Add or Update the Fstab File

Abstract

This page provides further information for customizing the /etc/fstab file which controls the mounting of filesystems at boot time.

In KIWI NG, all major filesystems that were created at image build time are handled by KIWI NG itself and setup in /etc/fstab. Thus there is usually no need to add entries or change the ones added by KIWI NG. However depending on where the image is deployed later it might be required to pre-populate fstab entries that are unknown at the time the image is build.

Possible use cases are for example:

• Adding NFS locations that should be mounted at boot time. Using autofs would be an alternative to avoid additional entries to fstab. The information about the NFS location will make this image specific to the target network. This will be independent of the mount method, either fstab or the automount map has to provide it.

• Adding or changing entries in a read-only root system which becomes effective on first boot but can’t be added at that time because of the read-only characteristics.

Note

Modifications to the fstab file are a critical change. If done wrongly the risk exists that the system will not boot. In addition this type of modification makes the image specific to its target and creates a dependency to the target hardware, network, etc… Thus this feature should be used with care.

The optimal way to provide custom fstab information is through a package. If this can’t be done the files can also be provided via the overlay file tree of the image description.

KIWI NG supports three ways to modify the contents of the /etc/fstab file:

Providing an /etc/fstab.append file

If that file exists in the image root tree, KIWI NG will take its contents and append it to the existing /etc/fstab file. The provided /etc/fstab.append file will be deleted after successful modification.

Providing an /etc/fstab.patch file

The /etc/fstab.patch represents a patch file that will be applied to /etc/fstab using the patch program. This method also allows to change the existing contents of /etc/fstab. On success /etc/fstab.patch will be deleted.

Providing an /etc/fstab.script file

The /etc/fstab.script represents an executable which is called as chrooted process. This method is the most flexible one and allows to apply any change. On success /etc/fstab.script will be deleted.

Note

All three variants to handle the fstab file can be used together. Appending happens first, patching afterwards and the script call is last. When using the script call, there is no validation that checks if the script actually handles fstab or any other file in the image rootfs.