We could also do this with the sync command.Īnother popular option is status=progress, which provides visual progress updates as the disk image is copied. Finally, conv=sync tells dd that it must synchronize the data and metadata reads and writes when it completes.If we omit this, it will default to 512 bytes and take significantly longer. The block size bs option copies in one-megabyte chunks.Again, we make sure this is correct, or we could knock out our system! and the output file of the option pointing to our disk block device.with the input file if option pointing to the disk image file we’ve downloaded (FreeBSD 12.1).Piece by piece, here is what we’re doing with that command: To be sure we’re not writing all over something we would not want to lose, we’ll double and triple-check that we have the correct device for the “of” option: # dd if= of=/dev/sdc bs=1M conv=sync We run the dd command to copy raw data from our image file to the block device. This might be Linux or FreeBSD or even something else. Next, we get the ISO disk image file we want to copy. Remember that this will completely wipe out our USB disk! So, let’s first double-check that we’ve backed up anything we want to keep from there. ( /dev/sdc1 refers to the first partition, but we want to take over the whole disk.) So, we know we want to write our disk image over /dev/sdc. (In the GNOME GUI, it’s simply referred to as Disks): Or if it’s available, we can use the gnome-disks tool. If it’s not mounted but has been successfully plugged in, lsblk will show us the block devices: $ lsblk -e7 ![]() ![]() Here, we see that our USB drive is device /dev/sdc, and its first partition is currently mounted under /media/a/ESD-USB/. If our system has automatically mounted our USB drive, we’ll see it with df: $ df -hįilesystem Size Used Avail Use% Mounted on Everything there would be gone, replaced by what was on sda. This would slowly transfer everything from one disk to another, obliterating everything on the out file disk sdb. If we had two identical disks that Linux referred to as /dev/sda and /dev/sdb, we could make sdb a duplicate of sda using the command: dd if=/dev/sda of=/dev/sdb We could duplicate everything from one disk to another, including the partition table, the boot sector, and the access times of files in the filesystem - in fact, everything on a raw data level. If we want dd to get its input or output from a disk device or special device (such as /dev/urandom or /dev/zero), we use the options if and of (input and output files, respectively). Of course, we usually want to leave that to our filesystem. Programs can write and read to them, given sufficient permissions. This concept gives birth to the /dev/ directory’s sd* files, which represent our raw disks. It also relies on the Unix model that most things can be treated as files that is, they need to be opened, can be read from, written to, and then closed.
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