This element insert a helper script in the image that allows users to dynamically configure credentials at boot time. This is specially useful for troubleshooting.
Troubleshooting an image can be quite hard, specially if you can not get
a prompt you can enter commands to find out what went wrong. By default,
the images (specially ramdisks) doesn’t have any SSH key or password for
any user. Of course one could use the
devuser element to generate
an image with SSH keys and user/password in the image but that would be
a massive security hole and very it’s discouraged to run in production
with a ramdisk like that.
This element allows the operator to inject a SSH key and/or change the root password dynamically when the image boots. Two kernel command line parameters are used to do it:
If the operator append sshkey=”$PUBLIC_SSH_KEY” to the kernel command line on boot, the helper script will append this key to the root user authorized_keys.
If the operator append rootpwd=”$ENCRYPTED_PASSWORD” to the kernel command line on boot, the helper script will set the root password to the one specified by this option. Note that this password must be encrypted. Encrypted passwords can be generated using the
opensslcommand, e.g: openssl passwd -1.
The value of these parameters must be quoted, e.g: sshkey=”ssh-rsa BBBA1NBzaC1yc2E …”
Some base operational systems might require selinux to be in
permissive or disabled mode so that you can log in
the image. This can be achieved by building the image with the
selinux-permissive element for diskimage-builder or by passing
selinux=0 in the kernel command line. RHEL/CentOS are examples
of OSs which this is true.