Linux System Security: An Introduction to Basic Protection Strategies
Linux security requires attention to basic configurations; neglecting them can lead to risks like weak passwords and open ports. The core protective strategies are as follows: **Account Security**: Disable shared root access, use strong passwords (including uppercase, lowercase, numbers, and symbols), and **mandatorily use SSH key-based login** (generate a key pair locally, copy the public key to the server's `authorized_keys`, set permissions, and disable password authentication). Delete default/test accounts; use regular users with `sudo` for privilege elevation in daily operations. **File Permissions**: Follow the principle of least privilege. Set home directories to `700` (only the owner can operate), regular files to `644` (owner can read/write, others can read), and system files to `600`; avoid high-privilege settings like `777`. **Firewall**: Only open necessary ports (e.g., SSH 22, Web 80/443); default to blocking others. Use `iptables` or `firewalld` for configuration, and disable outdated services like Telnet. **System Updates**: Regularly perform `yum update`/`apt upgrade`, and restart after updates. Disable insecure services like Telnet to prevent vulnerability exploitation. **Log Monitoring**: Use tools like `journalctl`, `last`, and `auth.log` to monitor... (Note: The original text was truncated at "关注" and the translation reflects the uncompleted content as-is.)
Read MoreDetailed Explanation of Linux File Permissions: Must-Know Knowledge for Beginners
Linux file permissions are the core of system security, controlling user access methods to prevent misoperations or data breaches. Files are associated with three types of users: the owner (highest authority), the associated group (shared within the group), and others. Permissions are divided into three categories: read (r=4), write (w=2), and execute (x=1). Permissions can be represented in two forms: symbolic (e.g., `rwxrwxrwx`, where the first character indicates the file type, and the next three groups represent permissions for the three user categories) and numeric (octal, where the sum of permissions for the three user categories gives the value, e.g., `755`). Proficiency in mutual conversion between these forms is required. File and directory permissions differ: for files, `r` = view, `w` = modify/delete, `x` = execute; for directories, `r` = list contents, `w` = create/delete, `x` = enter. To modify permissions, use `chmod` (in symbolic or numeric form with `-R` for recursive directory changes) and `chown` (to change owner/group). Special permissions (SUID/SGID/SBIT) are used for specific scenarios. Mastery of symbolic-numeric conversion, `chmod` usage, and the differences between file and directory permissions enables proficiency through practice.
Read MoreLinux System Monitoring: Basic Tools and Performance Metrics
Linux system monitoring is fundamental for ensuring server stability and requires mastery of tools and metrics. Common tools include: process monitoring (`ps` for basic viewing, `top` for real-time dynamics, `htop` for tree-like structure/mouse operations); memory (`free -h` to check memory/cache, focusing on `available` and Swap); disk (`df -h` for partition inspection, `du -sh` for directory location, `iostat -x 1` for IO monitoring with `%util > 80%` indicating bottlenecks); and network (`ss -tuln` for port checking, `ss -s` for connection status). Key metrics: CPU load (should not exceed core count within 1 minute) and `wa` (high values indicate disk bottlenecks); memory should alert on Swap usage; disk monitoring requires cleaning when partition usage exceeds 85%. For system lag diagnosis: first use `top` to check load/CPU, then `free` for memory, `df` for disk confirmation, and `ss` to排查异常 connections. Through the "observe-analyze-optimize" cycle with tools and metrics, regular practice enables rapid problem localization and system stability maintenance.
Read MoreLinux Service Management: Starting, Stopping, and Checking Status
Linux services are background-running programs with specific functionalities. Managing services is fundamental to system operations and requires administrative privileges (e.g., `$ sudo`). Core operations are implemented via the `systemctl` command: `systemctl status [service_name]` checks the status (e.g., `active (running)`); `start/stop/restart` are used to start, stop, and restart services respectively; `list-units --type=service` lists all services, and `is-active [service_name]` quickly determines the running status. For enabling/disabling services at boot, use `enable/disable`, and verify with `is-enabled`. When services fail, `journalctl -u [service_name]` checks logs (e.g., port conflicts, configuration errors). Mastering these commands fulfills most service management requirements.
Read MoreLinux Server Basics: A Detailed Explanation of User and Permission Management
User and permission management in Linux is the core of system security and resource allocation. Users are the operating subjects, groups are used for unified permissions, and UID/GID are numerical identifiers (root UID=0). For user management: use `useradd` to create (add `-m` for home directory), `passwd` to set passwords, and `userdel -r` to delete. Switch identities with `su` and escalate privileges with `sudo` (requires adding to the sudo group). File permissions are represented by three sets of characters (rwx) for user/group/other permissions, set via numbers (e.g., 755) or symbols (e.g., u+x). Modify permissions with `chmod`, and change owners/groups with `chown`/`chgrp`. Directory permissions have special rules: execute permission (`x`) is required to enter, read permission (`r`) to view contents, and write permission (`w`) to create files. Special permissions include SUID (temporarily elevates program privileges, e.g., `passwd`), SGID (inherits group permissions for files), and SBIT (prevents accidental deletion, e.g., `/tmp`). `umask` controls default permissions for newly created files/directories (default 022, resulting in 644 for files and 755 for directories). Best practices: Follow the principle of least privilege, avoid routine operations as root, and regularly check high-risk permission files.
Read MoreLinux System Updates: A Beginner's Guide to Secure Upgrades
Updating the Linux system is a necessary step to ensure security and enhance performance, as it can fix vulnerabilities, optimize operations, add new features, and improve hardware compatibility. Before updating, important data (such as files in the `/home` directory and critical configurations) should be backed up, and non-essential services (e.g., `systemctl stop nginx`) should be shut down. For different distributions (Ubuntu/Debian use `apt`, CentOS/RHEL use `yum`/`dnf`), the core steps are: update package indexes → upgrade software → handle dependencies (`dist-upgrade`) → update the kernel (requires reboot) → clean up cache. After updating, check the system status (`dmesg | tail`), verify service operation (`systemctl status`), and confirm kernel and software versions (`uname -r`, etc.). Common issues include stuck updates (switching sources to resolve), system unbootability (rolling back the kernel), and software failures (reinstalling). Beginners should update at fixed times, prioritize backups, use official sources, and cautiously test beta versions.
Read MoreLinux Network Configuration: IP Address and Subnet Mask Setup
Configuring IP addresses and subnet masks on Linux servers is fundamental for network communication. An IP address (32-bit binary, dotted decimal format) identifies a device, while a subnet mask (32-bit, with 1s indicating network portions and 0s indicating host portions) distinguishes between network and host segments. To view current configurations, use `ip addr` (recommended for modern systems) or `ifconfig` (traditional, requiring `net-tools` installation on some systems). Temporary settings can be applied with `ip addr add <IP>/<mask_prefix> dev <interface>` or `ifconfig <interface> <IP> netmask <mask>`, which only persist during the current session. For permanent configuration, distributions vary: CentOS/RHEL 7+ requires editing `/etc/sysconfig/network-scripts/ifcfg-<interface>` and setting `BOOTPROTO=static` with IP/subnet parameters. Ubuntu 18.04+ uses `netplan`, editing `/etc/netplan/*.yaml` to disable DHCP and applying changes with `netplan apply`. Verification is done via `ip addr` to confirm the assigned IP, or by pinging local devices, same-subnet hosts, and the gateway. Key considerations: ensure unique IPs, correct subnet mask alignment, verify interface names (via `ip addr`), and use root/administrator privileges.
Read MoreLinux Firewall Configuration: Opening Ports and Security Policies
Linux firewalls are the core of server security, filtering traffic to prevent intrusions. Major tools include: firewalld (recommended for beginners, zone-based management such as public/trusted), iptables (underlying advanced), and ufw (Ubuntu-specific). Key firewalld configurations: Check status (systemctl), open temporary/permanent ports (e.g., 80), view rules (--list-ports). Note testing rules, backing up configurations, and avoiding tool conflicts. Mastering basic configurations reduces risks; advanced strategies (e.g., rate-limiting connections) can be extended for enhanced security.
Read MoreLinux User Permission Management: Resolving Common Issues for Beginners
This article introduces the basics of Linux permission management and solutions to common problems for beginners. The permission system can be analogized to an apartment building: users (residents), groups (families), and files/directories (rooms). Permissions include read (r=4), write (w=2), and execute (x=1). Common problem solutions: 1. Password reset: For regular users, administrators use `passwd` to change passwords. To reset the root password, enter single-user mode (add `init=/bin/bash` to Grub under CentOS, then execute `passwd root`). 2. Insufficient sudo privileges: Switch to root with `su -`, then use `visudo` to add the user's permission line. 3. Permission format parsing: For example, `-rw-r--r--` (regular file, owner can read/write, group/others only read). Modify permissions using `chmod` (numerical method like `755`, symbolic method like `u+x`). 4. Directory access denied: Execute permission is required. Use `chmod +x` or `chown` to change the owner/group. 5. Create user groups: Use `useradd`/`adduser` and `groupadd`, then `usermod -g/-G` to assign groups. Security prompt: Principle of least privilege, `
Read MoreLinux Server Basics: From Installation to Basic Configuration
Linux servers are the preferred choice for servers due to their stability, security, open-source nature, and ease of customization. Before installation, download the Ubuntu Server or CentOS Stream image, create a bootable USB using Rufus or dd, and boot from the USB drive at startup. During installation, select the language and time zone; for beginners, automatic partitioning is recommended. Set up a regular user and check the option to install OpenSSH. After installation, restart and log in. For basic configuration, set a static IP (using Netplan for Ubuntu and NetworkManager for CentOS), manage software with apt/yum/dnf, create a regular user, and disable direct root login. Use ufw on Ubuntu and firewalld on CentOS to enable the firewall. Subsequent learning topics include web server, database, and Docker deployment, with practice being key.
Read MoreMust-Know for Beginners: Linux Service Start and Stop Commands
This article introduces the basics of Linux service management, where mainstream distributions use the `systemctl` (systemd) tool to manage services. Key commands and their functions include: `start`/`stop` (start/stop), `restart` (restart), `reload` (reload configuration), `status` (check status), and `enable`/`disable` (enable/disable on boot), all requiring `root` or `sudo` privileges. Service names vary across distributions: for example, Apache is `httpd` in CentOS and `apache2` in Ubuntu; MariaDB (CentOS) or MySQL (Ubuntu) are the service names for database services. Common issues include: adding `sudo` for permission errors, using `status` or `journalctl` to troubleshoot startup failures, and searching for service names with `systemctl list-unit-files` if forgotten. Mastering core commands, service name differences, and troubleshooting methods enables proficient server service management.
Read MoreLinux System Maintenance: Disk Cleanup and Space Management
This article explains the necessity and methods of disk cleanup and space management for Linux servers. When disk space is insufficient, the system may become slow, applications cannot be updated, and even services may be affected, so regular cleanup and management are necessary. First, diagnose space usage: use `df -h` to check overall disk usage, `du -sh` to locate large directories, and `find` to search for large files (e.g., files exceeding 100MB). For cleanup, log files (e.g., `/var/log`) are a major space consumer. They can be automatically rotated using `logrotate` or manually emptied/deleted. System cache can be released by syncing data with `sync` and then setting `sysctl -w vm.drop_caches=3`. Temporary files (`/tmp`, `/var/tmp`) and APT cache (`apt clean`) can also be safely cleaned. Redundant files in user directories should be deleted after confirmation. If space remains insufficient after cleanup, a new disk can be mounted (requires formatting, creating a mount point, and configuring `/etc/fstab`). Partition expansion should be done cautiously with data backup. Daily maintenance suggestions: regularly check disk usage (cleanup is required when exceeding 80%), configure log rotation, avoid storing data in the root directory, and do not arbitrarily delete system files. The core is "locate -"
Read MoreLinux Server Security Hardening: Common Issues for Beginners
Linux server security is crucial for beginners. This article summarizes 7 common issues and their solutions: 1. Simple and long - unused passwords: Use strong passwords (8 characters with uppercase, lowercase, numbers, and special symbols), change them regularly, and switch to SSH keys (generate and upload public keys). 2. Disabling the firewall: Only open necessary ports (e.g., Web 80/443, SSH 22), and disable insecure services like Telnet. 3. Exposing SSH ports to the public network: Restrict IP access and use fail2ban to prevent brute - force attacks. 4. Unupdated system/software: Regularly update via yum/apt and enable automatic updates. 5. Permission confusion (777): Follow the principle of least privilege (directories 755, files 644) and avoid root abuse. 6. Ignoring logs: Configure log rotation and regularly check critical logs like auth.log. 7. Redundant services: Uninstall useless services (e.g., vsftpd) and close unused ports. Core principles: least privilege, closing entry points, timely updates, and log auditing. Beginners can start with strong passwords, restricting SSH access, and closing unnecessary services for long - term maintenance.
Read MoreLinux Command Complete Reference: A Must-Have Handbook for Beginners
This article introduces the basics of Linux commands and commonly used tools, covering core operations and beginner tips. The basic command format is "command [options] [arguments]". Essential beginner tips include: using --help or man for help, Tab completion, Ctrl+C to interrupt, Ctrl+L to clear the screen, and ↑/↓/Ctrl+R to manage history commands. Core operations: Use ls (-l/-a/-h) to view files and directories, cd to switch directories (relative/absolute paths and ~/. ..), touch/mkdir to create files/directories, and cp/mv/rm to copy, move, and delete (be cautious with rm). For system information, use uname -a, uptime, df -h/free -h, and ps/top to manage processes. For text processing, use cat/head/tail to view files and grep -r to search for text. Software package management is divided into Ubuntu (apt) and CentOS (yum), requiring sudo for privilege elevation. Beginner pitfalls: Pay attention to permissions (sudo), avoid dangerous commands (e.g., rm -rf *), and practice basic commands (ls, cd, etc.) to quickly master daily operations.
Read MoreLinux Server Infrastructure: From Installation to Service Deployment
This article introduces Linux server installation and basic service deployment, suitable for zero-basic learners. Linux is the preferred choice for servers due to its stability and security. Unlike the desktop version, the server version focuses on performance optimization. Installation preparation: Minimum hardware requirements are 1-core CPU, 2GB memory, and 20GB hard disk (SSD is better). Recommended distributions include CentOS (enterprise-grade stability) or Ubuntu Server (user-friendly for beginners). Taking CentOS 7 as an example, download the minimal ISO, perform automatic partitioning, set the root password, and restart. Basic configuration: Configure a static IP (to avoid changes), create a regular user, and disable direct root login. The firewall should only open necessary ports (e.g., 80 for web services). Core service deployment: Practical deployment of Nginx (web server), vsftpd (FTP server), and MariaDB (database), with installation, startup, and verification methods introduced respectively. Summary: The process is minimal installation → network security configuration → core service deployment. Security and stability are key, and subsequent exploration can be done on complex architectures (e.g., LAMP/LNMP).
Read MoreBeginner's Guide: Linux System Updates and Upgrades
Updating and upgrading the Linux system is actually straightforward for beginners. The core purposes are to fix vulnerabilities (security patches) and enhance software versions (new features/performance). Regular operations ensure the system is more secure and powerful. For beginners, follow these steps (taking Ubuntu/Debian and CentOS/RHEL as examples): 1. **Verify system information** (optional): Use `uname -a` to check the kernel and `lsb_release -a` to view the distribution. 2. **Update package lists**: For Ubuntu, run `sudo apt update`; for CentOS, use `sudo dnf check-update`. 3. **Perform system updates**: For Ubuntu, execute `sudo apt upgrade`; for CentOS, use `sudo dnf upgrade` and confirm as prompted. 4. **Resolve dependency conflicts**: Select `y` or `n` as prompted. For "keep configuration files," choose `N` to overwrite old configurations for safety. 5. **Reboot the system**: If the kernel or core components are updated, execute `sudo reboot` immediately. Pitfall avoidance: Back up data before updating; distinguish between distribution-specific commands (Ubuntu uses apt, CentOS uses dnf/yum); avoid updating during critical service operations; ensure network stability; if updates fail, check the software sources.
Read MoreSSH Service Configuration: A Detailed Explanation of Linux Remote Connection
SSH is a secure remote login protocol that encrypts data transmission, used for remote management of Linux servers (such as cloud servers and local servers), replacing insecure protocols like Telnet. Key configuration steps: Install `sshd` on the server (using `apt` for Debian/Ubuntu, `yum` for CentOS/RHEL), start it and set it to boot automatically (`systemctl start/ enable sshd`). Modify `/etc/ssh/sshd_config` (backup first). Critical configurations: Change the port (e.g., 22→2222 to prevent brute-force attacks), disable root login (`PermitRootLogin no`), allow specific users (`AllowUsers`), and disable password login in favor of key-based authentication (generate a key pair locally and use `ssh-copy-id` to transfer it to the server). Restart `sshd` after changes. Client connection: Use PuTTY on Windows, and the terminal on Linux/macOS with the command `ssh username@IP -p port`; key-based authentication is more secure. Security notes: Allow the port through the firewall (UFW or cloud security groups), disable direct root login, and regularly update the system and SSH. Common issues: Timeout (check IP/network), connection refused (check port/service), permission errors (
Read MoreServer Performance Optimization: An Introduction to Linux System Tuning
Linux system tuning aims to address server performance issues, enhance speed, stability, and resource utilization, and prevent business disruptions or degraded user experience. Common bottlenecks include CPU, memory, disk I/O, and network, with corresponding diagnostic tools: dstat (comprehensive status), top (CPU/load), free -h (memory), iostat -x 1 (disk I/O), and ss -tuln (network). Targeted tuning strategies: Optimize CPU by managing high - utilization processes; focus on memory caching (the larger the better) and Swap usage; improve disk I/O for random reads/writes (e.g., migrating to SSD); and reduce TIME_WAIT connections and limit connection numbers in the network. System parameters can be temporarily or permanently adjusted via sysctl, which requires testing and verification. Key considerations: Diagnose first before tuning—avoid blind adjustments. Regular monitoring (e.g., with dstat) and continuous iteration are crucial.
Read MoreLinux System Maintenance: Essential Basic Knowledge for Beginners
Maintaining Linux servers is an essential skill in the internet era. Linux, being stable, open-source, and secure, is the mainstream operating system for servers. Beginners can solve common issues such as file permissions and service startup by mastering basic operations. Core skills include: command-line operations (ssh login, basic commands like pwd/ls/cd); file system (root directory and core directory structures such as /etc/var); file operations (touch/mkdir/cp/mv/rm); permission management (rwx permission representation, chmod modification); processes and services (ps/top/kill for viewing and terminating processes, systemctl for managing services); network configuration (ip addr, ping, port checking, and firewall setup); system updates (apt/yum for updates, software installation and uninstallation); and log backup (tar compression, tail for log viewing). Learning suggestions: practice extensively using virtual machines or experimental platforms, utilize tools like Xshell/FinalShell, make good use of the man command for help, back up data before operations, and develop a cautious habit.
Read MoreEssential Linux Command Line Tips for Beginners
This article introduces the learning and use of the Linux command line. The reason for learning the command line is its directness and efficiency, which is suitable for server management, can complete complex tasks, and is more flexible than the graphical interface. Basic file directory operations include ls (list directories, e.g., ls -la shows detailed hidden files), cd (change directory, e.g., cd ~ returns to the home directory), pwd (show current path), mkdir (create directories), touch (create empty files), rm (delete, e.g., rm -rf is used with caution), cp (copy), mv (move/rename), etc. It should be noted that dangerous operations such as rm -rf require special caution. Efficiency tips include: shortcuts (Ctrl+C to interrupt, Ctrl+D to exit, etc.), wildcards (* for batch file matching), pipes | to combine commands (e.g., ls | grep "txt"), background operation &, using --help or man to check help, history commands (history) and Ctrl+R for search. Common problem solutions: For insufficient permissions, use sudo to elevate privileges; check command spelling or consult help if there is an error; exit with exit or Ctrl+D. Summary: The command line is a set of tools that can be mastered with more practice. Platforms like Runoob and Learn Linux Terminal are recommended for learning.
Read MoreDisk Space Management: Storage Optimization for Linux Servers
This article introduces the necessity, methods, and optimization strategies for disk space management on Linux servers. Insufficient disk space can lead to software installation failures, service errors, and even system crashes, thus requiring reasonable management. Core concepts include inodes (which record file metadata and are prone to exhaustion first) and blocks (the smallest unit for data storage). Tools for checking: `df -h` for overall space, `du -sh`/`du -ah` for directory sizes, and `df -i` for inode issues. Common problems and solutions: oversized logs (managed automatically by logrotate or manually cleared), temporary file accumulation (via tmpwatch or deleting files in /tmp), uncleaned large files (using find to locate large files), and unreasonable partitioning (adjusting LVM or separating partitions). For long-term optimization, regular backup cleanup, using external storage to share pressure, and setting up alert monitoring are recommended. Always confirm before deletion to avoid randomly clearing logs. The core principles are regular inspection, proactive cleanup, and long-term planning to ensure server stability.
Read MoreCommon Issues for Beginners: How to Troubleshoot Linux Service Startup Failures
Linux service startup failures are common issues for beginners. Here's a step-by-step troubleshooting guide: First, confirm the status with `systemctl status 服务名` (replace "服务名" with the actual service name); if it shows "failed", further investigation is needed. Next, use `journalctl -u 服务名` or service-specific logs (e.g., Nginx error log at `/var/log/nginx/error.log`) to identify errors, focusing on keywords like "syntax error", "port in use", or "permission denied". If the service is not installed, check with `yum list installed` (for RHEL/CentOS) or `dpkg -l` (for Debian/Ubuntu), then install it via `yum` or `apt`. Key areas to check include: configuration file syntax (e.g., `nginx -t` for Nginx), port conflicts (use `netstat -tuln` to check ports), dependent services (via `systemctl list-dependencies`), and permission issues (adjust ownership and file permissions). Following the order "status → logs → fix configuration/port/dependencies" and combining log analysis with command checks will help resolve issues quickly for beginners.
Read MoreDetailed Explanation of Linux Network Services: From DNS to FTP
This article introduces the basic content of Linux network services, with a focus on DNS and FTP services. Linux network services are core programs that provide network functions (such as domain name resolution and file transfer) for servers, helping to understand network communication logic and manage server maintenance. DNS (Domain Name System), as a "translator", converts domain names (e.g., www.baidu.com) into IP addresses. Its working principle includes local cache queries and recursive/iterative queries to DNS servers (e.g., 114.114.114.114). The Linux configuration file is /etc/resolv.conf, which records DNS server addresses. FTP (File Transfer Protocol), as a "courier", uses the control connection (port 21) to transmit instructions and data connections (port 20 or random ports) to transfer files. vsftpd is commonly used in Linux, and the configuration file vsftpd.conf controls anonymous or user permissions. Common issues: For DNS, check resolv.conf and use nslookup. For FTP, verify the status of vsftpd and the port (21). It is recommended to practice nslookup to test domain name resolution or anonymously connect to public FTP servers to enhance network service management capabilities.
Read MoreShell Scripting Basics: An Introduction to Linux Automation Tasks
The Shell is an interface program for Linux command-line interaction (e.g., bash), and a script is a text file of commands for automating tasks. Learning Shell enhances operational efficiency (batch processing, scheduled tasks), system maintenance (monitoring, deployment), and is cross-platform and general-purpose with simple, easy-to-learn syntax. Basic syntax includes: variables (starting with letters/underscores, no spaces in assignment, referenced with $), common commands (echo, pwd, ls, etc.), comments (# for single line), conditional judgment (if-else), and loops (for/while). For advanced use, tools like grep and awk can be combined. Improve proficiency by modifying examples, practicing complex scenarios (e.g., crontab), and using set -x for debugging.
Read MoreBeginner's Guide: Configuring Environment Variables in Linux
This article introduces the knowledge of Linux environment variables. Environment variables are information carriers for the system or programs (e.g., PATH records command paths). Their role is to allow programs to be found by the system and to set running parameters. To view environment variables, you can use `printenv`/`env` (for all variables) or `echo $VariableName` (for a single variable). For temporary configuration, use `export VariableName=Value`, which only takes effect in the current terminal session. For permanent configuration, modify the configuration files: for the user-level, edit `~/.bashrc` or `~/.zshrc` (effective for the current user); for the system-level, edit `/etc/profile` (effective for all users). After modification, use `source` to load the changes. Verification can be done by checking the newly added path with `echo $PATH` or testing relevant tools. Common issues include: forgetting to use `source` which leads to configuration not taking effect, path errors, and requiring `sudo` privileges for system-level configurations. In summary: use `export` for temporary settings, modify configuration files for permanence, and mastering environment variables can enhance efficiency.
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