Rsync

rsync copies only what differs between source and target, so repeated runs are fast. It works locally and over SSH (host:path).

The trailing slash

The most common mistake: a trailing slash on the source means “the contents of”, without it the directory itself is copied.

Command	Result
rsync -a photos /backup	/backup/photos/1.jpg
rsync -a photos/ /backup	/backup/1.jpg

A slash on the target makes no difference.

Examples

Command	Effect
rsync -aP /home /backup	Copies /home to /backup/home with progress, resumable.
rsync -avz /home/ server:/backups/home/	Copies to a server over SSH, compressed.
rsync -av --delete src/ dst/	Makes dst an exact mirror, deleting files missing in src.
rsync -av --exclude '.cache' src/ dst/	Skips matching files and directories.
rsync -avn --delete src/ dst/	Dry run: lists what would happen.
rsync -aHAX src/ dst/	Additionally keeps hard links, ACLs and extended attributes.
rsync -rltDv --modify-window=1 src/ /mnt/usb/	For FAT/exFAT targets, which have no owners or permissions and coarse timestamps.

Option	Meaning
-a	Archive: recursive, keeps symlinks, permissions, times, owner, group and devices (-rlptgoD).
-v	Lists the transferred files.
-z	Compresses during the transfer; only useful over a network.
-P	Shows progress and keeps partially transferred files, so a restart continues.
-n	Dry run.

Danger

--delete together with a wrong trailing slash or a swapped source and target deletes data in the target. Run the command with -n first.