command-center/omp-docs/tools/linux-power-management.md

---
type: reference
title: Linux Power Management
description: Sleep/wake troubleshooting, NVIDIA GPU power management, and diagnostics for Linux systems.
tags:
  - power-management
  - sleep
  - nvidia
timestamp: 2026-08-06
---

General sleep/wake configuration and diagnostics for Linux systems: systemd sleep, kernel states, NVIDIA GPU power management, wake sources, and diagnostic tools. Fleet scope: the dev workstation `blankpad` is an AMD Cezanne APU exposing **s2idle only** (`/sys/power/mem_sleep` shows no `deep`); the NVIDIA section applied to the retired **dankware** Alienware m16 R2 (see [Sleep/Wake Research](../research/index.md)) and to any future NVIDIA box.

---

## Systemd Sleep Configuration

### logind.conf (`/etc/systemd/logind.conf`)

Controls login manager behavior around sleep:

```ini
[Login]
HandlePowerKey=poweroff
HandleSleepKey=suspend
HandleHibernateKey=hibernate
HandleLidSwitch=suspend
HandleLidSwitchDocked=ignore
HoldoffTimeoutSec=5s
IdleAction=hibernate
IdleActionSec=30min
```

**Key setting**: `HoldoffTimeoutSec` — increase if sleep triggers are too aggressive.

### sleep.conf (`/etc/systemd/sleep.conf`)

Controls the actual sleep behavior:

```ini
[Sleep]
AllowSuspend=yes
AllowHibernation=yes
AllowHybridSleep=yes
HibernateMode=platform+shutdown
HibernateDelaySec=1800
```

**HibernateMode options**:
- `platform` — ACPI platform sleep (faster, firmware-dependent)
- `shutdown` — classic shutdown-to-disk (slower, more compatible)
- `shutdown+platform` — try platform first, fall back to shutdown

### Suspend-Then-Hibernate Flow

```
Suspend (RAM) --timeout--> Hibernate (disk)
    |
    +-- wake event --> Resume
```

### Custom Sleep Hooks

Create `/etc/systemd/system-sleep/` scripts for pre/post sleep actions:

```bash
#!/bin/bash
# /etc/systemd/system-sleep/hook
case "$1" in
    pre)  echo "Suspending..." ;;
    post) echo "Resumed!" ;;
esac
```

---

## Kernel Sleep States

### ACPI Sleep States

| State | Name | Power | Wake Time | Description |
|-------|------|-------|-----------|-------------|
| S0 | Working | Full | Instant | System is running |
| S1 | Sleep (halted) | ~10-20W | <1s | CPU halted, RAM refresh |
| S2 | Sleep | ~5-10W | ~1s | CPU cache flushed |
| **S3** | **Sleeping Standby** | **~1-5W** | **~1-2s** | **RAM retained, most power off** |
| S4 | Hibernate | 0W | ~10-30s | RAM written to disk |
| **S5** | **Soft Off** | **0W** | **~5-10s** | **Powered off but can wake** |

### Modern ACPI Sleep States (s2idle)

Modern laptops often **only support s2idle** (S0 idle):

```bash
$ cat /sys/power/mem_sleep
[s2idle] deep
```

| Mode | Name | Power | Characteristics |
|------|------|-------|----------------|
| **s2idle** | "Suspend to Idle" | 3-8W | Shallow, firmware-managed, fast wake, higher drain |
| **deep** | S3 | 1-3W | Deeper sleep, slower wake, better battery |

### Setting Default Sleep State

Add to kernel command line (GRUB or systemd-boot):

```
mem_sleep_default=deep      # Prefer S3 deep sleep
mem_sleep_default=s2idle    # Force s2idle
```

**For GRUB:** Edit `/etc/default/grub`, add to `GRUB_CMDLINE_LINUX_DEFAULT`:
```
GRUB_CMDLINE_LINUX_DEFAULT="... mem_sleep_default=deep"
```

---

## NVIDIA GPU Power Management

### Enable NVIDIA Suspend Support

```bash
sudo systemctl enable nvidia-suspend.service
sudo systemctl enable nvidia-suspend-then-hibernate.service
sudo systemctl enable nvidia-hibernate.service
```

### NVIDIA Module Parameters

Edit `/etc/modprobe.d/nvidia.conf`:

```
options nvidia NVreg_PreserveVideoMemoryAllocations=1
options nvidia NVreg_EnableS0ixPowerManagement=1
```

### Check NVIDIA GPU State

```bash
# Is the NVIDIA GPU active?
lspci -vnn | grep -A 12 -i "vga"

# Force NVIDIA GPU to D3hot (fully off) before suspend
sudo tee /sys/bus/pci/devices/0000:01:00.0/power/control <<< auto
```

---

## Diagnostic Tools

### journalctl

```bash
# All sleep-related events in the last boot
journalctl -b -0 | grep -iE 'suspend|resume|sleep|wake|acpi'

# Real-time monitoring during a suspend attempt
journalctl -f &
systemctl suspend
# Wait for failure, then Ctrl+C
```

### powertop

```bash
sudo powertop          # Interactive view
sudo powertop --calibrate   # One-time setup
sudo powertop --auto-tune   # Apply recommendations
sudo powertop --html=/tmp/report.html --csv=/tmp/report.csv
```

### tlp — Advanced Power Management

```bash
sudo pacman -S tlp tlp-rdw   # Arch
sudo apt install tlp         # Debian/Ubuntu
sudo systemctl enable --now tlp
sudo tlp-stat
```

### dmesg

```bash
dmesg | grep -iE 'suspend|resume|acpi|pm_'
dmesg -wH                    # Watch mode, human-readable
```

---

## Wake Source Management

### Checking Wake Sources

```bash
# What can wake the system?
cat /proc/acpi/wakeup | grep enabled

# What woke the system last time?
journalctl -b -1 | grep -iE 'PM: wakeup|wakeup source|acpi: wakeup'
```

### Toggling Wake Sources

```bash
# Toggle a device's wake capability
echo XHCI | sudo tee /proc/acpi/wakeup
echo RP01 | sudo tee /proc/acpi/wakeup
```

### Persistent Wake Source Configuration

Create a systemd service:

```ini
# /etc/systemd/system/config-wake-sources.service
[Unit]
Description=Configure ACPI wake sources
Before=sleep.target

[Service]
Type=oneshot
ExecStart=/bin/bash -c 'echo XHCI > /proc/acpi/wakeup'
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
```

---

## Common Kernel Parameters

| Parameter | Description |
|-----------|-------------|
| `mem_sleep_default=deep` | Prefer S3 deep sleep |
| `pcie_aspm=force` | Force ASPM (aggressive power saving) |
| `pcie_aspm.policy=performance` | Disable ASPM (fixes some issues) |
| `acpi_osi=!` | Hide OS identity from ACPI |
| `usbcore.autosuspend=-1` | Disable USB autosuspend |

---

## Testing Sleep Modes

```bash
# Suspend to RAM
systemctl suspend

# Hibernate to disk
systemctl hibernate

# Suspend then hibernate
systemctl suspend-then-hibernate

# Freeze (CPUs idle, RAM on)
systemctl freeze
```

### Automated Stress Test

```bash
#!/bin/bash
for i in $(seq 1 10); do
    echo "=== Cycle $i ==="
    date
    echo mem | sudo tee /sys/power/state 2>/dev/null || systemctl suspend
    echo "Resume $i: SUCCESS"
    sleep 5
done
```

---

## Quick Reference: Action Items

```bash
# 1. Enable NVIDIA suspend support
sudo systemctl enable nvidia-suspend.service
sudo systemctl enable nvidia-suspend-then-hibernate.service

# 2. Add NVIDIA power management module parameter
echo 'options nvidia NVreg_PreserveVideoMemoryAllocations=1' | sudo tee /etc/modprobe.d/nvidia-preserve.conf

# 3. Reboot
sudo reboot

# 4. Test suspend
systemctl suspend

# 5. After resume, check for errors
dmesg | tail -30
journalctl -b -0 | grep -iE 'error|fail|nvidia' | tail -20
```