From Blue-IT.org Wiki
Using Citrix under Ubuntu is now possible without any problems. At least for me with the new Citrix workspace app since version 1912 :-) The old Citrix receiver is not maintained any more. Please switch to the new app.
You can download both, the desktop and webbrowser app for linux here:
Use the debian packages for ubuntu.
SSL error 61
If you get the ssl error "You have not choosen to trust 'global sign root ca' ... " you have make avaiable the certificates to citix:
sudo ln -s /usr/share/ca-certificates/mozilla/* /opt/Citrix/ICAClient/keystore/cacerts