Select the TWO true statements about dd.
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands hard
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Choose 2.
Correct if= and of= name the input and output files, and each defaults to standard input or standard output when omitted.
Correct. With neither operand dd is a plain copy from stdin to stdout, which is what lets it sit in the middle of a pipeline.
Correct count= limits the copy to that many input blocks, each of the size given by bs=.
Correct. `bs=512 count=1` therefore copies exactly the first 512 bytes, which is the classic way to capture or restore an MBR.
Not correct dd takes conventional Unix options, so `dd -i /dev/sda -o disk.img` is the correct form.
Wrong. dd is unusual in taking key=value operands with no leading dashes, an inheritance from the IBM JCL syntax it was modelled on. Only --help and --version use the normal form.
Not correct dd refuses to write to a block device that currently holds a mounted filesystem.
Wrong. dd performs no such check, which is precisely why a mistyped of= can overwrite a live disk. Nothing warns you and nothing asks.
Not correct seek= skips the given number of blocks at the start of the input before reading.
Wrong, that is skip=. seek= skips blocks at the start of the OUTPUT, which is how you write into the middle of an existing image.
Why
dd copies blocks, and every part of its behaviour is expressed as key=value operands: if, of, bs, count, skip for the input side, seek for the output side, and conv for transformations such as conv=notrunc. Because it writes to whatever of= names without confirmation, and block devices accept raw writes, the operand is worth reading twice before pressing Enter.
Where this comes from
- Cited
- manual page dd(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 103 and space the ones you get wrong.
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