When fetches an image from Glance, LibvirtDriver creates a lockfile that has a name corresponding to the image. It is not deleted automatically even if the image is delete from Glance. So lockfiles may accumulate in long term. Although this may be not so harmful, a little bit ugly.
The following is a list of files under /var/lib/nova in my compute node. Many old lockfiles are left in /var/lib/nova/instances/locks.
$ ls -lR /var/lib/nova/instances/
/var/lib/nova/instances/:
total 16
drwxr-xr-x 2 nova nova 4096 Nov 2 18:38 _base
-rw-r--r-- 1 nova nova 37 Nov 29 21:03 compute_nodes
drwxr-xr-x 2 nova nova 4096 Nov 1 17:59 locks
drwxr-xr-x 2 nova nova 4096 Sep 11 17:41 snapshots
/var/lib/nova/instances/_base:
total 24840
-rw-r--r-- 1 nova nova 20068399 Oct 4 20:30 03d8e206-6500-4d91-b47d-ee74897f9b4e
-rw-r--r-- 1 nova nova 5362320 Oct 4 20:30 cc60167d-4d4a-45af-afbb-8757aa6b7946
/var/lib/nova/instances/locks:
total 0
-rw-r--r-- 1 nova nova 0 Oct 4 20:40 nova-03d8e206-6500-4d91-b47d-ee74897f9b4e
-rw-r--r-- 1 nova nova 0 Oct 28 20:22 nova-46da6595b4561f079dc41f96efa7ab6881c5c1e9
-rw-r--r-- 1 nova nova 0 Oct 4 20:30 nova-5ca6db469255e9ab1ffa96cce880b1fc96fe0a4d
-rw-r--r-- 1 nova nova 0 Sep 11 17:26 nova-9e881789030568a317fad9daae82c5b1c65e0d4a
-rw-r--r-- 1 nova nova 0 Sep 16 18:57 nova-ab3ee132785116ec5192292c364e56a750f37f5b
-rw-r--r-- 1 nova nova 0 Sep 27 14:31 nova-abccd35ab48d01849de73d759104bb09c210bef7
-rw-r--r-- 1 nova nova 0 Nov 1 17:59 nova-b779965eca6fd7bfb1c4e34f8c3e9eb10aa97d6a
-rw-r--r-- 1 nova nova 0 Oct 4 20:40 nova-cc60167d-4d4a-45af-afbb-8757aa6b7946
-rw-r--r-- 1 nova nova 0 Oct 7 10:49 nova-f70c681bc242f3a6f6a64a5c28ce05e3be846b6a
-rw-r--r-- 1 nova nova 0 Oct 4 20:33 nova-fa750326e354854db61fe2d30d0d7e1049f4ea1b
-rw-r--r-- 1 nova nova 0 Nov 29 21:03 nova-storage-registry-lock
-rw-r--r-- 1 nova nova 0 Oct 4 20:40 nova-_var_lib_nova_instances__base_03d8e206-6500-4d91-b47d-ee74897f9b4e
-rw-r--r-- 1 nova nova 0 Oct 28 20:22 nova-_var_lib_nova_instances__base_46da6595b4561f079dc41f96efa7ab6881c5c1e9
-rw-r--r-- 1 nova nova 0 Oct 4 20:40 nova-_var_lib_nova_instances__base_5ca6db469255e9ab1ffa96cce880b1fc96fe0a4d
-rw-r--r-- 1 nova nova 0 Sep 11 17:26 nova-_var_lib_nova_instances__base_9e881789030568a317fad9daae82c5b1c65e0d4a
-rw-r--r-- 1 nova nova 0 Sep 16 18:57 nova-_var_lib_nova_instances__base_ab3ee132785116ec5192292c364e56a750f37f5b
-rw-r--r-- 1 nova nova 0 Sep 27 14:31 nova-_var_lib_nova_instances__base_abccd35ab48d01849de73d759104bb09c210bef7
-rw-r--r-- 1 nova nova 0 Nov 1 17:59 nova-_var_lib_nova_instances__base_b779965eca6fd7bfb1c4e34f8c3e9eb10aa97d6a
-rw-r--r-- 1 nova nova 0 Oct 4 20:40 nova-_var_lib_nova_instances__base_cc60167d-4d4a-45af-afbb-8757aa6b7946
-rw-r--r-- 1 nova nova 0 Oct 24 16:39 nova-_var_lib_nova_instances__base_f70c681bc242f3a6f6a64a5c28ce05e3be846b6a
-rw-r--r-- 1 nova nova 0 Oct 4 20:33 nova-_var_lib_nova_instances__base_fa750326e354854db61fe2d30d0d7e1049f4ea1b
/var/lib/nova/instances/snapshots:
total 0
This sounds like an actual bug, but a cosmetic one which should be triaged as low (https:/ /wiki.openstack .org/wiki/ BugTriage# Task_2: _Prioritize_ confirmed_ bugs_.28bug_ supervisors. 29)