Tutorial on the use of dd command in Linux-Linux Operation and Maintenance-php.cn

The dd command copies a file using blocks of the specified size, and performs the specified conversion while copying. The following article mainly introduces you to the relevant information about the use of the dd command inLinux. It has certain reference and learning value for everyone. Friends who need it can take a look below.

This article mainly introduces to you the relevant content about the use of dd command in Linux, and shares it for your reference and study. Let’s take a look at the detailed introduction:

一. The Linux dd command copies a file using blocks of a specified size, and performs specified conversions while copying.

Usage:dd [OPERAND]

ParametersComments:

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

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Optional parameters of CONVS

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

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Optional parameters of FLAGS

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)

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Note:If the place where the number is specified ends with the following characters, the corresponding number will be multiplied:

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

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2. Usage Example

1. Back up the entire local /dev/hdb disk to /dev/hdd

dd if=/dev/hdb of=/dev/hdd

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2. Back up the entire /dev/hdb disk data to the image file in the specified path

dd if=/dev/hdb of=/root/image

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3. Back up the entire /dev/hdb data, compress it using the gziptool, and save it to the specified path

dd if=/dev/hdb | gzip > /root/image.gz

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4. Split a file into 3 files

#文件大小为2.3k [Oracle@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

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5. Merge the split files into 1

#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 ~]$

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6. Insert dataat the specified positionin the output file without truncating the output file

You need to use theconv=notruncparameter

[oracle@rhel6 ~]$ dd if=2.sql of=1.sql bs=1k seek=1 count=2 conv=notrunc

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