Dangerous Commands
Dry run / previewRun Rsync Without Deleting Your Backup
You need to preview an rsync operation before moving or deleting files.
Command
rsync -avhn --delete ./source/ ./backup/Before you run this
System impact: Preview only. Still verify source and destination paths before running the real command.
When not to use it: Do not assume dry-run output is safe if the source and destination paths are reversed.
Expected output
A list of files that would be copied, updated, or deleted.
System impact
Dry run / preview. The dry run prints intended changes without modifying files.
When to use it
Use this before any sync involving deletes, production data, or backups.
When not to use it
Do not assume dry-run output is safe if the source and destination paths are reversed.
Recovery / rollback
No state is changed during the dry run. If you remove `-n`, make a backup first.
next steps
Related commands
Preview What Rsync Would Delete
`rsync --delete` is useful. It is also how people erase the wrong side.
rsync -avhn --delete ./source/ ./backup/ | grep '^deleting'
Preview Backup Drift with rsync
Rsync can tell you what would change before it changes anything.
rsync -ain --delete source/ backup/
Print a Dry-Run Removal Script
The reviewable cleanup command is the one you print before you run.
find /var/tmp/uploads -xdev -type f -mtime +7 -printf 'rm -i -- %p\n' 2>/dev/null
Compare Source and Backup File Lists
A backup can be missing files and still look plausible at a glance.
comm -3 <(find source -type f | sed 's#^source/##' | sort) <(find backup -type f | sed 's#^backup/##' | sort)
Inspect Permissions Before Changing Them
The permission fix was easy. Knowing what not to chmod was the hard part.
namei -l /var/www/example/index.html
Study mapping
Use this as independent command practice: read the notes, predict the output, then compare it with the example before using a real shell.
Independent study support only. No affiliation, endorsement, exam dumps, or real exam questions.