Linux systemd and Service Processes

systemctl status nginx

# Show status, recent logs, and the service main PID.

systemctl show -p MainPID nginx

# Extract the tracked main PID for a unit.

systemctl cat nginx

# Print the unit file and drop-ins defining a service.

systemctl list-units --type=service --state=running

# List active services managed by systemd.

journalctl -u nginx -n 100 --no-pager

# Read recent logs associated with one systemd unit.

journalctl _PID=1234 -n 100 --no-pager

# Filter the journal by process ID.

sudo systemctl start nginx

# Start a service unit.

sudo systemctl stop nginx

# Stop a service unit gracefully.

sudo systemctl restart nginx

# Restart a service unit.

sudo systemctl reload nginx

# Ask a service to reload its configuration.

sudo systemctl kill -s SIGKILL nginx

# Signal all or selected processes in a service cgroup.

sudo systemctl kill --kill-whom=main -s SIGUSR1 nginx

# Signal only the service main process.

sudo systemctl reload-or-restart nginx

# Use reload when available, else restart.

systemd-cgls

# Display control groups and the processes inside them.

systemd-cgtop

# Show top cgroups by CPU, memory, and I/O load.

loginctl list-sessions

# Inspect active user sessions and seats under systemd-logind.

loginctl show-session 2

# Inspect one logind session in detail.

systemctl show -p ControlGroup nginx

# Reveal the cgroup path tied to a unit.

systemd-run --scope htop

# Run an interactive process in its own transient scope unit.

systemd-run --unit=myjob --remain-after-exit /usr/bin/sleep 60

# Launch a one-off command as a transient service unit.

sudo systemctl set-property myjob.service CPUQuota=50%

# Apply runtime resource-control properties to a unit.

sudo systemctl set-property myjob.service MemoryMax=1G

# Limit service memory through cgroup controls.