I created an account here so i could get involved as i've been having issues with Linux and obtaining A20 too.
I'm trying to install a fresh copy of A20 on x64 Ubuntu 20.04.3 LTS [Headerless] and i've been having issues too (mostly not working out what to put after the 'app_update 294420' as i've been told a few ways). I hear its best to fresh install than update from A19 to A20.
I've tried the following using the switch (-beta latest_experemenal) provided by
@Beelzybub above (Thank you!) also shown on the valve site
https://developer.valvesoftware.com/wiki/7_Days_to_Die_Dedicated_Server.
The following assumes that steamcmd has been installed via APT alongside its 64 bit prereqs (i put at the bottom). It also assumes you want to install to /home/7dtd :]. I'll let you know my findings with the first time run of the app as soon as i get the time. I hope the following works for you
@prieshas
Dont run steamcmd as root. I do my installs bit by bit instead of using one line at at time though i know this is not as efficient.
steamcmd
force_install_dir /home/7dtd
login anonymous
app_update 294420 -validate -beta latest_experimental
quit
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steamcmd for ubuntu x64 (not needed for x86)
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SteamCMD APT install with 64 bit prereqs
sudo add-apt-repository multiverse
sudo dpkg --add-architecture i386
sudo apt update
sudo apt install lib32gcc1 steamcmd
ln -s /usr/games/steamcmd steamcmd