NOTE: This article is written for our first generation Cloud Control Panel. A version of this article is also available for our next-generation Cloud Control panel.
When should I use Rescue Mode?
If your Linux system has become non-bootable or is suffering from critical system errors, you can use Rescue Mode to recover your system data. These problems may be caused by file system corruption, boot file corruption, or other configuration errors. Normally, if your system encounters any problem during the boot process, you would boot in to a maintenance mode environment known as Single User Mode that would allow you to login with your root password and check for any errors. Unfortunately, using Single User Mode has its share of problems:
Your system is read-only and you cannot make corrective changes.
- Most services such as networking are disabled. This would prevent you from copying your data to another server.
- You would have to access your server using the Console, which is slower than using a traditional SSH login.
To avoid having to use Single User Mode, you can bring your server up in Rescue Mode through the Rackspace Cloud Control Panel.
What is Rescue mode?
Rescue mode grants the root user full access to your non-bootable server’s filesystem. You can use it to modify problems in configuration files or to copy data from your Cloud Server to a remote location. Rescue Mode through the Rackspace Cloud Control Panel is similar to booting into single-user mode with networking enabled.
Getting your server into Rescue mode
- Log in to the Rackspace Cloud Control Panel. Click on Hosting > Cloud Servers, and select the server that you want to bring up in Rescue Mode.
- From the section labeled Actions For This Server you will see the button marked Rescue.
- Once you click the Rescue button, read the information on the pop-up window which describes the Rescue Mode process, and then press the button marked Enter Rescue Mode.
- Notice that, for Linux servers, the rescue environment is limited to 90 minutes. This means that you will only have 1.5 hours to correct the problems on your server before it automatically reverts to its original state.
- The server will go through the process of building into Rescue Mode showing the progress in the Status field.
- When the Rescue Mode build is complete, the status will show "Rescue Mode" preceded by a red 'X'
Connecting to your server in Rescue Mode
- Next, you will receive an e-mail from Rackspace Cloud Support with your new temporary password to login into Rescue Mode, as seen below. This email will be sent to the Primary Contact on the account. The red arrow in this image points to the location of your temporary Rescue Mode password. You will notice that Linux servers are allowed 90 minutes in Rescue Mode, while Windows servers are allowed 24 hours.
- Once you have received the new password, you can use an SSH client to connect to your server using the public IP address and the temporary root password to login to Rescue Mode.
Troubleshooting your server in Rescue Mode
You'll get output that looks similar to what is below:
- Look at the different disk names that are found. A disk entry looks like:
Disk /dev/sdb1: 2147 MB
- This shows us the device and the size of the disk. Here is a description of the different disks in this screenshot:
- The first block, the one with the size of about 2GB, is the rescue mode filesystem.
- The second block, the one in the screenshot with a size of 10.2GB, is the server's file system. Its size will be different depending on the size of your server, of course.
- The third block will be your swap space.
- Once you've identified the block for your server's file system check out that part after "Disk" that looks like a file path. In the example above, the device is:
- That could also be "/dev/sdb1" or "/dev/xvdb1". It can be different depending on the distribution image used to build your server. Now that you know your file system's device you can assign it a directory and mount it for access. Plug your file system device into the following command in place of "/dev/diskdevice":
mount /dev/diskdevice /mnt
- For example, for /dev/sda1 the command would be:
mount /dev/sda1 /mnt
- Now you can access your files through the /mnt directory. Just remember that you'll need to put "/mnt" in front of the usual paths you'd use to get to files. For example, if you have a problem in the /etc/fstab file you need to fix, you'd actually access that file at:
- If you were to just edit "/etc/fstab" while in rescue mode you'd change the fstab for the rescue mode file system, not your normal file system.
Exiting Rescue Mode
- That’s it! Once you are done troubleshooting your system, you can exit Rescue Mode by clicking the link labeled Exit Rescue Mode in the Rackspace Cloud Control Panel under your Server Details page.
Now that we've seen different ways to connect to a Linux Cloud Server, we're going to cover some important security concepts for keeping them safe, starting with a discussion about Host Key Fingerprints.