Setting folder size limits in CentOS

Creating folders with quotas primarily utilizes loop devices in Linux.

In Linux, there is a special type of block device called a loop device. A loop device is a virtual block device created by mapping a normal file on the operating system. In other words, a loop device is a virtual device used to treat a file as a virtual disk medium. After association, the loop can be formatted; this essentially involves performing certain operations on the associated file, allowing it to be mounted and used like a disk.

In other words, a circular device can virtualize files as block devices to simulate the entire file system, so that users can treat it as a hard drive, CD-ROM drive, or floppy drive and mount it as a directory.

Here are the specific steps to create a quota folder:

1. First, use the dd command to create a quota file of 20MB.

dd if=/dev/zero ibs=2M count=10 of=/usr/local/test.img

if=/dev/zero: indicates that the input file is /dev/zero; /dev/null can also be used.

ibs=2M: IBlockSize indicates that the block size is 2M.
of=/usr/local/test.img: Output file

2. Associate the test.img file with the loop device.

losetup /dev/loop0 /usr/local/test.img

3. Creating a file system on the virtual device is actually an operation on test.img, because it has already been associated with /dev/loop0.

mkfs /dev/loop0

4. Mount the file device to the target folder to complete the quota function for the folder (/usr/local/test02).

mount /dev/loop0 /usr/local/test02

5. Resources need to be released when no longer in use.

umount /usr/local/test02 losetup -d /dev/loop0

6. Add the command to start the program to the /etc/rc.d/rc.sysinit file.

The script `/etc/rc.d/rc.sysinit` starts system services, such as setting system environment variables, setting the system clock, loading fonts, checking and loading file systems, and generating system startup log files.

  losetup -a |wc -l