kentut

Small systemd timer/service to drop Linux page cache when RAM usage crosses a configurable threshold.

What it does

• Checks MemTotal and MemAvailable from /proc/meminfo
• Computes used RAM percentage
• Runs sync and echo 3 > /proc/sys/vm/drop_caches when the threshold is reached
• Applies a cooldown to avoid running too often

This is useful if you want to keep a repeatable copy of the setup outside /etc and /usr/local/bin, so you can reinstall it after a fresh OS install.

Files

• bin/kentut: main command
• systemd/kentut.service: oneshot service
• systemd/kentut.timer: periodic timer
• systemd/kentut.env: editable configuration
• install.sh: install files into system locations
• uninstall.sh: remove installed files

Default behavior

• Threshold: 70%
• Cooldown: 900 seconds
• First run: 2 minutes after boot
• Interval: every 1 minute

Install

cd ~/Downloads/kentut
sudo ./install.sh

After install, you can run:

kentut
kentut -t 5m
kentut -t 5s
kentut -t 5h -m 50%
kentut -m 50
kentut --status
kentut --watch 30s --dry-run
sudo kentut --set-threshold 55
sudo kentut --enable
sudo kentut --disable
sudo kentut --force

Configure

Edit:

sudo nano /etc/default/kentut

Available variables:

• THRESHOLD_PCT=70
• COOLDOWN_SECONDS=900
• STATE_FILE=/run/kentut.last

command

• kentut: run immediately using current threshold
• kentut -t 5m: wait 5 minutes, then run the check
• kentut -t 5s: wait 5 seconds, then run the check
• kentut -t 5h: wait 5 hours, then run the check
• kentut -m 50 or kentut -m 50%: use 50% as the threshold for that run
• kentut --force: drop cache without checking threshold
• kentut --dry-run: simulate the action without writing to drop_caches
• kentut --status: print current RAM usage, threshold, cooldown, and last run
• kentut --watch 30s: run in a loop every 30 seconds
• kentut --set-threshold 55: persist threshold to /etc/default/kentut
• kentut --enable: enable and start kentut.timer
• kentut --disable: disable and stop kentut.timer
• kentut --start: start kentut.timer
• kentut --stop: stop kentut.timer
• kentut --restart: restart kentut.timer
• kentut --json: return status or update output as JSON
• kentut --notify: send a desktop notification when notify-send is available
• kentut -h or kentut --help: show English help

Notes:

• -m only overrides the threshold for the current command.
• The persistent threshold for the systemd service still comes from /etc/default/kentut.
• Dropping page cache still requires root because it writes to /proc/sys/vm/drop_caches.
• Running kentut without root can do the countdown and memory check, but if the threshold is hit it will stop and tell you to use sudo or the system service.
• --set-threshold also requires root because it edits /etc/default/kentut.
• --enable, --disable, --start, --stop, and --restart also require root because they call systemctl on the system timer.

Then reload and restart the timer:

sudo systemctl daemon-reload
sudo systemctl restart kentut.timer

Verify

systemctl status kentut.timer
systemctl status kentut.service
journalctl -u kentut.service --no-pager

Uninstall

cd ~/Downloads/kentut
sudo ./uninstall.sh