We are going to primarily reference the dd command to demonstrate the creation of our large files. Additionally, you might need the assistance of the following listed commands. To make this article guide interesting, we are going to create a 10GB file on our Linux system. The command we are going to use is as simple as demonstrated below. Make sure your Linux system can accommodate the file size you want to create through the following df command.
On my end, I have 14GB of free disk space. It will be sufficient to accommodate the 10GB file we want to create. As highlighted on the above screen capture, the 10g. To use the decimal unit, use the B suffix. If you do not care about the contents of the file, you can also use the fallocate and the truncate commands. Instead of writing any data in the file, these commands only manipulate the allocated disk space of the file. Since these commands do not put any character in the file, you can generate a file of any size in a few seconds.
The fallocate command supports only the btrfs, ext4, ocfs2, and xfs file systems. The truncate command supports all modern file systems. The fallocate command allocates all of the space to the file without writing a single byte of data in the file. It means, if you use the fallocate command to create a 20GB file, you will get a file that consumes 20GB actual disk space but contains no data. The truncate command creates a sparse file instead of the actual file.
The difference between a sparse file and an actual file is that a sparse file doesn't consume all allocated space. It only consumes the space that is used by data. For example, you created two 50GB files; one from the fallocate command another from the truncate command. The first file immediately consumes all allocated 50GB space while the second file consumes only the space that is required by the actual data.
Since the truncate command does not put any data in the file, the actual consumed disk space remains unchanged. Let's take one more example. Suppose you have 5 GB disk space and you want to create a file of 10GB for testing. Since the fallocate command allocates all assigned space immediately, you can't create a file of 10GB if you only have 5GB disk space. In this case, you can use the truncate command. I tried truncate. It produced a zero-sized file using the syntax above. The 'man page' for fallocate says that the files it creates are full of empty space rather than data.
It appears that it wouldn't be useful for some expected cases like "how long does it take to copy a 1G file". It creates a file the right size. This is the best answer to this question. But, if you were to then upload the resultant file somewhere, it would read zeroes for the entire thing. If you want to run this under OSX, then you'll need to do this: brew install coreutils.
This will add a g in front of the command, so you have to run it like this: gtruncate -s 10G foo. Hope this helps! It seems that it does not work on a NTFS partition. Community Bot 1 1 1 silver badge. Brian Brian k 28 28 gold badges silver badges bronze badges. Why did you ask the question? I had to Google for the answer, so I put it here, so it could be discussed and kept up to date I know people are voting Grundlefleck down for XP whoring, but he does have a point - one of the ways to use this site as envisioned by Jeff and Joel is to put a question and answer for something you just discovered.
Thanks Paul. Though I'm not so bothered about the points, I am bothered about things I find on Google which may be flawed in some way I'd never find out about unless I asked here. To quote from the faq's "It's also perfectly fine to ask and answer your own programming question, but pretend you're on Jeopardy: phrase it in the form of a question. Show 3 more comments. Benedikt Waldvogel Benedikt Waldvogel The default block size is , but you can change that with obs argument.
Note that using the seek argument and increasing the seek value will typically decrease the execution time of the command, but it will also result in a sparse file.
The total size of the file that is generated is dependent on the values provided to the count and bs arguments. The total size of the generate file in bytes is the product of count and bs. If the content of the file is not important then you can create the file with a bunch of null values.
The above command will generate a output file named output. The content may not still be human readable, but you are guaranteed to have non-null characters including some end of line EOL characters.
That means that you have a file with lines in them and can use the file as input to programs that expect some kind of data. The above command will generate output. Another command that can be used to generate large files in Linux is the fallocate command.
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