When I try to update my application packages using composer in terminal it shows me Killed error and terminate the process. It is mainly due to server Memory Issue. You can fix using bellow command. I test this command on my live server and it works well for me.
/bin/dd if=/dev/zero of=/var/swap.1 bs=1M count=1024
sudo /sbin/swapon /var/swap.1
After running this command re-run your composer command.
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