用法：dd [操作数] ...
　或：dd 选项
Copy a file, converting and formatting according to the operands.

  bs=BYTES        read and write up to BYTES bytes at a time
  cbs=BYTES       convert BYTES bytes at a time
  conv=CONVS      convert the file as per the comma separated symbol list
  count=N         copy only N input blocks
  ibs=BYTES       read up to BYTES bytes at a time (default: 512)
  if=FILE         read from FILE instead of stdin
  iflag=FLAGS     read as per the comma separated symbol list
  obs=BYTES       write BYTES bytes at a time (default: 512)
  of=FILE         write to FILE instead of stdout
  oflag=FLAGS     write as per the comma separated symbol list
  seek=N          skip N obs-sized blocks at start of output
  skip=N          skip N ibs-sized blocks at start of input
  status=LEVEL    The LEVEL of information to print to stderr;
                  ‘none‘ suppresses everything but error messages,
                  ‘noxfer‘ suppresses the final transfer statistics,
                  ‘progress‘ shows periodic transfer statistics

N and BYTES may be followed by the following multiplicative suffixes:
c =1, w =2, b =512, kB =1000, K =1024, MB =1000*1000, M =1024*1024, xM =M
GB =1000*1000*1000, G =1024*1024*1024, and so on for T, P, E, Z, Y.

Each CONV symbol may be:

  ascii     from EBCDIC to ASCII
  ebcdic    from ASCII to EBCDIC
  ibm       from ASCII to alternate EBCDIC
  block     pad newline-terminated records with spaces to cbs-size
  unblock   replace trailing spaces in cbs-size records with newline
  lcase     change upper case to lower case
  ucase     change lower case to upper case
  sparse    try to seek rather than write the output for NUL input blocks
  swab      swap every pair of input bytes
  sync      pad every input block with NULs to ibs-size; when used
            with block or unblock, pad with spaces rather than NULs
  excl        fail if the output file already exists
  nocreat    do not create the output file
  notrunc    不截断输出文件
  noerror    读取数据发生错误后仍然继续
  fdatasync    结束前将输出文件数据写入磁盘
  fsync    类似上面，但是元数据也一同写入

FLAG 符号可以是：

  append    追加模式(仅对输出有意义；隐含了conv=notrunc)
  direct    使用直接I/O 存取模式
  directory    除非是目录，否则 directory 失败
  dsync        使用同步I/O 存取模式
  sync        与上者类似，但同时也对元数据生效
  fullblock    为输入积累完整块(仅iflag)
  nonblock    使用无阻塞I/O 存取模式
  noatime    不更新存取时间
  nocache   Request to drop cache.  See also oflag=sync
  noctty    不根据文件指派控制终端
  nofollow    不跟随链接文件
  count_bytes  treat ‘count=N‘ as a byte count (iflag only)
  skip_bytes  treat ‘skip=N‘ as a byte count (iflag only)
  seek_bytes  treat ‘seek=N‘ as a byte count (oflag only)

Sending a USR1 signal to a running ‘dd‘ process makes it
print I/O statistics to standard error and then resume copying.

Options are:

      --help        显示此帮助信息并退出
      --version        显示版本信息并退出

GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
请向<http://translationproject.org/team/zh_CN.html> 报告dd 的翻译错误
Full documentation at: <http://www.gnu.org/software/coreutils/dd>
or available locally via: info ‘(coreutils) dd invocation‘