Master Linux Basics: OS Overview, Commands, Users & Permissions

操作系统概述

Linux 操作系统安装

Linux 文件系统

Linux 命令操作

Linux 权限管理

用户和用户组

用户操作命令

权限操作

Linux 进程管理

Linux 其他常用命令大全

Linux 系统软件安装

常用软件安装

Operating System Overview

Operating System (OS) is software that manages and controls computer hardware and software resources, running directly on the bare metal. All other software must rely on the OS to operate.

Linux Installation

For detailed installation steps, refer to the Linux installation tutorial.

Linux File System

/var : Variable files such as logs, spools, and temporary files.

/home : User files, configuration, documents, and caches.

/proc : Virtual files representing kernel and process information; they do not occupy disk space.

/bin : Essential binary executables needed at system startup, usable by all users.

/etc : System configuration files (firewall, startup scripts, etc.).

/root : Home directory of the superuser.

/dev : Device files; hardware is abstracted as files for easy read/write operations.

Linux Command Operations

pwd : Show the current directory.

cd : Change directory. Examples: cd [directory] , cd ~ , cd .. , cd - , cd / .

ls : List files. Options: ls -l , ls -a , ls -la .

mkdir : Create directories. mkdir folder , mkdir -p path/to/folder .

rmdir : Remove empty directories. rmdir folder , rmdir -p path .

rm : Delete files or directories. rm -rf file_or_dir , rm -ri file_or_dir .

cp : Copy files or directories. cp -r src dest , cp -ri src dest .

mv : Move or rename files/directories. mv old_name new_name .

touch : Create an empty file. touch filename .

vi : Powerful text editor. Use vi ++ filename to edit or create a file.

vi has three modes: command mode, insert mode, and last‑line mode (accessed with Esc : ).

cat : Display file contents or create a file with redirection ( cat > filename ).

head : Show the beginning of a file. Example: head -n 10 filename .

tail : Show the end of a file or follow updates. tail -f filename , tail -n 20 filename .

Because the consequences of forced deletion are severe, it is generally not recommended to use rm -rf . The rm command without the r option cannot delete directories, only files.

User and Group

A user is a collection of permissions identified by a unique UID. Users belong to at least one group, identified by a GID. UID and GID values above 500 are typically used for regular users to avoid conflicts with system accounts.

The root user has the highest privileges and belongs to the root group. Only root can add or delete users. When a user is created without specifying a group, a group with the same name is automatically created.

User Management Commands

su : Switch user. su username or su - username .

whoami : Show the current logged‑in user.

groups : List groups the current user belongs to.

id : Show UID and GID of the current user.

useradd : Add a new user. useradd username or useradd -u UID username .

passwd : Change a user's password. Example: passwd sang .

userdel : Delete a user. userdel username or userdel -r username to also remove the home directory.

usermod : Modify user information. Examples: usermod -l newname oldname , usermod -g newgroup username .

groupadd : Add a new group. groupadd groupname or groupadd -g GID groupname .

Permission Operations

Linux defines three basic permissions: read (r), write (w), and execute (x). Use ls -l to view permissions. drwxr-xr-x 2 root root 4096 Sep 23 2011 bin Explanation of the fields from left to right: directory flag, owner permissions, group permissions, others permissions, link count, owner, group, size, date, name.

The chmod command changes permissions. Syntax: chmod [options] [mode] file.

Permission mode uses u, g, o for owner, group, others, with + or - to add or remove r, w, x. Example: chmod u+rwx,g+rw,o+rw file1 Numeric mode uses octal numbers: 7 = rwx, 5 = r-x, 4 = r--, etc. Example:

chmod 753 file1

chmod 777 file1

Linux Process Management

Use ps to view running processes and obtain their PIDs. ps -ef | grep [process_keyword] Sample output shows user, PID, PPID, CPU usage, and command path.

Use kill to terminate a process. Example: kill -9 PID.

Other Common Commands

clear : Clear the terminal screen.

man : Show manual pages for commands.

mnt : Mount filesystems.

SSH service commands: service sshd start , service sshd restart , service sshd stop .

Run a JAR in the background: nohup java -jar jar-0.0.1-SNAPSHOT.jar & .

Software Installation

Common installation methods:

tar : Extract tar, tar.gz, or tar.bz2 packages. Example: tar -zxvf package.tar.gz , tar -jxvf package.tar.bz2 , tar -xvf package.tar .

rpm : Install, query, or remove RPM packages. Examples: rpm -ivh package.rpm , rpm -qa | grep name , rpm -e package.rpm .

yum : Resolve dependencies and install RPMs from repositories. Example: yum install package .