j'ai fait les yum history undo et le probleme persiste.
j'ai profité pour noter les messages lors du xinit et le reproduire le plus fidèlement possible ci-dessous
#xinit
Xauth : file /root.serverauth.1454 does not exist
http ://bugs.freedesktop.org
http ://wiki.x.org/wiki/GitPage for a git instruction
X.org X Server 1.16.2.901 (1.16.3 RC1)
Release date 2014-12-09
Build opeating system : Linux. (.......)
Kernel command line : BOOT_IMAGE =/vmlinuz-3.17.7-300.fc21.x86_64 root=UUID=5e1d3 b03-4324-43bd_bde2-79f785321b37ro vconsile.font=latarcyrheb-sum16 rhgb quiet Lang = fr_UTF8
Build dat : 10 december 2014 12:37 AM
Build ID : xorg-x11-server 1.16.2.901-1fc21current version of pixam : 0.32.6
........
(==) Log file="/var/log/Xorg.0.log", Time =Mon Jan 19 11:05
(==) Using config directory "/usr/share/X11/xorg.conf.d"
(II) [KMS] Kernel modesetting enable
(EE) fatal server error :
(EE) no screen found (EE)
(EE) please consult http://wikei.x.org for help
(EE) please also check the logfile at :"var/log/Xorg.0.log
(EE) Server terminated with error (1). closing log file
xinit giving up
xinit unable to connect to X server : connection refused
xinit server error
et voila le contenu de la commande
# grep EE ~/var/log/Xorg.0.log
[847.266](EE) RADEON(0) : [drm] failed to set drm interface version
[847.266](EE) RADEON(0) : Kernel mode settingsetup failed
[847.266](EE) screen found, but not have a useable configuration
[847.266](EE) no screen found