In user authentication, a "salt" is used to add randomness to a password before hashing. This helps protect against common attacks like rainbow table attacks and ensures that even the same password will have different hash values due to the unique salt.

In Docker, an "image" is a lightweight, stand-alone, executable software package that includes everything needed to run a piece of software. Docker containers are created from these images, allowing you to run applications in an isolated environment.

The Linux tool sysctl allows administrators to view and set system and kernel parameters at runtime. It's a powerful utility for fine-tuning and configuring various aspects of the Linux kernel to optimize performance and behavior.

When creating a case statement in Bash, each case is ended with the word esac. The esac keyword marks the end of the case statement, and it's used to close the case block.

The scp (secure copy) command is commonly used for securely copying files between remote systems. It uses SSH to encrypt the data during the transfer, ensuring security.

The correct answer is "fdisk." The fdisk command is used to create and manage disk partitions on a Linux system. It does not format the partition directly but is used to create and manage the partition structure. Formatting is typically done using tools like mkfs.

Shared libraries in Linux are typically stored in the /lib directory. These libraries contain code that various programs and applications use to perform common functions, such as input/output operations, memory management, and more.

The "groups" command in Linux displays information about the group membership of a user. It lists all the groups a user is a member of. This can be helpful for checking a user's group associations.

For performance tuning, the "netstat" command provides a real-time view of the system's current network connections. Netstat displays information about network interfaces, routing tables, masquerade connections, and more. It's a valuable tool for diagnosing network issues and monitoring network activity.

The /etc directory in Linux contains system configuration files. These files store configuration settings for various system components and applications.