INC-2026-04-04: Razer Blade 18 High Fan Noise & Elevated Temperature

Incident Summary

Field Value

Detected

2026-04-04 ~18:50 PDT (user report - sudden fan noise)

Mitigated

2026-04-04 ~19:15 PDT (killed runaway waybar process)

Resolved

2026-04-04 ~19:44 PDT (CSS fixes applied, waybar stable at 0% CPU)

Duration

~54 minutes (detection to resolution)

Severity

P3 (Medium) - System functional but thermally stressed

Impact

CPU at 86°C, fans at max RPM, CPU throttled to 800 MHz

Root Cause

Waybar CSS box-shadow declarations and infinite animations caused GTK3 software rendering loop at 50-96% CPU

Timeline

Time (PDT) Event

~18:50

User noticed sudden high fan noise after plugging in AC power

18:51

Initial diagnostics: CPU at 86°C, GPU at 54°C idle (7W, 0% util). GPU ruled out.

18:52

Process analysis: waybar PID 2140 at 96.1% CPU identified as heat source

18:53

Killed waybar, temps began dropping (86°C → 79°C)

18:54

Restarted waybar — returned to 52% CPU immediately. Not a one-off.

19:00

CSS animations commented out (glow-pulse, text-flicker, subtle-breathe). Still 53% CPU.

19:02

All remaining animations disabled. Still 52% CPU. Animations not sole cause.

19:10

Minimal config test (clock only): 0.0% CPU. Confirmed modules are fine.

19:15

Full modules + minimal CSS: 0.0% CPU. Confirmed CSS is the root cause.

19:25

Removed media module — still 57%. playerctl -F ruled out.

19:29

Disabled transition: all properties — still 58%. Not transitions alone.

19:32

Disabled box-shadow via sed — introduced CSS parse errors (unclosed comments)

19:40

Read full style.css, identified all corrupted lines. Properly removed multi-line box-shadow blocks, stray */ fragments, and last active animation (border-glow-cycle)

19:44

Waybar stable at 0.0% CPU. No CSS parse errors. Temps: 56°C and dropping.

19:46

Final thermal reading: CPU 56°C, ACPI 54°C. 30°C drop from peak. Incident resolved.

Symptoms

Sudden onset of high fan noise when AC power plugged in
CPU package temperature at 86°C during light desktop use (terminal, browser)
CPU throttled to 800 MHz (min frequency) — still couldn’t cool down
GPU completely idle (54°C, 7W, 0% utilization) — not the cause
System uptime was 1 day 20 hours at time of incident

Investigation

Phase 1: Thermal Baseline

paste <(cat /sys/class/thermal/thermal_zone*/type) \
      <(awk '{printf "%.1f°C\n", $1/1000}' /sys/class/thermal/thermal_zone*/temp)

Table 1. Initial readings (18:51 PDT)
Sensor	Temperature
x86_pkg_temp (CPU)	86.0°C
acpitz	81.0°C
SEN1/SEN2 (VRM/SSD)	53-54°C
NVIDIA RTX 5090	54°C (idle)
iwlwifi	60°C

Phase 2: Process Analysis

top -b -n1 | awk 'NR>=7 && NR<=12'

Result

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   2140 evanusm+  20   0 2391024  93284  77544 R  96.1   0.1     11,21 waybar
   2084 evanusm+  20   0 1570524 203848 113288 S   4.8   0.3  35:45.76 Hyprland

waybar at 96.1% CPU — single core pinned. 11 minutes 21 seconds of accumulated CPU time.

Phase 3: GPU Verification

nvidia-smi

Result — GPU is innocent

|   0  NVIDIA GeForce RTX 5090     Off |   00000000:01:00.0 Off |                  N/A |
| N/A   54C    P8              7W /   95W |      17MiB /  24463MiB |      0%      Default |

Processes:
|    0   N/A  N/A            2084      G   Hyprland                                  6MiB |

Only Hyprland on GPU at 6 MiB. Firefox and kitty NOT on dGPU (unlike INC-2026-03-27).

Phase 4: Isolation Testing

Systematic elimination to identify root cause:

Test Config CPU Result

Minimal (clock only, minimal CSS)

1 module, no styling

0.0%

Full modules, minimal CSS

All modules, * {font-size:14px}

0.0%

Full modules, full CSS (no animations)

All modules, animations commented

53%

Full modules, full CSS (no transitions)

All modules, transitions + animations off

58%

Full modules, full CSS (no box-shadow)

All modules, box-shadow + animations + transitions off

CSS parse error (broken comments)

Full modules, properly cleaned CSS

Removed box-shadow blocks, fixed syntax, disabled last animation

0.0%

Conclusion: Full modules + minimal CSS = 0%. The CSS itself was the sole cause.

Phase 5: CSS Forensics

The style.css (605 lines, Catppuccin Mocha / Glass Island theme) contained:

Property Count

alpha() function calls

~80+

box-shadow declarations

8 (including multi-line)

border-radius

~20

transition: all

4

Infinite animation:

7 (pulse, glow-pulse, text-flicker, border-glow-cycle, subtle-breathe)

linear-gradient

3

text-shadow

2

Findings

Primary: Multi-line box-shadow with alpha() compositing forced GTK3 into software rendering path for every widget repaint
Contributing: Seven infinite CSS animations triggered constant repaints every frame, each requiring expensive shadow recalculation
Trigger: The degradation was progressive over 1 day 20h uptime — GTK3’s rendering pipeline accumulated overhead until it entered a CPU spin
Correlation: Plugging in AC power likely triggered a battery state class change (.charging), causing a style recalculation cascade on all widgets simultaneously

Root Cause

Technical explanation: GTK3’s CSS engine performs box-shadow rendering in software (CPU), not GPU-accelerated. The waybar theme used 8 box-shadow declarations combined with alpha() transparency compositing and 7 infinite CSS animations. Each animation frame triggered a repaint cycle that required recalculating shadows and alpha blending for every affected widget. Over ~44 hours of uptime, GTK3’s rendering pipeline degraded until the repaint cost exceeded one frame budget, causing a sustained CPU spin at 50-96%.

Why it happened:

Immediate cause: GTK3 CSS repaint loop driven by box-shadow + alpha() compositing
Contributing factors: 7 infinite CSS animations forcing constant repaints, ~44h uptime without waybar restart
Trigger: AC power plug-in caused battery class change (.charging), cascading style recalculation
Systemic issues: No awareness that GTK3 CSS box-shadow is CPU-rendered, no performance testing of the theme

Resolution

CSS Changes Applied

Removed all box-shadow declarations (GTK3 renders these in software):

/* REMOVED - multi-line box-shadow from window#waybar */
/* REMOVED - box-shadow from tooltip */
/* REMOVED - box-shadow from #custom-power:hover */
/* REMOVED - box-shadow from @keyframes glow-pulse (replaced with opacity) */
/* REMOVED - box-shadow from @keyframes border-glow-cycle */

Disabled all infinite CSS animations:

/* DISABLED: glow-pulse, text-flicker, subtle-breathe, border-glow-cycle */
/* Conditional animations retained: pulse on .urgent and .critical (only fires on state) */

Disabled all transition: all properties:

/* DISABLED: transition: all 0.2s/0.3s ease on 4 selectors */

Verification

Table 2. Post-fix thermal readings (19:46 PDT)
Sensor	Before	After
x86_pkg_temp	86°C	56°C
acpitz	81°C	54°C
SEN1/SEN2	53-54°C	46-48°C
waybar CPU	96.1%	0.0%
CPU frequency	800 MHz (throttled)	Normal scaling

Waybar at 0.0% CPU after 30 seconds
Temperatures within normal range (CPU 56°C idle)
Fan noise returned to baseline
No CSS parse errors in waybar log
All modules functional (workspaces, clock, media, battery, network, etc.)

Impact Assessment

Systems Affected

System

Status

Impact Duration

modestus-razer

Resolved

~54 minutes

User comfort

Restored

Fan noise eliminated

Business Impact

Users affected: 1 (personal workstation)
Data loss: No
Hardware risk: Sustained 86°C for unknown duration (possibly hours before detection)
Workaround: Killing waybar provided immediate relief

Prevention

Short-term (This Week)

Remove box-shadow from waybar CSS - Evan
Disable infinite CSS animations - Evan
Disable transition: all properties - Evan
Create missing ~/.local/bin/waybar-*-info.sh scripts (5 missing on-click handlers) - Evan
Document normal thermal baseline (CPU 56°C idle, 85°C load) - Evan

Long-term (This Quarter)

Set up thermal monitoring script (alert if CPU >80°C sustained) - Evan
Add waybar restart to a daily systemd timer as a defensive measure - Evan
Performance-test any future CSS theme changes before committing - Evan
Evaluate whether alpha() can be replaced with solid colors for further CPU savings - Evan

Lessons Learned

What Went Well

Systematic isolation methodology narrowed from "fans are loud" to exact CSS root cause in <1 hour
Minimal config test definitively separated modules from CSS
Previous incident (INC-2026-03-27) provided context for GPU vs CPU thermal analysis
GPU was quickly ruled out, preventing a repeat of the dGPU investigation

What Could Be Improved

Initial hypothesis (CSS animations) was partially correct but led to 15 minutes of sed-based comment edits that introduced CSS parse errors — should have read the file directly from the start
Multiple incorrect assumptions tested sequentially (animations, transitions, playerctl, box-shadow) when a single minimal-CSS test would have isolated the class of problem immediately
No performance baseline existed for waybar CPU usage

Key Takeaways

GTK3 CSS box-shadow is CPU-rendered — never use box-shadow with alpha() in waybar themes. It forces software rendering on every repaint.
transition: all on frequently-updated widgets is expensive — waybar modules update every 2-5 seconds, triggering transition recomputation each time.
Isolation tests beat hypothesis chasing — the minimal CSS test took 30 seconds and gave a definitive answer. Should have run it first instead of fifth.
Long-running GTK3 processes degrade — waybar at 44h uptime had accumulated enough rendering overhead to enter a CPU spin. Consider periodic restarts.
Same class as Hyprland borderangle bug — infinite animations on Wayland compositors/bars are CPU poison (documented in CLAUDE.md).

CLI Reference: Diagnostic Commands Used

This incident was diagnosed entirely from the terminal. The commands below are organized by technique, with explanations of the advanced patterns.

Process Substitution — `<(command)`

Process substitution creates a temporary file descriptor from a command’s output, allowing commands that expect filenames to read from pipelines instead.

# Merge two command outputs side-by-side with paste
# <(cmd1) creates fd for thermal zone names
# <(cmd2) creates fd for temperatures converted from millidegrees
paste <(cat /sys/class/thermal/thermal_zone*/type) \
      <(awk '{printf "%.1f°C\n", $1/1000}' /sys/class/thermal/thermal_zone*/temp)

paste normally takes two files. Process substitution feeds it two "virtual files" — one with zone names, one with converted temperatures. The awk divides millidegree readings by 1000 and formats to one decimal place.

# Ephemeral waybar config via process substitution
# waybar -c expects a file path — <(echo '...') creates one on the fly
waybar -c <(echo '{"layer":"top","modules-center":["clock"],"clock":{"format":"%H:%M"}}') \
       -s <(echo '* {font-size:14px; color:#cdd6f4; background:#1e1e2e;}') &disown 2>/dev/null

This runs waybar with an inline config and CSS without creating any temp files. The -c and -s flags both receive /proc/self/fd/NN paths pointing to the echo output. Critical for isolation testing — no files to clean up.

Command Substitution — `$(command)`

# Kill a process by name — $(pgrep) returns the PID inline
kill $(pgrep -x waybar)

# Use PID in ps — pgrep finds it, xargs passes it to ps
pgrep -x waybar | xargs ps -o pid,pcpu,etime --no-headers -p

Batch-Mode top with awk Filtering

# top -b = batch mode (non-interactive, stdout)
# -n1 = single snapshot
# awk filters to rows 7-12 (skips header, shows top processes)
top -b -n1 | awk 'NR>=7 && NR<=12'

# Filter top output for a specific process
top -b -n1 | awk '/waybar/ {print $1, $9, $10, $12}'
# $1=PID, $9=%CPU, $10=%MEM, $12=COMMAND

Thermal Zone Reading with awk Math

# Linux exposes temps in millidegrees (86000 = 86.0°C)
# awk converts inline with printf formatting
awk '{printf "%.1f°C\n", $1/1000}' /sys/class/thermal/thermal_zone*/temp

# CPU frequency in MHz (kernel reports in kHz)
awk '{printf "%.0f MHz\n", $1/1000}' /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq | sort -rn | head -5

# Power draw in watts (kernel reports in microwatts)
awk '{printf "%.1f W\n", $1/1000000}' /sys/class/power_supply/BAT*/power_now

nvidia-smi Queries

# Full dashboard view
nvidia-smi

# Structured CSV query — specific fields, no headers
nvidia-smi --query-gpu=temperature.gpu,power.draw,fan.speed,utilization.gpu \
  --format=csv,noheader

# Per-process GPU monitoring (single snapshot)
nvidia-smi pmon -c 1

Process Hunting

# Top CPU consumers — command ps to bypass aliases
command ps aux --sort=-%cpu | awk 'NR<=15 {printf "%-8s %5s %5s %s\n", $1, $3, $4, $11}'

# Runaway processes (>20% CPU sustained)
command ps aux --sort=-%cpu | awk '$3>20'

# Check if a process is running
pgrep -x waybar && echo "running" || echo "not running"

sysfs Exploration

# CPU governor, max/current frequency
grep . /sys/devices/system/cpu/cpu0/cpufreq/scaling_{governor,max_freq,cur_freq}

# AC power status — awk ternary for human-readable output
cat /sys/class/power_supply/AC*/online | \
  awk '{print ($1==1) ? "AC Connected" : "On Battery"}'

# Find fan RPM sensors across all hwmon devices
find /sys/class/hwmon -name 'fan*_input' -exec sh -c \
  'echo "$(cat $(dirname {})/name): $(cat {}) RPM"' \;

CSS Forensics with grep

# Count expensive CSS properties
grep -cE 'box-shadow|backdrop-filter|blur|opacity|border-radius|transition|alpha\(' ~/.config/waybar/style.css

# Find specific properties with line numbers
grep -nE 'transition:' ~/.config/waybar/style.css

# Find uncommented animation properties (exclude CSS comments)
grep -n 'animation:' ~/.config/waybar/style.css | grep -v '/\*'

# Find unclosed CSS comments (opened but not closed on same line)
awk '/\/\*/ && !/\*\// {print NR": "$0}' ~/.config/waybar/style.css

sed for CSS Property Invalidation

# Prefix property name with underscore — GTK ignores unknown properties
# Safer than commenting (no nesting issues)
sed -i 's/box-shadow:/_box-shadow:/g' ~/.config/waybar/style.css

Attempting to wrap CSS properties in /* … */ comments with sed is fragile. Multi-line values and nested comments cause parse errors. Prefer the underscore-prefix technique or edit the file directly.

Journal & Kernel Log Queries

# Kernel messages filtered for thermal events
journalctl -k --since "1 hour ago" --no-pager | grep -iE 'thermal|throttl|trip'

# dmesg with ISO timestamps, filtered for hardware warnings
dmesg --time-format iso | tail -50 | grep -iE 'thermal|fan|throttl|error|warn'

Background Process Management

# Start waybar in background, detach from terminal
waybar &disown 2>/dev/null

# Chain: start waybar, wait 30s, then check CPU
waybar &disown 2>/dev/null && sleep 30 && top -b -n1 | awk '/waybar/ {print $1, $9, $10, $12}'

# Kill + restart + verify in one pipeline
kill $(pgrep -x waybar) 2>/dev/null && waybar &disown 2>/dev/null

Pattern: Isolation Testing

The most valuable technique from this incident — binary search by swapping components:

# Test 1: Minimal config (is waybar itself the problem?)
waybar -c <(echo '{"layer":"top","modules-center":["clock"],"clock":{"format":"%H:%M"}}') \
       -s <(echo '* {font-size:14px;}') &disown 2>/dev/null

# Test 2: Full modules + minimal CSS (modules or CSS?)
waybar -s <(echo '* {font-size:14px; color:#cdd6f4; background:#1e1e2e;}') &disown 2>/dev/null

# Test 3: Full modules + full CSS minus one module (which module?)
sed -i '11s/"custom\/media", //' ~/.config/waybar/config
waybar &disown 2>/dev/null

Each test changes exactly one variable. 30 seconds of runtime with top -b -n1 gives a definitive CPU reading. This methodology identified the CSS as the sole culprit in 3 tests.

Related

INC: Razer Battery Drain — Previous thermal/power incident on same device (dGPU cause)
RCA: Kroki Orphan Containers — Pattern of orphaned processes causing heat

Metadata

Field

Value

Incident ID

INC-2026-04-04-001

Author

Evan Rosado

Created

2026-04-04

Last Updated

2026-04-04

Status

Resolved

Post-Incident Review

2026-04-04 (same session)