Cyber Security Threat Intelligence

Hacking Linux: Master These Advanced Commands and Take Control

by adminadda on | 2024-02-23 17:20:46 130

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Hacking Linux: Master These Advanced Commands and Take Control

Linux has lengthy been revered as an working machine that places the user in control. With its open source model, strong community aid, and reputation for protection, Linux gives extraordinary customization for energy customers. While Windows and Mac provide simplified interfaces that limit superior configuration, Linux invitations customers to tinker underneath the hood. 

But this power comes with complexity. For casual customers, Linux can seem impenetrable. Mastery of the command line is needed for having access to Linux's massive abilities. Though graphical interfaces like GNOME and KDE provide user-pleasant get admission to, the actual magic happens at the terminal.

This guide objectives to demystify Linux for intermediate users who want to unencumber superior commands for management, scripting, networking, and extra. We'll cover little-recognized but effective tools for taking complete manage of your Linux environment. From tweaking device settings to automating complicated obligations, these instructions will rework you from consumer to administrator. 

Linux does not keep your hand. The open supply community expects users to dig in and get their palms grimy. This guide will offer the know-how had to open the hood and tinker with confidence. Buckle up and get ready to hack Linux at an expert stage.

Basic Linux Commands:

Linux presents a effective command line interface for dealing with your device. While Linux gives a graphical computer interface, the command line presents you finer control and allows you to access advanced capabilities. Here are a number of the fundamental commands every Linux person should know:

Navigation:

  • pwd - Print working directory. Shows you the path of the current directory you're in.
  • ls - List directory contents. Shows files and subfolders in the current directory.
  • cd - Change directory. Navigate to a new directory by specifying the path.
  • cd .. - Go up one directory level.
  • cd ~/ - Go to home directory.

File Management:

  • mkdir - Make a new directory.
  • rmdir - Remove an empty directory.
  • cp - Copy files and directories.
  • mv - Move or rename files and directories.
  • rm - Delete files (use -r to delete directories).
  • cat - Output file contents to the terminal.
  • less - View file contents interactively.
  • tail - Output the last lines of a file.
  • head - Output the first lines of a file.
  • grep - Search for text patterns inside files.

Process Management:

  • ps - List running processes.
  • top - Interactive process monitor.
  • kill - Terminate a process by ID.
  • bg - Run a process in the background.
  • fg - Bring a background process to the foreground.
  • jobs - List current background processes.

These commands form the foundation for effectively using Linux. Master them before moving on to more advanced tools.

Users and Permissions:

Managing users and permissions is critical for controlling access to your Linux system. Here are some advanced commands for users and permissions:

User Accounts:

  • useradd - Create a new user account. Specify the username with -m to create a home directory.

  • usermod - Modify a user account. Useful for changing info like the home directory, shell, or appending groups.

  • userdel - Delete a user account and associated files.

  • chage - Change password aging settings like expiration date.

Groups:

  • groupadd - Create a new group.

  • groupmod - Modify a group name or GID.

  • groupdel - Delete a group.

  • gpasswd - Administer groups and members. Add/remove users from groups.

  • newgrp - Log in to a new group to inherit the permissions.

File Permissions:

  • chmod - Change file permissions with octal notation or letters/symbols.

  • chown - Change file owner and group owner.

  • setfacl - Set file access control lists for more granular permissions.

  • getfacl - View the ACLs on a file.

Properly managing users, groups, and permissions is critical for security and access control in Linux. Mastering these advanced user and permission commands will give you greater control.

Package Management:

Most Linux distributions come with a package manager that handles installing, removing, and updating software packages. Package managers make it easy to find, install, update, or remove applications on your system without having to compile anything from source code. Here are some of the most common package management commands:

Installing Packages

  • apt install (Debian/Ubuntu) - Install a new package using the APT package manager. For example, apt install nmap installs the Nmap network scanner.

  • dnf install (Fedora/Red Hat/CentOS) - Similar to apt, this installs new packages using DNF on RPM-based distros. For example, dnf install wireshark installs the Wireshark packet analyzer.

  • pacman -S (Arch Linux) - Installs packages using Pacman on Arch Linux. For example, pacman -S firefox installs the Firefox web browser.

  • zypper install (openSUSE) - Installs packages on SUSE/openSUSE using the Zypper package manager. Like zypper install gimp to get the GIMP image editor.

Removing Packages

  • apt remove - Removes an installed package but keeps configuration files in case you install it again later.

  • dnf remove - Removes a package and its configuration files on RPM distros.

  • pacman -R - Uninstalls a package using Pacman on Arch.

  • zypper remove - Removes packages on SUSE/openSUSE.

Updating Packages

  • apt update - Updates the package source list on Debian/Ubuntu.

  • apt upgrade - Actually upgrades all installed packages to the latest versions.

  • dnf update - Updates packages on RPM-based distros.

  • pacman -Syu -Synchronize and upgrade packages on Arch.

  • zypper update - Updates packages on SUSE/openSUSE.

Package managers streamline installing, removing and updating software on Linux. Mastering these commands allows you to easily add or remove applications and keep your system up-to-date.

Advanced File Management:

Linux provides powerful commands for managing files and directories efficiently. Here are some advanced file management capabilities in Linux:

Find - The find command is used to search for files based on various criteria such as name, size, date, permissions etc. Some examples:

 
# Find files by name
find . -name "*.txt"

# Find files larger than 1M
find . -size +1M

# Find files modified in last 7 days
find . -mtime -7

grep - grep is used to search for text patterns inside files. 
It can recursively search entire directory structures. Some examples:
 
# Search for 'error' in all .log files
grep -R "error" *.log

# Search for lines that don't contain 'localhost'
grep -v "localhost" /etc/hosts

Symlinks - Symbolic links act as advanced shortcuts pointing to directories, programs or files. They allow efficient file management without duplicating data. For example:

 
ln -s /usr/local/bin/python3 /usr/bin/python

Permissions - The chmod command allows modifying file/directory permissions for owner, group and others. Octal notation represents read/write/execute permissions. Some examples:

 
# Give read/write perms to owner and read to others 
chmod 644 file.txt 

# Give execute perm for everyone
chmod +x script.sh

Mastering advanced file management commands gives you precise control over files and directories in Linux. These tools help automate tasks and enable efficient system administration.

Networking Commands:

Linux provides powerful networking capabilities through the command line interface. Here are some advanced commands for managing network connections, firewalls, and services in Linux:

View Network Connections

  • ifconfig - View information about network interfaces including IP address, MAC address, Tx/Rx packets, and more.

  • ip addr show - Similar to ifconfig, shows IP addresses assigned to interfaces.

  • netstat - Display routing tables, network connections, interface statistics, masquerade connections, and multicast memberships. Useful for checking current connections.
  • lsof -i   - Lists open sockets and network connections from all processes.
  • ss   - Utility to investigate sockets. Similar to netstat but shows more TCP and state information.

Firewall Management:

  •  iptables - Command line tool to configure Linux kernel firewall implemented within Netfilter. Allows defining firewall   rules to filter traffic.
  •  ufw - Uncomplicated firewall, frontend for managing iptables rules. Simplifies adding rules for common scenarios.
  •  firewall-cmd - Firewall management tool for firewalld on RHEL/CentOS systems. Used to enable services, open ports,   etc.

Services:

  •  systemctl - Used to manage system services. Can start, stop, restart, reload services.
  • service - Older way to control services. Works on SysV init systems.
  • chkconfig - View and configure which services start at boot on RedHat-based systems.  
  • ntsysv - Text-based interface for enabling/disabling services in SysV systems.

These advanced networking commands allow full control over connections, firewall policies, and services from the Linux command line. Mastering them is key for any Linux system administrator.

Process Monitoring :

Proper process monitoring is essential for administering and managing a Linux system. There are several useful commands for viewing and controlling processes on Linux.

Top:

The `top` command provides a dynamic real-time view of the running processes on the system. It displays a list of processes sorted by various criteria including CPU usage, memory usage, process ID, and more. `top` updates the display frequently to show up-to-date CPU and memory utilization. 

Key things to look for in `top` include:

  •  CPU usage percentages per process
  •  Memory and swap memory used per process  
  • Total CPU and memory usage statistics

`top` is useful for identifying processes using excessive resources and narrowing down sources of performance issues.

ps:

The ps (process status) command generates a snapshot of currently running processes. It's used to view detailed information on processes. Useful options include:

  •  aux - Displays all processes for all users   
  •  ef- Shows full process tree including child processes
  •  forest- Visual process tree output 

`ps` can be combined with `grep` to search for processes matching specific keywords or process IDs.

kill:

The `kill` command sends signals to processes to control them. The main usage is terminating processes by signal number `9` or `15` (SIGKILL or SIGTERM). 

First find the process ID (PID) using `ps`, then execute:

kill [OPTIONS] PID

Common options:

  • KILL - Forcefully terminate the process 
  • TERM - Gracefully terminate the process

jobs :

The `jobs` command lists any jobs running in the background for the current shell session. Background processes can be started with `&` after the command.

Key options for `jobs` include:

  • l - Display process IDs in addition to the job number.
  • p- Display process group ID only.
  • n - Display information only about jobs that have changed status since last notification.

`jobs` enables managing multiple processes running in the background from one shell session.

This covers the key commands for monitoring and controlling Linux processes - `top`, `ps`, `kill`, and `jobs`. Mastering these tools is critical for advanced Linux administration. Proper process management keeps the system running smoothly.

 Advanced Administration:

Becoming an advanced Linux administrator requires mastering some key skills like managing cron jobs, disk storage, and the boot process. Here's what you need to know:

 Cron Jobs:

The cron daemon allows you to schedule commands or scripts to run automatically at a specified time/date. Cron jobs are configured by editing the crontab file. Some examples of cron jobs include:

  • Running system maintenance tasks like updates or cleanups
  • Scheduling backups or data exports
  •  Automating emails or notifications

To view existing cron jobs, use `crontab -l`. To edit the crontab, use `crontab -e`. Each line follows the format:

* * * * * command to execute
- - - - -
| | | | |
| | | | ----- Day of week 
| | | ------- Month
| | --------- Day of month
| ----------- Hour
------------- Minute

Some tips for using cron:

  • Use full paths for commands
  •  Write logs or output to a file
  •  Use multiple lines for long/complex jobs
  • Set the MAILTO variable to get email notifications 

Disk Management:

Managing disk storage is critical for monitoring space usage and preventing failures. Useful commands include:

  •  df - Report file system disk space usage
  • du - Estimate file space usage
  • mount - Mount file systems
  • fdisk - Partition table manipulator
  • mkfs - Make file systems 

When managing disk usage, keep an eye on storage limits and utilize disk quotas for users if needed. Monitor for failures with `dmesg`. Schedule regular file cleanups and archives. 

Add more storage by partitioning a new disk with fdisk, creating a file system with mkfs, and mounting it at the desired mount point.

The Boot Process:

Understanding the Linux boot process helps in troubleshooting issues. The key stages are:

  • BIOS initialization - Performs hardware checks
  • Bootloader (GRUB) - Loads the kernel 
  •  Kernel initialization - Mounts the root filesystem
  • Init system (systemd) - Starts services/daemons
  •  Login prompt - User can now log in

Customize the boot process by editing configs for GRUB or systemd. Useful commands include `dmesg` for kernel logs, `systemctl` for systemd services, and `journalctl` for logging.

Optimizing the boot process involves removing unnecessary services, drivers, or features. Troubleshoot by examining logs and looking for bottlenecks.

Scripting:

Scripting allows you to automate repetitive tasks and create your own commands and programs in Linux. This saves time and effort compared to typing the same commands over and over. The two main scripting languages used on Linux systems are Bash shell scripting and Python.

 Bash Shell Scripting:

Bash is the default shell on most Linux distributions and it has its own scripting language. Bash scripts have a .sh file extension and can run many commands together, use variables, control flows like conditionals and loops, and more. Some examples of tasks to automate with Bash:

  • System backups
  •  Bulk file operations 
  • Cron jobs
  •  Application installations

You can run Bash scripts by calling `bash` and the script name:

bash myscript.sh

Or make the script executable with `chmod +x` and then run it directly:

./myscript.sh

Some key Bash scripting skills include:

  • Variables and command substitutions
  • Control flows (if, for, while, case) 
  • Functions
  • Input/output redirection
  •  Working with strings and numbers

Overall, shell scripting allows you to unleash the full power of the Linux command line and automate your workflow.

Python Scripting:

Python is a popular general purpose programming language frequently used for Linux scripting and automation. Some examples of Python scripts on Linux include:

  •  System monitoring 
  •  Web applications (with Flask or Django)
  •  Automating sysadmin tasks
  •  Machine learning
  •  Interacting with APIs

Python emphasizes code readability and has extensive libraries and modules to help you script anything from file operations to web scraping. Some key Python skills for Linux include:

  •  Variables and data structures (lists, dicts)
  • Control flows (if, for, while)
  • Functions 
  •  File I/O
  •  Importing modules

Python scripts have a .py extension and can be run like:

python myscript.py

Overall, Python provides a full-featured scripting language to control your Linux system and automate complex tasks.

Conclusion:

Linux offers advanced users an incredible amount of power and control over their systems. By mastering some of the commands we've covered in this guide, you can customize your Linux environment, automate tasks, monitor system resources, secure your machine, and optimize performance.

The key takeaways from this guide include:

  •  How to manage users and permissions to control access to your system
  •  Using package managers like apt and rpm to install and update software 
  • Advanced file management tricks like symlinks, checksums, and compression
  •  Networking commands like ip, ping, traceroute to troubleshoot connectivity 
  • Tools like top, htop, lsof for monitoring processes and open files
  •  Administrative commands like iptables, ssh, cron for security and automation  
  •  Scripting with Bash and Python to create customized tools and workflows

With this advanced knowledge under your belt, you can truly customize Linux to suit your needs. The extensive documentation and active communities around most Linux distros allow you to continue expanding your skills. Mastering these advanced tools requires time and practice, but enables you to get the most out of your Linux machines.

Whether you manage servers, develop software, or just want more control over your desktop OS, hacking Linux unlocks new possibilities. Hopefully this guide has provided a solid introduction to expanding your Linux powers. Thejourney doesn't stop here though. With over 500+ pages of man pages to read, you could spend a lifetime mastering the depth of Linux!















 

 

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