linux-tmux-dracula-cpu-temp

name: linux-tmux-dracula-cpu-temp description: "Show CPU temperature in the tmux status bar via the Dracula theme, with dynamic color based on the value, on Linux (desktops, servers, SBCs). Update-safe — uses /sys/class/thermal/ sysfs and does not patch the dracula plugin. Use when working with tmux on any Linux box and the user mentions adding a CPU temp segment to the tmux status line."

Show Linux CPU temp in the tmux status bar (Dracula, colored, update-safe)

Companion to the macOS version (tmux-dracula-cpu-temp). The mechanism is the same — append a status-right segment after the tpm run line so dracula stays untouched — but the temp source is the kernel sysfs thermal zone, which exists on most Linux systems (desktops, servers, and SBCs alike). KVM guests usually don't expose it.

Tested on:

Raspberry Pi Zero W (armv6, BCM2835)
Raspberry Pi Zero 2 W (aarch64, BCM2710A1)
Orange Pi Zero 2 W (aarch64, Allwinner H618)

1. Find the right thermal zone

The mapping of thermal_zone0, thermal_zone1, etc. is not stable or standardized across systems. On one machine thermal_zone0 might be the CPU package; on another it could be the ACPI chassis sensor, the WiFi card, or a battery sensor. Don't assume thermal_zone0 is always the CPU.

To find what each zone represents, check its type:

for z in /sys/class/thermal/thermal_zone*; do
    echo "$z: $(cat $z/type) = $(cat $z/temp)"
done

The temperature value is in millidegrees Celsius (e.g. 45000 = 45.0°C).

Look for a type like x86_pkg_temp, cpu-thermal, acpitz, or similar — that's the one to use. The script below defaults to thermal_zone0; adjust the path if your CPU is on a different zone.

If no thermal zone exists at all, the box doesn't expose CPU temperature (typical for cloud KVM guests like Oracle Cloud, RackNerd, etc.). On RPi you can also use vcgencmd measure_temp, but the sysfs path is universal.

2. Wrapper script

~/.tmux/scripts/cpu_temp.sh (POSIX sh, no bashisms — works on busybox / dash too):

#!/bin/sh
# Print colored CPU temp segment for tmux status bar (Linux sysfs).
# Dracula palette: dark_gray=#282a36, cyan=#8be9fd, green=#50fa7b,
#                  orange=#ffb86c, red=#ff5555, comment=#6272a4.

f=/sys/class/thermal/thermal_zone0/temp
if [ ! -r "$f" ]; then
  printf '#[fg=#282a36,bg=#6272a4] |n/a'
  exit 0
fi

t=$(awk '{printf "%.0f", $1/1000}' "$f")

if   [ "$t" -lt 50 ]; then bg='#8be9fd'; ico='🥶'   # cyan   cold
elif [ "$t" -lt 65 ]; then bg='#50fa7b'; ico='😎'   # green  normal
elif [ "$t" -lt 75 ]; then bg='#ffb86c'; ico='🥵'   # orange warm
else                       bg='#ff5555'; ico='🔥'   # red    hot
fi

printf '#[fg=#282a36,bg=%s] |%s%s°C' "$bg" "$ico" "$t"

chmod +x ~/.tmux/scripts/cpu_temp.sh

Bands chosen for passively-cooled SBCs:

<50°C cold (cyan)
50–64°C normal (green)
65–74°C warm (orange)
≥75°C hot (red) — RPi soft-throttles at 80°C, so 75 is a sane warning band.

3. Wire it into `~/.tmux.conf`

At the very bottom, after the tpm run line:

run '~/.tmux/plugins/tpm/tpm'

# Append CPU temp segment to status-right (after dracula has set it).
# Script emits its own color based on temp value. Survives TPM updates.
set -ag status-right "#(~/.tmux/scripts/cpu_temp.sh)"

4. Reload (and clean up duplicates if needed)

tmux source-file ~/.tmux.conf

Gotcha: duplicated segments after deploy

If b0o/tmux-autoreload is enabled (very common in dracula setups) it will detect the conf edit and re-source in parallel with your manual source-file. Both runs race past dracula's set -g status-right "" reset, leaving you with 2× or 3× of each segment. Fix:

tmux set -g status-right ""
tmux source-file ~/.tmux.conf

Verify only one of each appears:

tmux show -gv status-right | grep -oE 'cpu_info|ram_info|cpu_temp' | sort | uniq -c
# expect:
#   1 cpu_info
#   1 cpu_temp
#   1 ram_info

Gotcha: emoji width on narrow terminals (phone SSH)

This one bites hard. On a ~40-column phone SSH session the status line starts wrapping its last 1-2 characters onto a second row, and every 5-second redraw adds another wrapped row until the screen is a stack of half-drawn status bars.

Root cause: tmux and your terminal disagree on how wide an emoji is. tmux measures the status with its own Unicode width table; some emoji it counts as 1 cell while your terminal renders them as 2. tmux thinks the line fits, doesn't truncate, and the terminal then paints it 1 cell too wide -- and because the status row sits at the bottom with autowrap on, it wraps and scroll-accumulates on every refresh.

It is not all emoji -- only the ones with Unicode Emoji_Presentation=No (legacy "text-presentation" pictographs): 🌡 ☀ ❄ ♨ ✈ ☁ ❤ ✏. tmux follows the spec and counts these 1 cell; terminals render them as 2. Emoji with Emoji_Presentation=Yes (🔥 🥵 🥶 😎 💻 🧊 …) are counted 2 by tmux, matching the terminal -- those are safe.

The thermometer 🌡 (U+1F321) is one of the bad ones, which is why an earlier version of this skill overflowed. The fix: use an Emoji_Presentation=Yes glyph instead. The script above picks a width-2 face per temperature band (🥶/😎/🥵/🔥), so tmux and the terminal always agree and the status never overflows.

Things that do NOT work

Variation Selector-16 (U+FE0F): appending ️ to force emoji presentation does not change tmux's width count (verified on tmux 3.6b -- 🌡️ still measures width 1).
Trimming spaces: shaving a space compensates for one bad emoji but is fragile -- add another text-presentation emoji and it breaks again. Fix the glyph, not the spacing.

Probe any glyph's tmux width

Stash the string in a user option and pad it with #{p<N>:...}, which uses tmux's own width math (a bare literal after p: is treated as a variable name, so the option indirection is required):

tmux set -g @m '🌡'
tmux display -p '[#{p8:#{@m}}]'   # width = 8 - (trailing spaces)
tmux set -gu @m

Width 1 = will overflow on a 2-cell-rendering terminal; width 2 = safe.

The general cure (terminal side)

The disagreement is really the terminal violating Unicode's default-presentation rule. Many terminals (Blink, Termius, WezTerm, kitty) expose a Unicode-width / "ambiguous = narrow" setting. Making the terminal spec-compliant renders text-presentation emoji as 1 cell too -- then tmux and terminal agree for every emoji and you can use any glyph, thermometer included.

See tmux-dracula-cpu-temp for the macOS / Apple Silicon variant (uses smctemp instead of sysfs, with higher temp bands).