working

app/sbin/swapon

@@ -0,0 +1,98 @@
+#!/bin/bash
+#
+# swapon — create, enable and persist an 8GB swap file.
+#
+# Runs on each managed server (Alpine/OpenRC). Deploy with ./update_sbin, then:
+#
+#     rex doas /4server/sbin/swapon
+#
+# The script aborts if any swap is already active or if /swapfile already
+# exists, so it is safe to run against the whole fleet.
+#
+# Optional first argument: swap size in MiB (default 8192 = 8GB).
+
+set -euo pipefail
+
+SWAPFILE="/swapfile"
+SWAP_SIZE_MB="${1:-8192}"
+FSTAB="/etc/fstab"
+
+log() {
+    echo "[$(hostname)] $*"
+}
+
+die() {
+    echo "[$(hostname)] ERROR: $*" >&2
+    exit 1
+}
+
+case "$SWAP_SIZE_MB" in
+    ''|*[!0-9]*) die "swap size must be a positive integer in MiB" ;;
+esac
+[ "$SWAP_SIZE_MB" -gt 0 ] || die "swap size must be greater than zero"
+
+# Remove a partially created swap file if anything fails before it is enabled.
+CREATED=0
+cleanup() {
+    [ "$CREATED" -eq 1 ] || return 0
+    [ -e "$SWAPFILE" ] || return 0
+    if grep -q "^${SWAPFILE}[[:space:]]" /proc/swaps; then
+        return 0
+    fi
+    log "removing incomplete ${SWAPFILE}"
+    rm -f "$SWAPFILE"
+}
+trap cleanup EXIT
+
+# --- must run as root ---------------------------------------------------
+[ "$(id -u)" -eq 0 ] || die "must be run as root (use: rex doas /4server/sbin/swapon)"
+
+# --- abort if swap is already active ------------------------------------
+# /proc/swaps always has a header line; anything more means swap is in use.
+if [ "$(wc -l < /proc/swaps)" -gt 1 ]; then
+    echo "[$(hostname)] ERROR: swap is already active:" >&2
+    cat /proc/swaps >&2
+    exit 1
+fi
+
+# --- abort if the swap file already exists ------------------------------
+if [ -e "$SWAPFILE" ]; then
+    die "$SWAPFILE already exists; remove it manually before recreating swap"
+fi
+
+# --- persistence requires OpenRC's swap service --------------------------
+[ -x /etc/init.d/swap ] || \
+    die "/etc/init.d/swap not found; cannot persist swap across reboots"
+
+# --- make sure there is enough room on / ---------------------------------
+AVAIL_KB=$(df -Pk / | awk 'NR==2 {print $4}')
+# Leave a 100MiB margin for filesystem metadata.
+REQUIRED_KB=$((SWAP_SIZE_MB * 1024 + 102400))
+[ "$AVAIL_KB" -ge "$REQUIRED_KB" ] || \
+    die "not enough free space on / (need ${SWAP_SIZE_MB}MiB, have $((AVAIL_KB / 1024))MiB)"
+
+# --- create the swap file -----------------------------------------------
+log "creating ${SWAP_SIZE_MB}MiB swap file at ${SWAPFILE}"
+CREATED=1
+dd if=/dev/zero of="$SWAPFILE" bs=1M count="$SWAP_SIZE_MB"
+chmod 600 "$SWAPFILE"
+/sbin/mkswap "$SWAPFILE"
+
+# --- persist across reboots ---------------------------------------------
+# OpenRC's swap service runs `swapon -a`, which reads /etc/fstab.
+if ! grep -qE "^[[:space:]]*${SWAPFILE}[[:space:]]" "$FSTAB"; then
+    # Terminate the last line first in case fstab has no trailing newline.
+    [ -z "$(tail -c 1 "$FSTAB")" ] || echo >> "$FSTAB"
+    echo "${SWAPFILE} none swap sw 0 0" >> "$FSTAB"
+    log "added ${SWAPFILE} to ${FSTAB}"
+fi
+
+rc-update add swap boot >/dev/null 2>&1 || \
+    die "could not add the swap service to the boot runlevel"
+
+# --- enable it now -------------------------------------------------------
+# Absolute path avoids recursing into this script if /4server/sbin is on PATH.
+/sbin/swapon "$SWAPFILE"
+
+log "swap enabled:"
+cat /proc/swaps