📄 docs: Add readme

README.md

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+# cifs-watch
+
+## Overview
+
+`cifs-watch` is a lightweight Bash watchdog that automatically monitors and repairs **CIFS/SMB network mounts** defined in `/etc/fstab`. It keeps your NAS/file-server shares mounted and healthy even after network hiccups or reboots.
+
+Designed for **homelab** and **server** environments. Script file is named `cifs-watch` (no `.sh` extension).
+
+---
+
+## Features
+
+- Smart discovery of CIFS lines in `/etc/fstab` (supports 4–6 fields; skips `noauto`).
+- Network-aware checks (DNS resolution, optional ping, **TCP/445**).
+- Health probe with a short timeout to catch stale mounts.
+- Repair flow: `mount -o remount` → fallback `umount` + clean `mount`.
+- Logs to syslog and optional file (`/var/log/cifs-remount.log`).
+- `--dry-run`, `--verbose` flags for safe testing.
+- Works with cron or a systemd timer.
+- **Per-server backoff** to reduce noisy retries when a host is offline.
+
+---
+
+## How It Works
+
+1. **Discovery** — scans `/etc/fstab` for uncommented `cifs` entries like:
+   ```
+   //nas.local/media  /mnt/media  cifs  vers=3.0,credentials=/root/.smbcreds  0  0
+   //192.168.1.50/share /mnt/share cifs credentials=/root/.creds,iocharset=utf8 0 0
+   ```
+2. **Reachability** — ensures the server resolves, optionally pings, and has TCP/445 open.
+3. **Health probe** — times a quick `ls` against the mountpoint.
+4. **Repair** — remount or unmount/remount as needed, with retries and logging.
+
+---
+
+## First-Run Setup
+
+1. **Install prerequisites**
+   ```bash
+   sudo apt install cifs-utils
+   ```
+2. **Credentials file**
+   ```bash
+   sudo nano /root/.smbcreds
+   ```
+   ```
+   username=myuser
+   password=mypassword
+   domain=MYDOMAIN   # optional
+   ```
+   ```bash
+   sudo chmod 600 /root/.smbcreds
+   ```
+3. **Add to `/etc/fstab`**
+   ```
+   //192.168.1.10/media  /mnt/media  cifs  vers=3.0,credentials=/root/.smbcreds,uid=1000,gid=1000,file_mode=0644,dir_mode=0755  0  0
+   ```
+   > Avoid `noauto` if you want the script to manage the mount.
+
+4. **Test manually**
+   ```bash
+   sudo mount -a
+   sudo ls /mnt/media
+   ```
+
+5. **Verify connectivity**
+   ```bash
+   ping -c 2 192.168.1.10
+   nc -zv 192.168.1.10 445
+   ```
+
+---
+
+## Installation
+
+```bash
+sudo install -m 0755 cifs-watch /usr/local/sbin/cifs-watch
+sudo touch /var/log/cifs-remount.log && sudo chmod 600 /var/log/cifs-remount.log
+```
+
+**Test it:**
+```bash
+sudo /usr/local/sbin/cifs-watch --dry-run --verbose
+sudo /usr/local/sbin/cifs-watch --verbose
+```
+
+Logs:
+- `/var/log/cifs-remount.log`
+- `journalctl -t cifs-watch` or `journalctl -u cifs-watch.service`
+
+---
+
+## Automating with systemd
+
+Create the following two files:
+
+**`/etc/systemd/system/cifs-watch.service`**
+```ini
+[Unit]
+Description=Monitor and repair CIFS mounts
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/sbin/cifs-watch
+Nice=10
+```
+
+**`/etc/systemd/system/cifs-watch.timer`**
+```ini
+[Unit]
+Description=Run cifs-watch periodically
+
+[Timer]
+OnBootSec=2min
+OnUnitActiveSec=5min
+AccuracySec=30s
+Unit=cifs-watch.service
+
+[Install]
+WantedBy=timers.target
+```
+
+Enable and start:
+```bash
+sudo systemctl daemon-reload
+sudo systemctl enable --now cifs-watch.timer
+```
+
+---
+
+## Command-Line Options
+
+| Option | Description |
+|--------|-------------|
+| `-n`, `--dry-run` | Simulate actions (no remounts) |
+| `-v`, `--verbose` | Detailed output |
+| `--logfile PATH` | Override/disable file logging (empty string disables) |
+| `-h`, `--help` | Show usage |
+
+---
+
+## Optional: Per-Server Backoff
+
+Prevents hammering an offline NAS with constant retries.
+
+- State file: `/var/tmp/cifs-watch-backoff.json` (line-delimited JSON; last row for a host wins).
+- Window: `BACKOFF_MINUTES=10` by default. Set to `0` to disable.
+- Backoff state is reset on reboot (uses `/var/tmp`).
+
+Example log flow:
+```
+[WARN] Server NOT reachable: nas.local (skipping /mnt/media)
+[INFO] Backoff started: will not retry nas.local for 10 minutes
+...
+[INFO] Backoff expired: rechecking nas.local
+[INFO] Server reachable: nas.local — attempting repair
+```
+
+---
+
+## Exit Codes
+
+| Code | Meaning |
+|------|---------|
+| `0` | All mounts healthy |
+| `1` | One or more mounts failed or unreachable |
+| `2` | Usage/dependency error |
+
+---
+
+## Cron Alternative
+
+```
+*/5 * * * * /usr/local/sbin/cifs-watch >/dev/null 2>&1
+```
+
+---
+
+## Troubleshooting
+
+- Mount works manually but not via script → check credentials path/permissions and DNS (`getent ahosts servername`).
+- “Transport endpoint not connected” → script will unmount/remount automatically.
+- No CIFS entries found → ensure `cifs` type and not commented lines in `/etc/fstab`.
+- NAS offline noise → ensure backoff is enabled (default 10 minutes).
+
+---
+
+## License
+
+MIT — see `LICENSE`.