Linux Services and Networking, Systemd vs Cron.pdf

Linux services and networking

1. Linux Services and
Networking
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2. Service Management in Linux
●Linux provides robust tools for managing system services
●Key tools: Cron and Systemd
●Ensures services run smoothly and efficiently
●Essential for system administrators and DevOps
professionals
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3. Overview of Cron
Cron: a time-based job scheduler in Unix-like systems
Used for scheduling repetitive tasks
Cron jobs defined in crontab files
Commonly used for:
●Automated backups
●System maintenance
●Scheduled scripts

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4. Crontab Syntax
Crontab file format:
●* * * * * command_to_execute
●Fields: minute, hour, day of month, month, day of week
Examples:
●0 0 * * * /path/to/script.sh (runs daily at midnight)
●0 5 * * 1 /path/to/script.sh (runs every Monday at 5 AM)

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5. Managing Cron Jobs
View crontab: crontab -l
Edit crontab: crontab -e
Remove crontab: crontab -r
Use proper permissions and paths
Monitor cron logs for troubleshooting

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6. Overview of Systemd
Systemd: a system and service manager for Linux
Provides parallelization capabilities
Uses units to manage services, mounts, and devices
Key commands: systemctl, journalctl
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7. Systemd Unit Files
●Unit files: configuration files that define services
●Located in /etc/systemd/system/ and /usr/lib/systemd/system/
●Common unit file sections:
○[Unit]: metadata and dependencies
○[Service]: service-specific settings
○[Install]: installation settings

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8. Managing Services with Systemd
Start a service: systemctl start service_name
Stop a service: systemctl stop service_name
Enable a service: systemctl enable service_name
Disable a service: systemctl disable service_name
Check service status: systemctl status service_name
View logs: journalctl -u service_name

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9. Key Differences Between Cron and Systemd
●Cron:
○Time-based scheduling
○Simpler, lightweight
○Ideal for repetitive tasks
●Systemd:
○More comprehensive service management
○Handles dependencies and parallelization
○Suitable for complex service orchestration

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10. Practical Examples
Cron:
●Backup script: 0 2 * * * /usr/local/bin/backup.sh
●Clean temp files: 0 0 * * 0 /usr/local/bin/clean_temp.sh
Systemd:
●Custom service unit: foo.service, foo.timer
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[Unit]
Description=My Custom Service

[Service]
ExecStart=/usr/local/bin/my_se
rvice.sh

[Install]
WantedBy=default.target

[Unit]
Description=Run daily backup

[Timer]
OnCalendar=daily
Persistent=true

[Install]
WantedBy=timers.target

11. Introduction to Logging
●Importance of logging in system administration and DevOps
●Types of logs: application logs, system logs
●Overview of common logging tools and their benefits

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12. Types of Logs and Locations
●Application logs:
○Located in application-specific directories (e.g., /var/log/nginx/)
○Example tools: tail, grep for real-time monitoring
●System logs:
○Managed by the operating system (e.g., /var/log/syslog,
/var/log/messages)
○Example tools: journalctl for systemd logs on Linux

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13. Useful Command-Line Tools
tail command:
●Used for viewing the last few lines of a log file
●Example: tail -n 100 /var/log/syslog (displays last 100 lines of syslog)
grep command:
●Filters log entries based on a specified pattern
●Example: grep "ERROR" /var/log/nginx/error.log (finds ERROR entries in
nginx error log)

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14. Log Rotation
●Importance of log rotation for managing log file size and maintenance
●Example tools: logrotate for automated log rotation configuration
Slide 5: Monitoring and Analysis
●Monitoring logs:
○Use watch command to monitor log files in real-time
○Example: watch -n 10 tail /var/log/syslog (updates syslog every 10
seconds)
●Log analysis:
○Use awk or sed for simple log parsing and analysis tasks
○Example: awk '{print $4, $5, $6}' /var/log/apache2/access.log
(extracts specific fields from Apache access log)
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15. Introduction to File Sharing and Tools
File sharing facilitates collaboration by enabling seamless access to files across networks.
Key file sharing tools include:
●SCP (Secure Copy): Securely transfers files between systems using SSH.
●Rsync (Remote Sync): Efficiently synchronizes files and directories locally or across
networks.
●Samba: Provides file and print services for seamless integration between Linux and
Windows environments.

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16. Usage and Examples
SCP (Secure Copy):
●Used for one-time secure file transfers.
●Example: scp local_file.txt remote_user@remote_host:/remote/path/
Rsync (Remote Sync):
●Ideal for synchronizing large directories or backups.
●Example: rsync -avz /local/directory/
remote_user@remote_host:/remote/directory/
Samba:
●Enables seamless file and printer sharing across heterogeneous networks.
●Example: Setting up a shared folder accessible from Windows and Linux.

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17. Key Differences
SCP (Secure Copy):
●Focuses on secure file transfer over SSH.
●Example: scp file.txt user@remote_host:/path/to/destination
Rsync (Remote Sync):
●Efficiently synchronizes files and directories, minimizing data transfer.
●Example: rsync -avz /local/dir/ user@remote_host:/remote/dir/
Samba:
●Provides file and print services for Windows clients in a Linux environment.
●Example: Setting up a shared folder accessible from Windows and Linux.

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18. Network Overview
●Network Components
○Nodes: Devices connected to the network (e.g., computers, servers, routers).
○Networks: Interconnected nodes facilitating communication.
○Protocols: Rules governing communication (e.g., TCP/IP, HTTP).
●Types of Networks
○LAN (Local Area Network): Limited geographical area (e.g., office building).
○WAN (Wide Area Network): Spans large geographical areas (e.g., across cities or countries).
○VPN (Virtual Private Network): Securely extends a private network across a public network (e.g.,
internet).
●Network Devices
○Router: Directs data between networks.
○Switch: Connects devices within a LAN.
○Firewall: Controls incoming and outgoing network traffic based on security rules.

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19. TCP/IP Model
Importance of network architecture understanding.
Overview of TCP/IP model layers:
●Application Layer
●Transport Layer
●Internet Layer
●Link Layer
Application Layer: Interacts directly with applications (e.g., HTTP, FTP).
Transport Layer: Manages data delivery (e.g., TCP, UDP).
Internet Layer: Handles addressing and routing (e.g., IP).
Link Layer: Manages physical connection (e.g., Ethernet).

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20. Network Security
Encryption: Secures data in transit (e.g., SSL/TLS).
Access Control: Restricts network access based on user roles.
Intrusion Detection/Prevention Systems (IDS/IPS): Monitor and
respond to network threats.

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21. IP Addressing and Subnetting
IPv4 vs. IPv6: Differences and benefits of IPv6.
Subnetting: Divides networks into smaller segments.
DHCP (Dynamic Host Configuration Protocol): Automates IP address assignment.

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22. Introduction to Routing
●Routing: The process of directing network traffic from its source to its destination
across multiple networks.
●Importance: Efficient routing ensures timely and reliable delivery of data.
Concept of Routing
●Routing Logic: Determines the best path for data packets based on routing metrics
such as shortest path, lowest latency, or least cost.
●Router Role: Devices that forward data packets between networks based on routing
decisions.

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23. Routing Table
Routing Table: A database stored in routers that contains information about known network paths.
Components:
●Destination Network: The IP address or network address of the destination.
●Next Hop: The IP address of the next router or gateway along the path to reach the destination.
●Interface: The network interface through which the router can reach the destination.
Routing Table Example
●Example Entry:
○Destination Network: 192.168.1.0/24
○Next Hop: 10.0.0.1
○Interface: eth0
●Purpose: Helps routers make forwarding decisions based on the destination IP address of incoming packets.
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24. Introduction to Network Configuration Tools
Network Configuration Tools: Essential utilities for managing network interfaces in Linux
systems.
Importance: Efficient management of network settings enhances connectivity and
troubleshooting.
ifconfig: Configures and displays network interface parameters.
ip link show: Lists network interfaces and their state.
ip addr show: Displays IP addresses assigned to network interfaces.
ip route: Manages IP routing tables for network communication.
route: Manages IP routing tables for network communication.
ifup / ifdown: Scripts to bring up or down network interfaces.
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25. ifconfig, ifup, ifdown
ifconfig: Displays and configures network interface parameters.
Usage:
●View interface details: ifconfig
●Configure interface: sudo ifconfig eth0 192.168.1.10 netmask 255.255.255.0
●Enable interface: sudo ifconfig eth0 up
●Disable interface: sudo ifconfig eth0 down
ifup and ifdown: Scripts to bring up or down network interfaces.
Usage:
●Enable interface: sudo ifup eth0
●Disable interface: sudo ifdown eth0

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26. route
route: Displays and manipulates IP routing tables.
Usage:
●Show routing table: route -n
●Add a route: sudo route add -net 192.168.2.0 netmask 255.255.255.0 gw 192.168.1.1
●Delete a route: sudo route del -net 192.168.2.0 netmask 255.255.255.0

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27. IP
●ip link show: Lists network interfaces and their state.
●Usage:
○Display all interfaces: ip link show
○Show specific interface: ip link show eth0
●ip addr show: Displays IP addresses assigned to network interfaces.
●Usage:
○Show IP addresses: ip addr show
○Show addresses for specific interface: ip addr show eth0
●ip route: Displays and manipulates IP routing tables.
●Usage:
○Show routing table: ip route show
○Add a route: sudo ip route add 192.168.2.0/24 via 192.168.1.1 dev eth0
○Delete a route: sudo ip route del 192.168.2.0/24

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28. Introduction to Network Troubleshooting
Tools
Network Troubleshooting Tools: Essential utilities for diagnosing and resolving network
issues in Linux systems.
Summary:
●Ping: Tests connectivity to remote hosts using ICMP echo requests.
●Traceroute: Traces the path packets take from source to destination.
●/etc/services: Lists network services and associated port numbers.
●Netstat: Displays network connections, routing tables, and interface statistics.

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29. Ping
Ping: Verifies connectivity to a remote host by sending ICMP echo requests.
Usage:
●Test connectivity: ping google.com
●Specify number of packets: ping -c 5 google.com
●Continuous ping: ping -i 2 google.com

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30. Traceroute
Traceroute: Traces the route packets take from source to destination.
Usage:
●Trace route to destination: traceroute google.com
●Specify maximum hops: traceroute -m 30 google.com
●Use ICMP instead of UDP: traceroute -I google.com

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31. /etc/services
●/etc/services: Lists network services and associated port numbers.
●Usage:
○View services and ports: cat /etc/services
○Lookup specific service: grep ssh /etc/services

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32. Netstat
Netstat: Displays network connections, routing tables, interface statistics, and more.
Example: netstat -at
The netstat -a command shows the listening and non-listening sockets for network
connections, the -t flag shows only tcp connections.
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33. Introduction to DNS (Domain Name System)
DNS (Domain Name System): Vital system that translates domain names (e.g.,
google.com) into IP addresses (e.g., 192.168.1.1).
Importance:
●Internet Navigation: Enables users to access websites and services using
human-readable domain names.
●Network Communication: Essential for devices to locate and communicate with each
other across networks.
●Service Availability: Ensures reliable and efficient internet services by resolving
domain names to IP addresses accurately.

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34. Components of DNS
DNS Components:
●DNS Resolver: Client software that initiates DNS queries.
●DNS Server: Stores DNS records and responds to queries from resolvers.
●DNS Zones: Administrative domains managed by DNS servers.
●DNS Records: Information stored in DNS databases (e.g., A, AAAA, CNAME, MX records).
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35. Handling DNS Requests
●DNS Request Process:
○Step 1: Resolver sends a query to the local DNS server.
○Step 2: Local DNS server checks its cache; if not found, it queries authoritative
DNS servers.
○Step 3: Authoritative DNS server responds with the requested DNS record.
○Step 4: Response is returned to the resolver, which then resolves the domain
name.

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36. /etc/hosts File
/etc/hosts File: Local text file mapping IP addresses to hostnames on a system.
Purpose:
●Provides local hostname resolution without querying DNS servers.
Practical Use Cases:
●Local Hostname Resolution:
○127.0.0.1 localhost
○192.168.1.10 myserver.example.com
●Override DNS Resolution:
○192.168.1.100 internal.example.com
Benefits:
●Speeds up access to local resources.
●Facilitates testing and development environments.

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37. DNS Tools: nslookup
nslookup: Command-line tool to query DNS servers and resolve hostnames.
Usage:
●Query DNS server: nslookup google.com
●Reverse lookup: nslookup 8.8.8.8

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38. DNS Tools: dig
dig (Domain Information Groper): Advanced DNS querying tool for DNS troubleshooting.
Usage:
●Query DNS records: dig google.com
●Specify DNS server: dig @8.8.8.8 google.com
●Query specific record types: dig MX google.com

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39. Assignment: Network Configuration and Troubleshooting
Objective: Configure network settings, troubleshoot DNS resolution, and utilize network troubleshooting tools on a local Linux machine.
Part 1: Network Configuration
1.Set Up Network Interface:
○Configure your primary network interface (eth0 or enp0s3) with a static IP address 192.168.1.100 and netmask
255.255.255.0 using the appropriate command (ifconfig or ip).
2.Verify Network Configuration:
○Use ip addr show or ifconfig to confirm the interface settings and ensure connectivity to your local network.
Part 2: DNS Configuration and Troubleshooting
3.Edit /etc/hosts File:
Edit the /etc/hosts file to include the following entries:

127.0.0.1 localhost
192.168.1.100 myserver.example.com
○
4.Test DNS Resolution:
○Verify DNS resolution for localhost and myserver.example.com using ping and nslookup.
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You have to submit a pdf containing screenshots of
running the commands and their outputs here