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
