i just went to restore a system from a failed server. i loaded the 3Cx software i had on file. went to restore the database and it says it is a newer version than on the pbx. says i need v18 update 3. when i go to download the linux file from the download page there is one file there doesn't say what version it is. how do i get a specific version download so i can restore this server?
That is not possible. A Linux 3CX is always installed with the latest version, with a v18 that is u9. If you really need a v18u3, then that is a problem. You will not be able to restore the backup, some of the prerequisites are missing. You probably need a v18u5.
Either reinstall everything with a current 3CX (the recommended way) ...
...or try the following (not supported and I think this would not be working because you can't activate it):
install a current Linux 3CX v18u9.31
uninstall the 3cxpbx package only (apt -y remove 3cxpbx)
use apt list -a 3cxpbx to list the possible installable variants
use apt -y install 3cxpbx=18.0.5.415 to install the lowest possible version
start the first run / install wizard and restore your backup of the v18u3
if this ist working (I think not), then go further with:
make adjustments if necessary and test it
and then update (via overwrite) the 3CX main version by main version in single steps, e.g. with apt -y install 3cxpbx=18.0.6.908 as next and so on
log in every version now and then and make adjustments if necessary and test it
If everything works up to the latest version, 18.0.9.31, then I would make another backup, cleanly reinstall 3CX and restore this last backup there.
If this is not working, install and set up all from scratch.