Alpine local backup

When Alpine Linux boots in diskless mode, it initially only loads a few required packages from the boot device.

However, local adjustments to what-gets-loaded-into-RAM are possible, e.g. by installing a package or adjusting the configuration files in /etc. The modifications can be saved to an overlay file (.apkovl) that can be automatically loaded when booting, to restore the saved state.

The .apkovl file that contains the custom configuration can be saved to writable storage with Alpine's local backup utility lbu. By configuring a local package cache the additional packages the configuration depends on, can also be kept available on local, writable storage.

Note: If you installed Alpine in "sys" disk mode, you don't need to use lbu to save the system state. With a system disk, all modifications are written directly to disk. Nevertheless, lbu can be useful for some maintenance tasks.

Warning:

By default, an lbu commit only stores modifications below /etc, with the exception of the /etc/init.d/ directory.

However, lbu include enables modifying that set of included files, and can be used to specify additional files or folders.

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 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 use partitions on internal disks, however, you need to prepare a specific /etc/fstab entry manually, and save the configuration, as follows (setup-alpine does not list them for saving configs or package cache):

1. Boot the diskless system from ISO (as shown at Installation)
2. If necessary, create and format a partition as explained in "Setting up_disks manually, for diskless and data disk mode installs". For the examples we will use /dev/sdXY

Bug: Initramfs-init does not respect apkovl device fstab entry, so the partition can not be mounted to /boot. The workaround given there does not seem to work (e.g. mkdir -p /boot/ovl_dev/cache ; touch /boot/ovl_dev/cache/.boot_repository)

=> Alternative: Configure the /etc/fstab to mount the writable partition to /media/sdXY instead of /boot (i.e. conforming to the hot/cold-plug mountpoints):
3. mkdir /media/sdXY
4. echo "/dev/sdXY /media/sdXY ext4 noatime,ro 0 0" >> /etc/fstab
(Mounting read-only is possible, because the tools temporarily remount it writable for their operation.)
5. Use mount -a to load the partitions listed in /etc/fstab. Look at the output of mount to verify that the /etc/fstab changes have been applied correctly.
6. 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 setup-lbu sdXY and mkdir /media/sdXY/cache ; setup-apkcache /media/sdXY/cache
7. If the partition is large enough, it can be useful to edit lbu.conf to uncomment and set BACKUP_LIMIT=3. For example, to allow reverting to a previous, working state if needed.

# apk add nano # nano /etc/lbu/lbu.conf

8. Finally, generate the first .apkovl file containing all the previous changes with Alpine_local_backup, by executing lbu commit, so the customizations that were just made will persist a reboot.

From then on, whenever packages are installed or newly configured, and the changes should be kept, execute lbu commit again.

Notes:

For a virtual machine, the QEMU example shows how an ISO image can automatically boot with .apkovl customizations.
The Include special files section explains how to include custom files outside of /etc in the .apkovl file.
Alpine_Linux_package_management#Local_Cache covers managing a local package cache.
- The packages get listed in /etc/apk/world which gets saved with the lbu, for them to be automatically installed when the live system boots.
It's possible to load an APKOVL file from a webserver, by supplying a custom url with the APKOVL kernel boot parameter.
- If you don't have a web server you can run busybox's httpd temporarily to serve an .apkovl - busybox httpd -p 127.0.0.1:80.
To customize the boot sequence further, one may refer to PXE_boot#Specifying_an_apkovl and How_to_make_a_custom_ISO_image_with_mkimage.

Committing changes

The lbu tool has several subcommands to manage the .apkovl:

lbu
lbu commit (Same as 'lbu ci')
lbu package (Same as 'lbu pkg')
lbu status (Same as 'lbu st')
lbu list (Same as 'lbu ls')
lbu diff
lbu include (Same as 'lbu inc' or 'lbu add')
lbu exclude (Same as 'lbu ex' or 'lbu delete')
lbu list-backup (Same as 'lbu lb')
lbu revert

In the examples below, you will find some characters with special meaning:

| = or ('lbu commit|ci' means that you can type ether 'lbu commit' or 'lbu ci')
[ ] = optional (In 'lbu commit|ci [-nv]' you can skip the '-n', '-v' or '-nv' part if you don't want it)

Basic "commit" command

When you "commit" or save changes you've made to your system, lbu will generate a file named something like myboxname.apkovl.tar.gz ('myboxname' will be the same as the hostname). The file (which contains your modifications) is called your "apkovl". You will need to save your apkovl on suitable media (floppy, usb, cf, etc.).

usage: lbu commit|ci [-nv] [<media>]

Options:
  -d	Remove old apk overlay files.
  -e	Protect configuration with a password.
  -n	Don't commit, just show what would have been committed.
  -p <password>	Give encryption password on the command-line
  -v	Verbose mode.

The following values for <media> are supported: floppy usb
If <media> is not specified, the environment variable LBU_MEDIA will be used.

Password protection will use aes-256-cbc encryption. Other ciphers can be
used by setting the DEFAULT_CIPHER or ENCRYPTION environment variables.
For possible ciphers, try: openssl -v

The password used to encrypt the file, can be specified with the -p
option or by using the PASSWORD environment variable.

The environment variable can also be set in /etc/lbu/lbu.conf

Creating an .apkovl "package" elsewhere than on the configured media

To "commit" changes, but override the destination of the generated apkovl file, use lbu package instead of lbu commit:

usage: lbu package|pkg -v [<dirname>|<filename>]

Options:
  -v   Verbose mode.

If <dirname> is a directory, a package named <hostname>.apkovl.tar.gz will
be created in the specified directory.

If <filename> is specified, and is not a directory, a package with the
specified name will be created.

If neither <dirname> nor <filename> is specified, a package named
<hostname>.apkovl.tar.gz will be created in the current working directory.

Creating and saving an apkovl from a remote host

To create an apkovl from a client on a remote server, it's possible to use lbu package via SSH with - as the apkovl name:

On the server:

ssh root@client "lbu package -" >client.apkovl.tar.gz

Checking what will be added to your apkovl

lbu status lists what will be saved the next time you run lbu commit. Its default output is incremental, that is, it shows only the files that have changed since the last commit.
This can be overridden with the -a flag:

usage: lbu status|st [-av]

Options:
  -a    Compare all files, not just since last commit.
  -v    show include and exclude lists.

Another option is lbu list. This works like lbu status -a but the format of the output is a bit different. (It's strictly equivalent to lbu package -v /dev/null).

usage: lbu list|ls

A third option is lbu diff. This shows the same incremental changes that lbu status (without -a) does, but in a different format.

 usage: lbu diff

Include special files/folders to the apkovl

Assume you have some files you want to save permanently, but they are not located in /etc.
e.g. /root/.ssh/authorized_keys (used by sshd to authenticate ssh-users). Such files/folders can be added to lbu's include list with the following command:

usage: lbu include|inc|add [-rv] <file> ...
       lbu include|inc|add [-v] -l

Options:
  -l	List contents of include list.
  -r	Remove specified file(s) from include list.
  -v	Verbose mode.

Note: This information used to be maintained in /etc/lbu/include. Now it's maintained together with the exclude list in /etc/apk/protected_paths.d/lbu.list. Either way, the command lbu include only modifies lbu's configuration. You will need to run lbu commit to actually create/modify your apkovl.

Exclude specific files/folders from the apkovl

Assume you have some files located in /etc or one of its subfolders you do not want to save. It could be a log file or status file that for some reason isn't in /var/log/ but in a location that would otherwise be tracked by lbu. Such files/folders can be added to lbu's exclude list by manually editing the file or using the following command:

usage: lbu exclude|ex|delete [-rv] <file> ...
       lbu exclude|ex|delete [-v] -l

Options:
  -l	List contents of exclude list.
  -r	Remove specified file(s) from exclude list.
  -v	Verbose mode.

Note: As stated above, this information is now maintained in /etc/apk/protected_paths.d/lbu.list. The command lbu exclude also only modifies lbu's configuration.
You will need to run lbu commit to actually create/modify your apkovl.

Execute a script as part of a backup

Sometimes it's necessary to run a script before or after a backup. Scripts in two optional directories enable that:

/etc/lbu/pre-package.d
/etc/lbu/post-package.d

Files in those directories are run using run-script rules (meaning they must have the executable bit set, they are run in alphabetical order, and cannot contain an extension. e.g. runme works, but runme.sh does not. Also the shebang line on the first line should be indicated, e.g. #!/bin/sh .)

The scripts in pre-package.d are run before apkovl is created. Scripts in post-package.d are run after apkovl is created.

Example

Rather than adding the raw database directories to /etc/lbu/include, you can do a "database dump". e.g. postgresql:

Create /etc/lbu/pre-package.d/sqldump with the following contents:
```
pg_dumpall -U postgres | gzip -c >/root/pgdatabases.gz
```
Mark the file executable: chmod +x /etc/lbu/pre-package.d/sqldump
Create /etc/lbu/post-package.d/sqldumpdelete with the following contents:
```
rm -f /root/pgdatabases.gz
```
Mark the file executable: chmod +x /etc/lbu/post-package.d/sqldumpdelete
Finally, add the database dump file to the list of files to back up: lbu include root/pgdatabases.gz

Now when you do a lbu commit, the sql databases are dumped and gzipped to /root/pgdatabases.gz. The temporary file is deleted at the end of the lbu commit.

On a catastrophic restore, the databases are not automatically restored (that's not lbu's job), but you will find a complete database dump in the /root directory, where it can be restored manually.

P.s. These scripts are also launched when starting the commands: diff, list-backup, package, revert, status.

Multiple backup versions

Lbu can now keep multiple backups so you can revert back to older configurations. Set BACKUP_LIMIT in /etc/lbu/lbu.conf to the number of backups you want to keep.

If you've set BACKUP_LIMIT, then the previously active .apkovl will be renamed before creating the new file.

You can list the currently available backups with:

lbu list-backup [<media>]

and you can revert to an older one with:

lbu revert <filename> [<media>]

NOTE: Nothing is changed on your running system when "reverting", it only affects which apkovl is considered active at the next boot.