The DD command __linux below Linux

LINUX-DD Command Detailed

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

Name: DD
Use rights: All user dd This instruction is defined in manual as convert and copy a file

How to use:
DD [option]


If you want to see manual online, try:
DD--help

Or
Info DD

If you want to see how this version is:
DD--version

Input or output
DD If=[stdin] Of=[stdout]

Force input or output size to how many bytes
Bs:dd-ibs=[byte]-obs=[size]

How many Bytes are you forced to do at a time?
Cbs=bytes

Skip a paragraph before outputting
Seek=blocks

Skip a paragraph before entering
Skip=blocks

Of course you can use this to easily copy discs (Note that your disc is a standard iso9660 format to do so.) )

DD If=/dev/cdrom Of=cdrom.iso
The contents of the if and after are adjusted according to your requirements.

Then give the system the instructions to burn:

Cdrecord-v Cdrom.iso
This is not about Cdrecord, so the instructions above are the simplest but not necessarily compatible with your hardware environment ...
Function: Copies the specified input file to the specified output file, and can be converted to format during the copy process. You can use this command to realize the function of the diskcopy command under DOS. First use the DD command to write the data on the floppy disk as a storage file, and then put the storage file into the second floppy disk, complete the function of diskcopy. It should be noted that the storage files on the hard disk should be removed with the RM command. The system defaults to using standard input files and standard output files.

Syntax: DD [Options]

if = input file (or device name).

of = output file (or device name).

ibs = Bytes Read bytes bytes at a time, that is, the number of bytes read into the buffer.

Skip = Blocks skips the Ibs*blocks block at the beginning of the read buffer.

Obs = bytes Writes bytes bytes At a time, that is, the number of bytes written to the buffer.

BS = bytes Sets the number of bytes in the read/write buffer (equal to setting IBS and OBS).

CBS = byte convert bytes byte at a time.

Count=blocks only copies the input blocks blocks.

Conv = ASCII converts EBCDIC code to Ascil code.

Conv = EBCDIC converts ascil code to EBCDIC code.

CONV = IBM converts ascil code to alternate EBCDIC code.

CONV = block Converts a bit of change to a fixed character.

CONV = Ublock Converts a fixed bit into a change bit.

CONV = UCase converts letters from lowercase to uppercase.

CONV = LCase converts letters from uppercase to lowercase.

CONV = Notrunc does not truncate the output file.

CONV = Swab Exchange Each pair of input bytes.

CONV = NoError does not stop processing when an error occurs.

Conv = sync the size of each input record to the size of the IBS (filled with nul).

　

Example 1: To copy the contents of a floppy disk to another floppy disk, use/tmp as a temporary storage area. Insert the source disk into the drive and enter the following command:

$ dd if =/dev/fd0 of =/tmp/tmpfile

After the copy is complete, remove the source disk from the drive, insert the target disk, and enter the command:

$ dd if =/tmp/tmpfile of =/dev/fd0

After the floppy copy is complete, you should delete the temporary file:

$ rm/tmp/tmpfile

　

Example 2: Write the net.i file to the floppy disk and set the number of read/write buffers.

(Note: The contents of the floppy disk will be completely overwritten)

$ dd if = net.i of =/dev/fd0 bs = 16384

　

Example 3: Copy the file sfile to the file Dfile.

$ dd If=sfile Of=dfile

Example 4: Create a 100M empty file

DD If=/dev/zero of=hello.txt bs=100m count=1

=============================================

/dev/null, the nickname is bottomless pit, you can output any data to it, it take all, and will not hold.
/dev/zero is an input device that you can use to initialize the file.

/dev/null------It is an empty device, also known as a bit bucket (bit bucket). Any output written to it will be discarded. If you do not want the message to be displayed or written to the file in standard output, you can redirect the message to the bucket.
/dev/zero------The device provides an endless supply of 0, you can use any number you need-the equipment to provide much more. He can be used to write string 0 to a device or file.
$ dd If=/dev/zero of=./test.txt bs=1k count=1
$ ls-l
Total 4
-rw-r--r--1 Oracle DBA 1024 16:56 test.txt

eg

$ find/-name Access_log 2>/dev/null