Halves old logs

tanos.sh

#!/bin/bash

set -euo pipefail

treshold=${HIGH_WATER_PCT:-85}
cleanup_dir=${DIR:-/var/log/remote/}
fraction=${DELETE_FRACTION:-0.5}

(
	if ! flock -n 9 ; then
		>&2 echo "Unable to acquire lock!"
		exit 3
	fi
	if [[ "$(df --output=pcent "$cleanup_dir" | tail -1 | grep -o '[0-9]*')" -lt "$treshold" ]] ; then
		logger -p syslog.info "tanos.sh: cleanup is not needed"
		exit 0
	fi
	tmpfile=$(mktemp)
	function cleanup {
		rm -f "$tmpfile"
	}
	trap cleanup EXIT

	find -L "$cleanup_dir" -type f -printf '%C@\t%b\t%p\0' | sort -z -s -k 1n -k 2rn -t $'\t' > "$tmpfile"
	total="$(awk -F $'\t' -v RS='\0' '{s+=$2} END {print s;}' "$tmpfile")"
	awk -F $'\t' -v RS='\0' -vORS='\0' -vs="$total" -vfr="$fraction" '{if (deleted < (s*fr)) {deleted += $2; print;}}' "$tmpfile" | \
		cut -zf3- | xargs -r -0 rm -f
	# just in case if some deleted files were used by syslog right now
	systemctl reload syslog-ng || true
	find -L "$cleanup_dir" -empty -mindepth 1 -delete
	logger -p syslog.info "tanos.sh: cleanup succeeded"
) 9>/var/lock/log-gc.lock