Server recovery

Available in VPC

This document describes how to recover a server that does not boot properly.

Enter Single Mode

For any of the following situations, enter Single mode and recover the server.

• Lost admin password
• Problem occurred in Using fstab

You can enter Single mode and recover the server as follows:

1. Select a server to boot from the server list, and then click the [Force stop] button.
   
2. Click [Start] to boot the stopped server, and click the [Server connection console] button.
   
3. Check how to enter Single mode for each OS to perform the server recovery procedures.
   • CentOS
   • Ubuntu

Enter CentOS Single Mode

You can enter single mode in CentOS and recover the server as follows:

1. Enter e in the Select Kernel version page to enter the Edit booting parameter page.
   
2. Edit the parameter as follows, press [Ctrl] + [x], and start the OS with the edited booting parameter.
   • Edit ro into rw init=/sysroot/bin/bash.
   • Delete rhgb quiet.
     
3. Enter single mode.
   
4. Run the following commands and mount the partition region of the server.

   :/# chroot /sysroot
   

Enter Ubuntu Single Mode

You can enter single mode in Ubuntu and recover the server as follows:

1. Enter e in the Select Kernel version page to enter the Edit booting parameter page.
   
2. Edit the parameter as follows, press [Ctrl] + [x], and start the OS with the edited booting parameter.
   • Edit ro into rw single init=/bin/bash.
     
3. Enter single mode.
   

Change the boot kernel

You can change the boot kernel for each OS and recover the server as follows:

• CentOS
• Ubuntu

Change the CentOS boot kernel

The following describes how to change the boot kernel in CentOS. In this section, it is described with the example of changing the boot kernel into CentOS Linux (3.10.0-1127.19.1.el7.x86_64) 7 (Core).

1. Run the following commands to check the current kernel settings.

   [root@centos ~]# grub2-editenv list
   saved_entry=CentOS Linux (3.10.0-1127.el7.x86_64) 7 (Core)
   

2. Run the following command to check the kernel list.

   [root@centos ~]# grep ^menuentry /boot/grub2/grub.cfg | cut -d "'" -f2
   CentOS Linux (3.10.0-1127.19.1.el7.x86_64) 7 (Core)
   CentOS Linux (3.10.0-1127.el7.x86_64) 7 (Core)
   CentOS Linux (0-rescue-4bfdd392cea14cb58d22427c1c69c5df) 7 (Core)
   

3. Change the default boot kernel settings, run the following command, and check the changed kernel settings.

   [root@centos ~]# grub2-set-default "CentOS Linux (3.10.0-1127.19.1.el7.x86_64) 7 (Core)"
   
   [root@centos ~]# grub2-editenv list
   saved_entry=CentOS Linux (3.10.0-1127.19.1.el7.x86_64) 7 (Core)
   

4. Reboot the server, run the following command, and check the kernel.

   [root@centos ~]# reboot
   
   [root@centos ~]# uname -r
   3.10.0-1127.19.1.el7.x86_64
   

Change the Ubuntu boot kernel

The following describes how to change the boot kernel in Ubuntu. In this section, it is described with the example of changing the boot kernel into 4.15.0-118-generic.

1. Run the following commands to check the current kernel settings.

   root@ubuntu:~# cat /etc/default/grub | grep GRUB_DEFAULT
   GRUB_DEFAULT=0
   

2. Run the following command to check the kernel list.

   root@ubuntu:~# awk -F"--class" '/menuentry/ && /with Linux/ {print $1}' /boot/grub/grub.cfg | awk '{print i++ " : " $5,$6,$7,$8}' | sed -e "s/'/ /g"
   0 : 4.15.0-118-generic    
   1 : 4.15.0-118-generic (recovery mode)  
   2 : 4.15.0-76-generic    
   3 : 4.15.0-76-generic (recovery mode)
   

3. Change the default boot kernel settings, run the following command, and check the changed kernel settings.

   root@ubuntu:~# vi /etc/default/grub
   
   root@ubuntu:~# grub-set-default 0
   Searching for GRUB installation directory ... found: /boot/grub
   
   root@ubuntu:~# grub-editenv list
   saved_entry=0
   
   root@ubuntu:~# update-grub
   Sourcing file `/etc/default/grub'
   Generating grub configuration file ...
   Found linux image: /boot/vmlinuz-4.15.0-118-generic
   Found initrd image: /boot/initrd.img-4.15.0-118-generic
   Found linux image: /boot/vmlinuz-4.15.0-76-generic
   Found initrd image: /boot/initrd.img-4.15.0-76-generic
   Found linux image: /boot/vmlinuz-4.15.0-22-generic
   Found initrd image: /boot/initrd.img-4.15.0-22-generic
   done
   

4. Reboot the server, run the following command, and check the kernel.

   root@ubuntu:~# reboot
   
   root@ubuntu:~# uname -r
   4.15.0-118-generic
   

How to recover data through snapshot when the server cannot be recovered

If the server cannot be recovered by entering Single mode or changing boot kernel, you can recover stored data by creating a new storage in the server you want using a created snapshot.
The following describes how to recover the data using the snapshot.

1. Create a snapshot.

   • See Create snapshot

2. Create a storage using snapshot and mount it in the server.

   • See Create storage with snapshot
   Note

   • Since the storage data is read and recovered from the snapshot, skip the disk partition and storage format tasks.
   • If a snapshot was created from another server's default storage for booting or from one of the existing storages of a server with added storage, the identifiers of the original server's storage and the created storage will overlap, making mounting impossible.
   • See Change storage identifier and change the created storage's identifier.

3. Connect to the path to mount the storage and recover the data.