diff --git a/ubuntu/apt.md b/ubuntu/apt.md
new file mode 100644
index 0000000..746452c
--- /dev/null
+++ b/ubuntu/apt.md
@@ -0,0 +1,40 @@
+was getting this error:
+
+pt@r710:~$ sudo apt update
+[sudo] password for pt:
+Hit:1 http://download.virtualbox.org/virtualbox/debian bionic InRelease
+Hit:2 http://archive.ubuntu.com/ubuntu bionic InRelease
+Hit:3 https://dl.yarnpkg.com/debian stable InRelease
+Hit:4 https://deb.nodesource.com/node_13.x bionic InRelease
+Hit:5 http://apt.postgresql.org/pub/repos/apt bionic-pgdg InRelease
+Hit:6 http://ppa.launchpad.net/certbot/certbot/ubuntu bionic InRelease
+Get:7 http://archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
+Hit:8 https://download.jitsi.org stable/ InRelease
+Ign:9 https://dl.packager.io/srv/deb/pghero/pghero/master/ubuntu 18.04 InRelease
+Get:10 http://archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]
+Get:11 https://cloud.r-project.org/bin/linux/ubuntu bionic-cran40/ InRelease [3,626 B]
+Get:12 http://archive.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]
+Get:13 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages [1,726 kB]
+Err:11 https://cloud.r-project.org/bin/linux/ubuntu bionic-cran40/ InRelease
+  The following signatures were invalid: EXPKEYSIG 51716619E084DAB9 Michael Rutter <marutter@gmail.com>
+Ign:14 https://download.webmin.com/download/repository sarge InRelease
+Hit:15 https://download.webmin.com/download/repository sarge Release
+Get:17 https://dl.packager.io/srv/deb/pghero/pghero/master/ubuntu 18.04 Release
+Get:19 http://archive.ubuntu.com/ubuntu bionic-updates/universe amd64 Packages [1,680 kB]
+Fetched 3,663 kB in 2s (1,627 kB/s)
+Reading package lists... Done
+Building dependency tree
+Reading state information... Done
+All packages are up to date.
+W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://cloud.r-project.org/bin/linux/ubuntu bionic-cran40/ InRelease: The following signatures were invalid: EXPKEYSIG 51716619E084DAB9 Michael Rutter <marutter@gmail.com>
+W: Failed to fetch https://cloud.r-project.org/bin/linux/ubuntu/bionic-cran40/InRelease  The following signatures were invalid: EXPKEYSIG 51716619E084DAB9 Michael Rutter <marutter@gmail.com>
+W: Some index files failed to download. They have been ignored, or old ones used instead.
+
+ran the following command using key signature from above.
+it is supposed to import the gpg key from the target repository into the local database.
+[askubunut](https://askubuntu.com/questions/131601/gpg-error-release-the-following-signatures-were-invalid-badsig)
+
+pt@r710:~$ gpg --keyserver keyserver.ubuntu.com --recv-keys 51716619E084DAB9
+gpg: key 51716619E084DAB9: public key "Michael Rutter <marutter@gmail.com>" imported
+gpg: Total number processed: 1
+gpg:               imported: 1