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This article is about how to use the dd command in Linux. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

Dd

After actual measurement, the fastest way to back up two disks directly under Linux is to use

Do not exceed 5000k that can be increased under dd if=/dev/sda of=/dev/sdb bs=30000k% IDE environment under 30m SATA environment.

The hard disk mirror backup of 40g is completed in 25 minutes and starts smoothly.

1 disk free space cleared # dd if=/dev/zero of=/tmp/delete.me bs=8M; rm delete.me2 make image # dd if=/dev/sdb conv=sync,noerror bs=64K | gzip-c > ~ / mybackup.img.gz3 save partition format # fdisk-l / dev/sdb > ~ / sdb_fdisk.info4 restore method # gunzip-c ~ / mybackup.img.gz | dd of=/dev/sdb conv=sync,noerror bs=64K

Use the linux command dd to create files of a certain size.

Linux create file command: dd command

Copies the specified input file to the specified output file, and the format can be converted during the copy process. Syntax:

CODE: [Copy to clipboard] dd (option)

QUOTE:

If = enter the file (or device name).

Of = output file (or device name).

Ibs = bytes reads bytes bytes at a time, that is, the number of bytes read into the buffer.

Skip = blocks skips the ibs*blocks block at the beginning of the read-in buffer.

Obs = bytes writes bytes bytes at a time, that is, the number of bytes written to the buffer.

Bs = bytes also sets the number of bytes in the read / write buffer (equal to setting obs and obs).

Cbs = bytes converts bytes bytes at once.

Count = blocks copies only the input blocks blocks.

Conv = ASCII converts EBCDIC codes to ASCII codes.

Conv = ebcdic converts ASCII codes to EBCDIC codes.

Conv = ibm converts ASCII codes to alternate EBCDIC codes.

Conv = blick converts variable bits to fixed characters.

Conv = ublock converts the fixtures into motions.

Conv = ucase changes letters from lowercase to uppercase.

Conv = lcase changes letters from uppercase to lowercase.

Conv = notrunc does not truncate the output file.

Conv = swab swaps each pair of input bytes.

Conv = noerror does not stop processing when there is an error.

Conv = sync adjusts the size of each input record to the size of ibs (filled with ibs).

Fdformat command

Low-level formatted floppy disk.

Example:

Create an empty file of 100m

Dd if=/dev/zero of=hello.txt bs=100M count=1

The above is the use of the linux create file command: dd.

two。 Case analysis

2.1. Data backup and recovery

2.1.1 full disk data backup and recovery

Backup

Back up the local / dev/hdx entire disk to / dev/hdy: dd if=/dev/hdx of=/dev/hdy

Back up the full / dev/hdx data to the image file in the specified path: dd if=/dev/hdx of=/path/to/image

Back up / dev/hdx the whole data, compress it with gzip tool and save it to the specified path: dd if=/dev/hdx | gzip

> / path/to/image.gz

Restore

Restore backup files to the specified disk: dd if=/path/to/image of=/dev/hdx

Restore the compressed backup files to the specified disk: gzip-dc / path/to/image.gz | dd of=/dev/hdx

2.1.2. Remote backup with netcat

Execute this command on the source host to back up / dev/hda:dd if=/dev/hda bs=16065b | netcat

1234 execute this command on the destination host to receive data and write / dev/hdc:netcat-l-p 1234 | dd of=/dev/hdc

Bs=16065b

The following two instructions are changes in the destination host instructions that use bzip2 gzip to compress the data and save the backup file in the

Front directory:

Netcat-l-p 1234 | bzip2 > partition.img

Netcat-l-p 1234 | gzip > partition.img

2.1.3. Backup MBR

Backup:

Backup the MBR information of the 512Byte size at the beginning of the disk to the specified file: dd if=/dev/hdx of=/path/to/image

Count=1 bs=512

Restore:

Write the backup MBR information to the beginning of the disk: dd if=/path/to/image of=/dev/hdx

2.1.4. Backup floppy disk

Back up the floppy drive data to the disk.img file in the current directory: dd if=/dev/fd0 of=disk.img count=1 bs=1440k

2.1.5. Copy memory data to hard disk

Copy the data in memory to the mem.bin file in the root directory: dd if=/dev/mem of=/root/mem.bin

Bs=1024

2.1.6. Copy an iso image from a CD

Copy the CD data to the root folder and save it as a cd.iso file: dd if=/dev/cdrom of=/root/cd.iso

2.2. Increase Swap partition file size

Create a file large enough (256m in this case): dd if=/dev/zero of=/swapfile bs=1024 count=262144

Change this file to a swap file: mkswap / swapfile

Enable the swap file: swapon / swapfile

To load the swap file automatically every time you boot, you need to add a line to the / etc/fstab file: / swapfile swap

Swap defaults 0 0

2.3. Destroy disk data

Fill the hard drive with random data: dd if=/dev/urandom of=/dev/hda1

It can be used to destroy data in some necessary situations. After performing this operation, / dev/hda1 will not be able to mount, create and copy operations

Unable to execute.

2.4 disk Management

2.4.1. Get the most appropriate block size

By comparing the command execution time shown in the dd instruction output, you can determine the best block size size for the system:

Dd if=/dev/zero bs=1024 count=1000000 of=/root/1Gb.filedd 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

2.4.2 Test the read and write speed of the hard disk

The read / write speed of the test hard disk can be calculated from the execution time of the two command outputs:

Dd if=/root/1Gb.file bs=64k | dd of=/dev/null

Hdd if=/dev/zero of=/root/1Gb.file bs=1024 count=1000000

2.4.3. Repair hard disk

When the hard drive is not in use for a long time (such as a year or two), magnetic flux point will be generated on the disk. When the head reads

Difficulties can be encountered in these areas and may result in an Imax O error. When this situation affects the first sector of the hard disk, it may result in

The hard drive is scrapped. The following command has the potential to bring this data back to life. And the process is safe and efficient.

Dd if=/dev/sda of=/dev/sda

Thank you for reading! This is the end of the article on "how to use dd commands in Linux". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

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