Updated example config with notes on if_modified flag

README.md

@@ -5,12 +5,14 @@ snaphots of ZFS datasets (pools, filsystems) according to a set of
 configurable schedules. Options for interval and crontab-style
 schedules are available.
 
-The daemon only includes an installer for macOS at the moment,
-but a multi-platform installer is coming soon.
+The daemon includes an installer for macOS `launchd`. For Linux,
+see the example `systemd` config file in `docs`. Modify as needed,
+copy to `/etc/systemd/system` folder, run `systemctl start zasd`
+and `systemctl enable zasd` as root to run on boot.
 
-As of now, snapshots are conditional. A snapshot will only be taken
-if a dataset has been modified since the last snapshot. An option
-to turn this off per schedule is coming soon.
+Snapshots may be made conditional with the `if_modified` option
+on each schedule. In this mode, a snapshot will only be taken if
+a dataset has been modified since the last snapshot.
 
 The daemon should not interfere with other snapshots you have
 on the system, unless you give them names that adhere to the
@@ -20,4 +22,9 @@ using similar syntax for something else, you may need to change
 the `separator` setting in `zasd.conf.py`.
 
 **DISCLAIMER:** This program is still in beta. Use at your own
-risk. It works fine on my system, but your mileage may vary.
+risk. It works fine on my system, but your mileage may vary.
+
+## Requirements
+
+* `apscheduler` PIP package
+* `fswatch` program

docs/zasd.example.service

@@ -0,0 +1,12 @@
+[Unit]
+Description=ZFS Automatic Snapshot Daemon
+
+[Service]
+User=root
+WorkingDirectory=/root/zasd/src
+ExecStart=/usr/bin/python3 zasd.py
+Restart=always
+SyslogIdentifier=zasd
+
+[Install]
+WantedBy=multi-user.target

src/zasd.conf.example.py

@@ -1,5 +1,5 @@
-#zfs_path        = '/usr/local/bin/zfs'
-#fswatch_path    = '/usr/local/bin/fswatch'
+#zfs_path        = '/sbin/zfs'
+#fswatch_path    = '/usr/bin/fswatch'
 
 # Tab size for indented log messages
 #tab_size        = 2
@@ -34,6 +34,12 @@ defaults = dict(
 
 # Whether to ignore triggers on filesystems whose files
 # have not been modifed since the trigger was last fired
+# Enabling this for a filesystem will cause an instance
+# of fswatch to launch for every ZFS filesystem. This
+# may use a lot of open file descriptors, so maybe avoid
+# if you have large filesystems with lots of folders.
+# Taking snapshots unconditionally is probably more
+# reliable.
 #    if_modified     = False,
 
 # Priority for snapshot; if more than one trigger fires

src/zasd.py

@@ -121,10 +121,12 @@ def get_snapshot_zfs_name(snapshot):
 
 # Generate ZFS identifier string from arguments
 def make_snapshot_zfs_name(dataset, tag_or_snapshot, serial=None):
+    global config
+
     if serial is None:
         return '{}@{}'.format(dataset, tag_or_snapshot)
     else:
-        return '{}@{}:{}'.format(dataset, tag_or_snapshot, serial)
+        return '{}@{}{}{}'.format(dataset, tag_or_snapshot, config['separator'], serial)
 #
 # Configuration functions
 
@@ -199,7 +201,7 @@ async def snapshot_creation_task(schedule, fs):
     serial = make_snapshot_serial()
     recursive = schedule['recursive']
 
-    if get_fs_flag(fs, tag):
+    if not schedule['if_modified'] or get_fs_flag(fs, tag):
         # Clear tag-modified flags for this tag on filesystem
         clear_fs_flag(fs, tag)
 
@@ -239,13 +241,21 @@ def snapshot_matches_tag(snapshot, tag):
 
 # Get tag of snapshot
 def get_snapshot_tag(snapshot):
-    (tag, serial) = get_snapshot_fields(snapshot)
-    return tag
+    fields = get_snapshot_fields(snapshot)
+    if len(fields) == 2:
+        (tag, serial) = fields
+        return tag
+    else:
+        return ''
 
 # Get serial number of snapshot
 def get_snapshot_serial(snapshot):
-    (tag, serial) = get_snapshot_fields(snapshot)
-    return serial
+    fields = get_snapshot_fields(snapshot)
+    if len(fields) == 2:
+        (tag, serial) = fields
+        return serial
+    else:
+        return ''
 
 # Get tuple of fields in snapshot name
 def get_snapshot_fields(snapshot):
@@ -302,18 +312,24 @@ def load_snapshot_schedules():
 
 async def main_task():
     global config, event_loop, scheduler, fs_listeners
-
     
     scheduler = AsyncIOPriorityScheduler(
             event_loop = event_loop,
             executors  = {'default': AsyncIOPriorityExecutor()})
  
+    monitor = False
+    for schedule in get_schedules():
+        if schedule['if_modified']:
+            monitor = True
+
     # Watch file system mountpoints
-    fs_listeners = dict()
-    for fs in zfs_get_filesystems():
-        await event_loop.subprocess_exec(
-                lambda: FSWatchProtocol(fs), config['fswatch_path'], '-o', fs['mountpoint'], stdout=PIPE)
- 
+    if monitor:
+        logger.info('Starting file system watcher')
+        fs_listeners = dict()
+        for fs in zfs_get_filesystems():
+            await event_loop.subprocess_exec(
+                    lambda: FSWatchProtocol(fs), config['fswatch_path'], '-o', fs['mountpoint'], stdout=PIPE)
+     
     load_snapshot_schedules()
     
     scheduler.start()

src/zasd/config.py

@@ -44,6 +44,7 @@ DEFAULT_CONFIG = {
         'disabled':     False,
         'filesystems':  ['tank'],
         'recursive':    True,
+        'if_modified':  False,
         'tag':          'zasd',
         'trigger':      IntervalTrigger(hours=12),
         'priority':     1,