Linux create a file with size

The fallocate is one of the lesser known commands for creating files. What makes fallocate different then the rest is that it allows you to create files of specific sizes.

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Why would you do that? One practical use of fallocate is in increasing the swap file in Linux. With fallocate, you can quickly create a swap file of predetermined size. This is a much quicker way of creating huge files because it allocates uninitialized blocks.

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This is a lot faster than creating a huge file and filling it with zeroes. The option l determines the size of the file being created. You can use the following for the length of the file:.

Generate or Create a Large text file in Linux

I hope you know the difference between MB and MiB. Unlike the hard disk manufacturers, operating systems work in the power of 2. Use the ls command with option -h and you can see the size of the file:.

Do you know some other useful example of the fallocate command? Do share it with us in the comments below. Liked the article?

linux create a file with size

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You are right, Rosika. Not only to make swap file smaller but also to make it bigger. One thing I can think of is testing a round Robin script for deleting older files once a folder reaches a certain size.

You could test the script by creating a half dozen files that will fill up the folder to the size you need to kick off the file deletion. Please log in again. The login page will open in a new tab.Joinsubscribers and get a daily digest of news, geek trivia, and our feature articles.

For example, there are a few easy-to-use methods for creating text files, should you need to do so. Our first method for creating text files uses the cat command.

After pressing Enter, you are not returned to the terminal prompt. Instead, the cursor is placed on the next line, and you can start entering text directly into your file. Type your lines of text, pressing Enter after each line. To verify your file was created, you can use the ls command to show a directory listing for the file:.

You can also use the cat command to view the contents of your file. Just type the following command at the prompt, and then press Enter:. You can also create a text file using the touch command. One difference between using this command and the cat command we covered in the last section is that, while the cat command lets you enter text into your file immediately, using the touch command does not.

Another big difference is that the touch command lets you create multiple new files with a single command. You can use the ls command to verify the existence of your new file:. You can also create multiple new files at once with the touch command. Just add as many extra file names separated by spaces as you want to the end of the command:.

You can also create a text file using the standard redirect symbol, which is usually used to redirect the output of a command to a new file. If you use it without a preceding command, the redirect symbol just creates a new file. Like the touch command, creating a file this way does not let you enter text into the file right away. Unlike the touch command, though, creating a file using the redirect symbol only lets you create one file at a time.

You are given no indication that the file was created, but you can use the ls command to verify the existence of your new file:. These three methods should allow you to quickly create text files at the Linux terminal, whether you need to enter text into them immediately or not. The Best Tech Newsletter Anywhere. Joinsubscribers and get a daily digest of news, comics, trivia, reviews, and more. Windows Mac iPhone Android. Smarthome Office Security Linux.Review your favorite Linux distribution.

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Click Here to receive this Complete Guide absolutely free. Hi Guys, I wanted to create a 2 GB file on the currenct directory. How can i create a 2 GB file through scripting and check its size shld go till 2 GB. Hi Swapna.

Use fallocate Command to Create Files of Specific Size in Linux

Originally Posted by Swapna Originally Posted by mohans.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. It only takes a minute to sign up. If your application ie. You can also use logrotate 8 to rotate your logs, it has size parameter which you can use for your purpose:.

With this, the log file is rotated when the specified size is reached. Size may be specified in bytes defaultkilobytes sizekor megabytes sizem. If your program doesn't need to write any OTHER files that would be larger than this limit, you can inform the kernel of this limit using ulimit. Before you run your command, run this to setup a MB file size limit for all process run in your current shell session:.

This will protect your system but it might be jaring for the program writing the file. As eyazici suggestsconsider setting up logrotate to prune log files once they reach a certain size or age.

You can discard old data or archive it for a period of time in a series of compressed files. You may create a new filesystem image, mount it using loop device and put the log file on that filesystem:. In package apache2-utils is present utility called rotatelogsit may be helpful for you. Full manual you may read on this link. I'm certain the original poster has found a solution. Here's another one for others that may read this thread Curtail limits the size of a program's output and preserves the last MB of output with the following command:.

Since it is text, I would write a script in your favorite language and pipe it to that. For that, instead of MB I would think of a 'reasonable' number of lines to keep track of. It has a couple of obvious short-cuts, but overall it does what you asked for. It will split the log into a chunks of a limited size, and the amount of chunks is limited too.

All can be specified via the command-line arguments. Log file is also specified via the command line. Note a small gotcha if you use it with the daemon that forks into background. Using a pipe will prevent the daemon from going to background. In this case there is a likely bash-specific syntax to avoid the problem:. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 8 years, 9 months ago.

Active 9 months ago. Viewed 50k times. Caleb 58k 13 13 gold badges silver badges bronze badges. Do you want the program killed after MB?By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. It needs to be stated that truncate on a file system supporting sparse files will create a sparse file and fallocate will not.

A sparse file is one where the allocation units that make up the file are not actually allocated until used. The meta-data for the file will however take up some considerable space but likely no where near the actual size of the file. You should consult resources about sparse files for more information as there are advantages and disadvantages to this type of file. A non-sparse file has its blocks allocation units allocated ahead of time which means the space is reserved as far as the file system sees it.

Also fallocate nor truncate will not set the contents of the file to a specified value like ddinstead the contents of a file allocated with fallocate or truncate may be any trash value that existed in the allocated units during creation and this behavior may or may not be desired.

The dd is the slowest because it actually writes the value or chunk of data to the entire file stream as specified with it's command line options. This behavior could potentially be different - depending on file system used and conformance of that file system to any standard or specification. Therefore it is advised that proper research is done to ensure that the appropriate method is used.

Just to follow up Tom's post, you can use dd to create sparse files as well:. This will create a file with a "hole" in it on most unixes - the data won't actually be written to disk, or take up any space until something other than zero is written into it.

Found this approach here. This approach is especially useful to subsequently mmap the file into memory. If your testing network upload speeds, this may not be the best idea if your application is doing any compression, a file full of zeros compresses really well.

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Using this command to generate the file. So you could put yourself in a situation where you think your uploading a 10KB file but it would actually be much less. There are lots of answers, but none explained nicely what else can be done. Looking into man pages for ddit is possible to better specify the size of a file. This will generate 4 MB text file with random characters in current directory and its name "4mb. Learn more. How to create a file with a given size in Linux?

Ask Question. Asked 11 years, 6 months ago.

linux create a file with size

Active 3 months ago. Viewed k times.This tutorial explains how to generate or create files of different sizes such as; large text file, empty file, MB file, 1 GB file, specific size file, and custom data file in Linux for testing and debugging purposes. Linux offers several commands for creating, manipulating and managing text files. Broadly, we can categorize these commands in two types; regular text manipulating commands and system text manipulating commands.

These commands are used to create and maintain regular text files. These commands are optimized for manipulating the text easily. These commands include several features and functions to make the text editing easier.

These commands are also known as the text editors. These commands are used to create or generate the dummy or sample files. These commands are optimized for creating any size of text file speedily. These commands don't include any feature or function to manipulate the text. Some popular system text manipulating commands are the dd, yes, fallocate, truncate, and touch. It depends on the requirement. If you want to store some meaningful data in the text file, use the regular text manipulating command.

If you want to create a file for testing and debugging purposes, use the system text manipulating command. Let's take a simple example. Suppose, you want to store some products' information in a text file. In this case, you should always use a regular text editor.

But, if you want to create a Mb or 1GB text file for testing, you should never use a regular text editor. Creating a large text file for testing from the regular text editor is only a waste of time. For example, suppose, you need a 1GB text file to test an archive utility. If you create this file from the regular text editor, you may have to spend more than one hour in adding, creating, and copying the useless text in this file. But, if you use a system text manipulating command, you can create this file in less than a minute.

In the below section, we will understand how to use the system text manipulating commands to create files of any size for testing and debugging purposes. To create a large text file of the specific size, we can use the dd command. The dd command takes four arguments; source, destination, block-size, and counter.There are a number of different ways to compress files using the Linux command line.

This article includes practical examples that show how to use the zip command to compact and organize files within your file system. Zipped files are used when you need to save space and copy large files from one place to another. If you have 10 files that are all megabytes in size and you need to transfer them to an ftp site, the transfer could take a considerable amount of time depending on your processor speed. If you compress all 10 files into a single zipped archive and the compression reduces the file size to 50MB per file, then you only have to transfer half as much data.

The previous command is fine for archiving all the files in a folder but it only includes files that aren't hidden. It's not always this simple. Imagine you wanted to zip your home folder so that you can back it up to a USB drive or external hard drive.

Your home folder includes hidden files. This creates a file called home. You must be in the home folder for this to work. The problem with this command is that it only includes the files in the home folder and not the folders, which brings us to the next example.

If you want to add new files to an existing archive or update the files in an archive, use the same name for the archive file when running the zip command. For example, imagine you have a music folder with four albums in it and you create an archive called music.

Now imagine one week later you download two new albums. To add the new albums to the zip file, simply run the same zip command as you did the previous week. If the zip file has a list of files in it and one of the files on the disk has changed, then the amended file is updated in the zip file. If you have a zip file that is supposed to contain the same file names every time and you want to update that file with any changes that have been made to those files then the -f switch helps you do this.

When you run the following command the zip file will contain the updated files file4 and file5 but file7 and file8 will not be added. So you created a massive zip file with hundreds of files and now realize that there are four or five files in the zip file that you don't need there. Without having to zip all those files again, you can just run the zip command with the -d switch as follows:. If you have files in one zip file and you want to copy them to another zip file without extracting them first and rezipping them, use the -u switch.

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Assume you have a zip file called "variousmusic. If the zip file you are copying to doesn't exist, it is created. The next switch is a really useful one because it lets you use the output of other commands to insert files into your zip file. Assume you want to create a file called lovesongs. The above command isn't percent perfect because it picks up words like "clover" as well, but you get the idea. To add all the returned results from the above command to a zip file called lovesongs.

If you are backing up your computer but the only media you have available for backing up to is a set of blank DVDsthen you have a choice.

linux create a file with size

You can keep zipping files until the zip file is 4. If you have a zip archive that is broken, you can try and fix it using the -F command and if that fails, the FF command. This is useful if you have created a split archive using the -s switch, and you lost one of the archive files.

If you have sensitive information that you want to store in a zip file, use the -e command to encrypt it.

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