Forum Linux.redhat Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

Bonjour à tous

J'ai suivi ce tuto pour upgrader une vm centos 6.4 vers 7
http://linuxsysconfig.com/2014/07/upgrade-to-centos-7/

Seulement au reboot j'obtiens ce message:
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

Je n'ai pas la main sur l'infra virtuelle, j'ai donc demandé à mon hébergeur d'effectuer les actions suivantes en rescue mode:
yum remove kernel
yum update
yum install kernel

D'après mon hébergeur ça n'a pas résolu le problème. De plus il me dit avoir laissé la vm en rescue mode.
Pourtant j'arrive à me connecter à la vm en ssh et voici ce que j'obtiens et qui me semble bizare compte tenu du rescue mode:
[root@ ~]# runlevel
N 3
You have new mail in /var/spool/mail/root
[root@prod-app01 ~]# uname -r
3.10.0-229.el7.x86_64
[root@prod-app01 ~]#
Linux prod-app01 3.10.0-229.el7.x86_64 #1 SMP Fri Mar 6 11:36:42 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
[root@prod-app01 ~]# cat /etc/centos-release
CentOS Linux release 7.1.1503 (Core)

[root@prod-app01 ~]# more /var/log/boot.log
[ OK ] Started Show Plymouth Boot Screen.
[ OK ] Reached target Paths.
[ OK ] Reached target Basic System.
[ OK ] Found device Virtual_disk.
Starting File System Check on /dev/disk/by-uuid/50f4c73a-f7d2-4302-a90c-6f59fde2315c…
[ OK ] Started dracut initqueue hook.
[ OK ] Reached target Remote File Systems (Pre).
[ OK ] Reached target Remote File Systems.
systemd-fsck[288]: /dev/sda1: clean, 304337/12984320 files, 30987473/51916544 blocks
[ OK ] Started File System Check on /dev/disk/by-uuid/50f4c73a-f7d2-4302-a90c-6f59fde2315c.
Mounting /sysroot…
[ OK ] Mounted /sysroot.
[ OK ] Reached target Initrd Root File System.
Starting Reload Configuration from the Real Root…
[ OK ] Started Reload Configuration from the Real Root.
[ OK ] Reached target Initrd File Systems.
[ OK ] Reached target Initrd Default Target.

Welcome to CentOS Linux 7 (Core)!

[ OK ] Stopped Switch Root.
[ OK ] Stopped target Switch Root.
[ OK ] Stopped target Initrd File Systems.
Stopping File System Check on /dev/disk/by-uuid/50f4c73a-f7d2-4302-a90c-6f59fde2315c…
[ OK ] Stopped File System Check on /dev/disk/by-uuid/50f4c73a-f7d2-4302-a90c-6f59fde2315c.
[ OK ] Stopped target Initrd Root File System.
[ OK ] Created slice User and Session Slice.
[ OK ] Created slice system-getty.slice.
[ INFO ] PNFS blkmaping enablement. is not active.
[DEPEND] Dependency failed for pNFS block layout mapping daemon.
Mounting RPC Pipe File System…
[ OK ] Reached target Slices.
[ OK ] Listening on /dev/initctl Compatibility Named Pipe.
[ OK ] Listening on Delayed Shutdown Socket.
Mounting Huge Pages File System…
[ OK ] Reached target Encrypted Volumes.
[ OK ] Listening on udev Kernel Socket.
[ OK ] Listening on udev Control Socket.
Starting udev Coldplug all Devices…
Starting Apply Kernel Variables…
Starting Create list of required static device nodes for the current kernel…
Mounting Debug File System…
Mounting POSIX Message Queue File System…
[ OK ] Set up automount Arbitrary Executable File Formats File System Automount Point.
Expecting device dev-disk-by\x2duuid-22a27c26\x2dbe4a\x2d4138\x2d8b…c585dc031c.device…
Starting File System Check on Root Device…
[ OK ] Stopped Trigger Flushing of Journal to Persistent Storage.
Stopping Journal Service…
[ OK ] Stopped Journal Service.
Starting Journal Service…
[ OK ] Started Journal Service.
[ OK ] Started Apply Kernel Variables.
[ OK ] Started udev Coldplug all Devices.
[ OK ] Mounted Huge Pages File System.
[ OK ] Mounted POSIX Message Queue File System.
[ OK ] Mounted Debug File System.
[ OK ] Started Create list of required static device nodes for the current kernel.
Starting Create static device nodes in /dev…
[ OK ] Started Create static device nodes in /dev.
Starting udev Kernel Device Manager…
systemd-fsck[343]: /dev/sda1: clean, 304337/12984320 files, 30987473/51916544 blocks
[ OK ] Started File System Check on Root Device.
Starting Remount Root and Kernel File Systems…
[ OK ] Started udev Kernel Device Manager.
[ OK ] Started Remount Root and Kernel File Systems.
Starting Configure read-only root support…
Starting Load/Save Random Seed…
[ OK ] Reached target Local File Systems (Pre).
Mounting /services/kpk360/media…
Mounting NFSD configuration filesystem…
[ OK ] Mounted RPC Pipe File System.
[ OK ] Started Load/Save Random Seed.
[ OK ] Mounted /services/kpk360/media.
[ OK ] Mounted NFSD configuration filesystem.
[ OK ] Started Configure read-only root support.
[ OK ] Reached target Local File Systems.
Starting Tell Plymouth To Write Out Runtime Data…
Starting Create Volatile Files and Directories…
[ OK ] Started Create Volatile Files and Directories.
Starting Update UTMP about System Reboot/Shutdown…
[ OK ] Started Update UTMP about System Reboot/Shutdown.
[ OK ] Started Tell Plymouth To Write Out Runtime Data.
[ OK ] Found device Virtual_disk.
Activating swap /dev/disk/by-uuid/22a27c26-be4a-4138-8b54-efc585dc031c…
[ OK ] Activated swap /dev/disk/by-uuid/22a27c26-be4a-4138-8b54-efc585dc031c.
[ OK ] Reached target Swap.
[ OK ] Reached target System Initialization.
[ OK ] Reached target Timers.
[ OK ] Reached target Paths.
[ OK ] Listening on RPCbind Server Activation Socket.
[ OK ] Listening on D-Bus System Message Bus Socket.
[ OK ] Reached target Sockets.
[ OK ] Reached target Basic System.
Starting IPv6 firewall with ip6tables…
Starting Dump dmesg to /var/log/dmesg…
Starting Preprocess NFS configuration…
Starting GSSAPI Proxy Daemon…
Starting D-Bus System Message Bus…
[ OK ] Started D-Bus System Message Bus.
Starting Login Service…
[ OK ] Started Preprocess NFS configuration.
[ OK ] Started Dump dmesg to /var/log/dmesg.
[ OK ] Started GSSAPI Proxy Daemon.
[ OK ] Started IPv6 firewall with ip6tables.
Starting LSB: Bring up/down networking…
[ OK ] Started Login Service.
[ OK ] Started LSB: Bring up/down networking.
[ OK ] Reached target Network.
Starting LSB: start and stop tomcat…
[ OK ] Reached target Network is Online.
Starting Notify NFS peers of a restart…
Starting Postfix Mail Transport Agent…
Starting OpenSSH server daemon…
[ OK ] Started OpenSSH server daemon.
[ OK ] Started Notify NFS peers of a restart.
[ OK ] Reached target NFS client services.
[ OK ] Reached target Remote File Systems (Pre).
[ OK ] Reached target Remote File Systems.
Starting LSB: Logentries agent for log monitoring…
Starting LSB: Start & Stop the NetVault:Backup services…
Starting Trigger Flushing of Journal to Persistent Storage…
[ OK ] Started Trigger Flushing of Journal to Persistent Storage.
Starting Permit User Sessions…
[ OK ] Started Permit User Sessions.
Starting Command Scheduler…
[ OK ] Started Command Scheduler.
Starting Job spooling tools…
[ OK ] Started Job spooling tools.
Starting Terminate Plymouth Boot Screen…
Starting Wait for Plymouth Boot Screen to Quit…

Si je suis bien en rescue mode alors comment se fait il que je sois en init 3 et que j'ai ssh, que je puisse interagir avec le système comme si il était démarré?

Dernière question comment puis-je résoudre le problème kernel panic au moment du boot?