Systemd & Services

Overview

Systemd is the init system and service manager for RHEL 10. It manages services, sockets, timers, mounts, and more through unit files.

# Check service status
systemctl status httpd

# Enable and start a service
sudo systemctl enable --now httpd

# Stop and disable
sudo systemctl disable --now httpd

# List failed units
systemctl --failed

# List all loaded units
systemctl list-units --type=service --state=running

# View unit file
systemctl cat httpd

Custom Unit Files

# Create a custom service
sudo tee /etc/systemd/system/myapp.service <<'EOF'
[Unit]
Description=My Application
After=network.target
Wants=network.target

[Service]
Type=simple
ExecStart=/opt/myapp/bin/myapp
Restart=on-failure
RestartSec=5
User=myapp
Group=myapp

[Install]
WantedBy=multi-user.target
EOF

sudo systemctl daemon-reload
sudo systemctl enable --now myapp.service

Socket Activation

Socket activation starts services on-demand when a connection arrives, reducing boot time and resource usage.

# Example socket unit
sudo tee /etc/systemd/system/myapp.socket <<'EOF'
[Unit]
Description=My App Socket

[Socket]
ListenStream=8080
Accept=no

[Install]
WantedBy=sockets.target
EOF

# Matching service (Type=simple, no ExecStart needed for socket activation)
sudo systemctl enable --now myapp.socket

Quadlet Files (RHEL 10)

Quadlet files let you manage Podman containers through systemd using .container and .volume unit files, similar to Docker Compose.

# Create a Quadlet container file
sudo tee /etc/systemd/system/myapp.container <<'EOF'
[Unit]
Description=My App Container

[Container]
Image=registry.access.redhat.com/ubi10/ubi-minimal
Exec=echo hello
Port=8080:80
Volume=data:/app/data:Z

[Install]
WantedBy=multi-user.target
EOF

# Optional volume file
sudo tee /etc/systemd/system/myapp.volume <<'EOF'
[Volume]
Driver=local
EOF

sudo systemctl daemon-reload
sudo systemctl enable --now myapp.container

Timers (cron replacement)

# Create a timer unit
sudo tee /etc/systemd/system/backup.timer <<'EOF'
[Unit]
Description=Daily Backup Timer

[Timer]
OnCalendar=daily
Persistent=true

[Install]
WantedBy=timers.target
EOF

# Matching service
sudo tee /etc/systemd/system/backup.service <<'EOF'
[Unit]
Description=Run Backup

[Service]
Type=oneshot
ExecStart=/usr/local/bin/backup.sh
EOF

sudo systemctl enable --now backup.timer
systemctl list-timers --all

Journal & Logs

# View logs for a service
sudo journalctl -u httpd

# Follow logs in real time
sudo journalctl -u httpd -f

# Logs since last boot
sudo journalctl -b

# Logs from a specific time range
sudo journalctl --since '2026-05-01' --until '2026-05-02'

# Persistent logging (survives reboot)
sudo mkdir -p /var/log/journal
sudo systemd-tmpfiles --create --prefix /var/log/journal
sudo systemctl restart systemd-journald

Targets (Runlevels)

# Current default target
systemctl get-default

# Change to multi-user (no GUI)
sudo systemctl set-default multi-user.target

# Change to graphical (with GUI)
sudo systemctl set-default graphical.target

# List available targets
systemctl list-unit-files --type=target