Comptia Linux+ Tutorial

1. Filesystem Hierarchy Standard (FHS)
The Filesystem Hierarchy Standard (FHS) defines the structure and purpose of directories in Unix-like systems. It ensures consistency, predictability, and ease of administration. By following FHS, administrators and scripts know where to find essential files and binaries across all distributions.

2. Understanding /etc, /usr, /bin, /sbin
- /etc: Contains system configuration files. Example: /etc/fstab lists mounted filesystems.
- /usr: Holds read-only user data like applications and libraries (e.g., /usr/bin/).
- /bin: Essential user binaries (e.g., ls, mkdir) available in single-user mode.
- /sbin: System binaries (e.g., reboot, ifconfig) usually for root.

Example:
cat /etc/passwd – view user info
ls /bin – list essential commands

3. /var, /tmp, /home, /boot roles
- /var: Variable files like logs (/var/log), mail, and print spools.
- /tmp: Temporary files. Cleared on reboot.
- /home: User home directories (e.g., /home/alice).
- /boot: Files needed to boot, like kernel images and grub.

Example:
ls /boot – shows kernel and bootloader files

4. /proc and /sys virtual filesystems
- /proc: Provides process and kernel info as files (e.g., /proc/cpuinfo).
- /sys: Exposes hardware info and allows tuning of device parameters.

Example:
cat /proc/meminfo – shows memory usage
ls /sys/class/net – shows network interfaces

5. /opt, /media, /mnt, /dev
- /opt: Optional add-on software packages.
- /media: Mount points for removable media (USB, CD-ROM).
- /mnt: Temporary mounts for sysadmin use.
- /dev: Device files representing hardware (e.g., /dev/sda).

Example:
ls /dev – list devices
mount /dev/sdb1 /mnt – mount USB to /mnt

6. FHS compliance tools
Tools like lintian or checksec on Debian-based systems check if software packages follow FHS guidelines.

Example:
sudo apt install lintian
lintian mypackage.deb – check FHS compliance of a package

7. Permissions and special files
Unix filesystems use permission bits (rwx) and support special file types:
- Block devices: /dev/sda
- Character devices: /dev/tty
- Named pipes and sockets
Example:
ls -l /dev/sda
crw-rw---- 1 root tty 4, 0 /dev/tty0

8. User and system data separation
FHS separates system files from user files:
- System-wide binaries: /usr/bin
- User data: /home/username

Example:
echo "Hello" > ~/test.txt – writes to user's home

9. Mounted filesystems
Mounting allows integration of storage devices into the directory tree.
- /etc/fstab: Lists devices and their mount points
- mount/umount: Mount/unmount devices

Example:
sudo mount /dev/sdb1 /mnt
cat /etc/fstab

10. Evolution of FHS
The FHS evolved to support multi-user, modular systems and new technologies like containers. Systemd has introduced directories like /run for runtime files. FHS is maintained by the Linux Foundation and adopted by all major distros.

11. Applying FHS in scripts
Scripts should reference standard paths to ensure portability and compliance.
Example:
```bash #!/bin/bash LOGFILE="/var/log/myscript.log" echo "Starting process..." >> "$LOGFILE" cp /etc/hosts /tmp/hosts_backup echo "Done." >> "$LOGFILE" ```

1. BIOS vs UEFI initialization
- BIOS (Basic Input/Output System): Legacy firmware interface, limited to 2.2TB disks and uses MBR.
- UEFI (Unified Extensible Firmware Interface): Modern replacement for BIOS. Supports GPT, secure boot, and graphical interfaces.
UEFI loads bootloaders from the EFI System Partition (ESP), typically /boot/efi.

2. MBR and GPT partitions
- MBR (Master Boot Record): Supports up to 4 primary partitions and 2TB disk size.
- GPT (GUID Partition Table): Supports unlimited partitions (usually 128), and >2TB disks. Required for UEFI systems.

Example:
sudo fdisk -l – show partition table (MBR or GPT)

3. GRUB/GRUB2 installation & configuration
GRUB (GRand Unified Bootloader) loads the Linux kernel.
- Installed via grub-install
- Configured in /etc/default/grub and /boot/grub/grub.cfg (auto-generated)

Example:
sudo grub-install /dev/sda
sudo update-grub

4. Kernel parameters editing
Kernel boot options can be modified in GRUB at boot or permanently in /etc/default/grub using the GRUB_CMDLINE_LINUX variable.

Example:
GRUB_CMDLINE_LINUX="quiet splash"
Then run: sudo update-grub

5. PXE boot and network-based boot
PXE (Preboot Execution Environment) allows booting over a network using TFTP and DHCP.
Used for diskless systems and mass deployments.

Example tools: dnsmasq, tftp-hpa, pxelinux.0

6. Boot from ISO/HTTP/NFS
Many distros support booting live systems over HTTP/NFS/ISO:
- Use grub or iPXE to specify ISO or HTTP boot source.

Example (GRUB):
```bash menuentry "Boot ISO" { set isofile="/boot/ubuntu.iso" loopback loop (hd0,1)$isofile linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile initrd (loop)/casper/initrd } ```

7. initramfs and init systems
- initramfs: A small root filesystem loaded into memory before the real root system, used to load kernel modules.
- Init systems: systemd (most common), SysVinit, Upstart

Example:
lsinitramfs /boot/initrd.img-$(uname -r) – view contents

8. Boot logs and debugging (dmesg, journalctl)
- dmesg: Displays kernel ring buffer messages (early boot logs)
- journalctl: Displays system logs via systemd journal

Example:
dmesg | grep error
journalctl -b – logs from current boot

9. Kernel panic recovery
Kernel panic is a critical error; to recover:
- Use a live USB/CD to chroot and fix the problem
- Reinstall or fix bootloader/kernel
- Add recovery kernel in GRUB

Example recovery:
```bash sudo mount /dev/sda1 /mnt sudo chroot /mnt grub-install /dev/sda update-grub ```

10. Multi-boot configuration
Multi-boot allows multiple OSes on one system.
GRUB can detect and manage multiple entries.
Each OS may reside on separate partitions.

Example:
Install Linux after Windows. Then:
sudo os-prober
sudo update-grub – adds Windows/Linux to GRUB menu

1. fdisk, parted, gdisk basics
These are partitioning tools used to create, modify, or delete disk partitions:
- fdisk: CLI tool for MBR disks.
- parted: Handles both MBR and GPT.
- gdisk: Advanced tool for GPT disks.

Example:
sudo fdisk /dev/sda
sudo parted /dev/sdb
sudo gdisk /dev/sdc

2. Creating ext2/3/4, XFS, Btrfs
These are common Linux filesystems:
- ext2/3/4: Traditional filesystems
- XFS: High-performance journaling
- Btrfs: Modern with snapshots and checksums

Example:
sudo mkfs.ext4 /dev/sdb1
sudo mkfs.xfs /dev/sdb2
sudo mkfs.btrfs /dev/sdb3

3. Swap management
Swap is disk space used when RAM is full. It can be a file or partition.

Example:
sudo mkswap /dev/sdX2
sudo swapon /dev/sdX2
free -h – see active swap

4. Mounting/unmounting & fstab
Mounting links a filesystem to a directory. /etc/fstab ensures persistent mounts.

Example:
sudo mount /dev/sdb1 /mnt
sudo umount /mnt
cat /etc/fstab

5. Logical Volume Management (LVM) basics
LVM abstracts physical storage for flexible volume management.
- PV: Physical Volume
- VG: Volume Group
- LV: Logical Volume

Example:
```bash sudo pvcreate /dev/sdb1 sudo vgcreate myvg /dev/sdb1 sudo lvcreate -L 5G -n mylv myvg sudo mkfs.ext4 /dev/myvg/mylv sudo mount /dev/myvg/mylv /mnt ```

6. Thin provisioning, resizing volumes
Thin provisioning saves space by allocating it only when needed.
Resizing allows expanding or shrinking volumes.

Example (extend):
sudo lvextend -L +1G /dev/myvg/mylv
sudo resize2fs /dev/myvg/mylv

7. RAID levels and software RAID
RAID (Redundant Array of Independent Disks):
- RAID 0 (striping), RAID 1 (mirroring), RAID 5/6/10
Software RAID uses mdadm.

Example:
sudo mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb /dev/sdc

8. Disk quota configuration
Quotas limit disk usage per user/group.

Example:
- Enable in /etc/fstab:
/dev/sdb1 /home ext4 defaults,usrquota,grpquota 0 2
- Commands:
sudo quotacheck -cum /home
sudo quotaon /home
sudo edquota username

9. Filesystem checks (fsck, xfs_repair)
Used to check and repair filesystems:
- fsck for ext2/3/4
- xfs_repair for XFS

Example:
sudo fsck /dev/sdb1
sudo xfs_repair /dev/sdb2

10. Remote filesystem mounting (NFS, CIFS)
Mount network shares via:
- NFS for Linux/Linux
- CIFS for Windows/Linux

Example:
sudo mount -t nfs 192.168.1.10:/share /mnt
sudo mount -t cifs //server/share /mnt -o user=guest

1. Using APT, DNF/YUM, Zypper
- APT (Debian/Ubuntu):
sudo apt update
sudo apt install nginx
- DNF/YUM (Fedora/Red Hat):
sudo dnf install httpd
- Zypper (openSUSE):
sudo zypper install apache2

2. RPM and dpkg operations
- RPM (Red Hat):
rpm -ivh package.rpm – install
rpm -qa – list installed packages
- dpkg (Debian):
sudo dpkg -i package.deb
dpkg -l

3. Managing repositories & package sources
- APT sources: /etc/apt/sources.list and /etc/apt/sources.list.d/
- YUM/DNF: /etc/yum.repos.d/*.repo
- Zypper: zypper repos

Example:
sudo add-apt-repository ppa:deadsnakes/ppa
sudo dnf config-manager --add-repo URL

4. Version pinning and rollback
- APT pinning: /etc/apt/preferences
- Hold version:
sudo apt-mark hold packagename
- Rollback with YUM:
yum history list
yum history undo ID

5. Snap, Flatpak, AppImage usage
- Snap:
sudo snap install vlc
- Flatpak:
flatpak install flathub org.gimp.GIMP
- AppImage: Just download & run:
chmod +x file.AppImage && ./file.AppImage

6. Building/installing software from source
- Common steps:
```bash tar -xvzf source.tar.gz cd source ./configure make sudo make install ```
Useful when no package is available for your distro.

7. Verifying package integrity (signatures, checksums)
- GPG signature check:
gpg --verify file.sig file
- SHA256 checksum:
sha256sum filename

Example:
Download checksum file from trusted source, then:
sha256sum -c checksum.txt

8. Dependency resolution troubleshooting
- Tools automatically handle dependencies, but sometimes you get broken packages.
- APT fix:
sudo apt --fix-broken install
- DNF debug:
dnf repoquery --requires

9. Automatic updates & unattended upgrades
- APT:
sudo apt install unattended-upgrades
sudo dpkg-reconfigure unattended-upgrades
- DNF:
dnf-automatic service can be enabled.

10. Container image management (build, pull, list)
- Pull image:
docker pull ubuntu:latest
- Build image:
docker build -t myapp .
- List:
docker images

1. Shell types (bash, sh, zsh)
- bash: Bourne Again SHell, default in many Linux distros.
- sh: Original Bourne shell, basic scripting.
- zsh: Extended shell with better features like autocomplete and themes.

Example:
echo $SHELL – shows current shell
chsh -s /bin/zsh – change default shell to zsh

2. Variables, history, aliases
- Variables store data:
NAME="Majid"
echo $NAME
- History stores commands:
history
- Aliases simplify commands:
alias ll="ls -la"

3. Command chaining, subshells, redirections
- Chaining:
cmd1 && cmd2 runs cmd2 if cmd1 succeeds
cmd1 || cmd2 runs cmd2 if cmd1 fails
- Subshells:
(cd /tmp && ls) runs in a subshell
- Redirections:
command > file (overwrite),
command >> file (append),
command 2>&1 redirects stderr to stdout

4. Pipes, tee, xargs usage
- Pipes (|) send output of one command to another:
ls -l | grep ".txt"
- tee writes output to file and stdout:
ls | tee file.txt
- xargs build argument lists:
find . -name "*.log" | xargs rm

5. Environment management and PATH
- Environment variables control shell behavior.
- PATH variable defines where executables are searched:
echo $PATH
- Add directory to PATH:
export PATH=$PATH:/new/path

6. Searching with grep, sed, awk
- grep: Search text patterns:
grep "error" logfile
- sed: Stream editor, substitution:
sed 's/old/new/g' file.txt
- awk: Text processing and reporting:
awk '{print $1}' file.txt

7. find, locate, whereis utilities
- find: Search files by name, size, date:
find / -name "file.txt"
- locate: Fast file search using database:
locate file.txt
- whereis: Locate binary/source/man pages:
whereis ls

8. File metadata tools (stat, file)
- stat file.txt: Shows detailed file info (size, permissions, timestamps)
- file file.txt: Shows file type

9. Text filters and formatting
Tools like cut, sort, uniq, head, tail manipulate text streams.

Example:
cat file.txt | sort | uniq -c – count unique lines

10. Shell configuration files (~/.bashrc, /etc/profile)
- ~/.bashrc: User-specific shell settings.
- /etc/profile: System-wide environment variables and startup scripts.
- Reload config:
source ~/.bashrc

1. systemd architecture and units
systemd is a system and service manager for Linux, replacing SysVinit.
Units are resources managed by systemd (services, sockets, devices). Common types:
- .service for services
- .timer for scheduled jobs
- .socket for sockets

2. systemctl commands (enable/disable/start)
Manage services with systemctl:
- sudo systemctl start nginx.service
- sudo systemctl enable nginx.service (start on boot)
- sudo systemctl disable apache2.service
- sudo systemctl status sshd.service

3. Managing cron, crontab, at jobs
- cron: daemon that runs scheduled jobs
- Edit cron jobs with crontab -e
- at: schedule one-time jobs

Example cron entry (runs daily at 3am):
0 3 * * * /usr/bin/backup.sh

4. Logging with syslog/journalctl
- Traditional syslog writes logs to /var/log/
- systemd's journalctl reads logs:
journalctl -u nginx (nginx logs)
journalctl -b (current boot logs)

5. Running services in containers
Services can run isolated in containers like Docker:
docker run -d --name nginx nginx

6. Background jobs & job control (bg, fg, nohup)
- command & runs job in background
- jobs lists background jobs
- fg %1 brings job 1 to foreground
- nohup command & runs job immune to hangups

7. Resource limits (ulimit)
Limits system resources per shell:
ulimit -a shows current limits
Example: Limit open files:
ulimit -n 1024

8. Automation via timers (systemd timers)
systemd timers replace cron in some cases.
Example timer unit runs every 5 mins:
[Timer]
OnBootSec=5min
OnUnitActiveSec=5min

9. Service profiling and performance tuning
Use tools like systemd-analyze to profile boot time:
systemd-analyze blame
Tune services by adjusting unit files and resource limits.

10. Dependency services and boot ordering
systemd manages dependencies between services with directives like:
Requires=, After=, Before=
Ensures services start in the correct order.

1. Kernel architecture overview
The Linux kernel manages hardware and system resources. It is modular, allowing loading/unloading components (modules) at runtime.

2. lsmod, insmod, rmmod, modprobe usage
- lsmod: Lists currently loaded modules
- insmod: Insert a module (requires exact path)
- rmmod: Remove a loaded module
- modprobe: Smart module loader handling dependencies

Example:
lsmod | grep usb
sudo modprobe snd_hda_intel

3. Persistent module configuration
Add module names to /etc/modules-load.d/*.conf or /etc/modules to load at boot.

4. Monitoring /proc and /sys interfaces
- /proc/modules: Info on loaded modules
- /sys: Kernel device info, e.g., /sys/class/net/eth0

5. Device file management (/dev)
- Device files represent hardware (e.g., /dev/sda)
- Created dynamically by udev or manually with mknod

6. udev rules and dynamic devices
udev dynamically creates device files and manages permissions.
Rules in /etc/udev/rules.d/ customize behavior.

7. USB, PCI, Block device handling
- List USB devices:
lsusb
- PCI devices:
lspci
- Block devices:
lsblk

8. Driver installation and firmware
Drivers may require firmware blobs, often in /lib/firmware.
Install drivers via packages or compile manually.

9. Troubleshooting kernel module issues
Check dmesg logs:
dmesg | grep module_name
Use modprobe -r and reload modules.

10. Kernel updates and version control
Use package managers to update kernels:
sudo apt install linux-image-
Manage boot entries with GRUB.

1. TCP/IP stack overview
TCP/IP is the core protocol suite for networking. Layers include:
- Link Layer (Ethernet)
- Internet Layer (IP)
- Transport Layer (TCP/UDP)
- Application Layer (HTTP, DNS)

2. Configuring IP, routes, netmask
Configure IP with:
ip addr add 192.168.1.10/24 dev eth0
View routes:
ip route show
Add default route:
ip route add default via 192.168.1.1

3. DHCP & DNS client setup
- DHCP auto-configures IP addresses.
- Client config in /etc/dhcp/dhclient.conf or NetworkManager.
- DNS configured via /etc/resolv.conf.

4. Network tools (ping, traceroute, netstat)
- ping: Test connectivity.
- traceroute: Trace packet route.
- netstat: View open connections and ports.

5. host, dig, nslookup usage
- host: Simple DNS lookup.
- dig: Detailed DNS queries.
- nslookup: Interactive DNS client.

6. Configuring cloud/virtual NICs
Manage virtual NICs with ip link or via cloud-init in cloud environments.

7. Network bond, bridge, VLAN basics
- Bonding aggregates multiple NICs for redundancy/performance.
- Bridges connect multiple networks (used in virtualization).
- VLANs segment networks logically.

8. Firewalls (iptables, nftables, ufw)
- iptables: Classic firewall tool.
- nftables: Newer replacement for iptables.
- ufw: User-friendly frontend.

9. SSH, SCP, SFTP, rsync management
- SSH for secure remote login.
- SCP and SFTP for file transfer.
- rsync for efficient syncing.

Example:
scp file.txt user@remote:/path/
rsync -avz /local/dir user@remote:/remote/dir

10. Troubleshooting network issues
Common commands:
ip a – view interfaces
ping 8.8.8.8
traceroute google.com
Check firewall:
sudo iptables -L

1. X11, Wayland basics
- X11: Traditional display server protocol.
- Wayland: Modern replacement for X11 with improved security and performance.

2. Installing desktop environments (GNOME, KDE)
Install via package managers:
sudo apt install ubuntu-gnome-desktop
sudo dnf groupinstall "KDE Plasma Workspaces"

3. Configuring locale, timezone, language
Use locale to view settings.
Set timezone:
sudo timedatectl set-timezone America/Toronto
Configure locale with sudo dpkg-reconfigure locales or edit /etc/locale.conf.

4. Keyboard layout and input methods
Configure layout:
setxkbmap us
For multiple layouts, edit /etc/default/keyboard.

5. Font management
Install fonts by copying to /usr/share/fonts or ~/.fonts.
Use fc-cache -fv to update font cache.

6. Display resolutions, monitors
Use xrandr to list and set resolutions:
xrandr --output HDMI1 --mode 1920x1080

7. Accessibility settings
Enable screen readers, magnifiers in DE settings or via tools like orca.

8. Remote desktop (VNC, XRDP)
- VNC servers: tigervnc, tightvnc
- XRDP provides RDP access:
sudo apt install xrdp

9. GUI tools for system monitoring
Use tools like gnome-system-monitor, kde-system-monitor, or htop.

10. Troubleshooting GUI issues
Check logs:
cat ~/.xsession-errors
Restart display manager:
sudo systemctl restart gdm

1. top, htop, vmstat, iostat utility usage
- top: Real-time process viewer
- htop: Interactive, improved top
- vmstat: Reports virtual memory stats
- iostat: Disk I/O stats

2. CPU and memory bottleneck analysis
Use top or htop to identify processes with high CPU or memory usage.

3. Disk I/O and io stat tuning
Monitor disk I/O with iostat -xz 1.
Tune I/O scheduler via cat /sys/block/sda/queue/scheduler and select scheduler (cfq, noop, deadline).

4. Swap activity and paging
Monitor swap use:
swapon -s
Analyze paging with vmstat 1.

5. Process priority management (nice, renice)
- Set priority at launch:
nice -n 10 command
- Change running process priority:
renice -n 5 -p PID

6. Monitoring open files (lsof)
List open files for a process:
lsof -p PID
Find processes using a file:
lsof /var/log/syslog

7. Resource limits and cgroups
- ulimit for shell resource limits.
- cgroups limit resources for groups of processes.

8. Kernel tuning sysctl parameters
View current parameters:
sysctl -a
Modify temporarily:
sudo sysctl -w net.ipv4.ip_forward=1
Make permanent in /etc/sysctl.conf.

9. Performance logging and trend tracking
Use tools like sar (from sysstat package) for long-term monitoring.

10. Investigating zombies and orphan processes
- Zombies: Processes that have completed but still have an entry in the process table.
- Use ps aux | grep Z to find zombies.
- Orphans are adopted by init process.

1. User account creation and management
Commands like useradd, adduser create new users:
sudo useradd -m username
sudo passwd username sets password.

2. Group creation and assignment
- Create group:
sudo groupadd developers
- Add user to group:
sudo usermod -aG developers username

3. Managing user profiles and home directories
- Edit /etc/skel for default files.
- Manage disk quotas on home directories.

4. Password policies and expiration
Configure password aging with:
chage -l username
Enforce complexity with PAM modules.

5. sudoers file and privilege escalation
Edit /etc/sudoers with visudo for safe syntax.
Example entry:
username ALL=(ALL) ALL

6. Access control lists (ACLs)
Manage fine-grained permissions:
setfacl -m u:username:rwx /path
getfacl /path

7. User and group ID mapping
UID/GID must be unique, manage with usermod, groupmod.

8. Managing system and service accounts
Service accounts (like www-data) run services with limited privileges.

9. Locking and unlocking accounts
sudo usermod -L username locks account;
sudo usermod -U username unlocks.

10. User session management and monitoring
Use who, w, last to track logins.

1. Backup strategies and policies
Full, incremental, differential backups to balance storage and speed.

2. Using rsync for backups
Efficiently sync files:
rsync -av --delete /source/ /backup/

3. tar and gzip for archiving
Archive and compress:
tar czvf backup.tar.gz /folder

4. Scheduling backups with cron
crontab -e to add backup jobs:
0 2 * * * /usr/local/bin/backup.sh

5. Recovery techniques and verification
Test restore backups regularly.
Verify archive integrity:
tar tzvf backup.tar.gz

6. Snapshotting with LVM and Btrfs
Create filesystem snapshots for fast backups:
lvcreate -L1G -s -n snap1 /dev/vg0/lv0

7. Backup tools (Bacula, Amanda)
Enterprise backup solutions supporting automation and multiple clients.

8. Offsite and cloud backup solutions
Use tools like rclone or commercial cloud services.

9. Disaster recovery planning
Define RTO, RPO and ensure backups align with business needs.

10. Backup encryption and security
Encrypt backups using tools like GPG:
gpg -c backup.tar.gz

1. Virtualization basics and types (KVM, Xen)
Hardware-level virtualization enabling multiple OSes on one physical host.

2. Setting up KVM and QEMU
Install and create VMs:
sudo apt install qemu-kvm libvirt-daemon
virt-manager for GUI management.

3. Container basics (Docker, LXC)
Containers are lightweight, OS-level virtualization.

4. Docker commands and container lifecycle
- docker run -d nginx
- docker ps lists running containers
- docker stop container_id

5. Container networking and storage
Manage networks with Docker bridge and volumes for persistent storage.

6. Image management and registries
Pull/push images:
docker pull ubuntu
Use private registries for internal use.

7. Orchestration basics (Kubernetes)
Manage clusters of containers with Kubernetes pods, services, and deployments.

8. Container security best practices
Use minimal images, scan for vulnerabilities, and run containers with least privilege.

9. LXC/LXD management
Linux containers managed with lxc and lxd commands.

10. Troubleshooting virtualization issues
Check logs with journalctl -u libvirtd, verify CPU virtualization support.

1. Introduction to cloud concepts (IaaS, PaaS, SaaS)
Infrastructure as a Service, Platform as a Service, Software as a Service explained.

2. Working with cloud CLI tools (AWS CLI, Azure CLI)
Install AWS CLI:
curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip"
unzip awscliv2.zip
sudo ./aws/install

3. Managing cloud resources programmatically
Use CLI to create, manage VMs, storage, networks.

4. Infrastructure as Code (Terraform, CloudFormation)
Define infrastructure declaratively to version and automate deployments.

5. Automating tasks with Ansible, Puppet, Chef
Configuration management tools for repeatable deployments.

6. Container cloud services (EKS, AKS, GKE)
Managed Kubernetes services on AWS, Azure, GCP.

7. Serverless architecture basics
Running code without managing servers (AWS Lambda, Azure Functions).

8. Monitoring cloud resources
Use CloudWatch, Azure Monitor for performance and alerts.

9. Cloud security best practices
IAM policies, encryption, least privilege.

10. Cost management and optimization
Track spending, use reserved instances, and right-size resources.

1. Using Nagios, Zabbix
Open-source monitoring systems for hosts, services, and network.

2. Setting up Prometheus and Grafana
Metrics collection and visualization platform.

3. Log management with ELK stack
Elasticsearch, Logstash, Kibana for centralized log aggregation.

4. System and application log analysis
Use tools like journalctl, logrotate.

5. Alerting and notification setup
Configure alerts via email, SMS, or webhook integrations.

6. Distributed tracing basics
Track requests across microservices with tools like Jaeger.

7. Performance metrics collection
Collect CPU, memory, disk, network metrics.

8. Anomaly detection
Use machine learning or threshold-based alerts.

9. Historical data storage and retention
Archive logs for compliance and audits.

10. Troubleshooting monitoring issues
Validate configs, check network and permissions.

1. Using smartctl for disk health
Check SMART status:
sudo smartctl -a /dev/sda

2. Memory testing tools (memtest86+)
Bootable tools to test RAM for errors.

3. CPU diagnostics and benchmarking
Use stress-ng or sysbench for CPU load testing.

4. Temperature and fan speed monitoring
Tools: lm-sensors, hddtemp.
Example:
sudo sensors

5. Firmware updates and BIOS management
Update BIOS/firmware using vendor tools or fwupd.

6. Power management and UPS integration
Manage power saving with tlp, UPS monitoring via apcupsd.

7. Hardware inventory and reporting
List hardware with lshw, dmidecode.

8. PCI and USB device troubleshooting
Commands: lspci, lsusb, check kernel logs.

9. Kernel ring buffer and dmesg
Review boot and hardware messages:
dmesg | less

10. Replacing faulty hardware components
Identify issues with diagnostics, schedule maintenance.

1. SELinux modes and policies
Modes: enforcing, permissive, disabled.
Policies define access controls.

2. Managing SELinux contexts
View with:
ls -Z
Change context:
chcon -t httpd_sys_content_t /var/www/html/index.html

3. Troubleshooting SELinux issues
Use ausearch, sealert tools.

4. AppArmor profiles and status
Profiles control program capabilities.
Check status:
sudo aa-status

5. Switching between SELinux and AppArmor
Systems usually use one; disable one before enabling other.

6. Custom policy creation
Write and compile custom policies to allow specific actions.

7. Integrating with systemd
SELinux/AppArmor work with systemd for service confinement.

8. Auditing and logging
Security event logs stored and monitored for violations.

9. Best practices for security policies
Start permissive, test, then enforce.

10. Learning resources and tools
Use official docs, tutorials, and GUI tools.

1. Syslog and rsyslog basics
Syslog standardizes logging; rsyslog extends it.

2. Configuring centralized log servers
Collect logs from clients centrally.

3. Log forwarding and filtering
Configure rules to forward or drop logs.

4. Log storage and rotation
Manage log sizes with logrotate.

5. Searching and analyzing logs
Use grep, awk, or tools like ElasticSearch.

6. Security and compliance logging
Store logs securely for audits.

7. Alerting on log events
Integrate with monitoring for alerts.

8. Visualizing logs with Kibana
Dashboard to explore logs visually.

9. Troubleshooting logging infrastructure
Check connectivity and permissions.

10. Best practices for log management
Define retention policies and secure access.

1. Clustering concepts and benefits
Combine multiple servers for fault tolerance and load balancing.

2. Setting up cluster software (Pacemaker, Corosync)
Tools to manage resources and failover.

3. Resource agents and fencing
Scripts to manage resources and isolate failed nodes.

4. Load balancing basics
Distribute client requests across multiple servers.

5. Shared storage configurations
Use shared disks or network storage for clusters.

6. Failover testing and validation
Simulate node failures to test cluster response.

7. Monitoring cluster health
Use cluster management tools and logs.

8. Multi-site clustering
Geographically distributed clusters for disaster recovery.

9. Integrating with virtualization
Cluster virtual machines for HA.

10. Troubleshooting clustering issues
Check logs and communication between nodes.

1. Kubernetes architecture overview
Kubernetes manages containerized apps with master and worker nodes.

2. Pods, deployments, services basics
Pods are smallest deployable units; deployments manage replicas; services expose pods.

3. Using kubectl for cluster management
Command-line tool to interact with Kubernetes clusters.

4. ConfigMaps and Secrets management
Store config and sensitive data securely.

5. Scaling and rolling updates
Increase/decrease replicas; update without downtime.

6. Monitoring and logging containers
Use Prometheus, Fluentd, or ELK stack.

7. Network policies and security
Control traffic between pods.

8. Persistent storage in Kubernetes
Use PersistentVolumeClaims and storage classes.

9. Helm package manager basics
Manage Kubernetes apps as packages.

10. Troubleshooting Kubernetes clusters
Check pod status, logs, and events:
kubectl get pods, kubectl logs podname

1. System baseline configuration
Establish a secure, minimal system configuration as a starting point.

2. Minimizing installed packages
Remove unnecessary software to reduce attack surface:
sudo apt remove package_name

3. Disabling unused services
List services:
systemctl list-unit-files --type=service
Disable:
sudo systemctl disable service_name

4. Securing SSH configuration
Edit /etc/ssh/sshd_config to disable root login:
PermitRootLogin no

5. Applying security patches
Regularly update system:
sudo apt update && sudo apt upgrade

6. Using security scanners (Lynis, OpenVAS)
Scan system for vulnerabilities and misconfigurations.

7. Configuring auditd
Monitor and log security-relevant events.

8. Enforcing strong password policies
Use PAM modules to enforce complexity.

9. File integrity monitoring (AIDE)
Detect unauthorized changes to files.

10. System lockdown techniques
Use kernel lockdown and secure boot features.

1. Traditional Unix permissions
Read, write, execute for user, group, others.

2. Access Control Lists (ACLs)
Fine-grained permissions:
setfacl -m u:username:rwx /file
getfacl /file

3. Role-Based Access Control (RBAC)
Assign permissions based on user roles.

4. Mandatory Access Control (MAC)
Enforced by SELinux or AppArmor policies.

5. Using sudo for privilege escalation
Configure and limit sudo access.

6. PAM modules for authentication
Pluggable Authentication Modules configure login controls.

7. Managing user groups for access control
Group membership controls access to resources.

8. Directory and file permissions best practices
Principle of least privilege, avoid 777 permissions.

9. Network access controls (firewall rules)
Limit access via iptables, nftables.

10. Auditing access attempts
Review logs for failed/successful access attempts.

1. Centralized authentication (LDAP, Active Directory)
Manage user identities and authentication centrally.

2. Configuring PAM for centralized auth
Integrate PAM with LDAP or Kerberos.

3. Single Sign-On (SSO) concepts
Allow users to log in once for multiple services.

4. Multi-factor authentication (MFA)
Use TOTP or hardware tokens for added security.

5. Kerberos authentication
Ticket-based secure authentication protocol.

6. Managing user directories and groups
Organize identities with groups for permission control.

7. Password synchronization
Sync passwords across systems/services.

8. Account lifecycle management
Automate provisioning, de-provisioning.

9. Identity federation
Trust identities across different domains.

10. Auditing identity changes
Log and review account changes.

1. Overview of SELinux architecture
Mandatory Access Control system controlling access with policies.

2. Enforcing, Permissive, and Disabled modes
Enforcing applies policies; permissive logs violations; disabled turns off.

3. AppArmor basics and profiles
Profile-based security to restrict programs.

4. Managing SELinux contexts
View contexts:
ls -Z /path
Change with chcon.

5. Writing and troubleshooting policies
Use audit2allow to generate policy rules.

6. Tools for managing AppArmor profiles
aa-status, aa-complain, aa-enforce.

7. Troubleshooting SELinux/AppArmor denials
Check logs with ausearch, dmesg.

8. Integrating with system services
Policies apply to services launched by systemd.

9. Best practices for policy management
Start permissive, test, then enforce.

10. Learning resources and documentation
Official SELinux and AppArmor guides.

1. Introduction to iptables and nftables
iptables: legacy firewall; nftables: modern replacement.

2. Basic firewall rule syntax
Example:
sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

3. Creating and managing chains and tables
Chains: INPUT, OUTPUT, FORWARD.

4. Stateful vs stateless filtering
Stateful tracks connections, stateless filters packets independently.

5. Configuring default policies
Set default to DROP or ACCEPT:
sudo iptables -P INPUT DROP

6. Using firewalld on RHEL/CentOS
High-level firewall management tool:
firewall-cmd --list-all

7. Managing ports and services
Open ports:
sudo ufw allow 80/tcp

8. Logging dropped packets
sudo iptables -A INPUT -j LOG --log-prefix "iptables-drop: "

9. Firewall troubleshooting tips
Check rules order and status:
sudo iptables -L -v

10. Best practices for firewall policies
Use least privilege, document rules.

1. Symmetric vs asymmetric encryption
Symmetric uses same key; asymmetric uses public/private keys.

2. Using GPG for file encryption
Encrypt a file:
gpg -c file.txt
Decrypt:
gpg file.txt.gpg

3. SSL/TLS basics
Secure communication protocols for web and email.

4. Managing certificates with OpenSSL
Generate private key and CSR:
openssl req -new -newkey rsa:2048 -nodes -keyout key.pem -out req.csr

5. Disk encryption (LUKS)
Encrypt entire disks or partitions:
sudo cryptsetup luksFormat /dev/sdb1

6. Secure key storage
Use hardware security modules or TPM.

7. Encrypting network traffic (VPNs)
Use IPsec, OpenVPN for secure tunnels.

8. Password-based encryption (PBE)
Protect data using passwords with salting and iterations.

9. Encryption compliance standards
Follow industry standards (FIPS, GDPR).

10. Best practices for key management
Rotate keys regularly, restrict access.

1. Security audit concepts
Evaluate security posture through systematic review.

2. Using auditd for system auditing
Configure audit rules:
auditctl -w /etc/passwd -p wa -k passwd_changes

3. Compliance frameworks overview
Examples: PCI-DSS, HIPAA, GDPR.

4. Generating audit reports
Use ausearch and aureport.

5. Implementing controls and remediation
Fix audit findings to comply with standards.

6. Continuous monitoring
Real-time log analysis and alerting.

7. Policy management
Define security policies clearly.

8. Risk assessment techniques
Identify and prioritize risks.

9. Incident response planning
Prepare for security incidents.

10. Documentation and training
Keep detailed records and educate staff.

1. Importance of patch management
Keep systems secure by applying patches timely.

2. Using package managers for updates
apt, yum, or dnf.

3. Automating patch deployment
Use tools like unattended-upgrades or WSUS.

4. Testing patches before deployment
Prevent breakage by staging.

5. Patch rollback strategies
Use snapshots or backups.

6. Patch compliance reporting
Track patch status across systems.

7. Handling zero-day vulnerabilities
Quick response and mitigation.

8. Vendor security advisories
Monitor for patch announcements.

9. Scheduling maintenance windows
Minimize downtime during patching.

10. Documentation and communication
Keep stakeholders informed.

1. Using SSH securely
Use key-based authentication, disable password logins.

2. VPN overview and types
SSL VPN, IPsec VPN for secure tunnels.

3. Configuring OpenVPN
Server and client setup basics.

4. Using SSH tunnels
Forward ports securely over SSH.

5. Two-factor authentication for SSH
Use Google Authenticator PAM module.

6. Remote desktop with security
Use secure protocols like RDP over VPN.

7. Managing firewall rules for remote access
Allow necessary ports securely.

8. Auditing remote access logs
Monitor access for anomalies.

9. Session timeout and idle disconnect
Configure SSH to disconnect idle sessions.

10. Best practices for remote access
Use VPN, limit access, monitor logs.

1. IDS overview and types
Network-based (NIDS) and host-based (HIDS) IDS.

2. Installing Snort and Suricata
Popular open-source IDS tools.

3. Writing rules and signatures
Detect specific threats and behaviors.

4. Tuning IDS to reduce false positives
Adjust rules and thresholds.

5. Logging and alerting
Configure alerts for suspicious activity.

6. Integrating IDS with SIEM
Centralize alerts and correlate events.

7. Network traffic monitoring
Analyze packets for anomalies.

8. Incident response coordination
Use IDS alerts to trigger response plans.

9. Compliance and IDS
Use IDS to meet regulatory requirements.

10. Best practices and maintenance
Regular updates, rule tuning, and log review.

1. Bash script basics
Bash scripts automate command-line tasks with a series of commands in a file.

2. Script structure and shebang
Start scripts with #!/bin/bash to specify interpreter.

3. Variables and parameter expansion
Define variables: name="value", access with $name.

4. Control structures (if, for, while)
Conditional execution and loops for flow control.

5. Functions and scope
Encapsulate reusable code blocks:
my_func() { echo "Hello"; }

6. Handling input and arguments
Access script arguments with $1, $2,....

7. Exit status and error handling
Use exit and check status with $?.

8. Debugging scripts
Run with bash -x script.sh to trace execution.

9. Working with files and text
Use read, echo, and redirection.

10. Example: simple backup script

#!/bin/bash
backup_dir="/backup/$(date +%F)"
mkdir -p "$backup_dir"
cp -r /important/data/* "$backup_dir"/
echo "Backup completed at $(date)"

1. What is Git?
Distributed version control system to track changes in code.

2. Repository initialization
Create repo:
git init

3. Cloning repositories
git clone <url> to copy remote repos.

4. Staging and committing changes
Stage files:
git add file.txt
Commit:
git commit -m "Message"

5. Branching and merging
Create branch:
git branch new-feature
Switch branch:
git checkout new-feature
Merge:
git merge new-feature

6. Viewing history
git log to view commit history.

7. Remote repositories
Add remote:
git remote add origin <url>
Push changes:
git push origin main

8. Handling conflicts
Resolve merge conflicts manually.

9. Undoing changes
git checkout -- file.txt to discard local changes.

10. Git best practices
Commit often, write clear messages, use branches.

1. Python script setup
Start with #!/usr/bin/env python3 shebang.

2. Variables and data types
Strings, integers, lists, dictionaries.

3. Control flow: if, for, while
Basic branching and loops.

4. Functions and modules
Define reusable code with def.

5. File I/O
Read and write files:
open('file.txt', 'r').

6. Exception handling
Use try-except blocks for errors.

7. Using libraries
Import standard modules (e.g., os, sys).

8. Virtual environments
Isolate dependencies with venv.

9. Example: simple text processor

#!/usr/bin/env python3
filename = 'sample.txt'
with open(filename) as f:
    for line in f:
        print(line.strip())

10. Running Python scripts
python3 script.py

1. What is cron?
Cron schedules recurring tasks using crontab files.

2. Cron syntax
minute hour day month weekday command

3. Editing crontab
crontab -e to edit the current user’s jobs.

4. Environment variables in cron
Specify PATH and other variables.

5. Redirecting output
Use > /path/to/log 2>&1 for logging.

6. Cron vs systemd timers
systemd timers can replace cron with more features.

7. Debugging cron jobs
Check mail or log files for errors.

8. Running scripts with cron
Schedule bash or python scripts.

9. Examples
0 2 * * * /home/user/backup.sh (daily backup at 2am).

10. Best practices
Keep jobs simple, log output, test commands.

1. What are containers?
Lightweight, portable runtime environments for apps.

2. Docker vs Podman overview
Docker requires daemon; Podman runs daemonless.

3. Installing Docker and Podman
Use package managers:
sudo apt install docker.io podman

4. Basic Docker commands
docker run hello-world, docker ps.

5. Running containers with Podman
Similar commands:
podman run alpine.

6. Images and registries
Pull and push container images.

7. Managing volumes
Persist data outside containers.

8. Container networking basics
Bridge networks, port forwarding.

9. Building Dockerfiles
Instructions to create custom images.

10. Best practices
Keep images small, use official base images.

1. Why orchestration?
Manage multiple containers and services.

2. Kubernetes introduction
Popular container orchestration platform.

3. Pods, services, and deployments
Pods run containers; services expose pods; deployments manage scaling.

4. Helm package manager basics
Manage Kubernetes apps with charts.

5. Docker Swarm overview
Native Docker clustering and orchestration.

6. Compose files for multi-container apps
Define services with docker-compose.yml.

7. Scaling and rolling updates
Update apps without downtime.

8. Monitoring orchestration
Tools like Prometheus and Grafana.

9. Security considerations
Manage secrets and network policies.

10. Troubleshooting orchestration
Use logs and status commands.

1. What is configuration management?
Automate system configuration and deployment.

2. Popular tools: Ansible, Puppet, Chef
Agentless (Ansible) and agent-based (Puppet, Chef).

3. Writing playbooks and manifests
Define desired state for systems.

4. Idempotency concept
Repeated runs produce same result.

5. Inventory management
Track hosts and groups.

6. Roles and modules
Reusable config chunks.

7. Integration with CI/CD pipelines
Automate deployments.

8. Managing secrets and vaults
Secure sensitive data.

9. Testing and debugging configs
Validate before applying.

10. Best practices
Modular, documented configs.

1. Continuous Integration (CI) basics
Automatically test and merge code changes.

2. Continuous Delivery/Deployment (CD)
Automate release pipelines.

3. Popular CI/CD tools
Jenkins, GitLab CI, CircleCI.

4. Writing pipelines as code
Define workflows in YAML or Groovy.

5. Integrating tests and builds
Run unit, integration tests.

6. Deployment automation
Use scripts or tools to deploy.

7. Rollbacks and versioning
Handle failed deployments gracefully.

8. Monitoring pipeline health
Track build success and failures.

9. Security in pipelines
Manage secrets, scan for vulnerabilities.

10. Best practices
Keep pipelines simple, modular, fast.

1. What is Infrastructure as Code?
Manage infrastructure via configuration files.

2. Popular IaC tools
Terraform, CloudFormation.

3. Declarative vs imperative approaches
Declare desired state vs step-by-step commands.

4. Writing Terraform configurations
Example resource block:

resource "aws_instance" "web" {
  ami = "ami-123456"
  instance_type = "t2.micro"
}

5. State management
Track resource changes.

6. Applying and destroying infrastructure
terraform apply and terraform destroy.

7. Modules and reuse
Package config blocks.

8. Version control of configs
Store configs in Git.

9. Collaboration and workflows
Work with teams using branches and pull requests.

10. Best practices
Keep configs modular and documented.

1. Why container security matters
Containers share the host kernel, so vulnerabilities affect host.

2. Image scanning
Use tools like Clair or Trivy to scan for vulnerabilities.

3. Least privilege principle
Run containers with minimal permissions.

4. Using read-only filesystems
Prevent unauthorized changes.

5. Secrets management
Store sensitive data securely outside images.

6. Network segmentation
Isolate containers on different networks.

7. Runtime security tools
Falco and similar for behavioral monitoring.

8. Regular updates and patching
Keep base images and container software up-to-date.

9. Auditing and logging
Track container activity for forensics.

10. Best practices
Use official images, minimize layers, scan frequently.

1. Understanding the boot process
The boot process involves BIOS/UEFI, bootloader (GRUB), kernel loading, and init system startup.

2. Common boot failure symptoms
Black screen, stuck at GRUB, kernel panic, no login prompt.

3. Checking bootloader configuration
Inspect /boot/grub/grub.cfg or /etc/default/grub.

4. Using rescue and recovery modes
Boot with live CD/USB to access files.

5. Repairing GRUB
Example command:
sudo grub-install /dev/sda
sudo update-grub

6. Analyzing kernel panic messages
Read console output or logs from /var/log.

7. Verifying init system status
Use systemctl status.

8. Hardware issues affecting boot
Check cables, disks, RAM.

9. Boot log files
journalctl -b shows current boot logs.

10. Preventive measures
Keep backups, maintain updated bootloader.

1. Identifying storage problems
Slow access, I/O errors, disk not mounting.

2. Checking disk health
Use smartctl -a /dev/sdX to view SMART data.

3. Verifying partition tables
Use fdisk -l or parted.

4. Mounting errors
Check /etc/fstab syntax and device UUIDs.

5. Filesystem repair tools
fsck for ext filesystems, xfs_repair for XFS.

6. LVM troubleshooting
Check volume groups and logical volumes with vgdisplay, lvdisplay.

7. RAID issues
Use cat /proc/mdstat to check RAID status.

8. Disk space monitoring
Use df -h and du.

9. Detecting filesystem corruption
System logs and sudden crashes.

10. Backup and recovery
Always have recent backups before repairs.

1. Common network issues
No connectivity, intermittent drops, slow speeds.

2. Checking interface status
Use ip a or ifconfig.

3. Diagnosing routing problems
Use ip route.

4. Testing connectivity
Use ping, traceroute, mtr.

5. DNS resolution issues
Check /etc/resolv.conf, use dig or nslookup.

6. Firewall blocking
Verify iptables/nftables rules.

7. Network interface resets
Restart interfaces with ip link set dev eth0 down and up.

8. Logs and monitoring
Use journalctl -u NetworkManager or system logs.

9. Hardware diagnostics
Check cables, switches, NIC status.

10. Troubleshooting wireless
Inspect wpa_supplicant logs and signal strength.

1. Identifying crashed services
Use systemctl status <service>.

2. Checking logs
journalctl -u <service> or /var/log.

3. Restarting services
systemctl restart <service>.

4. Enabling auto-restart
Configure Restart=always in systemd unit files.

5. Monitoring service health
Use systemctl is-active.

6. Crash loops troubleshooting
Check service dependencies and logs.

7. Core dumps and analysis
Enable core dumps and analyze with gdb.

8. Resource exhaustion
Check memory and CPU limits.

9. Configuration errors
Validate service config files.

10. Using watchdogs
Automatic restarts on failures.

1. What is a kernel panic?
A fatal error in the kernel causing system halt.

2. Common causes
Hardware failure, driver bugs, corrupted modules.

3. Viewing panic messages
Check dmesg or serial console.

4. Analyzing crash dumps
Use kdump and crash tools.

5. Kernel module troubleshooting
Remove or update problematic modules.

6. Hardware diagnostics
Run memory tests, check disk health.

7. Boot parameters
Adjust kernel boot options.

8. Upgrading kernel
Patch known bugs.

9. Preventive measures
Keep backups and monitor system health.

10. Recovery steps
Use rescue mode and reinstall kernel if needed.

1. Signs of corruption
Unexpected crashes, file read/write errors.

2. Backup importance
Always backup before repairs.

3. Running filesystem checks
fsck on unmounted partitions.

4. Using journaling filesystems
Ext4, XFS reduce corruption risk.

5. Recovering data
Use testdisk, photorec.

6. Mount options to reduce corruption
Use noatime, data=writeback.

7. Hardware causes
Faulty cables, disks.

8. Monitoring disk health
Use SMART tools.

9. Preventive filesystem maintenance
Regular checks, controlled shutdowns.

10. Emergency recovery tools
Live CD rescue tools.

1. Overview of SELinux and AppArmor
Mandatory access control systems improving security.

2. Detecting failures
Access denials, permission errors.

3. Checking logs
Use ausearch, journalctl.

4. Setting permissive modes
Temporarily relax enforcement.

5. Managing policies
Use semanage, aa-status.

6. Troubleshooting tips
Analyze AVC denials.

7. Custom policy creation
Create or modify policies.

8. Tools for analysis
setroubleshoot, audit2allow.

9. Balancing security and usability
Avoid overly restrictive policies.

10. Best practices
Regularly update policies and audit logs.

1. What is performance regression?
A decline in system or application performance.

2. Monitoring tools
Use top, htop, iotop.

3. Profiling applications
Use perf, strace.

4. Identifying bottlenecks
CPU, memory, disk, or network.

5. Kernel tuning
Adjust sysctl parameters.

6. Resource limits
Check ulimit settings.

7. Application logs
Look for errors or warnings.

8. Recent changes impact
Review recent updates or config changes.

9. Testing fixes
Benchmark before and after.

10. Documenting results
Keep records for future reference.

1. Accessing remote systems
Use SSH for secure remote access.

2. Remote monitoring tools
Use Nagios, Zabbix, or Prometheus.

3. Remote logging
Configure syslog to central servers.

4. Collecting diagnostics data
Use tcpdump, strace, lsof.

5. Network troubleshooting remotely
Use ping, traceroute.

6. Using remote shells
Tools like mosh for improved experience.

7. File transfers
Use scp, sftp.

8. Monitoring resource usage
Use top, vmstat remotely.

9. Automated scripts
Use Ansible for automation.

10. Security considerations
Use keys, restrict access.

1. Importance of logs
Logs record system and application events for troubleshooting.

2. Log file locations
Commonly /var/log directory.

3. Using journalctl
Query systemd journal logs.

4. Log rotation
Manage log sizes with logrotate.

5. Auditd for security auditing
Setup and configuration.

6. Analyzing audit logs
Use ausearch, auditctl.

7. Correlating events
Link logs from multiple sources.

8. Centralized logging
Use ELK stack or Graylog.

9. Compliance requirements
Logs retention and integrity.

10. Best practices
Secure logs, monitor continuously.

1. Planning for recovery
Have documented backup and disaster recovery plans.

2. Restoring from backups
Test backup integrity regularly.

3. System rollback techniques
Use snapshots, rollback tools.

4. Emergency booting
Boot from live media or rescue environments.

5. Data recovery tools
Use testdisk, photorec.

6. Filesystem restoration
Rebuild corrupted filesystems if possible.

7. Network recovery
Restore network configurations.

8. Service recovery
Restart and reconfigure services.

9. Documentation and lessons learned
Keep logs and notes.

10. Continuous improvement
Update recovery plans regularly.

1. Identifying faulty hardware
Symptoms like crashes, errors, slow performance.

2. Using diagnostic tools
memtest86 for RAM, smartctl for disks.

3. Checking temperatures
Use lm-sensors.

4. Firmware and BIOS updates
Keep updated for stability.

5. Hardware replacement planning
Identify and procure replacements.

6. Stress testing
Use tools like stress-ng.

7. Monitoring hardware health
Continuous monitoring solutions.

8. Interpreting error codes
BIOS beep codes, logs.

9. Documentation
Record hardware issues.

10. Preventive maintenance
Scheduled checks and cleaning.

1. Deep policy analysis
Use semanage and audit2allow.

2. Troubleshooting denials
Analyze AVC logs.

3. Custom policy modules
Write and load custom modules.

4. AppArmor profile tuning
Use aa-complain, aa-enforce.

5. Policy simulation
Test changes without enforcement.

6. Debugging tools
setroubleshoot, audit2allow.

7. Balancing security vs usability
Minimize false positives.

8. Automating policy updates
Script common fixes.

9. Incident response integration
Correlate with IDS/IPS.

10. Documentation and training
Educate admins.

1. Benefits of centralized logging
Easier analysis, correlation, alerting.

2. Popular logging stacks
ELK (Elasticsearch, Logstash, Kibana), Graylog.

3. Syslog forwarding
Configure rsyslog or syslog-ng.

4. Log ingestion and parsing
Use Logstash filters.

5. Log storage and indexing
Efficient storage for quick search.

6. Visualization dashboards
Kibana or Grafana.

7. Alerting and notifications
Setup thresholds.

8. Security of logs
Encryption and access control.

9. Compliance support
Log retention policies.

10. Maintenance and scaling
Backup and scale storage.

1. What are HA clusters?
Groups of servers to provide failover and redundancy.

2. Cluster components
Nodes, shared storage, cluster manager.

3. Common HA software
Pacemaker, Corosync.

4. Failover mechanisms
Automatic service migration.

5. Resource monitoring
Ensure resources are healthy.

6. Quorum and fencing
Prevent split-brain.

7. Load balancing
Distribute workloads.

8. Testing failover
Simulate failures.

9. Backup and recovery
Plan cluster backups.

10. Best practices
Document configs and monitor continuously.

1. Overview of container orchestration
Managing container lifecycles with tools like Kubernetes.

2. Common orchestration issues
Pod crashes, scheduling failures, network problems.

3. Debugging Kubernetes
Use kubectl logs, kubectl describe.

4. Configuration errors
Validate manifests.

5. Resource limits and quotas
Prevent resource exhaustion.

6. Networking in clusters
CNI plugin issues.

7. Storage troubleshooting
Persistent volume claims.

8. Monitoring and alerts
Use Prometheus, Grafana.

9. Rolling updates and rollbacks
Manage application lifecycle.

10. Best practices
Maintain security and backups.

1. Importance of patch management
Keeping systems secure and stable.

2. Patch lifecycle
Identification, testing, deployment.

3. Using package managers
apt, yum, dnf.

4. Automating updates
Configure unattended upgrades.

5. Rollback strategies
Plan for faulty patches.

6. Patch compliance
Auditing patch status.

7. Security advisories
Monitor vendor updates.

8. Staging environments
Test patches before production.

9. Reporting and documentation
Keep update logs.

10. Best practices
Schedule regular patching windows.

1. Purpose of IDS
Detect unauthorized or malicious activity.

2. Types of IDS
Network-based and host-based.

3. Popular IDS tools
Snort, Suricata, OSSEC.

4. Installation and configuration
Basic setup examples.

5. Rule management
Writing and tuning detection rules.

6. Alerting mechanisms
Email, syslog, dashboards.

7. Integration with SIEM
Centralized event correlation.

8. Performance considerations
Resource impact on monitored hosts.

9. Incident response workflows
Responding to IDS alerts.

10. Maintaining IDS
Regular updates and rule tuning.