Today I was upgrading my Arch Linux box, (110 package to upgrade!!), suddenly when all the packages were downloaded, i got a message, that according to what I could read in the forums, it seems to be a common error when upgrading Arch Linux, but easy to solve anyway.

Here is the message I got:

:: Starting full system upgrade...
resolving dependencies...
looking for inter-conflicts...

Targets (112): acl-2.2.47-2  libcap-2.16-3  avahi-0.6.24-3  xproto-7.0.15-1  fixesproto-4.0-3  compositeproto-0.4-2  coreutils-7.2-1  damageproto-1.1.0-2  dash-0.5.5.1-2  dmxproto-2.2.2-2  gconf-2.26.0-3  
               hal-info-0.20090330-1  pm-utils-1.2.5-1  udev-141-1  hal-0.5.12git20090406.46dc48-1  gnome-keyring-2.26.1-1  libglade-2.6.4-1  libgcrypt-1.4.4-1  libtasn1-2.0-1  gnutls-2.6.5-1  tdb-3.3.3-1  
               smbclient-3.3.3-1  gnome-vfs-2.24.1-2  libgnome-2.26.0-2  sqlite3-3.6.12-1  libproxy-0.2.3-1  libsoup-2.26.0-1  libgweather-2.26.0-1  libical-0.43-1  evolution-data-server-2.26.0-1  
               libavc1394-0.5.3-2  libv4l-0.5.9-1  ptlib-2.6.1-1  kbproto-1.0.3-2  libx11-1.2.1-1  x264-20090216-1  opal-3.6.1-1  ekiga-3.2.0-1  icon-naming-utils-0.8.90-1  gnome-icon-theme-2.26.0-1  
               gsfonts-8.11-5  openjpeg-1.3-3  poppler-0.10.5-1  poppler-glib-0.10.5-1  evince-2.26.0-1  lcms-1.18-1  libidl2-0.8.13-1  xulrunner-1.9.0.8-1  firefox-3.0.8-1  fontcacheproto-0.1.2-2  
               fontsproto-2.0.2-2  gawk-3.1.6-3  gettext-0.17-3  libxext-1.0.5-2  ghostscript-8.64-5  hdparm-9.14-1  jack-audio-connection-kit-0.116.2-1  kernel26-firmware-2.6.29-1  kernel26-2.6.29.1-3  
               klibc-udev-141-1  libdrm-2.4.9-1  libfontenc-1.0.4-2  libxdamage-1.1.1-2  libgl-7.4-1  libgnomecanvas-2.26.0-1  libid3tag-0.15.1b-3  libmysqlclient-5.1.33-1  libogg-1.1.3-2  libsmbios-2.2.16-1  
               libstdc++5-3.3.6-3  libxcomposite-0.4.0-2  libxcursor-1.1.9-2  libxdmcp-1.0.2-2  lighttpd-1.4.22-3  libftdi-0.15-1  lirc-utils-0.8.5pre2-1  mailx-8.1.1-7  man-db-2.5.5-1  man-pages-3.20-1  
               mdadm-2.6.9-1  dri2proto-1.99.3-1  mesa-7.4-1  mpfr-2.4.1-1  ttf-dejavu-2.29-1  libxvmc-1.0.4-1  mplayer-28347-4  mysql-clients-5.1.33-1  mysql-5.1.33-2  nano-2.0.9-2  nginx-0.6.36-2  
               pygobject-2.16.1-1  python-numpy-1.3.0-1  pygtk-2.14.1-3  obmenu-1.0-6  pacman-mirrorlist-20090405-1  php-5.2.9-3  python-xlib-0.14-1  qt-4.5.0-4  redland-1.0.8-3  shared-mime-info-0.60-1  
               syslog-ng-3.0.1-6  tzdata-2009e-1  libnl-1.1-1  wpa_supplicant-0.6.9-1  xf86-input-evdev-2.2.1-1  xf86-input-keyboard-1.3.2-2  xf86-input-mouse-1.4.0-2  xf86-video-vesa-2.2.0-1  
               xorg-server-utils-7.4-4  xorg-server-1.6.0-3  xorg-utils-7.4-3  xterm-243-1  

Total Download Size:    0.00 MB
Total Installed Size:   845.20 MB

Proceed with installation? [Y/n] y
checking package integrity...
(112/112) checking for file conflicts               [#########################################################################################################################################################] 100%
error: could not prepare transaction
error: failed to commit transaction (conflicting files)
xorg-server: /usr/lib/xorg/modules/extensions/libdri.so exists in filesystem
xorg-server: /usr/lib/xorg/modules/libwfb.so exists in filesystem
Errors occurred, no packages were upgraded.

As suggested in the forums I tried to upgrade first the package givin the problem, which is in this case xorg, so I did this:

sudo pacman -S xorg-server

And the system respond this:

resolving dependencies...
looking for inter-conflicts...

Targets (2): xf86-input-evdev-2.2.1-1  xorg-server-1.6.0-3  

Total Download Size:    0.00 MB
Total Installed Size:   9.93 MB

Proceed with installation? [Y/n] y
checking package integrity...
(2/2) checking for file conflicts                   [#####################] 100%
error: could not prepare transaction
error: failed to commit transaction (conflicting files)
xorg-server: /usr/lib/xorg/modules/extensions/libdri.so exists in filesystem
xorg-server: /usr/lib/xorg/modules/libwfb.so exists in filesystem
Errors occurred, no packages were upgraded.

So I was stuck in the same place, but continue reading I found the solution which is to force the installation of the problematic package, so run something like this, depending on the package that is causing the problem in your specific case, for me the command should be:

sudo pacman -Sf xorg-server

And then,

sudo pacman -Syu

This time all was O.K.

I have also learned how good is the Arch Linux community.