Home > Articles > Operating Systems, Server > Linux/UNIX/Open Source

Marcel's Linux Walkabout: Keeping in Sync with Your Data

Yeah, sure. We all know that backups are important, but when you have a lot of data (MP3s and video clips, anyone?), keeping that information safe usually requires some serious backup hardware. CD-ROMs are only so big, and tape drives can be expensive. It's time to get creative. Join Marcel Gagne on his Linux Walkabout, and you'll learn how to keep your data safe and "in rsync".
Like this article? We recommend

In my latest Linux Walkabout, I found myself visiting an old problem: keeping data safe. If your system suffers a disk crash or other equally painful mishap, you can always reinstall the operating system and put back the applications, but data is paramount. In the end, it is really the only thing that is important. Knowing all that, it's amazing how difficult it can be for people to get that data backed up.

There are reasons, of course. Aside from just "not getting around to it," the obvious reason is that we have so much data these days. It has been a long time since we moved from diskettes to CD-ROMs, but even they are quickly filled. Many people I know who do regular backups are doing theirs to a disk on another machine. Machine A backs to machine B, which backs to C, which backs to A. In the absence of another machine, others still are backing up to a second disk on the same machine. Given that an extra hard drive added to a system is extremely inexpensive these days and high capacity tape drives can still cost substantially more, it isn't that unusual to find this kind of solution being used.

"Data, Meet rsync."

The ideal solution in any of these scenarios is to do one big backup; then simply make sure that the backup is always up-to-date. In other words, back up only what has changed. The result is a perfect mirror: One directory (and the accompanying subdirectories) is mirrored either locally or on a remote system. One of the best tools available to achieve this mirroring is a program called rsync.

With rsync, you can synchronize files and directories on one system with that of another. Because only those files that have been modified are transferred, the process can be very quick. You can do this with single files, whole directories, and subdirectories while maintaining file ownership and permissions, links, symbolic links, and so on. rsync has its own transport, or you can use OpenSSH to secure the transfer (something I'll cover later). You can even mirror with anonymous rsync if you wish...but as they say, I am getting ahead of myself.

You can find rsync at http://rsync.samba.org, and it is freely distributed under the GPL. That said, you may not have to go hunting for rsync. Your Linux distribution may already come with this handy piece of software, so check your distribution CDs first. If you go for the source instead, you'll find that building the package is simply a matter of the classic extract and build five-step.

   tar -xzvf rsync-2.5.6.tar.gz
   cd rsync-2.5.6
   su -c "make install"

This magic synchronization of files and directories is done using a client and server setup. At least one machine must play the role of server; although nothing stops you from running an rsync daemon on every one of your machines, however, the client machine must also have the rsync program installed. The server gets its information about who can access what from a configuration file called rsyncd.conf. You'll find that it probably lives in the /etc directory. The following listing is from an rsync server I've just set up:

hosts allow =
use chroot = no
max connections = 4
log file = /var/log/rsyncd.log
gid = nogroup
uid = nobody

    path = /mnt/data1/website
    read only = no
    comment = All our websites

    path = /mnt/extradrive/mailman
    read only = no
    comment = Mailman lists and archives

    path = /mnt/backups/marcel
    read only = no
    comment = Backup area for Marcel

The above configuration file needs a little explaining, but it is all very simple once you get the hang of it. For starters, if you've used Samba at all, you might have noticed that the format of the file is quite similar. Given that the author of rsync, Andrew Tridgell, is also one of the authors of Samba, that won't seem so strange. Backup areas are identified by a name in square brackets (website, mailman, etc.) The chief bits of information there are the path to the disk area and some kind of comment.

In each of these sections, I also specified "read only = no", but I could just as easily have added that to the top section (the one without a name in square brackets). That's the global section. Anything put up there applies to all other sections (which can then be overridden). Pay particular attention to the gid and uid sections—namely, the group and user id that the file transfer takes place as. The default is nobody, but you need to make sure that this is the case on your system. One of my servers has no nobody group, but rather a nogroup.

The "hosts allow" section identifies my local subnet as being the only set of addresses from which transfers can take place. The "log file" identifies a file to log information from the daemon. You can also specify a maximum number of connections, specific users who are allowed to transfer files (auth users), and a whole lot more. Run "man rsyncd.conf" for the full details. When your configuration is set, you can launch the rsync daemon, which interestingly enough is exactly the same program as the rsync command itself. rsync can be run from xinetd (or inetd) or as a daemon. To run it as a daemon (as I have chosen to do), do the following.

   rsync --daemon

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020