Which command creates a file named testfile containing 20 data blocks of 1024 kilobytes each from /dev/urandom?

• A. dd if=/dev/urandom of=testfile count=20 bs=1024k
• B. dd if=/dev/urandom of=testfile bs=1024k count=20
• C. dd if=/dev/zero of=testfile count=20 bs=1024
• D. dd if=/dev/urandom of=testfile count=20 bs=1024

Answer: (A)

The command tests how to generate a file of a precise size from a data source using dd, by controlling the amount of data read and written with block size and count. dd reads from an input and writes to an output; here the input is /dev/urandom (random data) and the output is testfile. The block size (bs) is 1024k, which means each read/write is 1 MiB. The count is 20, so dd processes 20 such blocks. That results in 20 MiB of data written to testfile, i.e., a file consisting of 20 data blocks of 1024 kilobytes each, with random content from /dev/urandom.

Using /dev/zero would yield zeros instead of random data, so that wouldn’t meet the requirement. A smaller block size, like bs=1024 (which is 1 KiB per block) with count=20, would only produce about 20 KiB total, not 20 MiB. The order of bs and count doesn’t change the result, so the essential concept is choosing a block size of 1024k and a count of 20 to achieve the desired total size from /dev/urandom.