Datasheet
“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 556 — #582
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23.1 Available Data Synchronization
Software
Data synchronization is no problem for computers that are permanently
linked by means of a fast network. In this case, use a network file system
like NFS and store the files on a server, enabling all hosts to access the same
data via the network. This approach is impossible if the network connec-
tion is poor or not permanent. When you are on the road with a laptop,
copies of all needed files must be on the local hard disk. However, it is then
necessary to synchronize modified files. When you modify a file on one
computer, make sure a copy of the file is updated on all other computers.
For occasional copies, this can be done manually with scp or rsync. How-
ever, if many files are involved, the procedure can be complicated and re-
quires great care to avoid errors, such as overwriting a new file with an old
file.
Caution
Risk of Data Loss
Before you start managing your data with a synchronization
system, you should be well acquainted with the program used
and test its functionality. A backup is indispensable for important
files.
Caution
The time-consuming and error-prone task of manually synchronizing data
can be avoided by using one of the programs that use various methods to
automate this job. The following summaries are merely intended to convey
a general understanding of how these programs work and how they can be
used. If you plan to use them, read the program documentation.
23.1.1 Unison
Unison is not a network file system. Rather, the files are simply saved
and edited locally. The program Unison can be executed manually to syn-
chronize files. When the synchronization is performed for the first time, a
database is created on the two hosts, containing check sums, time stamps,
and permissions of the selected files. The next time it is executed, Unison
can recognize which files were changed and propose transmission from or
to the other host. Usually all suggestions can be accepted.
556 23.1. Available Data Synchronization Software