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Archive for the ‘Debian’ Category

Chrooting Recent MySQL Versions on Debian and Ubuntu

I’ve posted a recipe for chrooting MySQL on Debian sarge a while ago. These instructions no longer work out of the box for newer MySQL packages from Debian and Ubuntu. The main problem is that the startup script added a few extra checks and script invocations that don’t understand the chroot environment. So here’s an updated plan:

  • Prepare the chroot directory. It’s recommended to use an extra partition/filesystem for it. I will use /srv/mysql (which is an LVM2 partition with an ext3 filesystem on my system) for the rest of the text.
  • Stop MySQL:
    /etc/init.d/mysql stop
  • Copy the databases to new location:
    mkdir -p /srv/mysql/var/lib
    cp -a /var/lib/mysql /srv/mysql/var/lib
  • Copy this script to /etc/default/mysql-chroot
  • Edit /etc/init.d/mysql:
    • Source the mysql-chroot script somewhere at the top:
      …
      test -x /usr/sbin/mysqld || exit 0
      
      . /etc/default/mysql-chroot
      
      SELF=$(cd $(dirname $0); pwd -P)/$(basename $0)
      …
    • Fix the disk space check:
      …
      # check for diskspace shortage
      datadir=`mysqld_get_param datadir`
      if LC_ALL=C BLOCKSIZE= df --portability $CHROOT_DIR$datadir/. | tail -n 1 | awk '{ exit ($4>4096) }'; then
        log_failure_msg "$0: ERROR: The partition with $datadir is too full!"
      …
    • Run setup_chroot right in the start section:
      …
      if mysqld_status check_alive nowarn; then
        echo "...already running."
      else
        setup_chroot
        /usr/bin/mysqld_safe > /dev/null 2>&1 &
      …
    • Somehow /var/run/mysqld/mysqld.pid disappears after each start. We have to create it each time, otherwise the stop command won’t work properly:
      …
      if mysqld_status check_alive warn; then
        log_end_msg 0
        ln -sf $CHROOT_DIR/var/run/mysqld/mysqld.pid \
                       /var/run/mysqld
        # Now start mysqlcheck or whatever the admin wants.
        output=$(/etc/mysql/debian-start)
      …
  • In /etc/mysql/debian.cnf, change the two socket lines to:
    socket = /srv/mysql/var/run/mysqld/mysqld.sock
  • In /etc/mysql/my.cnf:
    • Change the socket line in the [client] section to:
      socket = /srv/mysql/var/run/mysqld/mysqld.sock

      Don’t change the socket lines in the other sections!

    • Add
      chroot = /srv/mysql

      to the [mysqld] section.

  • Prepend /srv/mysql to the log files listed in /etc/logrotate.d/mysql-server
  • Make /usr/bin/mysql_upgrade_shell use the chrooted socket. Note: Currently these changes must be made each time mysql gets upgraded because upgrades override this file!
    …
    --password=*) password=`echo "$arg" | sed -e 's/^[^=]*=//'` ;;
    --socket=*) socket=`echo "$arg" | sed -e 's/^[^=]*=//'` ;;
    --ldata=*|--data=*|--datadir=*) DATADIR=`echo "$arg" | sed -e 's/^[^=]*=//'` ;;
    …
    fi
    $bindir/mysql_fix_privilege_tables --silent --user=$user --password=$password --socket=$socket $args
    exit 0
    …
    check_args="--check-upgrade --all-databases --auto-repair --user=$user --password=$password --socket=$socket"
    …
    $bindir/mysql_fix_privilege_tables --silent --user=$user --password=$password --socket=$socket $args
    …
  • Start MySQL:
    /etc/init.d/mysql start
  • Check /var/log/syslog for errors ;-)

Sun Java Packages for Debian and Ubuntu

Sun now allows redistribution of Java by Linux and Open-Solaris distributions.

As a result of this move, there are now packages of Sun’s Java for Debian and Ubuntu.
The packaging code is largely based on the code we are using for Blackdown Java for some years. The code is available under the MIT license from the jdk-distros project on java.net. (More info on Tom Marble’s blog.)

I’m glad Sun finally opens Java up a bit after years of restrictive licensing.

LVM Snapshots With Debian Sarge and Linux 2.6.16

I have upgraded this server to kernel 2.6.16.2. The next backup cycle resulted in a minor disaster: The backup process deadlocked at removing the first LVM2 snapshot and the snapshot source volumes were blocking write accesses. A cleanup shutdown was impossible and I had to hard-reset the machine.

After some searching I found out that you apparently need lvm2 2.02.01 or later and devmapper 1.02.02 or later to successfully remove snapshot volumes now. Unfortunately neither of these versions is available for sarge from Debian or backports.org yet, so I had to make my own backports.
As it turned out (see below), it is also necessary to use 2.6.16.12 or to apply the patch from this email to older 2.6.16 versions in order to reliably remove snapshots.

If you are brave enough, you can get the backported packages by adding

deb http://blog.blackdown.de/static/debian/lvm/ sarge main
deb-src http://blog.blackdown.de/static/debian/lvm/ sarge main

to /etc/apt/sources.list.

The repository contains debs for devmapper, dlm, lvm2, and lvm-common. The Release files is signed with my GPG key. If you have a recent apt version, you can authenticate the packages after importing the key with apt-key:

wget http://blog.blackdown.de/static/gpg.asc -O - | \
    sudo apt-key add -

April 15th, 2006: In about 40 backup cycles I’ve seen three lockups with 2.6.16.2 now. Until snapshots get fixed in 2.6.16, I’d recommend to stay with 2.6.15. I’m using 2.6.15.3 again now.

April 24th, 2006: Added note about “dm snapshot: fix kcopyd destructor” patch from Alasdair G Kergon. With this patch snapshots work fine for me again.

May 2nd, 2006: Alasdair G Kergon’s patch has been included in 2.6.16.12.

Securing WordPress 2 Admin Access With SSL

A few people have asked for an updated version of my Securing WordPress Admin Access With SSL guide. So here is an updated version for 2!

The situation has not changed much since WordPress 1.5: WordPress 2.0 still does not support HTTPS access to the admin area when the rest of the blog is served via normal HTTP and I still do not like logging in to my server over unencrypted connections, especially not when using public WLANs. Getting around this WordPress limitation requires quite a few steps:

The Goal

All communication involving passwords or authentication cookies should be done over HTTPS connections. wp-login.php and the wp-admin directory should only be accessible over HTTPS.
Normal reading access, as well as comments, tracebacks, and pingbacks still should go over ordinary HTTP.

The Plan

  • Add an HTTPS virtual host that forwards requests to the HTTP virtual host
  • Modify WordPress to send secure authentication cookies, so cookies never get sent over insecure connections accidentally
  • Require a valid certificate on HTTPS clients. That means to log in to WordPress you need both a valid certificate and a valid password. If someone manages to get your password, he still can not login because he does not have a valid certificate.

The Implementation

Note: This documentation assumes a Debian sarge installation with 2. Some things, in particular Apache module related ones, will be different on other systems.
The server used throughout the instructions is example.org/192.0.34.166. The server’s DocumentRoot is /blog and WordPress resides in /blog/wp. The value of WordPress’ home option is ‘http://example.org’ and the value of its site_url option is ‘http://example.org/wp’.

  • Prepare the SSL certificates:
    • Generate your own certificate authority (CA) if you don’t have one already (I’m using the makefile from OpenSSL Certificate Authority Setup for managing mine) and import it into your browser.
    • Generate a certificate for the SSL server and certify it with your private CA.
    • Generate a certificate for your browser and certify it with your private CA. Most browsers expect a PKCS#12 file, so generate one with
      $ openssl pkcs12 -export -clcerts \
          -in blogclient.cert \
          -inkey blogclient.key \
          -out blogclient.p12

      Then import blogclient.p12 into your browser.

  • Make WordPress SSL-ready:
    Apply this patch to the WordPress code. It makes the following changes:

    • Use secure authentication cookies in wp_setcookie()
    • Make check_admin_referer() work with HTTPS URLs
    • Use HTTPS URLs for notification mails
    • Use HTTPS URLS for redirects to wp-login.php
    • Only allow XML-RPC logins from the local host (ie. the HTTPS proxy)
    • Add the Mark-as-Spam feature from trunk

    The patch is against svn version 3825 of WordPress (ie. WordPress 2.0.3), when you apply it to a newer version, you will likely get some harmless ‘Hunk succeeded’ message. If you are getting ‘Hunk FAILED’ message, just send me note and I’ll update the patch.

  • Enable the necessary Apache modules:
    • Install mod_proxy_html. It will be used to replace absolute ‘http://example.org’ HTTP URLs in the WordPress output with ‘https://example.org’ HTTPS URLs:
      $ aptitude install libapache2-mod-proxy-html

      The module gets enabled automatically after installation.

    • Enable mod_proxy and mod_ssl
      $ a2enmod proxy
      $ a2enmod ssl

      Debian provides sane default configurations for both modules. You might want to take a look at the configuration files (ssl.conf and proxy.conf) nevertheless.
      I have changed SSLCipherSuite to

      TLSv1:SSLv3:!SSLv2:!aNULL:!eNULL:!NULL:!EXP:!DES:!MEDIUM:!LOW:@STRENGTH

      in ssl.conf in order to just allow TLS v1 and SSL v3 ciphers which provide strong encryption and authentication (see ciphers(1)).

    • If you are compressing WordPress output (that is if you enabled the ‘WordPress should compress articles (gzip) if browsers ask for them’ option) then also enable mod_headers:
      $ a2enmod headers
  • Configure Apache to listen on the HTTPS port
    $ cat > /etc/apache2/conf.d/ssl.conf << EOF
    <IfModule mod_ssl.c>
    	Listen 443
    </IfModule>
    EOF
  • Modify the blog virtual host to limit access to wp-login.php and wp-admin to the local host. Also completely deny access to files which should never be accessed directly. Here is an example: 10-wp2-example.org
  • Now setup the HTTPS virtual server: 20-wp2-example.org-ssl
    If you are compressing WordPress output you have to enable the RequestHeader line.
  • Enable the site and restart Apache
    $ a2ensite 20-blog-ssl
    $ /etc/init.d/apache2 restart
  • Remove the old WP cookies from your browser
  • Test the new setup!

February 1st, 2006: wp2-ssl.patch updated for WordPress 2.0.1

March 11st, 2006: WordPress 2.0.2 has been released, fixing some security issues. The HTTPS patch still applies fine to that version.

March 19th, 2006: Updated wp2-ssl.patch. Changes: Fix bug in list-manipulation.php, use HTTPS for ‘Login’ and ‘Register’ links, backport ‘Mark-as-Spam’ feature from trunk

May 1st, 2006: WordPress 2.0.3 has been released. Here is the updated wp2-ssl.patch.

July 29th, 2006: WordPress 2.0.4 has been released, fixing some security issues. Here is an updated version of the wp2-ssl.patch.

January 12st, 2007: wp2-ssl.patch updated for 2.0.6 and 2.0.7-RC1

January 15st, 2007: WordPress 2.0.7 has been released. The patch still applies fine to that version.

XOrg 6.9 evdev Fix for Big-Endian Machines

The new evdev driver in XOrg 6.9 is broken on big-endian machines (e.g. powerpc). Here’s a patch that fixes the problem.