Add script and sample crontab

2 files changed, 183 insertions, 0 deletions

diff --git a/example.cron b/example.cron
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+++ b/example.cron
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+# Example crontab for /etc/cron.d. See crontab(5).
+
+SHELL=/bin/sh
+
+# Make recursive snapshots of zroot and tank/foo, keeping 24
+# hourly, seven daily, eight weekly, 24 monthly, and unlimited yearly
+# snapshots.
+@hourly		root	snapshots.sh -c -p -t hourly -k 24 -r zroot tank/foo
+@daily		root	snapshots.sh -c -p -t daily -k 7 -r zroot tank/foo
+@weekly		root	snapshots.sh -c -p -t weekly -k 8 -r zroot tank/foo
+@monthly	root	snapshots.sh -c -p -t monthly -k 24 -r zroot tank/foo
+@yearly		root	snapshots.sh -c -t yearly -r zroot tank/foo
+
+# Make a non-recursive snapshot of tank/bar daily at 5:00,
+# preserving the three most recent snapshots.
+0 5 * * *	root	snapshots.sh -c -p -t my-custom-tag -k 3 tank/bar
diff --git a/snapshots.sh b/snapshots.sh
new file mode 100755
index 0000000..e4faaf0
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+++ b/snapshots.sh
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+#!/bin/sh
+
+# Manages ZFS snapshots.
+#
+# At least one of the following options must be provided to specify an
+# operation to perform:
+#
+#	-c	create snapshot(s)
+#	-p	prune snapshots
+#	-l	list snapshots
+#
+# If the -c or -p option is specified, at least one dataset must be specified
+# as well.
+#
+# If the -r option is specified, child datasets of the specified dataset(s)
+# will be recursively created, deleted, or listed.
+#
+# If the -c or -p option is specified, the -t option must be provided to
+# specify a tag.
+#
+# If the -p option is specified, the -k option must be provided to specify the
+# number of snapshots to keep for each dataset (including any newly created
+# snapshots).
+#
+# Usage: snapshots.sh [-cplrnvh] [-t tag] [-k num] [dataset ...]"
+#
+#	-c			create snapshot(s) (requires -t)
+#	-p			prune snapshots (requires -t and -k)
+#	-l			list snapshots
+#	-r			recursively create or delete snapshots
+#	-n			dry run: print commands that would be executed, but do not
+#				actually modify data
+#	-v			verbose mode
+#	-h			print usage
+#	-k num		keep *num* snapshots for each dataset, including any newly
+#				created snapshots
+#	-t tag		use *tag* as the snapshot name prefix
+
+set -e
+
+usage() {
+	printf "usage: %s [-cplrnvh] [-t tag] [-k num] [dataset ...]\n" "$0"
+}
+
+tag=
+keep=
+recursive=
+dry_run=
+verbose=
+create=
+prune=
+list=
+
+while getopts t:k:cplrknvh name; do
+	case $name in
+		t)	tag="$OPTARG";;
+		k)	keep="$OPTARG";;
+		c)	create=1;;
+		p)	prune=1;;
+		l)	list=1;;
+		r)	recursive=1;;
+		n)	dry_run=1;;
+		v)	verbose=1;;
+		h)	usage
+			exit 0;;
+		?)	usage
+			exit 2;;
+	esac
+done
+shift $((OPTIND - 1))
+
+if [ -z "$create" ] && [ -z "$prune" ] && [ -z "$list" ]; then
+	printf "At least one of -c, -p, and -l must be specified.\n"
+	usage
+	exit 1
+fi
+
+if [ "$#" -eq 0 ] && { [ -n "$create" ] || [ -n "$prune" ]; }; then
+	printf "At least one dataset must be specified\n"
+	usage
+	exit 1
+fi
+
+if { [ -n "$create" ] || [ -n "$prune" ]; } && [ -z "$tag" ]; then
+	printf "Missing -t option\n"
+	usage
+	exit 1
+fi
+
+if [ -n "$prune" ] && [ -z "$keep" ]; then
+	printf "Missing -k option\n"
+	usage
+	exit 1
+fi
+
+if [ -z "$prune" ] && [ -n "$keep" ]; then
+	printf "\-k option is only valid with -p\n"
+	usage
+	exit 1
+fi
+
+create_cmd='zfs snapshot'
+if [ -n "$recursive" ]; then
+	create_cmd="$create_cmd -r"
+fi
+readonly create_cmd
+
+destroy_cmd='zfs destroy'
+if [ -n "$recursive" ]; then
+	destroy_cmd="$destroy_cmd -R"
+fi
+readonly destroy_cmd
+
+# Create snapshots.
+if [ -n "$create" ]; then
+	for dataset in "$@"; do
+		# FreeBSD's date -I option uses a "+00:00" suffix rather than "Z", and
+		# the + character is illegal in snapshot names, so we have to specify
+		# the format manually.
+		cmd="$create_cmd ${dataset}@${tag}-$(date -z utc +%Y-%m-%dT%H:%M:%SZ)"
+
+		if [ -n "$dry_run" ] || [ -n "$verbose" ]; then
+			printf "%s\n" "$cmd"
+		fi
+
+		if [ -z "$dry_run" ]; then
+			$cmd
+		fi
+	done
+fi
+
+# Prune snapshots.
+if [ -n "$prune" ]; then
+	if [ -n "$prune_only" ]; then
+		keep=$((keep + 1))
+	fi
+
+	for dataset in "$@"; do
+		snapshots=$(zfs list -t snapshot -o name -S name -H "$dataset")
+		to_delete=$(printf "%s\n" "$snapshots" | grep "@${tag}-" | tail -n +"$((keep + 1))")
+		for s in $to_delete; do
+			cmd="$destroy_cmd $s"
+			if [ -n "$dry_run" ] || [ -n "$verbose" ]; then
+				printf "%s\n" "$cmd"
+			fi
+
+			if [ -z "$dry_run" ]; then
+				$cmd
+			fi
+		done
+	done
+fi
+
+# List snapshots.
+if [ -n "$list" ]; then
+	cmd="zfs list"
+	if [ -n "$recursive" ]; then
+		cmd="$cmd -r"
+	fi
+	snapshots=$($cmd -t snapshot -o name -s name -H "$@")
+
+	if [ -n "$tag" ]; then
+		printf "%s\n" "$snapshots" | grep "@${tag}-"
+	else
+		printf "%s\n" "$snapshots"
+	fi
+fi