snippets/bash/start.sh

#!/usr/bin/env bash

# Minecraft server start.sh
# for use in slapping in tmux and forgetting
# also rolls logs

# --- CONFIGURATION

# you can source an environment file like this:
#. .env

# auto-restart
AUTO_RESTART=${AUTO_RESTART:-1}        # 1 to enable
RESTART_DELAY=${RESTART_DELAY:-3}      # seconds
DONT_RESTART_IF=${DONT_RESTART_IF-130} # exit code

# java options
JAVA_BIN=${JAVA_BIN:-java}   # full path to the java binary
#JVM_FLAGS=                  # Java flags
#NO_DEFAULT_JVM_FLAGS=       # 1 to disable default flags
MEMORY_MIN=${MEMORY_MIN-4G}  # Xms
MEMORY_MAX=${MEMORY_MAX:-4G} # Xmx
GC=${GC:-ZGC}                # ShenandoahGC or ZGC
GC_PAR_THREADS=${GC_PAR_THREADS:-6} # "parallel" (runs while workers are stopped) thread count
                                    # recommended to set to just below total thread count
GC_CONC_THREADS=${GC_CONC_THREADS:-"$(( half=GC_PAR_THREADS / 2, half == 0 ? 1 : half ))"}
                                    # marker thread count, defaults to half of parallel

# mc options
MC_FLAGS=${MC_FLAGS-nogui}           # Minecraft flags
SERVER_JAR=${SERVER_JAR:-server.jar} # server JAR file

# ---

declare -A gcs=(
	[zgc]="-XX:+UseZGC"
	[shenandoahgc]="-XX:+UseShenandoahGC"
)

java_args=()

[[ "${MEMORY_MIN:+x}" == 'x' ]] && java_args+=(-Xms"${MEMORY_MIN}")
java_args+=(-Xmx"${MEMORY_MAX}")

(( ! NO_DEFAULT_JVM_FLAGS )) && java_args+=(-XX:+ParallelRefProcEnabled -XX:+DisableExplicitGC -XX:+PerfDisableSharedMem -XX:MaxGCPauseMillis=10)
if [[ "${MEMORY_MIN,,}" == "${MEMORY_MAX,,}" ]]; then
	java_args+=(-XX:+AlwaysPreTouch)
	[[ "${GC,,}" == 'zgc' ]] && java_args+=(-XX:-ZUncommit)
fi
if (( $(</proc/sys/vm/nr_hugepages) > 0 )); then
	java_args+=(-XX:+UseLargePages)
	[[ $(</sys/kernel/mm/transparent_hugepage/enabled) != 'never' ]] && java_args+=(-XX:+UseTransparentHugePages)
fi

java_args+=("${gcs[${GC,,}]}")
[[ "${GC_CONC_THREADS:+x}" == 'x' ]] && java_args+=(-XX:ConcGCThreads="${GC_CONC_THREADS}")
java_args+=(-XX:ParallelGCThreads="${GC_PAR_THREADS}")

# shellcheck disable=SC2206
java_args+=(${JVM_FLAGS})
# shellcheck disable=SC2206
java_args+=(-jar "${SERVER_JAR}" $MC_FLAGS)

{
	echo "Using settings:"
	echo "Java binary: ${JAVA_BIN?}"
	# shellcheck disable=SC2145
	echo "Options: ${java_args[@]@Q}"
	echo "Auto restart: $( (( AUTO_RESTART )) && echo 'enabled' || echo 'disabled' )"
} 2>&1


while true; do
	"${JAVA_BIN}" "${java_args[@]}" 2>&1 | tee ./"$(date -I)".log
	exitcode=$?

	echo "Process exited with code "$'\033'"[3$(( exitcode == 0 ? 2 : 1 ))m${exitcode}"$'\033'"[0m" >&2

	#shellcheck disable=SC2076
	(( AUTO_RESTART != 1 || DONT_RESTART_IF == exitcode )) &&
		exit "${exitcode}"

	echo "Restarting after ${RESTART_DELAY} seconds" >&2
	sleep "${RESTART_DELAY?}"
done