LINUX dd命令

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

command	english	中文
bs=BYTES	read and write up to BYTES bytes at a time	读或写的字节数
cbs=BYTES	convert BYTES bytes at a time	转换的字节数
conv=CONVS	convert the file as per the comma separated symbol list
count=N	copy only N input blocks	输入的块数
ibs=BYTES	read up to BYTES bytes at a time (default: 512)	每次读取的字节数
if=FILE	read from FILE instead of stdin	输入的文件 默认为stdio
iflag=FLAGS	read as per the comma separated symbol list	d
obs=BYTES	write BYTES bytes at a time (default: 512)	写的bytes 默认为512B
of=FILE	write to FILE instead of stdout	输出文件 默认为stdout
oflag=FLAGS	write as per the comma separated symbol list
seek=N	skip N obs-sized blocks at start of output	skip N个块输出时
skip=N skip N ibs-sized blocks at start of input	跳过 N个块输入时
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 =10001000, M =10241024, xM =M
GB =100010001000, G =102410241024, 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 丢弃缓存数据
  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.

$dd if=/dev/zero of=/dev/null& pid=$!
$ kill -USR1 $pid; sleep 1; kill $pid

18335302+0 records in
18335302+0 records out
9387674624 bytes (9.4 GB) copied, 34.6279 seconds, 271 MB/s

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
要获取完整文档，请运行：info coreutils 'dd invocation'

[root@localhost text]# dd if=/dev/zero of=/data/text.txt bs=1M count=1
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.006107 seconds, 172 MB/s
//以上命令可以看出dd命令来测试内存操作速度

[root@localhost text]# du -sh /data/text.txt 
1.1M    sun.txt