How to use xdelta and download only differential update files

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For those having a slow connection, it is possible to download a smaller differential file that contains only the new Alpine Linux version changes. If you have an ISO file of the version immediately prior to the latest version, you can then use the downloaded xdelta file to update to the latest ISO. You will still need to download the new ISO checksum file and test the integrity of the newly built ISO file. For xdelta to work you should have the three files on the same directory level, i.e.: alpine-1.10.3-1.10.4.xdelta, alpine-1.10.3-x86.iso (previous release) and the alpine-1.10.4-x86.iso.sha1

wget -c http://www.alpinelinux.org/cgi-bin/dl.cgi/v1.10/releases/alpine-1.10.3-1.10.4.xdelta
wget http://www.alpinelinux.org/cgi-bin/dl.cgi/v1.10/releases/alpine-1.10.4-x86.iso.sha1

Make sure you have xdelta3 installed and build the new ISO:

apk add xdelta3
xdelta3 -d alpine-1.10.3-1.10.4.xdelta

Check the integrity of the file:

sha1sum -c alpine-1.10.4-x86.iso.sha1

If checking the integrity of the file shows: alpine-1.10.4-x86.iso: OK then you are ready to continue.