linux命令行输入：
dd --help
Usage: dd [OPERAND]...
or: dd OPTION
Copy a file, converting and formatting according to the operands.
bs=BYTES read and write up to BYTES bytes at a time (default: 512);
overrides ibs and obs
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 do not truncate the output file
noerror continue after read errors
fdatasync physically write output file data before finishing
fsync likewise, but also write metadata
Each FLAG symbol may be:
append append mode (makes sense only for output; conv=notrunc suggested)
direct use direct I/O for data
directory fail unless a directory
dsync use synchronized I/O for data
sync likewise, but also for metadata
fullblock accumulate full blocks of input (iflag only)
nonblock use non-blocking I/O
noatime do not update access time
nocache Request to drop cache. See also oflag=sync
noctty do not assign controlling terminal from file
nofollow do not follow symlinks
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 display this help and exit
--version output version information and exit
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Full documentation at: <http://www.gnu.org/software/coreutils/dd>
or available locally via: info '(coreutils) dd invocation'
中文翻译如下：
用法：dd [OPERAND] ......
或者：dd OPTION
根据操作数复制文件，转换和格式化。
bs = BYTES一次读取和写入BYTES字节（默认值：512）;
覆盖ibs和obs
cbs = BYTES一次转换BYTES字节
conv = CONVS按照逗号分隔的符号列表转换文件
count = N仅复制N个输入块
ibs = BYTES一次读取BYTES字节（默认值：512）
if = FILE从FILE而不是stdin读取
iflag = FLAGS按逗号分隔的符号列表读取
obs = BYTES一次写BYTES字节（默认值：512）
of = FILE写入FILE而不是stdout
oflag = FLAGS根据逗号分隔的符号列表写入
seek = N在输出开始时跳过N个阻塞大小的块
skip = N在输入开始时跳过N ibs大小的块
status = LEVEL要打印到stderr的信息的级别;
'none'除了错误消息外都会抑制所有内容，
'noxfer'抑制最终转移统计，
'progress'显示定期传输统计信息
N和BYTES之后可以跟随以下乘法后缀：
c = 1，w = 2，b = 512，kB = 1000，K = 1024，MB = 1000 * 1000，M = 1024 * 1024，xM = M，
对于T，P，E，Z，Y，GB = 1000 * 1000 * 1000，G = 1024 * 1024 * 1024等。
每个CONV符号可以是：
ascii从EBCDIC到ASCII
从ASCII到EBCDIC的ebcdic
从ASCII到交替EBCDIC的ibm
阻止填充换行符终止的记录，其空格为cbs-size
unblock用换行符替换cbs-size记录中的尾随空格
lcase将大写更改为小写
ucase将小写更改为大写
稀疏尝试寻找而不是写入NUL输入块的输出
swab交换每对输入字节
每个输入块同步填充NUL到ibs大小; 使用时
使用block或unblock，填充空格而不是NUL
如果输出文件已存在，则excl失败
nocreat不创建输出文件
notrunc不截断输出文件
阅读错误后，noerror继续
fdatasync在完成之前物理写入输出文件数据
fsync同样，但也写入元数据
每个FLAG符号可能是：
追加附加模式（仅对输出有意义;建议使用conv = notrunc）
直接使用直接I / O数据
目录失败，除非目录
dsync使用同步I / O进行数据
同样地同步，但也用于元数据
fullblock累积整个输入块（仅限iflag）
非阻塞使用非阻塞I / O.
noatime不更新访问时间
nocache请求删除缓存。另见oflag = sync
noctty不从文件中分配控制终端
nofollow不遵循符号链接
count_bytes将'count = N'视为字节数（仅限iflag）
skip_bytes将'skip = N'视为字节数（仅限iflag）
seek_bytes将'seek = N'视为字节数（仅限oflag）
将USR1信号发送到正在运行的'dd'进程就可以了
将I / O统计信息打印到标准错误，然后重新开始复制。
选项包括：
--help显示此帮助并退出
--version输出版本信息并退出
GNU coreutils在线帮助：<http://www.gnu.org/software/coreutils/>
完整文档：<http://www.gnu.org/software/coreutils/dd>
或通过以下方式在本地获取：info'（coreutils）dd invocation'
范例如下：
1）把A文件(bootsect)内容拷贝到B文件(boot.img)
dd if=bootsect of=boot.img
2）从A文件(bootsect)拷贝指定字节BYTES的数据到B文件(boot.img)
dd ibs=BYTES if=bootsect of=boot.img
3）把A文件(system)指定字节后的内容拷贝到到B文件(boot.img)指定位置处，字节=ibs*seek参数
dd ibs=160 skip=1 seek=1 if=system of=boot.img