How to Use Rescue Mode on a Dedicated Server – Articles

Rescue Mode allows you to check the health of your Dedicated Server's hardware and connect to it via SSH to perform different troubleshooting tasks; a few of which are as follows:

Launch an fsck/e2fsck
Access the file system
Fix misconfigurations
Backup data
Check hardware devices

This article will walk you through the basics of using Rescue Mode.

Requirements

Getting Started with SSH
General Knowledge of Terminal

Booting in Rescue Mode

Log in to the OVHcloud Manager and select Bare Metal Cloud on the left-hand sidebar. Click Dedicated and virtual servers and choose the Dedicated servers option. Select your server on the ensuing page.

On the "Server status" page, click ... next to "Boot" and select Edit from the drop-down menu. On the ensuing screen, select the Boot in rescue mode option and then select rescue64-pro from the "Rescue available" drop-down menu.

After changing the boot setting, navigate to the "Service status" box and click the ... button next to "Status". Select Restart from the drop-down menu.

The server is now in Rescue Mode. Next, you will receive an email that contains new credentials to access the server via SSH. The email will also contain a link to a web interface from which you can perform various hardware tests. For more information about this, please check out the Performing a Hardware Check section of this article.

NOTE: If you do not see the email within five minutes of rebooting your server, please check your Spam folder.

When you are finished working in Rescue Mode, return to the OVHcloud Manager in your browser, change the "Boot" option back to "Boot from the hard disk" and then restart your server.

Mounting the Partition

To SSH into your server use the login credentials that were received via email. For more information regarding SSH, please check out our Getting Started with SSH article.

Once connected, locate the storage device for your Dedicated server, then mount it to the Rescue Mode environment.

Examples of the standard naming convention for different storage are:

/dev/sdX for SCSI and SATA devices
/dev/nvmeXnX for NVMe devices
/dev/mdX for RAID devices

NOTE: Please keep in mind that by default the storage for the Dedicated server is configured to use RAID 1 (mirroring), so the device address will be: /dev/mdX.
If, during the installation of the operating system, you opted out of using RAID, then the device address (e.g. /dev/sdX) and the partition will need to be mounted.

To view the storage devices that your server has, use the parted utility. Below is an example of the command and its output:

$ parted -l

Sample Output:

Model: ATA HGST HUS724020AL (scsi)
Disk /dev/sda: 2000GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name     Flags
 1      1049kB  537MB   536MB   fat32           primary  boot, esp
 2      537MB   1073MB  536MB   ext4            primary  raid
 3      1073MB  2000GB  1999GB  ext4            primary  raid
 4      2000GB  2000GB  536MB   linux-swap(v1)  primary

Model: ATA HGST HUS724020AL (scsi)
Disk /dev/sdb: 2000GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name     Flags
 1      1049kB  537MB   536MB   fat32           primary  boot, esp
 2      537MB   1073MB  536MB   ext4            primary  raid
 3      1073MB  2000GB  1999GB  ext4            primary  raid
 4      2000GB  2000GB  536MB   linux-swap(v1)  primary

Model: Linux Software RAID Array (md)
Disk /dev/md2: 536MB
Sector size (logical/physical): 512B/512B
Partition Table: loop
Disk Flags: 

Number  Start  End    Size   File system  Flags
 1      0.00B  536MB  536MB  ext4

Model: Linux Software RAID Array (md)
Disk /dev/md3: 1999GB
Sector size (logical/physical): 512B/512B
Partition Table: loop
Disk Flags: 

Number  Start  End     Size    File system  Flags
 1      0.00B  1999GB  1999GB  ext4

Example: As per the output, the server is equipped with two SCSI disks (/dev/sda & /dev/sdb) in a software RAID configuration (/dev/md3). All are highlighted in red in the sample output above.

After identifying the storage device, create a root directory within the /mnt directory, then use the mount command to add it to the Rescue Mode environment:

# mkdir /mnt/root

# mount /dev/mdX /mnt/root

Lastly, navigate to the newly mounted device:

# cd /mnt/root

You now have access to the entire file system.

chroot and Changing Your Password

Although you can edit the files in the /mnt/root directory, certain commands require root privileges on the system that is installed on the disk. Thus, change the apparent root directory to the directory in which we stored our files using the following command:

# chroot /mnt/root

You can now run commands on your mounted filesystem.

Now, we are able to change the root password using the following command:

# passwd root

NOTE: In this example, we are changing the password for the user root. If you wish to change a password for a different user, replace "root" in the command above with the username whose password you wish to change.

If you wish to change the password for a different user just append the username to the end of the above command and it will change the password for that user. If you don't specify a user, as we did above, you are changing the root password by default.

Conclusion

Rescue Mode is an important tool that can be used to perform maintenance on your own schedule or to reverse critical errors made during normal server administration. Having read this article, you should have a basic familiarity with how to get started using Rescue Mode with a Dedicated server.

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