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If libfoo is pulled in by the package bar, and I upgrade it by executing apt-get install libfoo, how will this affect reverse dependencies?

If I then remove the package bar, will libfoo still be removed by apt-get autoremove?

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up vote 6 down vote accepted

If you run apt-get install libfoo it will mark it as manually installed. This means it won't be removed by autoremove.

And as far as I know, running apt-get install libfoo won't upgrade libfoo. It's already installed as a dependency of bar and it'll automatically be the most updated version that it can be (while still compatible with bar).

If there's a newer version of libfoo that isn't compatible with bar's dependency (packages can state what version of a package they need including "newer than x" or "older than x"), libfoo will be held back.

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For libraries there's also the policy statement that a newer libfoo must not break any rdepends. Any time the library changes ABI it should also change SONAME, and we mandate that the SONAME be included in the package name (which is why you'll sometimes see libfoo1 and libfoo2 in the archive at the same time). – RAOF Nov 4 '10 at 4:13

1) If libfoo is a dependence, doing apt-get install libfoo will install only the version compatible with the other application using it.

2) If you remove bar and no other application is using libfoo, it will be removable with apt-get autoremove.

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These aren't necessarily true, and the second point is false. If you've run “apt-get install libfoo” then libfoo is marked as manually installed and isn't a candidate for autoremove. – RAOF Nov 4 '10 at 4:11

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