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Guide to the history Command: Viewing and Managing Shell Command History
The `history` command displays a list of commands that the user has previously executed in the terminal. This is very useful for easily finding and re-executing commands used in the past or remembering what tasks were performed. Through this guide, learn the basic usage of the `history` command and various options necessary for managing history.
hostname: Manage System Hostname
The hostname command is used to display or set the system's hostname. This name plays a crucial role in identifying and communicating with the system on the network.
init: System Initialization and Process Management
init is the first process executed (PID 1) in traditional Unix and Linux systems, acting as the parent process that manages all other system processes. It is responsible for system startup (booting) and shutdown, and controls the system's operating mode through runlevels. In modern Linux distributions, it is being replaced by systemd.
insmod: Insert Linux Kernel Module
The insmod command is used to insert a loadable kernel module (LKM) into the Linux kernel. It is typically used to load compiled module files, usually with a `.ko` extension, to add new functionality or enable hardware drivers. This command does not automatically resolve module dependencies, so modules with dependencies must be loaded manually first. In most cases, using the `modprobe` command is recommended.
iostat: Report CPU utilization and I/O statistics
iostat is a command that reports CPU utilization and device (disk, partition) input/output statistics in real-time or at specified intervals. It is useful for diagnosing system performance bottlenecks and resolving I/O-related issues.
iotop: Disk I/O Usage Monitoring
iotop is a utility for Linux systems that monitors disk I/O usage by processes or threads in real-time. It functions similarly to the 'top' command but focuses on disk read/write activity instead of CPU and memory usage. It is useful for diagnosing I/O bottlenecks in a system and identifying which processes are consuming significant disk resources.
journalctl: Real-time System Log Monitoring
journalctl is a powerful tool for querying and analyzing logs generated by the systemd journal. The `-f` option, in particular, is highly useful for diagnosing system issues or monitoring application behavior by tracking new log entries in real-time. It is similar to the traditional `tail -f` command but leverages the structured data of the systemd journal for more robust filtering and searching capabilities.
journalctl -xe: Detailed System Log Analysis and Problem Diagnosis
`journalctl -xe` is a command that displays the latest log entries from the `systemd` journal with detailed explanations. It is very useful for diagnosing system errors, warning messages, or problems with specific services, providing additional context and information needed for troubleshooting.
last: Check System Login and Reboot Records
The last command analyzes the `/var/log/wtmp` file to display a reverse chronological list of users who have logged into the system, their terminals, login times, logout times, and system reboot records. This allows you to track system usage history and use it for security audits.
lastb: View Failed Login Attempts
The lastb command displays a list of failed login attempts on the system. It typically reads the `/var/log/btmp` file, allowing you to see who failed to log in, when, and from which terminal, making it useful for security audits.
ldd: Check Shared Library Dependencies
The ldd command prints the shared libraries required by dynamically linked executables or shared libraries. This is useful for understanding which libraries a program depends on and where those libraries are located on the system.
login: System Login
The login command is used to start a user session and log into the system. Typically, it involves a username and password prompt in a terminal or console for authentication.