File size limits linux

how the file size is limited on a specific file system? [closed]

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can any one give the details .. I can not find it in the net.

2 Answers 2

The file size limit of a filesystem is generally decided by the size of the variable containing its file size. In a filesystem where the size is defined as a 32 bit unsigned integer you will not be able to store a file larger than 2^32-1 (=4294967295) bytes in size. On many modern filesystems file size is commonly stored as 64 bits which gives a maximum file size of 2^64 (16 EiB), a very large number.

The maximum size of the filesystem itself is generally limited by the size of the addresses of the filesystem blocks times the filesystem block size. On old FAT16 filesystems the addresses were limited to 16 bits (=65536 unique addresses) and block (or cluster) size were limited to maximum 64kB, this led to the limit of 4GB maximum filesystem size, this was the reason that a larger variant, FAT32, was developed. On modern filesystems such as NTFS, ext4, btrfs, and many others the maximum filesystem size is very large and not likely to be hit in a long time. However, because of limitations in the implementations, there are some artificial limits that are lower than the actual format limit in some cases, for example NTFS has a filesystem size limit of 256TB (according to Wikipedia).

I don’t really get what you are up to, but I try to answer nevertheless.

A file system limits its maximum file size due to several reasons:

• The field for the file size entry in the inode has a maximum size
• The numbers of blocks per file max be limited

For example, in a 32 bit field you can enter only a maximum value of 4*1024^3 — so this is the maximum size.

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How to Use the ulimit Linux Command

ulimit is a built-in Linux shell command that allows viewing or limiting system resource amounts that individual users consume. Limiting resource usage is valuable in environments with multiple users and system performance issues.

In this tutorial, you will learn to use the ulimit command in Linux with examples.

What Is limits.conf?

The limits.conf file is a configuration file that defines the system resource allocation settings ulimit uses. The full path to the configuration file is /etc/security/limits.conf.

Changing the values in the file persist after system reboot. Superuser permissions are required for editing the limits.conf file.

The first section of the limits.conf file looks like this:

ulimit, Soft Limit, and Hard Limit in Linux Explained

The following sections explain the ulimit syntax and the difference between two resource limitation types — a soft limit and hard limit.

Note: Use the top command to obtain information about the running processes and resource usage in a system.

ulimit Syntax

The ulimit command takes the following general syntax:

For example, to set the physical memory size in kilobytes, enter:

Flags

Use the ulimit flags to view or limit individual values for various system resources. When a [limit] is given, it is the new value of the specified resource.

Note: If your system doesn’t support a feature, the corresponding flag does not work.

[limit] Parameter

Adding a [limit] passes the new value for the specified resources. When omitted, the command prints the current soft limit value for the specified resource, unless you specify the -H flag.

The limit applies to both the soft and hard limit if neither the -H nor -S flags are specified.

Exit Values

The ulimit command has two exit values:

• 0 . Marks a successful completion.
• >0 . A request for a higher limit was rejected or an error occurred.

Soft Limit

The soft resource limits are kernel-enforced values for the corresponding resource. The soft limit is manageable by any user, and its maximum value cannot exceed the hard limit. The hard limit acts as a ceiling for the soft limit.

To view the detailed soft limits for the current user, run:

Hard Limit

The hard resource limit defines physical resource limit for a user. At the same time, the hard limit is the maximum value for soft limit. Only root users are allowed to change the hard limit.

To view the detailed hard limits for the current user, run:

Note: To avoid performance issues and noisy neighbors, choose one of our Bare Metal Cloud instances. With dedicated compute power, you do not have to worry about resource contention.

How to Use ulimit

Run the ulimit command by entering the command name in the terminal:

The output shows the resource amount that the current user has access to. In this example, the user has unlimited system resources. To view or set individual resource limits, use the available ulimit flags.

The following sections lists the most common uses of the ulimit command.

Detailed Limit Report

Get a detailed report with all resource limits for the current user by specifying the -a flag:

The output contains a detailed report about the resource limits for the current user.

Limit Process Number

Limit a user’s maximum process number by specifying the -u flag and the number of processes.

For example, we will limit the process number to 10:

Restricting the maximum process number per user prevents them from using up all the system’s resources. Limiting the process number also prevents the adverse effects of potential attacks such as fork bomb.

In the example above, we first limited the process number to 10, and then executed a fork bomb. The fork bomb would otherwise use up all the resources and make the system unresponsive.

Note: See why fork bombs are dangerous and what other Linux commands you should never run.

Limit File Size

The -f flag sets the maximum file size that a user can make. For example, the following command limits the file size to 50KB:

Test if the limit works by creating a larger file. For example, we used the cat command to redirect the /dev/zero output to a file, which would be much larger than 50KB:

The output states that the file size limit has been exceeded. Check the file size by running:

The ls command output shows that the file size is exactly 50KB, which is the limit we have previously set.

Limit Maximum Virtual Memory

Use the -v flag to set the maximum virtual memory amount available to a process. Limiting a process’ virtual memory stops it from using up all the memory and prevents thrashing.

For example, the following command limits the virtual memory available for a process to 1000KB:

Limit the Number of Open Files

The -n flag limits the number of simultaneously opened files (file descriptors). The following example sets the number of open files to five:

To test this, we will try to open multiple text files, which results in an error:

Edit limits.conf file to Change Soft or Hard Limit

To change the soft or hard limit, edit the values in the limits.conf file.

1. Open a terminal window and change the directory to /etc/security :

2. Open the limits.conf file using a text editor, such as the vim editor.

3. Change the limit values by editing the existing entries or adding a new one. Each limitation entry has four parts:

• . Defines a user, a group, or contains a wildcard ( * or % ).
• . Accepts two values — soft or hard .
• . Accepts any of the values listed in the configuration file.
• . An integer value expressed in a unit associated with .

$ touch 2gbarea $ truncate -s 2G 2gbarea $ mke2fs -t ext4 -F 2gbarea mke2fs 1.43.3 (04-Sep-2016) Discarding device blocks: done Creating filesystem with 524288 4k blocks and 131072 inodes Filesystem UUID: bf1b2ee8-a7df-4a57-9d05-a8b60323e2bf Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912 Allocating group tables: done Writing inode tables: done Creating journal (16384 blocks): done Writing superblocks and filesystem accounting information: done $ sudo mount 2gbarea up $ df -h up Filesystem Size Used Avail Use% Mounted on /dev/loop0 2.0G 6.0M 1.8G 1% /home/muru/up