一、Linux dd命令用指定大小的块拷贝一个文件，并在拷贝的同时进行指定的转换。
使用方法：dd [OPERAND]
参数注释：
bs=BYTES
read
and write BYTES bytes at a
time
(also see ibs=,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
BYTES bytes at a
time
(default: 512)
if
=FILE
read
from FILE instead of stdin(默认为标准输入)
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(默认为标准输出)
oflag=FLAGS write as per the comma separated symbol list
seek=BLOCKS skip BLOCKS obs-sized blocks at start of output
skip=BLOCKS skip BLOCKS ibs-sized blocks at start of input
status=WHICH WHICH info to suppress outputting to stderr;
'noxfer'
suppresses transfer stats,
'none'
suppresses all
CONVS的可选参数
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
nocreat
do
not create the output
file
excl fail
if
the output
file
already exists
notrunc
do
not truncate the output
file
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
noerror
continue
after
read
errors
sync
pad every input block with NULs to ibs-size; when used
with block or unblock, pad with spaces rather than NULs
fdatasync physically write output
file
data before finishing
fsync likewise, but also write metadata
FLAGS的可选参数
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
noctty
do
not assign controlling terminal from
file
nofollow
do
not follow symlinks
count_bytes treat
'count=N'
as a byte count (iflag only)
注意：指定数字的地方若以下列字符结尾，则乘以相应的数字：
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
二、使用实例
1、将本地的/dev/hdb整盘备份到/dev/hdd
dd
if
=
/dev/hdb
of=
/dev/hdd
2、将/dev/hdb全盘数据备份到指定路径的image文件
dd
if
=
/dev/hdb
of=
/root/image
3、备份/dev/hdb全盘数据，并利用gzip工具进行压缩，保存到指定路径
dd
if
=
/dev/hdb
|
gzip
>
/root/image
.gz
4、把一个文件拆分为3个文件
#文件大小为2.3k
[@rhel6 ~]$ ll db1_db_links.sql
-rw-r--r-- 1 oracle oinstall 2344 Nov 21 10:39 db1_db_links.sql
#把这个文件拆成每个文件1k，bs=1k，count=1，使用skip参数指定在输入文件中跳过多少个bs支读取
[oracle@rhel6 ~]$
dd
if
=db1_db_links.sql of=dd01.sql bs=1k count=1
1+0 records
in
1+0 records out
1024 bytes (1.0 kB) copied, 4.5536e-05 s, 22.5 MB
/s
[oracle@rhel6 ~]$
dd
if
=db1_db_links.sql of=dd02.sql bs=1k count=1 skip=1
1+0 records
in
1+0 records out
1024 bytes (1.0 kB) copied, 0.000146387 s, 7.0 MB
/s
[oracle@rhel6 ~]$
dd
if
=db1_db_links.sql of=dd03.sql bs=1k count=1 skip=2
0+1 records
in
0+1 records out
296 bytes (296 B) copied, 0.000204216 s, 1.4 MB
/s
#拆分出的文件
[oracle@rhel6 ~]$ ll
dd
*sql
-rw-r--r-- 1 oracle oinstall 1024 May 20 14:58 dd01.sql
-rw-r--r-- 1 oracle oinstall 1024 May 20 14:58 dd02.sql
-rw-r--r-- 1 oracle oinstall 296 May 20 14:58 dd03.sql
5、把拆分出的文件合并为1个
#合并操作，此时用到seek参数，用于指定在输入文件中跳过的bs数
[oracle@rhel6 ~]$
dd
of=1.sql
if
=dd01.sql
2+0 records
in
2+0 records out
1024 bytes (1.0 kB) copied, 0.000176 s, 5.8 MB
/s
[oracle@rhel6 ~]$
dd
of=1.sql
if
=dd02.sql bs=1k seek=1
1+0 records
in
1+0 records out
1024 bytes (1.0 kB) copied, 0.000124038 s, 8.3 MB
/s
[oracle@rhel6 ~]$
dd
of=1.sql
if
=dd03.sql bs=1k seek=2
0+1 records
in
0+1 records out
296 bytes (296 B) copied, 0.00203881 s, 145 kB
/s
#与拆分前的文件进行校验
[oracle@rhel6 ~]$
diff
1.sql db1_db_links.sql
[oracle@rhel6 ~]$
6、在输出文件中指定的位置插入数据，而不截断输出文件
需要使用conv=notrunc参数
[oracle@rhel6 ~]$
dd
if
=2.sql of=1.sql bs=1k seek=1 count=2 conv=notrunc