rsync's dangerous flags don't fail. They do a different job and exit 0.

Tue, 20 Oct 2026 13:00:00 +0000

The trap with rsync is that its dangerous flag combinations don't fail — they complete a different operation than the one you intended, and exit 0. --delete makes the destination match the source, so a mistyped or freshly moved source directory means rsync removes everything at the destination and reports success. Your cron log shows a clean run while the backup empties itself. A trailing slash changes the meaning too: /data/ syncs the directory's contents, while /data copies the directory itself into the destination — and on a mirror job, that difference decides what gets compared and what gets deleted.

The defense is previewing every destructive sync before running it live:

rsync -av --delete --dry-run /srv/www/ user@backup:/srv/backup/www/

Read the deleting … lines it prints; only when that list matches your expectations do you remove --dry-run. Note also that excludes take one pattern per flag — --exclude='*.log' --exclude='.git' — because a comma-separated list inside a single flag silently matches nothing.

If you'd rather compose the command with those guardrails enforced — a red warning when --delete is enabled without a dry run, per-pattern quoted excludes, and a live preview of the finished command — I built a visual rsync command builder with delete-flag guardrails that runs entirely in the browser.

Simple backups using Rsync with SSH

Thu, 12 Feb 2026 13:35:25 +0000

This post explains how to SSH with Rsync to make backup of your system efficiently and securely.

The only requisite to start here is an access to SSH somewhere.

Create your ssh keys

Here, i just create a keypair called “rsync”, ssh will create a private and a public key.

ssh-keygen -t ed25519 -o -a 100 -f ~/.ssh/rsync

After, just send the public key to the server with scp targeting your server.

 scp ~/.ssh/rsync.pub backup@SERVER

Create a backup script

Create a shell script named rsync-backup.sh with the following content:

#/usr/bin/env sh

set -o errexit

# All variables
SERVER="192.168.1.11"
BACKUP_FILE="/tmp/backup.filter"

# More efficient than playing with --include,--exclude
cat << EOF > "$BACKUP_FILE"
# Include patterns
+ /documents/***
+ /Downloads/***
+ /downloads/***
+ /images/***
+ /musics/***

# Exclude everything else
- /**
EOF

# And finally the rsync command
rsync -avP --delete -e "ssh -i $HOME/.ssh/rsync" \
    --bwlimit=400 \
    --filter="merge $BACKUP_FILE" \
    "$HOME/" "backup@${SERVER}:backups/"

The script here will backup your $HOME with only certain directory in the “include pattern list”. Just ensure the server address is correct.

I also limit the bandwidth because it break my wifi card (bad hardware…)

Execute the script

Just give permission and launch the script.

 chmod u+x rsync-backup.sh
./rsync-backup.sh

Conclusion

Using SSH with Rsync is an efficient and secure method for backing up your system. By generating SSH keys and creating a simple shell script, you can automate the backup process, ensuring that your important files are safely stored on a remote server.