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Using rsync Over A Network
One of the real beauties of rsync is that it can be used to copy files over a network. Af- ter all, the “r” in rsync stands for “remote.” Remote copying can be done in one of two ways. The first way is with another system that has rsync installed, along with a remote shell program such as ssh. Let’s say we had another system on our local network with a
lot of available hard drive space and we wanted to perform our backup operation using the remote system instead of an external drive. Assuming that it already had a directory named /backup where we could deliver our files, we could do this:
[me@linuxbox ~]$ sudo rsync -av --delete --rsh=ssh /etc /home
/usr/local remote-sys:/backup
[me@linuxbox ~]$ sudo rsync -av --delete --rsh=ssh /etc /home
/usr/local remote-sys:/backup
We made two changes to our command to facilitate the network copy. First, we added the
--rsh=ssh option, which instructs rsync to use the ssh program as its remote shell. In this way, we were able to use an ssh encrypted tunnel to securely transfer the data from the local system to the remote host. Second, we specified the remote host by prefixing its name (in this case the remote host is named remote-sys) to the destination pathname.
The second way that rsync can be used to synchronize files over a network is by using an rysnc server. rsync can be configured to run as a daemon and listen to incoming re- quests for synchronization. This is often done to allow mirroring of a remote system. For example, Red Hat Software maintains a large repository of software packages under de- velopment for its Fedora distribution. It is useful for software testers to mirror this collec- tion during the testing phase of the distribution release cycle. Since files in the repository change frequently (often more than once a day), it is desirable to maintain a local mirror by periodic synchronization, rather than by bulk copying of the repository. One of these repositories is kept at Georgia Tech; we could mirror it using our local copy of rsync and their rsync server like this:
[me@linuxbox ~]$ mkdir fedora-devel
[me@linuxbox ~]$ rsync -av --delete rsync://rsync.gtlib.gatech.edu/fe dora-linux-core/development/i386/os fedora-devel
[me@linuxbox ~]$ mkdir fedora-devel
[me@linuxbox ~]$ rsync -av --delete rsync://rsync.gtlib.gatech.edu/fe dora-linux-core/development/i386/os fedora-devel
In this example, we use the URI of the remote rsync server, which consists of a protocol (rsync://), followed by the remote host-name (rsync.gtlib.gatech.edu), fol- lowed by the pathname of the repository.