Improve how we get list of old snapshots

1. Add ordering by `creation` time (desc)
2. Do not filter out `NAME`, use `-H` instead.

Author: NikolayS

scripts/delete_old_zfs_snapshots.sh

@@ -5,7 +5,7 @@
 # on the machine, except:
 #   - the last $1 snapshots (the first parameter in the CLI call),
 #   - those snapthots that are used now,
-#   - snapshots having "clone" or "NAME" in the name (however, they are supposed to be
+#   - snapshots having "clone" in the name (however, they are supposed to be
 #     dependant; so with old 'main' snapshots, dependant ones will be deleted as well,
 #     thanks to '-R' option when calling 'zfs destroy').
 #
@@ -19,12 +19,11 @@ n=$1
 if [[ -z "$n" ]]; then
   echo "Specify the number of snapshots to keep (Example: 'bash ./scripts/delete_old_zfs_snapshots.sh 5' to delete all but last 5 snapshots)." 
 else
-  sudo zfs list -t snapshot -o name \
+  sudo zfs list -t snapshot -o name -s creation -H \
     | grep -v clone \
-    | grep -v NAME \
     | head -n -$n \
     | xargs -n1 --no-run-if-empty sudo zfs destroy -R
 fi
 
 ## An example of crontab entry, setting up auto-deletion of all unused ZFS snapshots except the last 3 ones.
-##     0 6 * * * sudo zfs list -t snapshot -o name | grep -v clone | grep -v NAME | head -n -3 | xargs -n1 --no-run-if-empty sudo zfs destroy -R 2>&1 | logger --stderr --tag "cleanup_zfs_snapshot"
+##     0 6 * * * sudo zfs list -t snapshot -o name -s creation -H | grep -v clone | grep -v NAME | head -n -3 | xargs -n1 --no-run-if-empty sudo zfs destroy -R 2>&1 | logger --stderr --tag "cleanup_zfs_snapshot"