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).

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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.

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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.

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First-Run Setup

1. Install prerequisites

   sudo apt install cifs-utils
   

2. Credentials file

   sudo nano /root/.smbcreds
   

   username=myuser
   password=mypassword
   domain=MYDOMAIN   # optional
   

   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

   sudo mount -a
   sudo ls /mnt/media
   

5. Verify connectivity

   ping -c 2 192.168.1.10
   nc -zv 192.168.1.10 445
   

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Installation

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:

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

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Automating with systemd

Create the following two files:

/etc/systemd/system/cifs-watch.service

[Unit]
Description=Monitor and repair CIFS mounts

[Service]
Type=oneshot
ExecStart=/usr/local/sbin/cifs-watch
Nice=10

/etc/systemd/system/cifs-watch.timer

[Unit]
Description=Run cifs-watch periodically

[Timer]
OnBootSec=2min
OnUnitActiveSec=5min
AccuracySec=30s
Unit=cifs-watch.service

[Install]
WantedBy=timers.target

Enable and start:

sudo systemctl daemon-reload
sudo systemctl enable --now cifs-watch.timer

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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

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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

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Exit Codes

Code	Meaning
0	All mounts healthy
1	One or more mounts failed or unreachable
2	Usage/dependency error

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Cron Alternative

*/5 * * * * /usr/local/sbin/cifs-watch >/dev/null 2>&1

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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).

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License

Released under the Unlicense. You can do whatever you want with this code. No warranty provided.