Delete Modes and Backup Dir

Deletion is where most sync incidents happen. Use controlled modes and recovery-friendly patterns.

Learning Focus

Learn how to mirror safely without turning a mount failure or a wrong path into mass deletion.

Concept Overview

rclone sync makes the destination match the source. That implies deletions when:

• The destination contains extra files not present in source.
• The source path is wrong, empty, or not mounted.

The goal is not "never delete". The goal is "delete predictably and recoverably".

Key Safety Flags

Flag	Purpose
--dry-run	Preview planned changes
--delete-before/--delete-during/--delete-after	Deletion timing control
--backup-dir	Move replaced/deleted files to safety location
--suffix	Append suffix for backup copies

Mapping

• Delete Modes
• Backup Dir
• Preflight Guardrails

Delete Timing (Before / During / After)

Mode	What it does	When to use
--delete-before	Deletes extras before upload	Rare; only when you must guarantee no extras early
--delete-during	Deletes while transferring	Large datasets where runtime matters
--delete-after	Deletes after a successful transfer	Safer default for many workloads

note

Even with --delete-after, a wrong source can still cause wrong deletes. Preflight checks are still mandatory.

Safer Mirror Pattern

safe-mirror.sh

rclone sync /srv/site remote-prod:site/current \
  --delete-after \
  --backup-dir remote-prod:site/rollback/$(date +%F-%H%M) \
  --suffix ".bak" \
  --log-file /var/log/rclone-safe-mirror.log

Preflight Guardrails (Must Have)

preflight-guards.sh

set -euo pipefail

SRC="/srv/site"
DST="remote-prod:site/current"

test -d "$SRC" || { echo "missing source: $SRC"; exit 1; }
test "$(ls -A "$SRC" | wc -l)" -gt 0 || { echo "source empty: $SRC"; exit 1; }
rclone lsd "${DST%/*}" >/dev/null

rclone sync "$SRC" "$DST" --dry-run -vv

warning

Never run destructive sync directly from a path that might be empty due to mount failure or script error.

danger

If your source is a mount (NFS, CIFS, FUSE, etc.), add a mount check before every run.

Safety Checklist

1. Confirm source path is mounted and non-empty.
2. Run dry-run and inspect delete list.
3. Keep --backup-dir enabled for critical datasets.

How Backup Dir Works

When --backup-dir is set, rclone moves files that would be overwritten/deleted into the backup dir.

Outcome	Without --backup-dir	With --backup-dir
Destination extra file	Deleted	Moved to rollback prefix
Destination file replaced	Overwritten	Previous version moved to rollback

This gives you an operational rollback path.

Common Pitfalls

Pitfall	Impact	Prevention
Sync from wrong source root	Massive remote deletion	Add preflight path sanity checks
No rollback location	Slow or impossible recovery	Use timestamped --backup-dir
Blind trust in automation	Silent data drift	Alert on unusual delete counts

Hands-On Practice

1. Create a lab destination prefix.
2. Upload two files.
3. Remove one locally.
4. Run a dry-run sync with --backup-dir and confirm you understand the rollback behavior.

practice-delete-safety.sh

mkdir -p /tmp/rclone-del && echo "a" > /tmp/rclone-del/a.txt && echo "b" > /tmp/rclone-del/b.txt
rclone sync /tmp/rclone-del remote-prod:labs/delete-safety/current --progress
rm /tmp/rclone-del/b.txt
rclone sync /tmp/rclone-del remote-prod:labs/delete-safety/current --dry-run -vv \
  --delete-after \
  --backup-dir remote-prod:labs/delete-safety/rollback/$(date +%F-%H%M) \
  --suffix .bak

What's Next

• Bisync Basics and Conflicts
• Rollback-Safe Sync Workflow