dd if=/dev/sdb of=/root/flashcopy
1257441=0 records in
1257440+0 records out
7643809280 bytes (7.6 GB) copied, 1220.729 s, 5.2 MB/s
Let’s break down this command:
dd
is your physical “copy” command;
if
designates your input file, with
/dev/sdb
representing your flash drive in
the /dev directory;
of
designates your output file; and
/root/flashcopy
is the
name of the file you want to copy the physical copy to. (For a more com-
plete explanation of the Linux system designation of drives within the /dev
directory, see Chapter 10.)
Numerous options are available to use with the
dd
command, and you
can do a bit of research on these, but among the most useful are the
noerror
option and the
bs
(block size) option. As the name implies, the
noerror
option
continues to copy even if errors are encountered. The
bs
option allows you
to determine the block size (the number of bytes read/written per block) of
the data being copied. By default, it is set to 512 bytes, but it can be changed
to speed up the process. Typically, this would be set to the sector size of the
Compressing and Archiving
99
device, most often 4KB (4,096 bytes). With these options, your command
would look like this:
kali >
dd if=/dev/media of=/root/flashcopy bs=4096 conv:noerror
As mentioned, it’s worth doing a little more research on your own, but
this is a good introduction to the command and its common usages.
Summary
Linux has a number of commands to enable you to combine and compress
your files for easier transfer. For combining files,
tar
is the command of
choice, and you have at least three utilities for compressing files—
gzip
,
bzip2
,
and
compress
—all with different compression ratios. The
dd
command goes
above and beyond. It enables you to make a physical copy of storage devices
without the logical structures such as a filesystem, allowing you to recover
such artifacts as deleted files.
E XERCISES
Before you move on to Chapter 10, try out the skills you learned from this
chapter by completing the following exercises:
1. Create three scripts to combine, similar to what we did in Chapter 8.
Name them
Linux4Hackers1
,
Linux4Hackers2
, and
Linux4Hackers3
.
2. Create a tarball from these three files. Name the tarball
L4H
. Note how the
size of the sum of the three files changes when they are tarred together.
3. Compress the
L4H
tarball with
gzip
. Note how the size of the file changes.
Investigate how you can control overwriting existing files. Now uncompress
the
L4H
file.
4. Repeat Exercise 3 using both
bzip2
and
compress
.
5. Make a physical, bit-by-bit copy of one of your flash drives using the
dd
command.
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