standard input or file, convert data according to the specified format, and then output to file, device or standard output. bs= Set ibs (input) and obs (output) to the specified number of bytes. cbs= When converting, only the specified number of bytes is converted at a time. conv= Specifies how the file is converted. conv = ASCII Converts the EBCDIC code to an ASCIl code. conv = ebcdic Converts the ASCIl code to an EBCDIC code. conv = ibm Converts the ASCIl code to an alternate EBCDIC code. conv = block converts the change bits to fixed characters. conv = ublock converts a fixed bit into a variable bit. conv = ucase converts letters from lowercase to uppercase. conv = lcase converts letters from uppercase to lowercase. conv = notrunc does not truncate the output file. conv = swab exchanges each pair of input bytes. conv = noerror Does not stop processing when an error occurs. conv = sync adjusts the size of each input record to the size of ibs (filled with NUL). count= Reads only the specified number of blocks. ibs= The number of bytes per read. if= Read from file. obs= The number of bytes per output. of= Output to file. seek= Skips the specified number of blocks at the beginning of output. skip= Skips the specified number of blocks at the beginning of reading. --help help. --version display version information ``` ## Examples ``` #1 whole disk data backup and recovery #Backup: dd if=/dev/hdx of=/dev/hdy #Back up the local /dev/hdx disk to /dev/hdy dd if=/dev/hdx of=/path/to/image #Back up /dev/hdx full disk data to the image file of the specified path dd if=/dev/hdx | gzip >/path/to/image.gz #Back up /dev/hdx full disk data and compress it with gzip tool and save it to the specified path #restore: dd if=/path/to/image of=/dev/hdx #Restore the backup file to the specified disk gzip -dc /path/to/image.gz | dd of=/dev/hdx #Restore the compressed backup file to the specified disk #2. Use netcat remote backup dd if=/dev/hda bs=16065b | netcat 1234 #Execute this command on the source host to back up /dev/hda netcat -l -p 1234 | dd of=/dev/hdc bs=16065b #Execute this command on the destination host to receive data and write to /dev/hdc netcat -l -p 1234 | bzip2 > partition.img                 netcat -l -p 1234 | gzip> partition.img #The above two instructions are the changes of the destination host command, respectively, using bzip2 gzip to compress the data, and save the backup file in the current directory. #3. Backup MBR #Backup: dd if=/dev/hdx of=/path/to/image count=1 bs=512 #Back up the 512Byte size MBR information from the disk to the specified file. #restore: dd if=/path/to/image of=/dev/hdx #Write the backed up MBR information to the beginning of the disk #4. Backup floppy disk dd if=/dev/fd0 of=disk.img count=1 bs=1440k #Back up the floppy drive data to the disk.img file in the current directory #5. Copy the memory data to the hard disk dd if=/dev/mem of=/root/mem.bin bs=1024 #Copy the data in the memory to the mem.bin file in the root directory. #6. Copy the iso image from the CD dd if=/dev/cdrom of=/root/cd.iso #Copy the disc data to the root folder and save it as a cd.iso file. #7. Increase the Swap partition file size dd if=/dev/zero of=/swapfile bs=1024 count=262144 #Create a file large enough (256M here) mkswap /swapfile #Turn this file into a swap file swapon /swapfile #Enable this swap file /swapfile swap swap defaults 0 0 #Automatically load the swap file every time you turn it on, you need to add a line to the /etc/fstab file. #8. Destroy disk data dd if=/dev/urandom of=/dev/hda1 #Fill the hard drive with random data and use it to destroy data where necessary. #After doing this, /dev/hda1 will not mount, and the create and copy operations will not be performed. #9. Get the most appropriate block size #dd if=/dev/zero bs=1024 count=1000000 of=/root/1Gb.file #dd if=/dev/zero bs=2048 count=500000 of=/root/1Gb.file #dd if=/dev/zero bs=4096 count=250000 of=/root/1Gb.file #dd if=/dev/zero bs=8192 count=125000 of=/root/1Gb.file #By comparing the command execution time displayed in the dd command output, you can determine the optimal block size size of the system.                 #10. Test hard disk read and write speed dd if=/root/1Gb.file bs=64k | dd of=/dev/null dd if=/dev/zero of=/root/1Gb.file bs=1024 count=1000000 #The read/write speed of the test hard disk can be calculated by the execution time of the last two commands. #11. Repair the hard disk dd if=/dev/sda of=/dev/sda #When the hard disk is left unused for a long time (for example, 1, 2 years), #a magnetic flux point is generated on the disk. When the head reads these areas, #it encounters difficulties and may cause I/O errors. #When this situation affects the first sector of the hard disk, #it may cause the hard disk to be scrapped. #The above command has the potential to bring these data back to life. #And this process is safe and efficient. ``` --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://evansastre.gitbook.io/srvops/linux/linux-fundamental/disk-management-1/dd.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.