Extract the install file
To do this procedure you will need curl, openssl and xz as well as grep.
Use curl to download the compressed installation file.
$ curl -4 -L --url 'https://download.freebsd.org/releases/amd64/amd64/ISO-IMAGES/13.2/FreeBSD-13.2-RELEASE-amd64-dvd1.iso.xz' -O
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 2858M 100 2858M 0 0 9704k 0 0:05:01 0:05:01 --:--:-- 12.2M
You may also download the SHA256 checksum data file :
$ curl -4 -L --url 'https://download.freebsd.org/releases/amd64/amd64/ISO-IMAGES/13.2/CHECKSUM.SHA256-FreeBSD-13.2-RELEASE-amd64' -O
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 1171 100 1171 0 0 6875 0 --:--:-- --:--:-- --:--:-- 6928
Then use OpenSSL to look at the SHA256 digital signature hash of the file :
$ openssl dgst -sha256 -r FreeBSD-13.2-RELEASE-amd64-dvd1.iso.xz
d1eaf7e4cfa239ea48190b01a373e0c6fd6dcfd6661c700fcd33c5ca20031a16 *FreeBSD-13.2-RELEASE-amd64-dvd1.iso.xz
The trivial check here is just to see if the SHA256 hash exists in the checksum data file :
$ grep -c 'd1eaf7e4cfa239ea48190b01a373e0c6fd6dcfd6661c700fcd33c5ca20031a16' CHECKSUM.SHA256-FreeBSD-13.2-RELEASE-amd64
1
The result "1" tells you that you have a perfect SHA256 signature match.
Then decompress the file to create an actual DVD iso file :
$ xz -dc FreeBSD-13.2-RELEASE-amd64-dvd1.iso.xz > FreeBSD-13.2-RELEASE-amd64-dvd1.iso
