Apr 13, 2012 · These options of dd make it indispensable for fine grained data manipulation whereas cat* can only operate on whole file objects, devices or streams. *As noted by Gilles in the comments, it is possible to combine cat with other tools to isolate parts of something, but cat still operates on the whole object.

Of course you can use cat or cp. But dd has more options such as only backup/restore the bootsector or copy a limited amount of random data from /dev/random. Wikipedia has a more detailed description of different use cases.

dd has an unusual command line syntax, so explaining how it works gives more of an opportunity to shine by explaining something that just writing cat /dev/sr0. Using dd with a large buffer size can have better performance, but it is not always the case (see some benchmarks on Linux). A major risk with dd is that it can silently skip some data.

Jul 5, 2018 · dd copies exactly count blocks of bs bytes, or 2880*512 bytes in total in this case (but see below).That will truncate or pad the concatenation of the two files to a fixed size (since /dev/zero gives as many zero bytes as required). 1440 kB is looks like the size of a 3.5" HD floppy disk, so perhaps someone wanted to make images that fit the floppy exactly.

Dec 11, 2015 · Here it says that when using dd through dm-crypt to overwrite a block device, only the default dd block size should be used because dm-crypt's block size is the same (512 bytes), and increasing dd's block size might prevent the final blocks from being written to. Does this also apply to openssl (in Linux)?

Apr 13, 2017 · From reading this, it seems that when copying data to a different hard drive, cat automatically uses the optimum block size (or very near it). I wonder how it determines the optimum block size, and whether the method cat uses can be applied to dd somehow.

Nov 19, 2024 · I was thinking of dd or cat the boot/efi partition to the beginning of a new 500GB SSD then dd or cat the Widows 7 partition to right after it. Hopefully leaving the rest of the space on that drive unallocated which I can expand later from within windows. Then dd or cat the Linux partition to another 250GB drive. All this would have to be done ...

dd is sometimes thought to be faster, but cat can beat it in practice. Nonetheless, dd has unique properties that make it genuinely useful sometimes. Problem: dd if=foo of=bar is not, in fact, the same as cat <foo >bar. On most unices¹, dd makes a single call to read(). (I find POSIX fuzzy on what constitutes “reading an input block” in dd.)

May 2, 2016 · cat file1 file2 > output But I need to skip first 1MB from the first file, and I only want 10 MB from the second file. Sounds like a job for dd. dd if=file1 bs=1M count=99 skip=1 of=temp1 dd if=file2 bs=1M count=10 of=temp2 cat temp1 temp2 > final_output

dd and cat are part of coreutils on archlinux. In my tests, cat does about 49 syscalls, whereas dd does 500+. If you examine the syscalls, you will see that cat does only 3 read calls, while dd does 250+, which means cat is doing more buffering than dd. I'm sure dd can be further tweaked to squeeze out more performance. I just wanted to show ...