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In /etc/apt/source.list,

deb precise universe
deb-src precise universe
deb precise-updates universe
deb-src precise-updates universe
deb precise-backports main restricted universe multiverse
deb-src precise-backports main restricted universe multiverse

I wonder what differences are between "precise" and "precise-updates" and "precise-backports" I only know "precise" means the code name of Ubuntu release 12.04. Thanks.

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The Ubuntu Help site has the answer:

  1. "Important Security Updates (raring-security)". Patches for security vulnerabilities in Ubuntu packages. They are managed by the Ubuntu Security Team and are designed to change the behavior of the package as little as possible -- in fact, the minimum required to resolve the security problem. As a result, they tend to be very low-risk to apply and all users are urged to apply security updates.
  2. "Recommended Updates (raring-updates)". Updates for serious bugs in Ubuntu packaging that do not affect the security of the system.
  3. "Pre-released Updates (raring-proposed)". The testing area for updates. This repository is recommended only to those interested in helping to test updates and provide feedback.
  4. "Unsupported Updates (raring-backports)". As the name states, these are unsupported new versions of packages which have been backported to an older release. Packages may contain new features, may introduce new interfaces, and bugs.

For example, the phpldapadmin package that was released for trusty has a serious packaging bug, where it expected a directory structure use in Apache 2.2, whereas trusty had Apache 2.4. It couldn't even be installed. The fix was released in trusty-updates.

For most users, enabling all four shouldn't be a problem most of the time. For a very stable environment, keep only security enabled. Keep updates enabled if some package you're using has a packaging issue. Updates packages have to conform to policies regarding stable updates, so they shouldn't cause breakage and keeping them enabled all the time is recommended. Keep proposed enabled if you don't mind testing out new things. This might cause things to break on occasion, so if you're not a fan of the " latest and greatest" philosophy, keep it disabled unless you have a problem and devs ask you to enable it. Keep backports enabled if you wish to have software that is typically only available for a newer release of Ubuntu.

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thanks. which one does "precise" belong to? – Tim Jul 11 '14 at 5:29
"For most users, enabling all four shouldn't be a problem.". I'd suggest not enabling proposed unless you're willing to have things break; updates going into proposed may be unstable (and I've seen this actually happen). You should enable proposed if you're affected by a bug and people working on the bug report ask you to enable it to test their fix. Also, updates doesn't contain only fixes to "packaging" issues, but all changes going into updates need to conform to stable release update policies, which are quite strict. So having updates enabled is also recommended. – roadmr Jul 11 '14 at 16:05
@roadmr you're right. The help page should be amended to reflect this. – muru Jul 11 '14 at 19:32

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