GitLab repository signing key was updated at the beginning of the April, so you can get an error during the signature verification.
This problem can be easily identified by NO_PUBKEY 3F01618A51312F3F message.
milosz@gitlab:~$ sudo apt update Hit:1 http://archive.ubuntu.com/ubuntu bionic InRelease Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB] Get:3 http://archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB] Get:4 https://packages.gitlab.com/gitlab/gitlab-ce/ubuntu bionic InRelease [23.3 kB] Err:4 https://packages.gitlab.com/gitlab/gitlab-ce/ubuntu bionic InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3F01618A51312F3F Fetched 201 kB in 2s (101 kB/s) Reading package lists... Done Building dependency tree Reading state information... Done 5 packages can be upgraded. Run 'apt list --upgradable' to see them. W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://packages.gitlab.com/gitlab/gitlab-ce/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3F01618A51312F3F W: Failed to fetch https://packages.gitlab.com/gitlab/gitlab-ce/ubuntu/dists/bionic/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3F01618A51312F3F W: Some index files failed to download. They have been ignored, or old ones used instead.
Import missing public key using curl.
milosz@gitlab:~$ curl --silent https://packages.gitlab.com/gpg.key | sudo apt-key add - OK
Alternatively, import missing public key using gpg.
milosz@gitlab$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3F01618A51312F3F Executing: /tmp/apt-key-gpghome.d7F7ffwgwy/gpg.1.sh --keyserver keyserver.ubuntu.com --recv-keys 3F01618A51312F3F gpg: key 3F01618A51312F3F: public key "GitLab B.V. (package repository signing key) <packages@gitlab.com>" imported gpg: Total number processed: 1 gpg: imported: 1
Continue as usual.
milosz@gitlab:~$ sudo apt update Hit:1 http://archive.ubuntu.com/ubuntu bionic InRelease Get:2 http://archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB] Get:3 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB] Get:4 https://packages.gitlab.com/gitlab/gitlab-ce/ubuntu bionic InRelease [23.3 kB] Fetched 201 kB in 2s (101 kB/s) Reading package lists... Done Building dependency tree Reading state information... Done 5 packages can be upgraded. Run 'apt list --upgradable' to see them.