Untitled Quiz

Linux System Administrator Duties

• Responsible for keeping the system running efficiently
• Monitoring system health (CPU, memory, disk usage, network) to prevent overload
• Identifying issues using tools like top, htop, or vmstat to pinpoint resource-intensive processes
• Tuning system settings (cache size, scheduling, network) to optimize performance based on workload
• Reviewing system logs to detect hardware/software errors or security issues
• Ensuring efficient hardware resource utilization (distributing workloads, cleaning up unused files)
• Proactively identifying and resolving potential issues to prevent system slowdowns or crashes

Piping and Redirecting

• Piping connects the output of one command to the input of another for extended functionality.

• Redirection saves command output to a file (e.g., ls -l > file_list.txt or ls -l >> file_list.txt).

Hard Links vs. Symbolic Links

• Hard Link: A direct reference to the original file, sharing the same data. Deleting the original file breaks the hard link.
• Symbolic Link (Soft Link): A shortcut or pointer to the original file. Deleting the original file breaks the symbolic link; it will not work.

Linux Distributions

• Ubuntu: Popular desktop distribution known for user-friendliness and community support. Focuses on regular updates and LTS versions.
• Fedora: Cutting-edge, development-focused distribution.
• Debian: Stable, highly reliable distribution commonly used for servers and desktops. Known for its comprehensive software repositories and robust community support.
• CentOS: Free and community-supported version of Red Hat Enterprise Linux. Focuses on stability.

RPM and YUM

• RPM (Red Hat Package Manager): A tool for managing software packages (installation, updating, removal and querying). It works with pre-compiled .rpm files.
• YUM (Yellowdog Updater Modified): A higher-level tool built on top of RPM that simplifies package management. It handles dependencies automatically and connects to online repositories for downloading and installing packages/updates. Commands are easy to use

Creating a YUM Repository

• Install createrepo: Necessary for creating a repository.

• Establish a directory for the repository (sudo mkdir /var/www/html/myrepo).

• Copy .rpm files to the repository directory (cp /path/to/your/rpm/files/*.rpm /var/www/html/myrepo/).

• Use createrepo to generate metadata for the repository (/var/www/html/myrepo/).

• Create myrepo.repo file in /etc/yum.repos.d/ for clients to recognize repository. Populate the file with baseurl, name,enabled, and gpgcheck parameters

Bash Shell

• A popular and default shell in many Linux systems.
• User-friendly for beginners and advanced users.
• Strong scripting capabilities using loops, conditionals, and functions.
• Offers command history and tab completion for efficiency.

C Shell (csh) and Korn Shell (ksh)

• C Shell: User-friendly, syntax similar to C programming. Designed for ease of job control and command history.
• Korn Shell: Combines features of Bourne Shell and C Shell, offering advanced scripting capabilities (like arrays and floating-point arithmetic). Faster execution compared to other shells.

Mounting a Device

• Plug in the device (USB drive, external hard disk, etc.).

• Find the device name using lsblk or fdisk -l. (e.g. /dev/sdb1).

• Create a mount point (e.g. sudo mkdir /mnt/usb).

• Use mount to attach the device to the mount point (sudo mount /dev/sdb1 /mnt/usb).

• Access the files through the mount point.

• Unmount the device when finished (sudo umount /mnt/usb).

Enabling SSH Server on RHEL

• Install the SSH server package (e.g. sudo yum install openssh-server).

• Start the SSH service (sudo systemctl start sshd).

• Enable SSH to start automatically at boot (sudo systemctl enable sshd).

• Allow SSH traffic through the firewall (sudo firewall-cmd --permanent --add-service=ssh). Reload firewall (sudo firewall-cmd --reload).

• Verify SSH service status (sudo systemctl status sshd).

File Systems Supported by Linux

• EXT4: Default filesystem for most Linux distributions (large files, volumes, fast, reliable).

• NTFS: Developed by Microsoft; commonly used by Windows. Linux can read and write through the ntfs-3g driver.

• FAT32: Simple, widely used but limited (maximum file size)filesystem for devices like USB drives. Supported by most Linux systems.

• Btrfs: Modern Linux filesystem; supports snapshots, versioning, and built-in tools for data integrity and management.

Partition vs. Logical Volume

• Partition: A fixed division of a physical storage device, acts as a basic structure for organizing data. Cannot easily change size without reformatting.
• Logical Volume (LV): A flexible, resizable storage unit managed by LVM. Allows grouping multiple physical devices, resizability, adding/removing LVs without losing data, making them more manageable compared to partitions

User Management Commands

• useradd: Creates new user accounts.

• usermod: Modifies existing user accounts (e.g., password, shell).

• userdel: Deletes user accounts.

Encrypted Volume Creation

• Install cryptsetup
• Identify the disk/partition (lsblk).
• Use cryptsetup luksFormat to format the device with LUKS encryption.
• Use cryptsetup luksOpen to open the encrypted volume.
• Create a filesystem (e.g., mkfs.ext4).
• Mount the encrypted volume.
• Configure (optional): add to /etc/fstab
• Close the encrypted volume when finished.

Snapshots in LVM

• Snapshots in LVM freeze the current state of an LVM volume as a new snapshot volume.
• Used for backups, allowing safe rollback to a previous state.
• Significantly easier on resources and operations than traditional backups due to fast snapshot creation.

Samba Server

• A software that allows Linux/Unix systems to share directories and files with Windows (and other systems) over a network.
• Enables cross-platform sharing of files and printers.

Network File System (NFS)

• A protocol for sharing files and directories between systems on a network.

• Client systems mount shared directories from the NFS server to access files remotely; this is similar to local storage.

• Advantages: Easy sharing across platforms; centralized storage for improved data consistency; transparent access.

• Disadvantages: Security concerns without proper configuration (unauthorized access); performance issues; dependence on network availability.

Firewalls

• A security system that controls network traffic based on predefined rules, protecting servers and networks from unauthorized access. Traffic filtering is used to determine whether to allow or block traffic.
• Firewalls block potentially malicious traffic from unauthorized sources (hackers/malware). They restrict access to certain ports and services. They act as a barrier and log traffic.

IP Masquerading

• Method for hiding private IP addresses behind a single public IP used to allow devices in a private network to access the internet.
• Requires IP forwarding enabled. Use to mask private IPs from external networks.
• It essentially masks private devices behind a single public IP for inbound traffic, maintaining security from unauthorized outside connections.

OpenSSL Certificates

• OpenSSL is a tool used for managing SSL/TLS certificates which are used for encrypting communication between servers and clients.
• Uses commands like openssl genrsa, openssl req, openssl x509 to generate private keys, create CSRs, and generate signed certificates.

Firewall Modules

• Firewall modules enhance firewall functionality with specific features (e.g., rate limiting).
• The limit module manages incoming/outgoing traffic rates, protecting against overload.

iptables

• A command-line tool in Linux for configuring a firewall by setting up, managing, and controlling the firewall.

• It filters and directs network traffic based on rules.

• Tables: filter (default), nat, mangle, raw

• Chains: INPUT(incoming), FORWARD(passing through), OUTPUT(outgoing)

• Rules: Specific conditions and actions applied to packets (e.g., allowing or blocking traffic).

DNS Server

• A server that translates domain names (like example.com) into IP addresses.

• Acts like a phonebook for the internet.

• Types of DNS Servers:

  • Recursive: Intermediary between user and other servers
  • Authoritative: Stores information about specific domains
  • Root: Top-level server for directing requests
  • TLD (Top Level Domain): Handles specific domains. (.com,.orgetc.)
  • Caching: Temporarily stores results for faster repeated lookups.

DHCP Server

• Dynamic Host Configuration Protocol server dynamically assigns IP addresses and other network settings (e.g., gateway, DNS server addresses) to devices on a network.
• Automates IP configuration for devices on a network without manual intervention; avoids conflicts and simplifies network administration.

Apache Modes

• Apache Mode: Various Multi-Processing Modules (MPMs) used in handling incoming client requests—ways to execute multiple requests simultaneously.

• Parameters:

  • MaxClients and MaxConnectionsPerChild: Limit to prevent overload or abuse.
  • Memory Usage: prefork uses more RAM than worker/event because processes are independent.
  • Scalability: worker/event modes scale better with increased traffic because of resource efficiency.
  • Response Time: worker/event modes have faster response times than prefork.

Email Protocols (MTA, MDA, MUA)

• MTA (Message Transfer Agent): Transfers emails between servers. Protocols like SMTP are used to send emails.
• MDA (Mail Delivery Agent): Delivers the email to the recipient's mailbox (local storage).
• MUA (Mail User Agent): The client application you use to send and receive emails (e.g., Outlook, Thunderbird).

Shell Scripts

• A script contains a series of commands in a text file; executed in order to automate tasks. Designed to be reusable and to avoid typing individual commands repeatedly.

High Availability (HA)

• Systems are reliable; operational and accessible with minimal downtime.
• Methods including redundancy (backup systems, load balancing), automatic failover protocols, monitoring, and geographic distribution enhance availability through continuous operation.