View source for Diskless Mode

In Diskless mode the entire operating system with all applications are first loaded into RAM and then only run from there. This is the method already used to boot the Alpine Linux <Code>iso</Code> installation images. Alpine Linux can be installed and configured so that the system continue to boot like this if "disk=none" is specified while running the <code>[[Alpine_setup_scripts#setup-alpine|setup-alpine]]</code> script. 

The mode is extremely fast and can save on unnecessary disk spin-ups, power, and wear. It is similar to what other linux distributions may call a "frugal" install or boot into with a "toram" option. 

Custom configurations may be preserved or "persist" across reboots by using the Alpine local backup tool <code>[[Alpine_local_backup|lbu]]</code>. It enables committing and reverting local configuration system state by using '''.apkovl''' files that are saved to a "local backup" location i.e a writable partition and loaded when booting. 
<!--
* The initial and possibly read-only installation media can remain the only boot device for the  "diskless" system. 

* Using the <code>[[Alpine_setup_scripts#setup-bootable|setup-bootable]]</code> script, it is also possible to [[Create_a_Bootable_Device|create a customizable boot device]] i.e a writable filesystem by copying the boot system from the read-only installation media to a writable partition (e.g. /dev/sdXY).
-->
== Installation  ==

<code>Setup-alpine</code> script stores the configs on a writable partition using <code>[[Alpine_local_backup|lbu]]</code>.
Use <code>[[Alpine_setup_scripts#setup-lbu|setup-lbu]]</code> script to configure a "local backup" location for the [[#Diskless Mode|diskless]] system, and <code>[[Alpine_local_backup|lbu commit]]</code> to then save the local configuration state as an .apkovl file. 

Later, another directory on that same partition or another available partition may also be mounted as /home, or for example, for selected important applications to keep their run-time and user data on it. If additional or updated packages have been added to the system, these may also be made available for automatic (re)installation during the boot phase without any (re)downloading, by enabling a [[Alpine_Package_Keeper#Local_Cache|local package cache]] on the writable storage.

If a writable partition is available, <code>setup-alpine</code> can be told to store the configs and the package cache on that writable partition. As per Bug: [https://gitlab.alpinelinux.org/alpine/alpine-conf/-/issues/10473 #10473] storing local configs and the package cache on '''internal disks''' requires manual steps listed under [[#Saving_and_loading_ISO_image_customizations| Saving and loading ISO image customizations]]  '''before''' running <code>[[Alpine_setup_scripts#setup-alpine|setup-alpine]]</code> script.

== Saving and loading ISO image customizations ==
<!--
Besides supporting a boot parameter to load customizations from a web server, Alpine's "diskless mode" ISO images try to load an .apkovl volume from system partitions. It is therefore possible to save customized running states to a .apkovl file on a writable partition, and have these automatically loaded when booting the ISO image.

{{Note|When the machine reboots, the remote repositories will not be available until after networking has started. That means packages newer than on your local boot media would not be available after a reboot, unless they were made to persistent, by having a [[#Local Cache|local package cache]] available on a local, writable, storage device.}}

The local package cache, which enables additional and updated packages to automatically be copied into RAM during boot, may be stored on the same partition as the .apkovl file.
-->

To save customized running states to a .apkovl file on a writable partition on internal disks, and have these automatically loaded when booting the boot device i.e ISO image, the following steps are needed to manually prepare a specific /etc/fstab entry, and save the configuration, as follows:
# Boot the diskless system from ISO and follow the [[Installation#Installation_Step_Details|Installation steps]] to complete the [[Installation#Base_configuration|base configuration]]. Now the pre-setup of [[#Diskless_Mode|"diskless"]] Alpine Linux system is considered complete.<br>  
# If necessary partition(s) are unavailable, manually [[Setting_up_disks_manually#Creating_partitions|create]] a partition. For the steps, we will use /dev/sdXY<br>
## Due to Bug: {{Issue|11589|The APKOVL loading of diskless setups doesn't work on btrfs and xfs filesystems, or nvme-based devices}}. So use only ext4 filesystem partitions on classic drives to store diskless mode states.
##  mkfs.ext4 creates ext4 filesystem with 64bit feature enabled by default, but extlinux may not be able to boot with that due to Issue {{Issue|14895}}. You may need to add "-O ^64bit" to mkfs.ext4 to circumvent this. The below command creates an ext4 partition with disabled journaling, to reduce write operations and allow the disk to spin down after the .apkovl and the packages have been read from the partition during the boot. 
#: {{Cmd|mkfs.ext4 -O ^has_journal,^64bit /dev/sdXY}}
# Due to a [https://gitlab.alpinelinux.org/alpine/mkinitfs/-/issues/5 bug], the partition can not be mounted to /boot. Configure the /etc/fstab to mount the writable partition to /media/sdXY instead of /boot i.e. conforming to the hot/cold-plug mountpoints. <br>
#: {{Cmd|mkdir /media/sdXY}}
#: {{cmd|echo "/dev/sdXY /media/sdXY ext4 noatime,ro 0 0" >> /etc/fstab}}
<!-- Mounting read-only is possible, because the [[Alpine_local_backup|lbu tools]] can temporarily remount it writable for their operation. -->
# Use {{Codeline|<code>mount -a</code>}} to load the partitions listed in {{Path|/etc/fstab}}. Look at the output to verify that the changes have been applied correctly.<br>
# If setup-alpine has not run before, it may be used and should now enable you to choose the partition for saving the local configs and package cache. 
<!-- If asked, there is no need to first unmount the partition, that would only be needed to allow installing on its parent disk.-->
# If setup-alpine has already been used to configure the diskless system, the storage settings may be modified directly with
#: {{cmd|setup-lbu sdXY}} 
# [[Alpine_Package_Keeper#Local_Cache|Local package cache]] can be enabled as follows:
#: {{cmd|mkdir /media/sdXY/cache}} 
#: {{cmd|setup-apkcache /media/sdXY/cache}}
# If the partition is large enough, it can be useful to edit {{Path|lbu.conf}} to uncomment and set {{Codeline|BACKUP_LIMIT{{=}}3}}. For example, to allow reverting to a previous, working state if needed. 
#: {{cmd|apk add nano}}
#: {{cmd|nano /etc/lbu/lbu.conf }}
# Finally, generate the first .apkovl file containing all the previous changes by executing <code>lbu commit</code>, so the customizations that were just made will persist a reboot.
#: {{cmd|lbu commit}}
# From now on, whenever packages are installed or newly configured, and the changes should be kept, execute <code>lbu commit</code>.

== Customizable boot device == 
{{Main|Create a Bootable Device}}
In the [[#Saving and loading ISO image customizations|above case]], the initial read-only installation media may remain the only boot device for the newly configured local "diskless" system.  It is possible to copy the boot system to a partition (e.g. /dev/sdXY) with <code>[[Alpine_setup_scripts#setup-bootable|setup-bootable]]</code> script and [[Create_a_Bootable_Device|create a customizable boot device]].

<!--
The below information is partially available in LBU page [[Alpine_local_backup#Creating_and_saving_an_apkovl_from_a_remote_host]]
It's possible to load an APKOVL file from a webserver, by supplying a custom url with the <code>APKOVL</code> kernel boot parameter. If you don't have a web server you can run busybox's httpd temporarily to serve an .apkovl - <code>busybox httpd -p 127.0.0.1:80</code>.
-->
== See Also ==
* [[Alpine_local_backup|Alpine Local backup Utility - ''lbu''']]
* [[Alpine_Package_Keeper#Local_Cache|Local package cache]]
* [[Manually editing a existing apkovl]]
* [[Back Up a Flash Memory Installation]]
* [[Alpine_Package_Keeper#Upgrading_"diskless"_and_"data"_disk_mode_installs|Upgrading Diskless Packages including Kernel upgrade]]
* [[Upgrading_Alpine#Upgrading_Alpine_Linux_on_other_removable_media_(such_as_CF/USB)|Upgrading Diskless to New Alpine Linux Release]]
* [[PXE boot#Specifying an apkovl|Diskless PXE Boot]]
* [[How to make a custom ISO image with mkimage]]
* [[QEMU#Live_mode|QEMU Diskless example]] 
* [[Alpine local backup#Include special files.2Ffolders to the apkovl|Include special files section]] - To include custom files outside of <code>/etc</code> in .apkovl file.

[[Category:Diskless]] [[Category:LBU]]