# Mizule

*Mizule* is a simple tool that checks the UUID of the filesystem mounted at
the specified path, and issues a warning if it has not changed within a given
time period (default 30 days).  This is useful, for example, to remind backup
operators to switch out the backup disk periodically.

## Usage

Check `/var/spool/burp` and warn if it has not changed in the last 30 days:

```sh
mizule /var/spool/burp
```

Check `/var/spool/burp` and warn if it has not changed in the last 10 days,
sending an email to `burp-admin@example.org`:

```sh
mizule /var/spool/burp --ttl 30 --mailto burp-admin@example.org
```

## Cache File

*Mizule* keeps track of the UUID of each of the filesystems it has seen in a
cache file.  This file is stored at `${XDG_CACHE_HOME}/mizule.json`.  If the
`XDG_CACHE_HOME` environment variable is not set, `${HOME}/.cache` is used.  If
the `HOME` environment variable is also not set, the cache file will be created
in the current working directory.


## Periodic Check with systemd Timer Unit

*Mizule* works best if it is scheduled to check the filesystem periodically.
One way to set up this schedule is to use a systemd timer unit.

`mizule@.service`:

```ini
[Unit]
Description=Check last filesystem change for %I
RequiresMountsFor=%I
After=network-online.target
Wants=network-online.target

[Service]
Type=oneshot
Environment=XDG_CACHE_HOME=/var/cache/mizule
ExecStart=/usr/local/bin/mizule %I --mailto burp-admin@example.org
```

`mizule@.timer`:

```ini
[Unit]
Description=Schedule filesystem check for %I

[Timer]
OnBootSec=5m
OnUnitInactiveSec=12h

[Install]
WantedBy=multi-user.target
```

To enable:

```sh
systemctl enable mizule@-var-spool-burp.timer
```

This will trigger the check 5 minutes after the machine boots, and then again
every 12 hours.