ignore "snaphost already exists"-errors when creating snapshots

zsnaplib/__init__.py

@@ -6,6 +6,7 @@ import sys
 
 time_format='%Y-%m-%d_%H%M'
 re_snapshot = re.compile(r'^(.*)@([0-9]{4}-[0-9]{2}-[0-9]{2}_[0-9]{4})$')
+re_err_ok = re.compile(r"cannot create snapshot '[^']+': dataset already exists")
 logger = 'zsnapper'
 
 class ZFSSnapshotError(Exception):
@@ -33,7 +34,12 @@ def do_zfs_command(args, zfs_cmd, pipecmd=None):
 
     (out, err) = ctrl_proc.communicate()
 
-    if ctrl_proc.returncode != 0:
+    # check if we try to create a snapshot that already exists. This can happen
+    # if the script is run every minute and it takes more time than that to
+    # create all snapshots
+    if ctrl_proc.returncode == 1 && re_match(re_err_ok, err):
+        pass
+    elif ctrl_proc.returncode != 0:
         raise ZFSSnapshotError('Failed to execute {}: {}'.format(cmd, err))
     return out