From f9504eb14a8bbbb2a9d103afef4d6fd76fab2b70 Mon Sep 17 00:00:00 2001
From: Tero <tero.huttunen@eternityproject.fi>
Date: Wed, 2 Sep 2026 08:20:38 +0300
Subject: [PATCH] Add feature to ask deletion already exsisting snapshots on
 remote end

---
 README.md            |  5 +++++
 zfs-move-over-ssh.sh | 22 ++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/README.md b/README.md
index 2b163e4..ed03b6f 100644
--- a/README.md
+++ b/README.md
@@ -160,6 +160,11 @@ Options:
   completed destination filesystems remain received. Re-running with the same
   source can create another timestamped snapshot; inspect both source and
   destination state before retrying.
+- Before each receive, the script checks whether the remote destination already
+  has the matching `move-YYYYMMDD-HHMMSS` snapshot. If it does, the script asks
+  whether to delete that specific remote snapshot and retry the transfer. Type
+  `y` only after confirming it is an incomplete or disposable migration
+  snapshot; any other response stops the script without deleting it.
 - A successful transfer is not a destructive move. Verify applications and
   data on the destination, then perform any source cleanup separately.
 
diff --git a/zfs-move-over-ssh.sh b/zfs-move-over-ssh.sh
index a651470..4582d59 100644
--- a/zfs-move-over-ssh.sh
+++ b/zfs-move-over-ssh.sh
@@ -113,6 +113,24 @@ run() {
     fi
 }
 
+remote_snapshot_exists() {
+    local remote_snapshot="$1"
+    ssh "${SSH_OPTIONS[@]}" "$REMOTE_HOST" \
+        "sudo -n zfs list -H -o name -t snapshot '$remote_snapshot' >/dev/null 2>&1"
+}
+
+remove_remote_snapshot() {
+    local remote_snapshot="$1"
+    local reply
+
+    printf 'Remote snapshot %s already exists. Delete it and retry? [y/N] ' "$remote_snapshot" >&2
+    read -r reply
+    [[ "$reply" =~ ^[Yy]([Ee][Ss])?$ ]] || die "remote snapshot was not deleted; stopping"
+
+    ssh "${SSH_OPTIONS[@]}" "$REMOTE_HOST" "sudo -n zfs destroy '$remote_snapshot'" \
+        || die "could not delete remote snapshot $remote_snapshot"
+}
+
 mapfile -t FILESYSTEMS < <(zfs list -H -o name -t filesystem -r "$SOURCE_POOL")
 ((${#FILESYSTEMS[@]} > 0)) || die "no filesystems found in $SOURCE_POOL"
 
@@ -120,6 +138,7 @@ printf 'Migration snapshot: %s\n' "$SNAPSHOT_NAME"
 for filesystem in "${FILESYSTEMS[@]}"; do
     destination="$(map_destination "$filesystem")"
     snapshot="${filesystem}@${SNAPSHOT_NAME}"
+    remote_snapshot="${destination}@${SNAPSHOT_NAME}"
 
     printf 'Transferring %s to %s:%s\n' "$filesystem" "$REMOTE_HOST" "$destination"
     run zfs snapshot "$snapshot"
@@ -129,6 +148,9 @@ for filesystem in "${FILESYSTEMS[@]}"; do
         printf ' %q' "${SSH_OPTIONS[@]}" "$REMOTE_HOST" "sudo -n zfs receive -uF '$destination'" >&2
         printf '\n' >&2
     else
+        if remote_snapshot_exists "$remote_snapshot"; then
+            remove_remote_snapshot "$remote_snapshot"
+        fi
         zfs send -p "$snapshot" | ssh "${SSH_OPTIONS[@]}" "$REMOTE_HOST" "sudo -n zfs receive -uF '$destination'"
     fi