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su: Switch User
The `su` command, short for 'substitute user' or 'switch user', is used to change the current user ID to another user's ID. It is commonly used to gain administrator privileges (root) or to perform tasks within another user's environment. It requires password authentication to gain privileges and is a critical command for security.
Guide to the sudo Command: Execute Commands with Administrative Privileges
`sudo` (short for substitute user do or superuser do) is a tool that allows a regular user to execute programs with the privileges of another user (usually the root user) in Linux and Unix-like operating systems. This enables management tasks to be performed safely while maintaining system security, making it much safer than performing all tasks directly as the root account. Through this guide, you will learn the basic usage of `sudo` and important security considerations.
sudoedit: Safely Edit Privileged Files
`sudoedit` is a command that allows you to safely edit files requiring `sudo` privileges. It reduces security risks by automatically copying the file for editing as a regular user and then copying it back to its original location. The `-l` option, in particular, lists files that the current user can edit via `sudoedit`.
sudoers: sudoers file
The `sudoers` file is a core configuration file on Linux and Unix-like systems that defines policies for granting administrator privileges to users via the `sudo` command. It specifies which users can run which commands as which other users, from which hosts, and is crucial for system security.
sum: Calculate File Checksums and Block Counts
The sum command calculates and outputs the 16-bit checksum and block count of a file. It is primarily used for a quick check of file integrity or to quickly compare if a file has been modified.
swapoff: Disable Swap Space
The swapoff command is used to disable swap space on a system. It can be used to disable a specific swap file or device, or to disable all swap space configured on the system at once. This is useful for optimizing memory usage or when replacing swap devices.
swapon: Activate Swap Space
The swapon command is used on Linux systems to activate a device or file for use as swap space. Swap space is an area on the hard disk that the system uses to store data when physical RAM is insufficient, playing a crucial role in system performance.
symlink: Create a Symbolic Link
The symlink command creates a symbolic link (soft link) to a file or directory. It acts as a pointer to the original file's location, and the link will be broken if the original file is deleted. While the `ln -s` command is more commonly used, the `symlink` utility offers fine-grained control over link creation through various additional options.
sync: Synchronize Disk Cache
The sync command forces the operating system to write all modified data from its memory buffers to the physical storage device. It is used to ensure data integrity by safely storing critical data before system shutdown, reboot, or unmounting a storage device.
sysctl: Managing Kernel Parameters
The sysctl command is used to view or set runtime parameters of the Linux kernel. These parameters can be accessed through the `/proc/sys` virtual file system, allowing dynamic changes to how the system operates (e.g., networking, memory, security).
systemctl Command Guide: The Core of systemd Service Management
`systemctl` is a key tool for managing the system and services of the systemd system manager. systemd is used as a standard to manage the system's boot processes, services, mount points, sockets, and more in modern Linux distributions. With `systemctl`, you can efficiently control the entire system by checking the status of services, starting/stopping/restarting them, and configuring whether they should run automatically at system boot. Learn various ways to utilize `systemctl` through this guide.
systemd: System and Service Manager
systemd is the most widely used system and service manager in modern Linux systems. Replacing traditional init systems, it comprehensively provides various core functionalities such as system booting, service management, device control, and log management.