What is rsync?
The unix-y command rsync will "synchronize" the contents of one directory to another, by copying (and optionally deleting) the files and directories. It works both locally and for "remote" hosts that have rsync enabled.
How does it work?
This is a command-line utility that you enter into your terminal shell using syntax like rsync [options] src dst:
rsync -a dir1/ user@remote_host:dir2 rsync -a user@remote_host:/home/user/dir1 /path-to-sync
The following examples are from digital ocean
BASIC IN-SYSTEM
src is always first argument, destination is always second
rsync -a dir1/ dir2 sync dir1/* to dir2/[files]
The slashes are important! If you leave it off the src it will *MOVE* dir1 to dir2
BASIC REMOTE
rsync -a dir1/ user@remote_host:dir2 rsync -a user@remote_host:/home/user/dir1 /path-to-sync
COMMON OPTIONS
-a archive recursive sync, preserving symlinks, etc -r -v verbose -n dry run (try -anv) -z compress -P combination of --progress and --partial (resume) --delete allow rsync to delete stuff from remote for TRUE SYNC
OTHER OPTIONS
-r recurse into directories --exclude= pattern to exclude (pattern-separated list) --include pattern to include (pattern-separated list) --backup specify a location to store backups in addition to source and dest
RSYNC DAEMONS
(needs expansion) typically running on TCP port 873 can connect directly to it