Displaying boot logs in the KVM
Find out how to diagnose a VPS by checking the boot log
Find out how to diagnose a VPS by checking the boot log
Last updated 5th July 2021
If your VPS has become unresponsive, you still have the possibility to access it from your Control Panel via KVM. The quickest way to diagnose the problem is to check the boot log of the server. However, the GRUB configuration needs to be modified in order for these logs to appear.
Please note that for some environments, the KVM is unable to provide any useful information because the boot sequence occurs in the serial console, or GRUB is configured in silent mode.
This guide explains how to activate boot logs that can help with troubleshooting a VPS.
OVHcloud is providing you with services for which you are responsible, with regard to their configuration and management. You are therefore responsible for ensuring they function correctly.
If you encounter any difficulties performing these actions, please contact a specialist service provider and/or discuss the issue with our community on https://community.ovh.com/en/. OVHcloud cannot provide you with technical support in this regard.
These modifications will change the GRUB configuration. OVHcloud cannot be held responsible for any loss or damage to your data caused by these operations. Be sure to perform backups of all your important data before any modifications.
If you still have access to your VPS via SSH, you can skip to step 6.
Log in to the OVHcloud Control Panel and initiate a server reboot in rescue mode. Refer to our rescue mode guide if necessary.
On older VPS ranges, your partitions will be automatically mounted in rescue mode. You can use the following commands to verify this and identify where your partition is mounted:
~$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 5.8G 0 5.8G 0% /dev
tmpfs 1.2G 17M 1.2G 2% /run
/dev/sda1 2.4G 1.5G 788M 66% /
tmpfs 5.8G 0 5.8G 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 5.8G 0 5.8G 0% /sys/fs/cgroup
/dev/sdb1 49G 1.2G 48G 3% /mnt/sdb1
/dev/sdb15 105M 3.6M 101M 4% /mnt/sdb15
~$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 2.5G 0 disk
└─sda1 8:1 0 2.5G 0 part /
sdb 8:16 0 50G 0 disk
├─sdb1 8:17 0 49.9G 0 part /mnt/sdb1
├─sdb14 8:30 0 4M 0 part
└─sdb15 8:31 0 106M 0 part /mnt/sdb15
The example output above shows that the system partition is mounted on /mnt/sdb1. (The primary disk is sdb, whereas sda is the rescue disk and sda1 is the primary rescue partition mounted on /).
If your VPS is of the current ranges, no automatic mounting will occur and the MOUNTPOINT
column should be empty. In that case, proceed with step 4.
On a legacy VPS in rescue mode, the primary disk is already mounted. Therefore, it first needs to be unmounted before remounting it in step 4:
~$ umount /dev/sdb1
If your VPS is of the current ranges, first make sure the mount folder is created:
~$ mkdir -p /mnt/sdb1
Enter the following commands to mount the partition with the appropriate settings:
~$ mount /dev/sdb1 /mnt/sdb1
~$ mount -t proc none /mnt/sdb1/proc
~$ mount -o bind /dev /mnt/sdb1/dev
~$ mount -t sysfs none /mnt/sdb1/sys/
The system partition is now mounted for use with the chroot
command, in order to carry out actions that require access to the sys
, dev
and proc
directories.
You now need to access and edit the GRUB files of your system. You can do this by using the chroot
command:
~$ chroot /mnt/sdb1
From now on, all commands that you enter will be applied to your VPS instead of the temporary rescue mode environment.
Create a backup copy of the config file:
~$ cp /etc/default/grub /root/grub.backup
In order to access the boot log with the KVM console, make sure you have the following value inside the file /etc/default/grub
:
GRUB_CMDLINE_LINUX_DEFAULT="console=ttyS0 console=tty0"
If this line is missing or different, modify the file with an editor and save it.
Then use the following command to regenerate the GRUB configuration file (the changes will be saved for the next reboot):
~$ update-grub
Create a backup copy of the config file:
~$ cp /etc/default/grub /root/grub.backup
In order to access the boot log with the KVM console, make sure you have the following values inside the file /etc/default/grub
:
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="console=ttyS0,115200n8 no_timer_check net.ifnames=0 crashkernel=auto rhgb"
GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0"
If these lines are missing or different, modify the file with an editor and save it.
Then use the following command to regenerate the GRUB configuration file (the values will be saved for the next reboot):
~$ grub2-mkconfig -o "$(readlink /etc/grub.cfg)"
Once you have done the modifications, reboot your VPS in 'normal' mode in your OVHcloud Control Panel. Boot log information should now appear when using the KVM console.
Activating rescue mode on a VPS
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