Allow multiple --pre/post-snapshot-cmd options. Add a usage example.

README.md

@@ -279,6 +279,19 @@ root@ws1:~# zfs-autobackup test --verbose
 
 This also allows you to make several snapshots during the day, but only backup the data at night when the server is not busy.
 
+## Running custom commands before and after snapshotting
+
+If you need, e.g. to quiesce a couple of mysql databases to make on-disk data consistent before snapshotting, try:
+
+```sh
+zfs-autobackup \
+    --pre-snapshot-cmd 'daemon -fP /tmp/mysql1_lock.pid jexec mysqljail1 mysql -s -e "set autocommit=0;flush logs;flush tables with read lock;\\! sleep 60"' \
+    --pre-snapshot-cmd 'daemon -fP /tmp/mysql2_lock.pid jexec mysqljail2 mysql -s -e "set autocommit=0;flush logs;flush tables with read lock;\\! sleep 60"' \
+    --post-snapshot-cmd 'pkill -F /tmp/mysql1_lock.pid' \
+    --post-snapshot-cmd 'pkill -F /tmp/mysql2_lock.pid' \
+    test
+```
+
 ## Thinning out obsolete snapshots
 
 The thinner is the thing that destroys old snapshots on the source and target.
@@ -493,7 +506,8 @@ Look in man ssh_config for many more options.
 ```console
 usage: zfs-autobackup [-h] [--ssh-config CONFIG-FILE] [--ssh-source USER@HOST]
                       [--ssh-target USER@HOST] [--keep-source SCHEDULE]
-                      [--keep-target SCHEDULE] [--other-snapshots]
+                      [--keep-target SCHEDULE] [--pre-snapshot-cmd COMMAND]
+                      [--post-snapshot-cmd COMMAND] [--other-snapshots]
                       [--no-snapshot] [--no-send] [--no-thinning] [--no-holds]
                       [--min-change BYTES] [--allow-empty]
                       [--ignore-replicated] [--strip-path N]
@@ -531,6 +545,12 @@ optional arguments:
   --keep-target SCHEDULE
                         Thinning schedule for old target snapshots. Default:
                         10,1d1w,1w1m,1m1y
+  --pre-snapshot-cmd COMMAND
+                        Run COMMAND before snapshotting (can be used multiple
+                        times.
+  --post-snapshot-cmd COMMAND
+                        Run COMMAND after snapshotting (can be used multiple
+                        times.
   --other-snapshots     Send over other snapshots as well, not just the ones
                         created by this tool.
   --no-snapshot         Don't create new snapshots (useful for finishing

zfs_autobackup/ZfsAutobackup.py

@@ -45,10 +45,10 @@ class ZfsAutobackup:
                             help='Target ZFS filesystem (optional: if not specified, zfs-autobackup will only operate '
                                  'as snapshot-tool on source)')
 
-        parser.add_argument('--pre-snapshot-cmd', metavar="COMMAND", type=str,
-                            help='Run COMMAND before snapshotting.')
-        parser.add_argument('--post-snapshot-cmd', metavar="COMMAND", type=str,
-                            help='Run COMMAND after snapshotting.')
+        parser.add_argument('--pre-snapshot-cmd', metavar="COMMAND", default=[], action='append',
+                            help='Run COMMAND before snapshotting (can be used multiple times.')
+        parser.add_argument('--post-snapshot-cmd', metavar="COMMAND", default=[], action='append',
+                            help='Run COMMAND after snapshotting (can be used multiple times.')
         parser.add_argument('--other-snapshots', action='store_true',
                             help='Send over other snapshots as well, not just the ones created by this tool.')
         parser.add_argument('--no-snapshot', action='store_true',

zfs_autobackup/ZfsNode.py

@@ -192,9 +192,9 @@ class ZfsNode(ExecuteNode):
             self.verbose("No changes anywhere: not creating snapshots.")
             return
 
-        if pre_snapshot_cmd:
-            self.verbose("Running pre-snapshot-cmd:\n\t{}".format(pre_snapshot_cmd))
-            self.run(cmd=shlex.split(pre_snapshot_cmd), readonly=False)
+        for cmd in pre_snapshot_cmd:
+            self.verbose("Running pre-snapshot-cmd")
+            self.run(cmd=shlex.split(cmd), readonly=False)
 
         # create consistent snapshot per pool
         for (pool_name, snapshots) in pools.items():
@@ -205,9 +205,9 @@ class ZfsNode(ExecuteNode):
             self.verbose("Creating snapshots {} in pool {}".format(snapshot_name, pool_name))
             self.run(cmd, readonly=False)
 
-        if post_snapshot_cmd:
-            self.verbose("Running post-snapshot-cmd:\n\t{}".format(post_snapshot_cmd))
-            self.run(cmd=shlex.split(post_snapshot_cmd), readonly=False)
+        for cmd in post_snapshot_cmd:
+            self.verbose("Running post-snapshot-cmd")
+            self.run(cmd=shlex.split(cmd), readonly=False)
 
     def selected_datasets(self, exclude_received, exclude_paths):
         """determine filesystems that should be backupped by looking at the special autobackup-property, systemwide