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I'm using Ubuntu 12.04 and at least once a week I get important and recommended updates. These weekly updates are normally between 50-100 Mb, and sometimes they're over 200 Mb.

I haven't installed anything new in a few months, but those large updates keep coming fairly consistently. It's hard to know what I'm actually downloading, but since it's labeled as important and recommended, it's hard to reject it.

My question: when I download that 100 Mb update, does the stuff it replaces get thrown away, or will I just keep accumulating more and more data just by running my system?

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up vote 2 down vote accepted

In general, updates to existing packages will overwrite existing files, and the installed size should stay the same, give or take a few percent.

Some packages are installed in parallel - for instance, each new kernel version is installed alongside the existing version (so that you can revert should the new version not work). Each kernel update adds O(100MB) to the installation, which will not automatically be freed until upgrade to a new Ubuntu version (but you can manually remove the older kernel packages).

The .deb packages recently installed by updates are stored in /var/cache/apt/archives. This directory can grow quite large - you can (harmlessly) clear it out with sudo apt-get clean if space usage becomes a problem.

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sudo apt-get autoremove should allow you to remove old kernel versions. – InkBlend Feb 21 '13 at 16:40
I'm not sure that removing previous kernels is as simple as sudo apt-get autoremove (…). – user25656 Feb 21 '13 at 17:03

Ubuntu has no support for incremental updates. That is why you need to download the whole package even if few bytes were changed.

When you instal updates only kernel packages are accumulate. This can let you recover your system in case of problems with new kernel. Other updates replace existing data and do not require much extra space, if any, except for cached *.deb files in /var/cache/apt/archives.

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