diff --git a/docs/installation/ubuntulinux.md b/docs/installation/ubuntulinux.md
index 51a078764f..38003ec198 100644
--- a/docs/installation/ubuntulinux.md
+++ b/docs/installation/ubuntulinux.md
@@ -55,7 +55,7 @@ packages from the new repository:
 
 3. Add the new `gpg` key.
 
-        $ apt-key adv --keyserver hkp://pgp.mit.edu:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D
+        $ sudo apt-key adv --keyserver hkp://pgp.mit.edu:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D
 
 4. Open the `/etc/apt/sources.list.d/docker.list` file in your favorite editor.