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.
dpkg -i --force-confmiss mysql-common.deb will recreate any missing configuration files, ie /etc/mysql/my.cnf in your case.
sudo dpkg --force-confmiss -i /var/cache/apt/archives/mysql-common*.deb mysql-apt-config as well. My mysql-apt-config is missing. Thanks Michael None of the above worked for me - maybe outdated - anyway, I found this solution:
apt-get -o Dpkg::Options::="--force-confmiss" install --reinstall mysql-common 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 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.
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.
/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. /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. /etc/mysql/my.cnf.orig. Then, naturally, make a tarball backup of /etc. :) You need to reinstall mysql-common with this command:apt-get install --reinstall mysql-common
It appears some of the other solutions won't work if the configuration files of the package are managed with ucf.
In this case you can use :
UCF_FORCE_CONFFMISS=1 apt-get --reinstall install [pkgname] 
7z x /path/to/foo.deb, then7z x data.tar.gz)....conf.dfolders, 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