Administration - Installation - Core: Ilias 6 "composer" ?

Hi,

i have to install Ilias 6 for a customer on RHEL7 from the tgz
The installation readme says at captial "Build PHP-Dependencies and Artifacts" run command
"composer install --no-dev"

But there ist no "composer" command.
I already searched the forum for that topic but havent found anything

Any idea?
Thanks
Reiner