Create image file linux

Linux / UNIX: Create Large 1GB Binary Image File With dd Command

1. fallocate command – Preallocate space to a file.
2. truncate command – Shrink or extend the size of a file to the specified size.
3. dd command – Convert and copy a file i.e. clone/create/overwrite images.
4. df command – Show free disk space.
5. du command – Show disk usage statistics.
6. ls command – List file size.

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	fallocate or dd command
Est. reading time	3 minutes

fallocate command syntax

The basic syntax is:
fallocate -l Image_Size_Here /path/to/image.img
Let us see how to create large 1GB binary file with fallocate.

Creating a large file on a Linux using fallocate command

The following command will create 1G file:

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Verify new disk image with the ls command:
$ ls -lh test.img
Sample outputs:

You can use stat or du command to verify block allocation:

dd command syntax

Note : The following information only exists for older version of Linux and/or when fallocate command is not available. If possible use fallocate command only for creating binary images. dd command based method is considered as old and not recommended, but presented here for historical reasons only.

The basic syntax is:
dd if=/path/to/input of=/path/to/output [options] ## OR ##
dd if=/dev/zero of=/path/to/output.img [options] ## OR ##
dd if=/dev/zero of=YOUR-IMAGE-FILE-NAME-HERE bs=1 count=0 seek=Size-HERE

Creating an image file with dd command

First, make sure you’ve sufficient disk space to create a image file using dd:
$ df -H

To create 1MB file (1024kb), enter:
$ dd if=/dev/zero of=test.img bs=1024 count=0 seek=1024

You will get an empty files (also known as “sparse file”) of arbitrary size using above syntax. To create 10MB file , enter:
$ dd if=/dev/zero of=test.img bs=1024 count=0 seek=$[1024*10]

To create 100MB file , enter:
$ dd if=/dev/zero of=test.img bs=1024 count=0 seek=$[1024*100] $ ls -lh test.img

To create 1GB, file:
$ dd if=/dev/zero of=1g.img bs=1 count=0 seek=1G
Sample output:

Verify file size (note bs factor in original dd command):
$ ls -lh 1g.img
$ stat 1g.img
$ du -h 1g.im

dd tip: Create a file with a given size in Unix or Linux

If truncate command not available, try the following syntax:
dd if=/dev/zero of=/path/to/fiie.img bs=YOUR-FILE-SIZE-HERE count=1
In this example, create a file with 1G (on *BSD/OS X use 1g) size:
$ dd if=/dev/zero of=1g.bin bs=1G count=1
Here is what I see:

Verify file size/blocks:
$ stat 1g.bin
Verification outputs:

Summing up

You learned how to create large 1GB (or any size of your choice) binary image file with dd and other command on Linux or Unix-like systems. See man pages for more info:
man dd
man fallocate

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Comments on this entry are closed.

I don’t think this works correctly unless the “count” argument is changed to something greater than 0.

Try something like this:

dd if=/dev/zero of=10Gtest bs=1M count=10000

I don’t think you have read and tested this yourself.

If using “count=0”, as the article suggests, you will still have the file of the specified size.

However, the output will show something like “0+0 records in” and “0+0 records out”.

Then if you check the file size:

it should show the proper size.

It’s even easier, using the format that the commenter Indie suggest:

JW is correct. Without a count setting – its generating a 0 byte file.

ls -alh will show a file size; but compare that to df -h – and you’ll see it doesn’t actually consume any space on disk

Bullshit the 10g one above doesnt create the proper file size at all. Check with the du command it replys the file size is 0.

I think the commenter “Indie” has already clarified this in a previous comment (in agreement with the author).

@JW, @sonassi, @stfu_and_die
If you think you’re right, why don’t tell the author of the article to either remove or edit the article? or write your own article?

Indie August 26, 2011 at 3:02 pm

The ls command will tell you the size of the file while du will tell you the Disk Usage. When you create the empty disk image with the above command it doesn’t write any data so it doesn’t actually allocate any blocks to the file.

If you type “stat disk.img” you’ll see that it’s using 0 blocks and thus no disk space is being consumed by the file, it’s only when you then write data to it that the blocks will then be allocated.

The FAQ has been updated with new and accurate information. However, I kept dd command based method for historical reasons only. I recommend using fallocate command on Linux.

Hope this helps!

can I supress the output of dd command?

Yes, send it to /dev/null.

dd args >/dev/null
OR
dd args >/dev/null 2>&1

Slightly easier version is to use a suffix for the size instead of trying to do the maths.

dd if=/dev/zero of=disk.img bs=1 count=0 seek=1G

to create a 1G file.

Yes this is work but there is concern .

When do ls -lh disk.img file its showing as 1G size but when u run the command

du -h disk.img it shows 0 bytes of size…..

Which one we can believe…i dont know…please clarify if you know about this…

The ls command will tell you the size of the file while du will tell you the Disk Usage. When you create the empty disk image with the above command it doesn’t write any data so it doesn’t actually allocate any blocks to the file.

If you type “stat disk.img” you’ll see that it’s using 0 blocks and thus no disk space is being consumed by the file, it’s only when you then write data to it that the blocks will then be allocated.

I have 2 tb harddrive and i want to clone only 1 tb to my other drive?

what command should i do

Hi, the question is old – but I’m happy to provide a nice answer – maybe this basic advice will help other people as well.
This isn’t exactly possible with dd. If you’d only dd 1tb of the 2tb drive and you’re lucky to be able to mount it, you’ll end up seeing correct filenames – but files will be corrupted entirely.
I’d rather suggest you:
? format your second hard-drive
? look which files/directories are using how much space, recommended tool is ncdu
? create a list of files you want to copy and use rsync to copy the files

How to check if the created file is empty, is there a way to check that?

Using /dev/zero will create a file for you, but the free space seems to remain the same on the disk. If you’re looking to make a filler file as I am in /var/lib/mysql so when the database fills up, I still have some space to work with.. you’ll want to substitute /dev/zero to /dev/random or something like that.

Here’s my attempt at creating a 1G filler file.
df output before:
/dev/mapper/VG01-LV_mysql
30959612 27519608 3439984 89% /var/lib/mysql
command:
dd if=/dev/zero of=1gig-filler.img bs=1000 count=0 seek=$[1000*1000*1]
0+0 records in
0+0 records out
0 bytes (0 B) copied, 3e-05 seconds, 0.0 kB/s

file:
-rw——- 1 root root 1000000000 Feb 13 12:26 1gig-filler.img

df output after (space is slightly different because the db is being used):
/dev/mapper/VG01-LV_mysql
30959612 27521072 3438520 89% /var/lib/mysql

I don’t see any use for using /dev/zero in this scenario. I’ve used it to wipe a disk clean… dd if=/dev/zero of=/dev/sda will clear a disk, but this file doesn’t take up real space.

Actually it might be the count=0 part that is making it not use any real space.. I can’t seem to get df to show me the space actively being used even with /dev/random.. I know I’ve done this successfully before.

How to delete that test file that is being created?

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How to make disk image with dd on Linux or Unix

What is a dd image?

Disk cloning is nothing but a mere process of creating an image of an entire disk. This can be useful for copying disks, backups, recovery and more. The dd command is easy to use tool for making such clones.

Warning: You should be very careful when using dd command; it can destroy data. Remember the order of input file (if=) and output file (of=).

How to clone an entire hard disk

The syntax is:
dd if=/dev/input/DEVICE-HERE of=/dev/OUTPUT/DEVICE-HERE bs=64K conv=noerror,sync
To clone /dev/sdc (250G) to /dev/sdd (250G) in Linux, enter:
# dd if=/dev/sdc of=/dev/sdd bs=64K conv=noerror,sync
To clone /dev/ada0 (250G) to /dev/adb0 (250G) in FreeBSD, enter:
# dd if=/dev/ada0 of=/dev/adb0 bs=64K conv=noerror,sync
Where,

1. if=/dev/file : Input device/file.
2. of=/dev/file : Output device/file.
3. bs=64k : Sets the block size to 64k. You can use 128k or any other value.
4. conv=noerror : Tell dd to continue operation, ignoring all read errors.
5. sync : Add input blocks with zeroes if there were any read errors, so data offsets stay in sync.

How to clone a partition

To clone /dev/sdc1 to /dev/sdd1, enter:
# dd if=/dev/sdc1 of=/dev/sdd1 bs=128K conv=noerror,sync
Sample outputs:

dd make disk image

You can boot from a live cd. Once booted, make sure no partitions are mounted from the source hard drive disk. You can store disk image on an external USB disk. The syntax is as follows
dd if=/dev/INPUT/DEVICE-NAME-HERE conv=sync,noerror bs=64K | gzip -c > /path/to/my-disk.image.gz
In this example, create disk image for /dev/da0 i.e. cloning /dev/da0 and save in the current directory:
# dd if=/dev/da0 conv=sync,noerror bs=128K | gzip -c > centos-core-7.gz
Sample outputs:

Fig.01: dd command in action

How to restore system (dd image)

The syntax is:
# gunzip -c IMAGE.HERE-GZ | dd of=/dev/OUTPUT/DEVICE-HERE
For example:
# gunzip -c centos-core-7.gz | dd of=/dev/da0

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Tip #1: Not enough disk space locally? Use remote box

You can send the image through ssh and save it on the remove box called server1.cyberciti.biz:
# dd if=/dev/da0 conv=sync,noerror bs=128K | gzip -c | ssh vivek@server1.cyberciti.biz dd of=centos-core-7.gz

Tip #2: See progress while making an image with dd

gdd (GNU DD) in action with progress bar running on MacOS X

Tip #3: Save extra information

• See how to save and restore MBR only.
• Not a fan of dd? See top 6 open source disk cloning and imaging softwares.
• Want to deal with corrupted disk? Try ddrescue command.

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