On: Remove first 300M lines from 700 GB file on 1TB di...

[tumetab1]

That doesn't fully explain it but I think I got it, each line is overwritten with what it's place on the 300th line after.

Something like

  readLineOffset = 301
  writeLineOffset = 1
  While not read eof
    line = Read(readLineOffset)
    Write(WriteLineOffset, line)
    readLineOffset ++
    writeLineOffset ++

[ComodoHacker → tumetab1]

dd reads and writes in blocks of bytes, not lines. You have to figure out where 300th line starts beforehand.