Add a script to automate ZFS snapshots cleanup.

Author: NikolayS

scripts/delete_old_zfs_snapshots.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+# 2019 © Postgres.ai
+
+# Use this script with caution! Note that this script is going to destroy all ZFS snapshots
+# 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
+#     dependant; so with old 'main' snapshots, dependant ones will be deleted as well,
+#     thanks to '-R' option when calling 'zfs destroy').
+#
+# Example of use:
+#    bash ./scripts/delete_old_zfs_snapshots.sh 5
+
+set -euxo pipefail
+
+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 \
+    | 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"