The Linux kernel contains four types of IO schedulers, namely NoopIOscheduler, AnticipatoryIOscheduler, DeadlineIOscheduler and CFQIOscheduler. Typically, disk read and write latency is caused by the head moving to the cylinder. In order to solve this delay, the kernel mainly adopts two strategies: caching and IO scheduling algorithms. Scheduling Algorithm Concepts When a block of data is written to or read from a device, the request is placed in a queue waiting for completion. Each block device has its own queue. The I/O scheduler is responsible for maintaining the order of these queues to utilize the media more efficiently. The I/O scheduler will unordered I/O

sblk is a command used to list all available block device information in a Linux system. Block devices refer to devices that can transmit data in blocks, such as hard disks, optical drives, USB flash drives, etc. The lsblk command can display the dependencies between block devices, as well as various attributes such as size, type, file system, mount point, etc. The lsblk command obtains information from the /sys virtual file system and udev database. If there is no udev database or lsblk is not compiled with udev support, then it will try to read the label, UUID and file system type from the block device, which requires root privileges. In this article, we will explain how to use the lsblk command to list the block devices of a Linux system to

Linux is an open source, portable, and customizable operating system that is widely used in various fields, such as servers, desktops, embedded devices, etc. The core of Linux is the kernel, which is responsible for managing hardware resources and providing basic services. However, the kernel is not an independent entity and requires a file system to store and access various data and programs. A file system is a method of organizing and managing files. It defines the file's name, location, attributes, permissions and other information. In Linux, there are many different types of file systems, such as ext4, xfs, btrfs, etc., each of which has its own characteristics and advantages. However, among all file systems, there is a special file system, which is the foundation and core of the Linux system, which is

Question: I want to use df command on Linux to check disk usage space. Can you give me some specific examples of the df command so I can make better use of it? On Linux, if you want to know how much space a specific file system takes up, or how much space is available for a specific file system, you can use the df command. The df command is a command that displays the available disk space of the file system for each filename parameter. If you do not specify any file names, the output will show the available space for all currently mounted file systems. By default, df displays disk space in 1K blocks. Linux has many command line or graphical interface tools that can tell you detailed information about current disk space usage, such as

Linux environment variable configuration When customizing software installation, it is often necessary to configure environment variables. Listed below are various methods of configuring environment variables. The environment description of all the examples below is as follows: System: Ubuntu14.0 User name: uusama Need to configure MySQL environment variables Path: /home/uusama/mysql/binLinux Reading environment variables Method of reading environment variables: The export command displays the current system definition All environment variables echo$PATH command outputs the value of the current PATH environment variable. The effect of executing these two commands is as follows uusama@ubuntu:~exportdeclare-xHOME="/home/uu

When observing the running status of online services on an online server, most people like to use the top command first to see the overall CPU utilization of the current system. For example, for a random machine, the utilization information displayed by the top command is as follows: This output result is simple to say, but complex, it is not so easy to understand it all. For example: Question 1: How is the utilization information output by top calculated? Is it accurate? Question 2: The ni column is nice. It outputs the CPU overhead when processing? Question 3: wa represents iowait, so is the CPU busy or idle during this period? Today we will conduct an in-depth study of CPU utilization statistics. Through today's study, you will not only understand c

As a Linux user, you will inevitably encounter various problems during the startup process. Among them, the two tools GRUB and SHIM are often the most likely to cause problems. GRUB is the GNU boot loader, and SHIM is a trusted boot (SecureBoot) solution. The two work together in the Linux system startup process, but they also make some users confused and distressed. This article will introduce you how to solve GRUB and SHIM problems during Linux system startup, allowing you to easily overcome these obstacles. When using the efibootmgr-v command to modify the efi startup item, I don’t know whether to choose GRUBX64.EFI or SHIMX64.EFI when specifying the boot program.

In Linux systems, the dd command is a highly respected tool with powerful and diverse functions, mainly used for file copying and conversion. Because it is widely used in disk copy and data copy operations, it is named the "disk copy" or "data copy" command. This article aims to comprehensively introduce the various uses of the dd command and provide rich sample code to help readers fully appreciate its functions and potential. The flexibility and customizability of the dd command make it a powerful tool for processing data conversion between files and devices, showing strong application value in various scenarios. Copy files The dd command can be used to copy files. The following example copies a file to another location: ddif=input.txtof=output.txt This will copy a file from i