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setgid: Understanding and Setting the SGID Bit
setgid is a special permission bit applied to files or directories. When set on a directory, all files and subdirectories created within it inherit the group ownership of the parent directory. When set on an executable file, the file is executed with the group ID of the file's owner. This is useful for simplifying group permission management in shared environments or for ensuring specific programs run with particular group privileges.
setuid: System Call to Change Process User ID
setuid is a system call used to change the real user ID, effective user ID, and saved set-user-ID of the calling process. It is primarily used to switch to lower privileges after performing tasks that require elevated permissions, or when a program with the SUID (Set User ID) bit set is executed with specific user privileges. It is a security-critical function and plays a key role in privilege management.
sha256sum: Calculate and Verify SHA256 Checksums
The sha256sum command is used to calculate the SHA256 hash value of a file or to verify the integrity of a file by comparing it against a pre-generated hash file. This is essential for ensuring file reliability in various scenarios, such as checking for file corruption after data transfer or verifying the integrity of downloaded software files.
shutdown: Safely Shutting Down Your System
The `shutdown` command is used to safely shut down or reboot the system. It notifies all users of the shutdown at a specified time and gracefully terminates all processes to prevent data loss.
strace: System Call and Signal Tracer
strace is a powerful diagnostic tool for Linux that traces and records the system calls (syscalls) made by a process and the signals it receives. It allows you to understand in detail how a program interacts with the kernel, making it useful for debugging, performance analysis, and security auditing.
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.
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.
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.