sysmig: migration runner + initial 4 migrations (swap, daemon trims)
- up/down/status interface, history in /var/lib/sysmig/applied - 001 swap 2GB + swappiness=10, 002-004 trim unneeded daemons (~56MB) - google-osconfig-agent intentionally kept - all messages/comments in ASCII English (console font safety)
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# sysmig
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Lightweight tool that manages host state in DB-migration (Flyway) style.
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Started for a 1GB VM (`ocrt-postgres`), but deployable to any machine
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via cloud-init.
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## Usage
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```bash
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sudo bash /opt/sysmig/sysmig up # apply all pending migrations (idempotent)
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sudo bash /opt/sysmig/sysmig down # roll back the last migration
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sudo bash /opt/sysmig/sysmig down all # roll back everything (reverse order)
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bash /opt/sysmig/sysmig status # show status (no root required)
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```
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- Migrations: `migrations/NNN-name.sh`, receiving `up`/`down` as `$1`
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- Applied history: `/var/lib/sysmig/applied` - applied entries never re-run
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- On failure the run aborts at that step; earlier steps stay applied
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## Adding a new migration
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1. Create `migrations/NNN-name.sh` (number higher than existing; leave gaps)
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2. Implement both `up` and `down` cases - both must actually work
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3. Commit & push, then on the server: `git pull && sudo bash sysmig/sysmig up`
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## cloud-init integration
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```yaml
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#cloud-config
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runcmd:
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- [ git, clone, <REPO_URL>, /opt/sysmig ]
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- [ bash, /opt/sysmig/sysmig, up ]
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```
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For a private repo you need an auth strategy:
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- **deploy key** (existing machines): register a read-only key on the repo
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- **fleet rollout**: make the repo public, or embed a read-only token in
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the https URL
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## Current migrations
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| # | name | effect |
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|----|----------------------------|-----------------------------------------------|
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| 001 | create-swap | 2GB swap + fstab + vm.swappiness=10 |
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| 002 | disable-networkd-dispatcher| reclaim ~27MB RAM |
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| 003 | purge-exim4 | reclaim ~21MB RAM (package removed) |
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| 004 | purge-haveged | reclaim ~8MB RAM (package removed) |
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## Roadmap
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- `005-install-postgres` - install PostgreSQL + create cluster
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- `010-tune-postgres` - 1GB tuning (shared_buffers=128MB, work_mem=4MB,
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max_connections=30, ...)
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#!/usr/bin/env bash
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# 001-create-swap - Create 2GB swap + fstab entry + vm.swappiness=10
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# up: enable swap (skipped if swap already active)
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# down: disable swap and remove file/fstab/sysctl entries
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set -euo pipefail
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case "${1:-}" in
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up)
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if swapon --show --noheadings | grep -q .; then
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echo " swap already active - skipping"
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exit 0
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fi
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if [[ ! -f /swapfile ]]; then
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fallocate -l 2G /swapfile || {
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dd if=/dev/zero of=/swapfile bs=1M count=2048 status=none
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}
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chmod 600 /swapfile
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mkswap /swapfile >/dev/null
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fi
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swapon /swapfile
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grep -q '^/swapfile' /etc/fstab || echo '/swapfile none swap sw 0 0' >> /etc/fstab
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if ! grep -rqs 'vm.swappiness' /etc/sysctl.d/ /etc/sysctl.conf; then
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echo 'vm.swappiness=10' > /etc/sysctl.d/99-swap.conf
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sysctl -p /etc/sysctl.d/99-swap.conf >/dev/null
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fi
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echo " swap 2GB enabled + fstab entry + vm.swappiness=10"
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;;
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down)
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swapoff /swapfile
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rm -f /swapfile
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sed -i '\|^/swapfile|d' /etc/fstab
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grep -q '^vm.swappiness=10$' /etc/sysctl.d/99-swap.conf 2>/dev/null \
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&& rm -f /etc/sysctl.d/99-swap.conf || true
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echo " swap removed"
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;;
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esac
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#!/usr/bin/env bash
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# 002-disable-networkd-dispatcher - Stop network event hook daemon (~27MB)
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# Unnecessary on a simple server with static network config. Package kept.
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set -euo pipefail
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case "${1:-}" in
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up) systemctl disable --now networkd-dispatcher.service
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echo " networkd-dispatcher stopped and disabled" ;;
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down) systemctl enable --now networkd-dispatcher.service
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echo " networkd-dispatcher re-enabled" ;;
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esac
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#!/usr/bin/env bash
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# 003-purge-exim4 - Remove default local mail server (~21MB)
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# Unnecessary if local mail (e.g. cron output) is not used.
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# Down reinstalls with Debian defaults (local delivery only).
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set -euo pipefail
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export DEBIAN_FRONTEND=noninteractive
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case "${1:-}" in
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up) systemctl disable --now exim4.service 2>/dev/null || true
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apt-get purge -y exim4-daemon-light >/dev/null
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apt-get autoremove --purge -y >/dev/null
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echo " exim4 stopped + package purged + deps cleaned" ;;
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down) apt-get update -qq
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apt-get install -y exim4-daemon-light >/dev/null
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systemctl enable --now exim4.service
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echo " exim4 reinstalled + restarted (default config)" ;;
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esac
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#!/usr/bin/env bash
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# 004-purge-haveged - Remove entropy daemon (~8MB)
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# Kernel 6.12 collects enough entropy on its own; haveged is redundant.
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set -euo pipefail
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export DEBIAN_FRONTEND=noninteractive
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case "${1:-}" in
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up) systemctl disable --now haveged.service 2>/dev/null || true
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apt-get purge -y haveged >/dev/null
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apt-get autoremove --purge -y >/dev/null
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echo " haveged stopped + package purged" ;;
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down) apt-get update -qq
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apt-get install -y haveged >/dev/null
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systemctl enable --now haveged.service
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echo " haveged reinstalled + restarted" ;;
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esac
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@@ -0,0 +1,89 @@
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#!/usr/bin/env bash
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# ============================================================================
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# sysmig - Host state migration tool (DB-migration style)
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#
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# sudo bash sysmig up Apply all pending migrations in order
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# sudo bash sysmig down Roll back the last applied migration
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# sudo bash sysmig down all Roll back everything (reverse order)
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# bash sysmig status Show status (no root required)
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#
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# - Migration files: ./migrations/NNN-*.sh (receive up|down as $1)
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# - Applied history: /var/lib/sysmig/applied (one filename per line, in order)
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# - Adding work: drop a numbered file into migrations/ -> picked up on next up
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# (e.g. 005-install-postgres.sh, 010-tune-postgres.sh ...)
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# - Safe to re-run on every boot (cloud-init); idempotent
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# ============================================================================
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set -euo pipefail
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MIG_DIR="$(cd "$(dirname "$0")/migrations" && pwd)"
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STATE_DIR=/var/lib/sysmig
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STATE_FILE=$STATE_DIR/applied
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say() { printf '\033[1;36m==>\033[0m %s\n' "$*"; }
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note() { printf ' %s\n' "$*"; }
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require_root() {
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[[ $EUID -eq 0 ]] || { echo "root required: sudo bash $0 ..." >&2; exit 1; }
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}
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is_applied() { grep -qx "$1" "$STATE_FILE" 2>/dev/null; }
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cmd_up() {
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require_root
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mkdir -p "$STATE_DIR"; touch "$STATE_FILE"
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local n=0 f name
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for f in "$MIG_DIR"/*.sh; do
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name=$(basename "$f")
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is_applied "$name" && continue
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say "UP $name"
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if bash "$f" up; then
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echo "$name" >> "$STATE_FILE"
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n=$((n+1))
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else
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echo "FAILED - aborting (earlier migrations stay applied)" >&2
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exit 1
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fi
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done
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if [[ $n -eq 0 ]]; then note "all migrations already applied"
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else note "$n migration(s) applied, recorded in state file"; fi
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echo; say "memory"; free -h
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}
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cmd_down_last() {
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require_root
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[[ -s "$STATE_FILE" ]] || { note "nothing to roll back"; return 0; }
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local name; name=$(tail -n 1 "$STATE_FILE")
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local f="$MIG_DIR/$name"
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[[ -f "$f" ]] || { echo "migration file not found: $f" >&2; exit 1; }
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say "DOWN $name"
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bash "$f" down
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sed -i '$d' "$STATE_FILE"
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}
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cmd_status() {
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say "migration status (history: $STATE_FILE)"
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local f name
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for f in "$MIG_DIR"/*.sh; do
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name=$(basename "$f")
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if is_applied "$name"; then note "[applied] $name"
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else note "[pending] $name"; fi
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done
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echo; say "memory / swap"
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free -h
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swapon --show 2>/dev/null || true
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}
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usage() { sed -n '2,15p' "$0"; exit 1; }
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case "${1:-}" in
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up) cmd_up ;;
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down) require_root
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if [[ "${2:-}" == "all" ]]; then
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while [[ -s "$STATE_FILE" ]]; do cmd_down_last; done
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note "full rollback complete"
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else
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cmd_down_last
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fi ;;
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status) cmd_status ;;
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*) usage ;;
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esac
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