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I've occasionally lost my config file "/etc/mysql/my.cnf", and want to restore it. The file belongs to package mysql-common which is needed for some vital functionality so I can't just purge && install it: the dependencies would be also uninstalled (or if I can ignore them temporarily, they won't be working).

Is there a way to restore the config file from a package without un-ar-ing the package file?

dpkg-reconfigure mysql-common did not restore it.

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i've always just extracted the package files with 7zip (7z x /path/to/foo.deb, then 7z x data.tar.gz).... – quack quixote Nov 9 '09 at 6:26
Personally, I like to setup something like etckeeper on my system right after I install. That way all changes and versions of configuration files get stored. (serverfault.com/questions/13091/advice-on-storing-etc-in-a-vcs) – Zoredache Nov 9 '09 at 6:54
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And this, kids, is why we have backups... – womble Nov 9 '09 at 7:08
@womble: actually, the situation is slightly different: i have a config file, but it's modified by me. I was not using conf.d folders, and when the package maintainer update it, upgrade process becomes really keen of displaying "config file modified" messages :) The reason is not that important to mention, so I decided to simplify my question – o_O Tync Nov 9 '09 at 13:19
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6 Answers

up vote 15 down vote accepted

dpkg -i --force-confmiss mysql-common.deb will recreate any missing configuration files, ie /etc/mysql/my.cnf in your case.

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Thanks! On Ubuntu, it was sudo dpkg --force-confmiss -i /var/cache/apt/archives/mysql-common*.deb – o_O Tync Nov 9 '09 at 13:26
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up vote 3 down vote

it's quite lame to point at backups just because the config file handling of dpkg / apt is so usability challenged... i mean install --reinstall --purge and not to mention that --reinstall still wouldn't reinstall a missing initscript.

enough of "don't fight debian", it's not cool to expect users to follow every twisted concept that the debian devs come up.

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up vote 2 down vote

You can find default mysql config files in /usr/share/doc/mysql-server-5.0/examples/ or similar. That may be all that you need unless you have some really special/esoteric configurations enabled.

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up vote 1 down vote

In Debian Squeeze — at least —, we also can do it this way, after su — or sudo for Ubuntu —

aptitude install -o Dpkg::Options::=--force-confmiss mysql-server

This will care for the dependencies of mysql-server and reset all the missing conf files of the lot, including mysql-common. Conflicting (remaining) files will be prompted out to be kept or reset.

Unfortunately, there is a bug in aptitude, and 

aptitude purge -o Dpkg::Options::=--force-all mysql-server

will not work. So we have to do it one by one with 

dpkg --force-all --purge  mysql-common  mysql-server  mysql-client …

This will remove any config file, original or modified, but custom files will be preserved, with an onscreen message. Note, by the way, that dpkg also recognizes --force-confnew and --force-confold options.

To get mysql-server dependencies' list print on screen :

aptitude --simulate remove mysql-server
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Thank you! Works excellent in Ubuntu 12.04 – Hendy Irawan May 5 at 20:24
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up vote 0 down vote

In my /etc/mysql/ directory, I have a my.cnf.orig file which contains the original contents of my.cnf.

I'm not sure where /etc/mysql/my.cnf.orig came from - that is, whether I created it, or the installation of mysql did it. I remember checking at one time that it was exactly the same as my.cnf

If you have such a thing, and no my.cnf you can copy one to the other.

sudo cp /etc/mysql/my.cnf.orig /etc/mysql/my.cnf

In any case, it's a simple text file of 3897 bytes and you could copy and paste from a generic Mysql configuration file.

It will be a good idea once you restore your /etc/mysql/my.cnf to make a copy so you can restore it easily in future.

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I usually make a backup of original-install configuration files by copying them to /path/to/foo.conf.orig ... if these are automatically installed, they're created when apt-get is installing a new version and detects you've altered the original configuration file. – quack quixote Nov 9 '09 at 6:10
Hmm, the more I think about it, the more it seems I created /etc/mysql/my.cnf.orig as a backup which wouldn't be overwritten by a fresh installation. But, putting it somewhere entirely different is a good idea. – pavium Nov 9 '09 at 6:14
I was trying to be generic; for my.cnf I would copy it to /etc/mysql/my.cnf.orig. Then, naturally, make a tarball backup of /etc. :) – quack quixote Nov 9 '09 at 6:19
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up vote 0 down vote

You need to reinstall mysql-common with this command:apt-get install --reinstall mysql-common

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