System Services

SystemD Service Management

Understanding SystemD

Init system and service manager
Unit types (services, mounts, timers)
Dependency management
System state control

Basic SystemD Commands

systemctl start service    # Start a service
systemctl stop service     # Stop a service
systemctl restart service  # Restart a service
systemctl status service   # Check service status

Service Management

systemctl enable service   # Enable at boot
systemctl disable service  # Disable at boot
systemctl is-active service # Check if running
systemctl is-enabled service # Check if enabled

Boot Process

Boot Sequence

BIOS/UEFI
Boot loader (GRUB)
Kernel initialization
SystemD initialization
User space startup

GRUB Configuration

grub2-mkconfig -o /boot/grub2/grub.cfg  # Update GRUB
grub2-set-default 0      # Set default entry
grub2-editenv list       # Show boot settings

Runlevels and Targets

Traditional runlevels (0-6)
SystemD targets
Target dependencies

SystemD Targets

systemctl list-units --type=target  # List targets
systemctl get-default              # Show default target
systemctl set-default multi-user.target  # Set default
systemctl isolate graphical.target # Change current target

Log Management

SystemD Journal

journalctl              # View all logs
journalctl -u service   # Service-specific logs
journalctl -f           # Follow new entries
journalctl --since today # Today's logs

Traditional Logging

/var/log/syslog        # System logs
/var/log/auth.log      # Authentication logs
/var/log/kern.log      # Kernel logs
/var/log/dmesg         # Boot messages

Log Rotation

logrotate              # Rotate log files
/etc/logrotate.conf    # Main configuration
/etc/logrotate.d/      # Service configurations

Hands-on Practice

Exercise 1: Service Management

Check service status:

systemctl status nginx
systemctl status sshd

Start and enable services:

sudo systemctl start nginx
sudo systemctl enable nginx

Exercise 2: Log Analysis

View system logs:

journalctl -p err
tail -f /var/log/syslog

Configure log rotation
Search for specific events

System Recovery

Emergency Mode

Boot into emergency target
Root filesystem repair
Password recovery

Recovery Procedures

systemctl emergency    # Emergency mode
systemctl rescue       # Rescue mode
fsck /dev/sda1         # File system check
passwd root           # Reset root password

Service Security

Security Best Practices

Minimal service exposure
Regular security updates
Service hardening
Audit logging

Service Hardening

systemctl list-dependencies   # Check dependencies
systemd-analyze security      # Security analysis
systemctl mask service        # Prevent service start

Additional Resources

Next Steps

Learn advanced service configuration
Master log analysis
Understand service dependencies
Study system recovery procedures