[SOLVED] Design principles as to how linux repository managers update themselves?

Issue

I know there are other applications also, but considering yum/apt-get/aptitude/pacman are you core package managers for linux distributions.

Today I saw on my fedora 13 box:

(7/7): yum-3.2.28-4.fc13_3.2.28-5.fc13.noarch.drpm       |  42 kB     00:00     

And I started to wonder how does such a package update itself? What design is needed to ensure a program can update itself?

Perhaps this question is too general but I felt SO was more appropriate than programmers.SE for such a question being that it is more technical in nature. If there is a more appropriate place for this question feel free to let me know and I can close or a moderator can move.

Thanks.

Solution

I've no idea how those particular systems work, but...

• Modern unix systems will generally tolerate overwriting a running executable without a hiccup, so in theory you could just do it.
• You could do it in a chroot jail and then move or something similar to reduce the time during which the system is vulnerable. Add a journalling filesystem and this is a little safer still.

It occurs to me that the package-manager needs to hold the package access database in memory as well to insure against a race condition there. Again, the chroot jail and copy option is available as a lower risk alternative.

Answered By - dmckee --- ex-moderator kitten

Answer Checked By - Willingham (WPSolving Volunteer)