Linux Special command--DD and Linux patch making

One, DD command detailed:

Official explanation: Convert and copy a file---transform and copy files

DD is a very useful command under Linux/unix, which is to copy a file with a block of the specified size and make the specified conversion at the same time as the copy

Grammar:

DD [OPERAND] ...

DD OPTION

Parameters:

If=file read from FILE instead of stdin

source file for specifying the source of the data stream

Of=file write to FILE instead of stdout

Target file for specifying the data flow storage destination

Bs=bytes Read and write BYTES BYTES at a time (also see ibs=,obs=)

Amount of data for one IO

Count=n Copy only N input blocks

How many BS specified blocks are copied

Format:

DD if= of= bs= count=

Two special device files

/dev/null:bit Bucket is known as a data black hole, you can enter any information to him without any output

/dev/zero: is an input device that you can use to initialize a file, which provides an infinite 0 string that can be used to write a string 0 to a file or device;

Eg: Create a file with a size of 64M

[[email protected] tmp]# mkdir zero[[email protected] tmp]# CD Zero[[email protected] zero]# ls-ltotal 0[[email protected ] zero]# dd If=/dev/zero of=/tmp/zero/file bs=1m count=6464+0 Records in64+0 records out67108864 bytes (MB) copied, 0.4 34439 S, 154 mb/s[[email protected] zero]# ls-lhtotal 64m-rw-r--r--1 root root 64M Apr 1 16:42 file

Application Examples:

App 1: Create a local loopback device file:

DD If=/dev/zero of=/path/to/somefile bs= count=

App 2: backup disk starts with 512 byte-sized MBR information to the specified file:

DD IF=/DEV/SDA of=/backup/mbr.backup bs=512 count=1

Restore MBR

DD If=/backup/mbr.backup OF=/DEV/SDA

Application 3: Destroying its MBR (instantly destroying its partitioned table, extremely destructive)

DD If=/dev/zero OF=/DEV/SDA bs=512 count=1

Apply 4, Destroy disk data

[email protected] zero]# DD if=/dev/urandom of=/dev/sdb

Second, text comparison, patch making and patching tools----diff,patch

Diff command

the diff command is a very important tool on Linux to compare the contents of a file, especially to compare two different versions of a file to find the place to change

Command format:

diff[parameter [file 1 or directory 1][file 2 or directory 2]

Linux Patch Production

diff [-u] file.old file.new >file.patch

Patch File.old <file.patch

Eg:[[email protected] ~]# diff functions Functions.1 4a5> #Author: [email protected][[email protected] ~]# diff-u func tions functions.1 > Functions.patch//Make patches [[email protected] ~]# patch functions <functions.patch//patch [email prot Ected] ~]# head-5 functions#-*-shell-script-*-## functionsthis file contains functions to BES used by most or All#shell s Cripts in The/etc/init.d directory. #Author: [Email protected]

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Linux Special command--DD and Linux patch making