guide.en-us.md

title	excerpt	updated
How to activate and use rescue mode	Find out how to use the OVHcloud customer rescue system to troubleshoot your dedicated server	2025-01-20

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Objective

Rescue mode is a tool provided by OVHcloud that allows you to boot into a temporary operating system for the purpose of diagnosing and resolving issues on your server.

Usual tasks the rescue mode is appropriate for include:

• Resetting your user password
• Diagnosing network problems
• Repairing a broken operating system
• Fixing a software firewall misconfiguration
• Testing disk performance
• Testing CPU and RAM

Warning

Backing up your data should be the first step in rescue mode if you do not already have recent backups available.

If you have any services still online, rescue mode will interrupt them as the machine is being rebooted into the auxiliary rescue environment.

This guide explains how to boot a server into rescue mode and how to use it.

Requirements

• A dedicated server in your OVHcloud account
• Access to the OVHcloud Control Panel

Instructions

To use rescue mode, you need to edit the sever's Netboot setting. Then the server has to be restarted.

Log in to your OVHcloud Control Panel, open the Bare Metal Cloud{.action} section and then Dedicated servers{.action}.

Click on your server's name to open the General information{.action} tab.

Activating rescue mode

In the General information box, click the button ...{.action} next to Boot. Click on Edit{.action} in the context menu.

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1: Rescue mode options

On the page Change the netboot, select Boot in rescue mode{.action}.

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The available options for rescue mode depend on the server type and the operating system installed.

• Customer rescue system (always available)
• Rescue system for Windows (available for Windows servers)
• iPXE / ipxe-shell (external open-source tool, always available)
• Legacy Windows rescue system (deprecated WinPE system, only relevant if your server does not meet the requirements for the current rescue system for Windows)

[!primary]

The instructions below will only cover the customer rescue system which is the most commonly used option.

Please refer to our dedicated guide for a detailed explanation on using the rescue system for Windows.

Select Customer rescue system{.action} in the drop-down menu.

2: Authentication options

The next choice determines the method of authentication for the SSH connection to the rescue mode system. This is mainly a matter of convenience since each rescue mode session is meant to be transitory and will be discarded once you reboot the server from its disk.

• Password authentication: You will be sent login credentials via email.
• Key authentication: You can use a public authentication key of your choice (compatible formats: RSA, ECDSA, ED25519).

Click on the relevant tab for your connection method:

[!tabs] Password authentication

Click Password authentication{.action}.

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The rescue mode notification email including its login details will be sent to the contact email address of your OVHcloud account. To use a different email address, enter it in the field Send new login details to the following email address.

Click Next{.action}.

Key authentication

Click Authentication via SSH key{.action}.

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You have two options:

• Select a key from the drop-down menu. You need to have at least one public key stored in the OVHcloud Control Panel already.
• Manually copy the public key string and paste it into the field Your Public SSH key.

To find out more about this topic, consult our guides:

• How to create and use keys for SSH authentication
• How to create and use keys for SSH authentication with PuTTY

[!success] You can add a default public key for the customer rescue system to a server via the OVHcloud API. See the guide section below for details.

Click Next{.action}.

3: Final steps to activate rescue mode

In the Summary step, click Confirm{.action}.

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You should now have a notification regarding the Netboot setting in the General information{.action} tab.

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The final step is to restart the server. Click the button ...{.action} next to "Status" in the Service status box, then click Restart{.action}. Click Confirm{.action} in the popup window.

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This "hard reboot" will take a few minutes to complete. You can check the current status in the tab named Tasks{.action}.

[!primary]

After you have finished your actions in rescue mode, remember to change the Netboot setting back to Boot from the hard disk{.action} before restarting the server.

Accessing your server in rescue mode via SSH

Once you have received the email informing you that rescue mode is enabled, you can log on to the rescue mode system and access your server.
This email is also available in your OVHcloud Control Panel as soon as it is sent. Click on the name associated with your NIC handle (Customer ID) in the menu bar in the top right-hand corner, then select Service emails{.action}.

[!primary]

Your SSH client will normally block the connection at first due to a mismatch of the ECDSA fingerprint. This is normal because the rescue mode uses its own temporary SSH server. To resolve this, you need to edit the file known_hosts of your local .ssh folder.
You have two options:

• Delete the fingerprint from the file. Your SSH client will then add a new fingerprint entry for the server when you are no longer using rescue mode. For a detailed explanation, refer to the section "Login and fingerprint" in our SSH introduction guide.

• Temporarily disable the fingerprint. Open the file known_hosts with a text editor and identify the fingerprint string of your server by its IP address. Add the character # at the start of the line. As a result, this line is now a "comment" and will be ignored by applications reading the file. Remember to revert this change before switching the Netboot back to the "normal" mode.

Click on the relevant tab for your selected connection method:

[!tabs] Password authentication

Open the command line application on your local device and enter the following command:

ssh root@SERVER_IP

Example:

ssh [email protected]

Enter the temporary rescue mode password when prompted.

[email protected]'s password:
root@rescue-customer-eu (ns9356771.ip-203-0-113.eu) ~ #

Find more information about SSH connections in our SSH introduction guide.
You can also use any SSH connection tool, such as PuTTY.

Key authentication

Open the command line application on your local device and enter the following command:

ssh -i USER_FOLDER/.ssh/KEY_FILE_NAME root@SERVER_IP

Example:

ssh -i ~/.ssh/MyAuthKey [email protected]

If prompted, enter your password to decrypt the private key file.

To learn more about this topic, consult our guides:

• How to create and use keys for SSH authentication
• How to create and use keys for SSH authentication with PuTTY

Mounting partitions to access your files

Unless you intend to configure the server's disks in a way that requires them to be detached (unmounted), you need to first mount the system partition in order to access your data from rescue mode.

Firstly, list all partitions in order to retrieve the name of the partition you need to mount:

lsblk

Output examples:

NAME      MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
sda         8:0    0  1.8T  0 disk
├─sda1      8:1    0  511M  0 part
├─sda2      8:2    0  1.8T  0 part
│ └─md127   9:127  0  1.8T  0 raid1
├─sda3      8:3    0  512M  0 part
└─sda4      8:4    0    2M  0 part
sdb         8:16   0  1.8T  0 disk
├─sdb1      8:17   0  511M  0 part
├─sdb2      8:18   0  1.8T  0 part
│ └─md127   9:127  0  1.8T  0 raid1
└─sdb3      8:19   0  512M  0 part

NAME        MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
nvme1n1     259:0    0 894.3G  0 disk
├─nvme1n1p1 259:2    0   511M  0 part
├─nvme1n1p2 259:3    0     1G  0 part
│ └─md2       9:2    0  1022M  0 raid1
├─nvme1n1p3 259:4    0 892.3G  0 part
│ └─md3       9:3    0 892.1G  0 raid1
└─nvme1n1p4 259:5    0   512M  0 part
nvme0n1     259:1    0 894.3G  0 disk
├─nvme0n1p1 259:6    0   511M  0 part
├─nvme0n1p2 259:7    0     1G  0 part
│ └─md2       9:2    0  1022M  0 raid1
├─nvme0n1p3 259:8    0 892.3G  0 part
│ └─md3       9:3    0 892.1G  0 raid1
├─nvme0n1p4 259:9    0   512M  0 part
└─nvme0n1p5 259:10   0     2M  0 part

Then mount the pertinent partition accordingly:

mount /dev/PARTITION_NAME /MOUNT_POINT/

The partition to mount should be easily identifiable by the SIZE indicated in the table (sda2 in the first example, nvme1n1p3 in the second). However, in a softRAID configuration (a default raid1 in the examples), you will need to use the identifier of the RAID volume (mdX).
Using the folder name mnt as mount point, for the first example the mount command would therefore be as follows:

mount /dev/md127 /mnt/

Command to enter for the second example:

mount /dev/md3 /mnt/

Warning

The examples above are merely illustrating the necessary steps based on a typical server configuration. The information in the output table depends on your server's hardware and its partition scheme. When in doubt, consult the documentation of your operating system.

If you require professional assistance with server administration, consider the details in the Go further section of this guide.

To see more technical information about the server's disks and partitions, enter:

fdisk -l

Some tasks may require that disks or partitions are detached. To do this, use the unmount command:

umount /mnt

VMware - Mounting a datastore

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You can mount a VMware datastore in a similar way as described in the previous segment.

List your partitions in order to retrieve the name of the datastore partition:

lsblk

fdisk -l

Mount the partition with the following command, replacing sdbX with the value identified in the previous step:

vmfs-fuse /dev/sdbX /mnt

If you have VMFS 6 datastores, access the sbin folder and create the mount folder:

cd /usr/local/sbin/
mkdir /mnt/datastore

List your partitions in order to retrieve the name of the datastore partition:

lsblk

fdisk -l

Mount the partition with the following command, replacing sdbX with the value identified in the previous step:

vmfs6-fuse /dev/sdbX /mnt/datastore/

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Once the mounting operation is done, you can access your files and carry out troubleshooting tasks inside the folder you have defined as mount point. Example:

cd /mnt

Certain operations on the file system (such as configuring user accounts) will require an additional step. Create a temporary chroot environment at the mount point with this command:

chroot /mnt/

You should now be able now apply all necessary changes to your system, for example to regain server access.

Exiting rescue mode

If relevant, return to the rescue mode login shell by entering:

exit

In your OVHcloud Control Panel, change the boot mode back to Boot from the hard disk{.action} and confirm.

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You can now restart the server from the rescue mode shell:

reboot

Alternatively, use the Restart{.action} function in the OVHcloud Control Panel.

How to add a default authentication key for rescue mode

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To speed up the process, you can add a public key as default for rescue mode SSH access to your server. This is only possible via the OVHcloud API.

To do this in the API web console, open the following API endpoint:

[!api]

@api {v1} /dedicated/server PUT /dedicated/server/{serviceName}

Enter the internal name of your server (ns1111111.ip-203-0-113.eu) in the appropriate field.

Then edit the text field below as follows:

{
  "rescueSshKey": "string"
}

Replace string with your full public key string.

The result should look as shown in the following example:

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When you have entered your values correctly, click the button EXECUTE{.action}.

The field Your Public SSH key: will now be filled automatically with this key string when changing the Netboot mode.

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Legacy Windows rescue system (WinPE rescue mode)

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Once you have received the email informing you that rescue mode is enabled, you can log on to the rescue mode system and access your server.
This email is also available in your OVHcloud Control Panel as soon as it is sent. Click on the name associated with your NIC handle (Customer ID) in the menu bar in the top right-hand corner, then select Service emails{.action}.

To use the Windows PE rescue mode GUI, you will need to download and install a VNC console or use the IPMI module (not available on all server models).

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The following tools are already installed in this mode:

Tool	Description
Mozilla ULight	A web browser.
Memory Diagnostics Tool	A Windows tool to test the RAM.
Explorer_Q-Dir	An alternative file explorer.
GSmartControl	A tool to check HDDs and SSDs.
PhotoRec	A tool to recover possibly lost files from a disk.
SilverSHielD	A SSH2 and SFTP server.
System Recovery	The built-in Windows system restore and troubleshooting tool.
TestDisk	A powerful data recovery application. You can use it to recover and modify corrupted partitions, find lost partitions, repair a boot sector and even rebuild a defective MBR.
FileZilla	An open-source FTP client. It supports SSH and SSL protocols, and has a clear and intuitive drag-and-drop interface. You can use it to transfer your data to an FTP server, like the FTP backup service included with most OVHcloud server models.
7-Zip	A utility for compressing and archiving files, which reads the following formats: ARJ, CAB, CHM, CPIO, CramFS, DEB, DMG, FAT, HFS, ISO, LZH, LZMA, MBR, MSI, NSIS, NTFS, RAR, RPM, SquashFS, UDF, VHD, WIM, XAR and Z. You can also use it to create your own archives in the following formats: BZIP2, GZIP, TAR, WIM, XZ, Z and ZIP.

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Go further

How to use the rescue mode for Windows

How to recover server access if your user password is lost

How to replace your authentication keys for SSH access if a key is lost

How to configure and rebuild software RAID

How to diagnose server hardware issues

How to use the IPMI console with a dedicated server

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