Creating a hard disk image using the dd utility. How to write an iso image of a distribution to a flash drive from the terminal in Ununtu and derivatives The dd utility used by the FBI to copy files

Quite often, system administrators need to copy various binary data. For example, sometimes you may need to make a backup hard drive, create an empty file filled with zeros to organize swap space or other virtual file system.

To solve all these problems, the dd linux utility is used, which simply copies data from one place to another at the binary level. It can copy a CD/DVD disc, a section on a disc, or even an entire HDD. In this article we will look at what the linux dd command is, its main options and parameters, and how to use it.

First you need to understand how the dd command works and what it does. In fact, this is an analogue of the utility only for block data. The utility simply transfers one block of data of the specified size from one place to another. Since everything, including devices, is considered a file in Linux, you can transfer devices to files and vice versa.

Using various utility options, you can influence the block size, and this, in turn, already affects the speed of the program. Next we will look at the main options of the utility and its capabilities.

dd command

The syntax of the utility is quite unusual, but at the same time very simple, once you remember and get used to it:

$dd if= copy_source of= destination options

Using the if parameter, you need to specify the source from which the blocks will be copied, this can be a device, for example, /dev/sda or a file - disk.img. Next, using the of parameter, you need to specify the destination device or file. Other parameters have the same syntax as if and of.

Now let's look at the additional options:

• bs- indicates how many bytes to read and write at a time;
• CBS- how many bytes need to be written at a time;
• count- copy the specified number of blocks, the size of one block is indicated in the bs parameter;
• conv- apply filters to the data stream;
• ibs- read the specified number of bytes at a time;
• obs- write the specified number of bytes at a time;
• seek- skip the specified number of bytes at the beginning of the reading device;
• skip- skip the specified number of bytes at the beginning of the output device;
• status- indicates how detailed the conclusion should be;
• iflag, oflag- allows you to set additional operation flags for the input and output device, the main ones: nocache, nofollow.

These were all the basic options you might need. Now let's move closer to practice and look at several examples of how to use the dd linux utility.

How to use dd?

Regular users use the dd command most often to create images DVDs or CD. For example, to save a disk image to a file, you can use the following command:

sudo dd if=/dev/sr0 of=~/CD.iso bs=2048 conv=noerror

The noerror filter allows you to disable response to errors. Next, you can create an image of the hard drive or partition on it and save this image to disk. Just be careful not to save to the same hard drive or partition, so as not to cause recursion:

dd if=/dev/sda of=~/disk.img

A file named disk1.img will be created in your home folder, which in the future can be deployed and restored to the damaged system. To write an image to a hard drive or partition, just swap the device addresses:

dd if=~/disk.img of=/dev/sda

A very important and useful option is bs. It allows you to greatly influence the speed of the utility. This parameter allows you to set the size of one block when transferring data. Here you need to specify a digital value with one of these format modifiers:

• With- one character;
• b- 512 bytes;
• kB- 1000 bytes;
• K- 1024 bytes;
• M.B.- 1000 kilobytes;
• M- 1024 kilobytes;
• G.B.- 1000 megabytes;
• G- 1024 megabytes.

The dd linux command uses just such a system, it is complex, but there is no escape from it. It will have to be understood and remembered. For example, 2b is 1 kilobyte, and 1k is also 1 kilobyte, 1M is 1 megabyte. By default, the utility uses a block size of 512 bytes. For example, to speed up disk copying, you can take blocks of 5 megabytes in size. To do this, use the following command:

dd if=/dev/sda of=~/disk.img bs=5M

The next parameter is count. Using it you can specify how many blocks need to be copied. For example, we can create a 512 megabyte file by filling it with zeros from /dev/zero or random numbers from /dev/random:

sudo dd if=/dev/zero of=file.img bs=1M count=512

Please note that this parameter does not indicate the size in megabytes, but only the number of blocks. Therefore, if you specify a block size of 1b, then you only need to take two blocks to create a 1KB file. This option can also be used to backup the MBR partition table. To do this, copy the first 512 bytes of the hard drive to a file:

sudo dd if=/dev/sda of=mbr.img bs=1b count=1

To restore, use the usual command to deploy the image to disk.

If the disk image is too large, you can redirect all output to the non-standard output stream of the gzip utility:

dd if =/dev/sda2 | bzip2 disk.img.bz2

You can also use the dd linux utility to copy files, although this is not its intended purpose:

dd if=/home/sergiy/test.txt of=/home/sergiy/test1.txt

As you know, the linux dd command writes data to disk directly in binary form, which means that zeros and ones are written. They override what was previously placed on the recording device. Therefore, to erase a disk, you can simply fill it with zeros from /dev/zero.

sudo dd if=/dev/zero of=/dev/sdb

Using dd this way results in the entire disk being completely erased.

conclusions

In this article we looked at how to use dd linux, what this utility can be used for and how useful it can be. It's an almost indispensable tool. system administrator, because with it you can do backups the whole system. And now you know how. If you have any questions, ask in the comments!

Using the dd utility, we will create an image of a flash drive with archiving of free space. Backup image will come in handy if the original suddenly stops working with important information. For example, a flash drive with private keys electronic signatures management of the organization. So, we have a 4GB flash drive /dev/sdd, the information on which takes up about 90MB.
du - sh / run / media / aleksey / Transcend

All commands are executed on behalf of the user root. Or in the corresponding distributions add before the commands sudo.
fdisk - l /dev/sdd

Disk /dev/sdd: 3.7 GiB, 3904897024 bytes, 7626752 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0xc653eaa4 Device Boot Start End Sectors Size Id Type /dev/sdd1 2048 7628543 7626496 3.7G b W95 FAT32

By creating a simple image with the command
dd if = /dev/sdd of = sdd . iso bs = 4M conv = noerror,
we condemn ourselves to storing a 4GB file. What if the flash drive had a capacity of 64GB? And not alone? A regular archiver will help us solve this problem, let’s take a standard one gzip.
dd if=/dev/sdd bs=4M conv=noerror | gzip - c > sdd . iso. zip
where is the key -c allows you to work with standard output.
After completing the work, let's look at the resulting file. ls - al sdd*

The resulting file is approximately 25MB in size. Real savings on disk space even compared to a 4GB file!
To restore a flash drive from an image, use reverse order commands
gunzip - c sdd . iso. zip | dd of = /dev/sdd conv = noerror bs = 4M

You can also archive images hard drives, where the volumes are an order of magnitude larger.

By the way! To make the process clearer, due to dd not having its own progress bar, I suggest using a small utility progress- Coreutils Progress Viewer. Installing it on Fedora is not difficult.
dnf install progress
For other distributions, the required repository can be found at https://pkgs.org/download/progress.
By installing and running the utility with the command watch progress in the second terminal (in the first we have an archiver and dd running) on ​​behalf of the same user, we will see something like this.

man progress will show you various useful keys of this utility.

    Rufus- free software with open source code for formatting removable USB storage media and creating bootable disks with various operating systems. The program is easy to use, high speed work and supports a multilingual interface.

You can download the program on the developer's website. The page contains links to download the standard version Rufus, and portable Rufus portable, which do not differ in anything except the name of the executable file and the location where the settings are stored. The program settings include the language used and settings for checking for updates. The standard version stores these settings in the registry, while the portable version stores these settings in a file rufus.ini program directory. Rufus does not require installation on the system - just download the executable file and run it. The program interface is very simple:

Overall, the program Rufus is not something unique in the field of tools for creating bootable media and its main advantage is ease of use. In order to create a bootable flash drive with its help, it is enough to have the original image of the bootable system and be able to click on the “Start” button. All selected parameters and settings, by default, are already designed for using the program to work on a standard computer.

Easiest and most convenient to use Rufus to create a bootable flash drive (bootable USB drive) from installation ISO images Windows drives or Linux, as well as disks disaster recovery systems and diagnostic tools.

When creating a bootable Windows flash drive, you just need to select the device to be written to and the bootable ISO image file. The program will set other parameters itself.

If you do not have an ISO image file, you can create one from a physical CD (or from a set of distribution files) using CD/DVD burning programs such as the well-known Nero, Alcohol, or the free CDBurnerXP or ImgBurn.

The procedure for creating a bootable USB flash drive with Windows is as follows: