Week 01: Configure Network Connections

This module covers connecting Linux computers together. Topics include Linux network configuration files, command line network configuration, and basic to advanced network troubleshooting.

Learning Objectives

• Describe Network Configuration Files
• Configure Networks with the Linux command line
• Perform Basic Network Troubleshooting
• Perform Advanced Network Troubleshooting

Network Configuration Files

Every Linux distribution uses network configuration files to define network settings. Debian-based distributions use interface files (e.g., /etc/network/interfaces). Red Hat-based distributions use scripts in /etc/sysconfig/network-scripts/. openSUSE uses /etc/sysconfig/network.

Example Debian static IP configuration for eth0:

iface eth0 inet static
    address 192.168.1.55
    netmask 255.255.255.0
    gateway 192.168.1.1
iface eth0 inet6 static
    address 2001:db8::1
    netmask 64

For DHCP (Debian):

iface eth0 inet dhcp
iface eth0 inet6 dhcp

Red Hat uses two files: one per interface (e.g., ifcfg-enp0s8) and a global /etc/sysconfig/network. Example interface file for DHCP:

DEVICE=enp0s8
BOOTPROTO=dhcp
ONBOOT=yes

Global network file:

HOSTNAME=centosServer
GATEWAY=192.168.1.1

Command Line Network Configuration

NetworkManager is a service for managing network configurations. It provides a GUI, but also command line tools: nmtui (text-based menu) and nmcli (comand line interface).

Common nmcli commands:

• nmcli con show – list connections
• nmcli con add – add new connection
• nmcli con mod – modify existing connection
• nmcli con del – delete a connection

Example to set static IPv4:

nmcli con mod eth0 ipv4.method manual ipv4.addresses 192.168.1.100/24 ipv4.gateway 192.168.1.1 ipv4.dns 8.8.8.8

Basic Network Troubleshooting

ping – sends ICMP echo requests to test connectivity. Useful options: -c (count), -i (interface), -4 or -6.

host – queries DNS. Examples:

host google.com
host 8.8.8.8
host -t ns google.com

dig – more flexible DNS query tool. Example:

dig google.com
dig @8.8.8.8 google.com

nslookup – also queries DNS. Example:

nslookup google.com
nslookup 8.8.8.8
nslookup -type=ns google.com

Advanced Network Troubleshooting

netstat – displays network connections, routing tables, and interface statistics. Common options: -a (all connections), -r (routing table), -t (TCP), -u (UDP).

ss – a modern alternative to netstat for socket statistics. Examples:

ss
ss -l  (listening sockets)
ss -t  (TCP sockets)
ss -u  (UDP sockets)

Week 02: Administering Users and Groups

Learning Objectives

• Add Linux Users
• Manage Linux User Groups
• Set up the Linux Environment for Users
• Interrogate Current User Information

Linux Users

Key files for user management:

• /etc/login.defs – default settings for passwords, UID ranges, etc.
• /etc/default/useradd – defaults for new users (group, home, shell, etc.)
• /etc/skel/ – skeleton directory; files here are copied to new user's home directory (.bashrc, .profile, etc.)
• /etc/passwd – user account information (username, UID, GID, home, shell)
• /etc/shadow – encrypted passwords and password aging info

The /etc/passwd format:

username:x:UID:GID:comment:home_directory:login_shell

Example:

aspeno:x:1001:1001:Aspeno:/home/aspeno:/bin/bash

The /etc/shadow format:

username:encrypted_password:last_change:min_age:max_age:warn:inactive:expire

Common commands:

• useradd username – create user. Options: -d (home directory), -s (shell)
• passwd username – set/change password. Options: -d (delete), -e (force expire), -l (lock)

Linux User Groups

Files: /etc/group (stores group info: group name, GID, member list). Types: primary group (default for file creation) and secondary (supplementary) groups.

Commands:

• groupadd groupname – create group. Options: -g GID, -p password
• usermod -g groupname username – change primary group
• usermod -aG groupname username – add user to supplementary group (preserve other groups)

Example: add user aspeno to the sudo group:

usermod -aG sudo aspeno

User Configuration

Environment files depend on shell startup method:

• Login shell: reads ~/.bash_profile, ~/.bash_login, ~/.profile (first found)
• Interactive non-login shell: reads ~/.bashrc
• Global files: /etc/profile, /etc/bashrc, /etc/profile.d/*

Common environment variables: HISTSIZE, PATH, PS1.

Query User Information

• whoami – current user
• who – list all logged-in users
• w – detailed user info (login time, idle, CPU usage, currant command)
• id – user/group IDs. Example: id aspeno, id -u aspeno, id -g aspeno, id -G aspeno
• last – historical login records

Week 03: Manage Disk Storage

Learning Objectives

• Partition Hard Drives
• Manage Linux File Systems
• Mount Linux File Systems
• Monitor Linux File Systems

Hard Drive Partitions

Two partition schemes: MBR (Master Boot Record) supports up to 4 primary partitions; GPT (GUID Partition Table) supports up to 128 partitions. GPT is required for disks > 2TB and UEFI boot.

Tools: fdisk for MBR, gdisk for GPT. Common interactive commands: n (new), d (delete), p (print), w (write).

Example:

fdisk /dev/sdb
# then use n, p, w etc.
gdisk /dev/sdb

Linux File Systems

Linux uses a virtual directory tree rooted at /. Standard directories per FHS: /boot (boot files), /home (user data), /usr (programs), /var (variable data), /mnt and /media (mount points).

Common file system types: ext3, ext4 (journaling, ext4 supports up to 16TB files), swap (virtual memory), NTFS (Microsoft), VFAT (USB drives, compatible across OS).

Linux File Systems Management

• mkfs -t ext4 /dev/sda1 – create an ext4 file system on a partition
• mount -t ext4 /dev/sda1 /mnt/media – temporary mount
• /etc/fstab – file to automatically mount at boot. Format: device mount_point fstype options dump pass. Example: /dev/sda1 / ext4 defaults 0 1

Linux File Systems Monitoring

• df -h – disk usage by partition (human-readable)
• du -h /path – disk usage by directory
• iostat -d – real-time disk statistics
• lsblk – list block devices (partitions and mount points)

Week 04: Managing Software Packages

Learning Objectives

• Compile Open-Source Packages
• Use Repository Tools
• Install and Update Packages

Open-Source Packages

• wget and curl – download files from the web. Example: wget http://example.com/file.tar.gz; curl -O http://example.com/file.tar.gz
• tar – archive files. Create: tar cvf archive.tar *.cpp. Extract: tar xvf archive.tar. List: tar tvf archive.tar
• gcc – compile C/C++ code. Example: gcc source.c -o myprogram

Software Packages

Packages bundle compiled applications. Two major package systems:

• Debian: dpkg – dpkg -i package.deb (install), dpkg -l (list), dpkg -r package (remove)
• Red Hat: rpm – rpm -ivh package.rpm (install), rpm -qa (list all), rpm -e package (erase)

Software Repositories

Repositories store tested packages. Tools:

• Debian: apt-cache search term, apt-get update (refresh index), apt-get upgrade (upgrade all), apt-get install wget
• Red Hat: yum install wget, yum remove wget, yum update wget

Lab Activities

Practice commands in a cloud Linux shell: host, dig, nslookup, ss, netstat, passwd, whoami, w, id, df, du, lsblk, wget, curl, tar, gcc.