Alguns exemplos, usando gsettings
:
# setting a proxy manual
gsettings set org.gnome.system.proxy.socks host '192.168.10.100'
gsettings set org.gnome.system.proxy.socks port 8080
gsettings set org.gnome.system.proxy mode 'manual'
gsettings set org.gnome.system.proxy mode 'none' # this will disable proxy setting
gsettings set org.gnome.system.proxy mode 'auto' # this will set the proxy automatic