Virtual Machine administration tips

How to mount remote filesystem with FUSE (Filesystem in USEr space) on CentOS or Ubuntu

On CentOS: - You will need to install a few packages that are not available in the standard CentOS repository. So, you must enable the EPEL repo:
```
yum install epel-release -y 
```
- Install FUSE (Filesystem in USEr space) and SSHFS packages
yum install fuse sshfs
- Load the FUSE module
```
modprobe fuse
```
- Confirm that the FUSE module is loaded
lsmod | grep fuse
fuse 84368 2
- Optionally, make sure the FUSE module is loaded upon a reboot
echo "modprobe fuse" >> /etc/rc.local
- Using SSHFS. Once the FUSE module is loaded, you can mount your remote partition using SSHFS:
sshfs user@remote_host:/remote_directory /local_mount_partition
If you have configured the login via ssh key authorization, you can use the following command:
```
sshfs user@remote_host:/remote_directory  /local_mount_partition -o IdentityFile=<absolute-path-with-key>
```
Note: If appear the following error
```
fuse: bad mount point `/local_mount_partition': Transport endpoint is not connected
```
execute: sudo fusermount -u /local_mount_partition

On Ubuntu: - First you have to install FUSE and SSHFS packages with the apt-get comand:

apt-get install fuse

apt-get install sshfs

Once the FUSE module is loaded, you can mount your remote partition using SSHFS:

sshfs user@remote_host:/remote_directory  /local_mount_partition

If you have configured the login via ssh key authorization, you can use the following command:

sshfs user@remote_host:/remote_directory  /local_mount_partition -o IdentityFile=<absolute-path-with-key>

Note: If appear the following error

fuse: bad mount point `/local_mount_partition': Transport endpoint is not connected

execute : sudo fusermount -u /local_mount_partition

How to use and configure Docker in your virtual machine

To use Docker in your virtual machine please set the MTU value at 1400 in the file /etc/docker/daemon.json. More in particular edit the file /etc/docker/daemon.json and then set

- - {
    "mtu" : 1400
    }

Rescue a Virtual Machine

Instance rescue provides a mechanism for access, even if an image renders the instance inaccessible. Two rescue modes are currently provided.

Ephemeral Virtual Machine

IMPORTANT WARNING

If the virtual machine has encrypted LUKS VOLUMES attached, it is mandatory to detach them before starting the rescue operation.

The steps needed to rescue an inaccessible ephemeral virtual machine on ADA Cloud are:

Step 0.

Create a rescuer virtual machine with a new key pair. Although this is not a fixed rule, it is suggested to create the rescuer machine using an image with same OS as the one on the inaccessible machine (same version or newer).
Login to the rescuer and update it. As an example, for Ubuntu virtual machines:
```
sudo apt update
sudo apt upgrade
```
Logout the rescuer and create a snapshot image of this virtual machine.

Step 1.

Select the instance you want to rescue and from the drop-down menu on the right select "rescue instance":
- In the menu that appears, select the image you just created from the rescuer machine.
Login via ssh to the broken machine using the rescuer username/key
Check that the boot of the machine has been correctly executed using the command
```
lsblk
```
you should see the rescuer machine (/dev/vda1) mounted and the inaccessible machine on the device /dev/vdb1

Mount such device /dev/vdb1

sudo mkdir /mnt/inaccessible_vm
sudo mount /dev/sdb1 /mnt/inaccessible_vm

Now you can access the files in the inaccessible machine to fix the problems (lsblk, fsck, xfs_repair, chroot, etc.) or backup important data
Once the operation is done, logout the virtual machine and from the Dashboard select "unrescue".

Virtual Machine booted from a Bootable Volume