Deleting All Lines in Vim
There are two common methods to delete all lines in Vim. First, in command mode, press `gg` to jump to the beginning of the file, then enter `dG`. Here, `gg` positions the cursor at the first line, and `dG` deletes from the current line to the end of the file. Second, directly enter `:%d` in command mode and press Enter. The `%` denotes the entire file range, and `d` is the delete command. After execution, the file content is cleared. If there are unsaved changes, Vim will prompt whether to save when exiting.
Read MoreCommand to Output Current Time in Ubuntu Terminal
In the Ubuntu system, the `date` command can output the current time. The basic `date` command displays the complete date and time, including the weekday, month, day, specific time, and time zone. To display only the time part, formatting parameters can be used, such as `date +"%H:%M:%S"` to output the 24-hour format time; `date +"%I:%M:%S %p"` to output the 12-hour format with AM/PM indicator.
Read MoreThe Use and Trade-offs of Foreign Keys in Databases
There is debate over whether foreign keys should be used in database design. While foreign keys ensure data integrity, they introduce issues such as reduced write performance, increased system coupling, high operational risks, poor flexibility, uncontrollable cascading operations, failure in distributed scenarios, and redundant validation with the application layer. The alternative is to ensure data integrity at the application layer. Foreign keys may be considered for small systems, but modern high-concurrency systems often avoid them. The essence lies in balancing the database's strong constraints with system performance and flexibility.
Read MoreChanging the Owner and Group of Folders and Files in Ubuntu
In the Ubuntu system, the `chown` command is used to modify the owner user and group of a file or folder. The basic syntax is `chown [options] username:group filename/foldername`. Common operation examples include: using `sudo chown username filename.txt` to change the file owner;
Read MoreChecking for Malicious Logins on Ubuntu System
In Ubuntu system, there are multiple ways to check for malicious login situations. To view login history, commands like `last`, `lastb`, and `last -i` can be used. For system log inspection, commands such as `sudo grep "Failed password" /var/log/auth.log` are applicable; in newer Ubuntu versions, `journalctl -u ssh -g "Failed password"` can be used instead. To check recently logged-in users, commands like `who`, `w`, and `lastlog` are useful. For SSH login records, `sudo grep sshd /var/log/auth.log` combined with relevant keywords can be employed.
Read MoreHow to Install or Update Graphics Card Drivers in Ubuntu System
There are common methods to update graphics card drivers in Ubuntu. The third method is recommended in the introduction. Method 1 uses the official repository: first, run `sudo apt update` to update the package list, then `sudo apt upgrade -y` to upgrade. Method 2 is for NVIDIA: you can install a driver management tool or use the graphical tool `sudo nvidia-settings`. Method 3 is to add the Graphics Drivers PPA repository by executing `sudo add-apt-repository ppa:graphics-drivers/ppa` and other steps in sequence.
Read MoreA Tool Website Developed with Python
This article introduces a feature-rich tool website developed using Python. It includes various tools such as document tools, PDF tools, image tools, audio tools, video tools, voice tools, and programming tools, which are commonly used in work or study.
Read MoreInstalling Docker on Ubuntu with GPU Support
This article introduces the installation and configuration of Docker using the Alibaba Cloud mirror source, with support for NVIDIA GPU usage. First, add the Alibaba Cloud GPG key and set up the repository, then update the apt source and install Docker. Next, add the domestic mirror source address in `/etc/docker/daemon.json` and restart the Docker service for configuration. Then, download and install nvidia-container-toolkit via the curl command, configure it as the Docker runtime, and finally test GPU support. Key steps
Read MoreStarting Programs with /etc/rc.local on Ubuntu 22.04
This article introduces the method to achieve program startup at boot using `/etc/rc.local` on Ubuntu 20.04 or 22.04 systems. It requires editing the `/lib/systemd/system/rc-local.service` file to add configurations, creating and granting execution permissions to `/etc/rc.local`, creating a soft link for the service, and enabling the relevant service. After the above steps, reboot the device to check if the startup at boot is successfully implemented. If a log file containing "Test Successful" is generated in the specified path, it indicates that the setup...
Read MoreImplementing Read-Write Splitting with Mycat Middleware for One-Master-One-Slave and Two-Master-Two-Slave Topologies
This document provides a detailed introduction to how to build a MySQL master-slave cluster using Mycat, along with testing for load balancing and high availability. The following is a summary of the main content: ### I. Environment Preparation 1. **Install the Server**: MyCat, version 2.0, has been installed. 2. **Install the Client**: MySQL-8.0.17 has been installed. 3. **Configuration File Check**: The configurations of `conf/mycat-server.xml` and `schema-mysql.sql` were checked and confirmed.
Read MoreImplementing MySQL Database Master-Slave Replication
This document provides a detailed introduction to how to configure Master-Slave Replication in MySQL database, accompanied by configuration steps and simple test cases. The key points summarized are as follows: ### Configuration Steps #### 1. Select servers as master and slave - Choose one MySQL server as the master and another as the slave. #### 2. Setup on the master server - First, add the following configurations to the master's `/etc/my.cnf` or `my.ini` configuration file:
Read MoreInstalling and Using Mycat for Distributed Database on CentOS
This article provides a detailed introduction to how to install and configure Mycat in a CentOS environment to achieve basic operations of distributed databases. Below is a summary of the content in the article, along with some possible missing information or steps supplemented. ### I. Environment Preparation 1. **System Requirements**: Ensure that a Java environment (e.g., JDK8) is installed. 2. **Network Configuration**: - Open the firewall and configure rules to allow the service ports of MySQL and Mycat to pass through. - Ensure that the network connections between all nodes are smooth.
Read MoreBuilding a High-Availability and High-Concurrency Website with Nginx and Tomcat on CentOS
This blog mainly introduces how to deploy and configure a Tomcat cluster on CentOS to achieve logical layer distributed deployment of websites. The specific steps include: ### 1. Preparation Work - Ensure all servers (in this example, node3 and node4) are installed with CentOS operating system. - Install JDK and set environment variables. ### 2. Install Tomcat Cluster #### Operations on the master node: 1. **Copy the Tomcat files to the specified directory**, for example, `/opt/tomcat7`.
Read MoreInstalling and Uninstalling CUDA and CUDNN on Ubuntu
You have provided a detailed introduction to installing CUDA 11.8 and CUDNN 8.9.6 on the Ubuntu system, and verified it through a simple PyTorch program. To ensure the completeness of the documentation and facilitate others' reference, I have organized and supplemented your content. ### Installation Environment - **Operating System**: Ubuntu 20.04 - **Python Version**: 3.7.13 ### Step 1: Install CUDA 11.8 1. **Add Repository Source**:
Read MoreSetting Up a Cloud Service Platform on CentOS
This article provides a detailed introduction to the process of creating a cloud server using KVM on CentOS systems. Below is a summary of key steps and precautions: ### I. Environment Preparation - **Install necessary software packages**: ```bash sudo yum install -y bridge-utils libvirt virt-install qemu-kvm iptables ``` ### II. Configure Network Bridging 1. **Create a network bridge device**:
Read MoreLearning SpringMVC Notes——Creating a SpringMVC Project with Intellij IDEA
This article introduces the creation and configuration of a SpringMVC project. First, a Spring project is created, the Spring MVC option is checked, and the required JAR packages are downloaded. Next, the lib folder is moved to WEB-INF and the configuration file path settings are adjusted. Path prefixes/suffixes are configured in `applicationContext.xml` and `dispatcher-servlet.xml` respectively, and the package scan is used to automatically scan Controller classes. Define Cont
Read MoreSQL Format Notes
This content mainly introduces the basic SQL statements for creating, modifying, and deleting tables, as well as data querying, inserting, updating, and deleting. First, when creating a table, you need to define the data types and constraints of columns; for modifying a table, you can add or delete columns/constraints, or change the properties of columns; for deletion, you can directly use the `drop table` command and optionally cascade delete related dependencies. Query statements use the `select` keyword to retrieve data from specified tables and support grouping and sorting. In addition, various conditional expressions are also introduced, such as `like`, `insert into...value` (note: the original text may have an incomplete `insert into...value` statement, which has been retained as is).
Read MoreSolving Chinese Garbled Characters in MySQL under XAMPP
This article introduces how to set up UTF-8 encoding in MySQL integrated with XAMPP. First, open the configuration file my.ini in the control panel and add four lines of code: default_character_set = utf8, character-set-server = utf8, collation-server = utf8_general_ci, and default_character_set = utf8. Then restart the MySQL service and ensure that when creating the database (the original content is incomplete, the translation ends here based on the provided text).
Read MoreDeveloping Java Web Projects with IntelliJ IDEA
This article introduces the basic steps to develop Java Web applications using IntelliJ IDEA Ultimate. First, download and install the software from the official website, choosing the trial version during installation. When creating a new Java Web project, configure the Tomcat path in the Application Server and add a JSP file. Finally, click the run button to automatically open the homepage in the browser; directly click the browse icon in the upper right corner of IDEA to preview the newly created hello.jsp page. The entire process simplifies the complex
Read MoreSetting up a Java Web Server on Ubuntu Server
This article details the steps to install and configure Tomcat, PHPMyAdmin, and resolve MySQL Chinese garbled characters issues on an Ubuntu server. Below is a summary of the content along with some supplementary information: 1. **Installing and Setting Up Apache2** - Changed the Apache2 service port to 8022 to avoid conflicts with other web services. - Started Apache. 2. **Installing PHPMyAdmin and Associating with Apache2** - Configured Apache to support p
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