diff --git a/.github/workflows/codeql-analysis.yml b/.github/workflows/codeql-analysis.yml
index 371605a34f..0026c0d168 100644
--- a/.github/workflows/codeql-analysis.yml
+++ b/.github/workflows/codeql-analysis.yml
@@ -11,7 +11,7 @@ on:
 jobs:
  analyze:
    name: Analyze
-   runs-on: ubuntu-latest
+   runs-on: ubuntu-22.04
    permissions:
      actions: read
      contents: read
diff --git a/.github/workflows/docker.yml b/.github/workflows/docker.yml
index 8bdfb1f8db..1d692b3838 100644
--- a/.github/workflows/docker.yml
+++ b/.github/workflows/docker.yml
@@ -14,7 +14,7 @@ permissions:
 jobs:
   ubuntu:
     if: startsWith(github.repository, 'Homebrew/')
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
       matrix:
diff --git a/.github/workflows/maintainers-man-completions.yml b/.github/workflows/maintainers-man-completions.yml
index b01c18bfc6..893f4dcb27 100644
--- a/.github/workflows/maintainers-man-completions.yml
+++ b/.github/workflows/maintainers-man-completions.yml
@@ -21,7 +21,7 @@ permissions:
 
 jobs:
   updates:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     if: github.repository == 'Homebrew/brew'
     steps:
       - name: Setup Homebrew
diff --git a/.github/workflows/spdx.yml b/.github/workflows/spdx.yml
index 57e004500e..444ca4d001 100644
--- a/.github/workflows/spdx.yml
+++ b/.github/workflows/spdx.yml
@@ -15,7 +15,7 @@ permissions:
 jobs:
   spdx:
     if: github.repository == 'Homebrew/brew'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Set up Homebrew
         id: set-up-homebrew
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index ab09dcac66..4429640597 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -20,7 +20,7 @@ concurrency:
 jobs:
   syntax:
     if: github.repository == 'Homebrew/brew'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Set up Homebrew
         id: set-up-homebrew
@@ -52,7 +52,7 @@ jobs:
     name: tap syntax (Linux)
     needs: syntax
     if: startsWith(github.repository, 'Homebrew/')
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Set up Homebrew
         id: set-up-homebrew
@@ -146,7 +146,7 @@ jobs:
 
   vendored-gems:
     name: vendored gems (Linux)
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Set up Homebrew
         id: set-up-homebrew
@@ -167,31 +167,31 @@ jobs:
 
   docker:
     needs: syntax
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Set up Homebrew
         id: set-up-homebrew
         uses: Homebrew/actions/setup-homebrew@master
 
       - name: Build Docker image
-        run: docker build -t brew --build-arg=version=16.04 .
+        run: docker build -t brew --build-arg=version=22.04 .
 
       - name: Deploy the Docker image to GitHub Packages and Docker Hub
         if: github.ref == 'refs/heads/master'
         run: |
           echo ${{secrets.HOMEBREW_BREW_GITHUB_PACKAGES_TOKEN}} |
             docker login ghcr.io -u BrewTestBot --password-stdin
-          docker tag brew "ghcr.io/homebrew/ubuntu16.04:master"
-          docker push "ghcr.io/homebrew/ubuntu16.04:master"
+          docker tag brew "ghcr.io/homebrew/ubuntu22.04:master"
+          docker push "ghcr.io/homebrew/ubuntu22.04:master"
           echo ${{secrets.HOMEBREW_BREW_DOCKER_TOKEN}} |
             docker login -u brewtestbot --password-stdin
-          docker tag brew "homebrew/ubuntu16.04:master"
-          docker push "homebrew/ubuntu16.04:master"
+          docker tag brew "homebrew/ubuntu22.04:master"
+          docker push "homebrew/ubuntu22.04:master"
 
   tests:
     name: ${{ matrix.name }}
     needs: syntax
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
         include:
@@ -244,7 +244,7 @@ jobs:
 
   test-default-formula-linux:
     name: test default formula (Linux)
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     env:
       HOMEBREW_BOOTSNAP: 1
     steps:
diff --git a/.github/workflows/triage-issues.yml b/.github/workflows/triage-issues.yml
index 7963be2688..93b7411565 100644
--- a/.github/workflows/triage-issues.yml
+++ b/.github/workflows/triage-issues.yml
@@ -29,7 +29,7 @@ jobs:
           contains(github.event.pull_request.labels.*.name, 'stale')
         )
       )
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Mark/Close Stale Issues and Pull Requests
         uses: actions/stale@v5
@@ -55,7 +55,7 @@ jobs:
           contains(github.event.pull_request.labels.*.name, 'stale')
         )
       )
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Mark/Close Stale `bump-formula-pr` and `bump-cask-pr` Pull Requests
         uses: actions/stale@v5
@@ -72,7 +72,7 @@ jobs:
 
   lock-threads:
     if: startsWith(github.repository, 'Homebrew/') && github.event_name != 'issue_comment'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Lock Outdated Threads
         uses: dessant/lock-threads@e460dfeb36e731f3aeb214be6b0c9a9d9a67eda6
diff --git a/.github/workflows/triage.yml b/.github/workflows/triage.yml
index 2ef2939e34..1b21dbc19f 100644
--- a/.github/workflows/triage.yml
+++ b/.github/workflows/triage.yml
@@ -18,7 +18,7 @@ concurrency: triage-${{ github.head_ref }}
 
 jobs:
   review:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     if: startsWith(github.repository, 'Homebrew/')
     steps:
       - name: Re-run this workflow
diff --git a/Library/Homebrew/os.rb b/Library/Homebrew/os.rb
index ac480c374f..0fc42af698 100644
--- a/Library/Homebrew/os.rb
+++ b/Library/Homebrew/os.rb
@@ -45,15 +45,12 @@ module OS
 
   ::OS_VERSION = ENV.fetch("HOMEBREW_OS_VERSION").freeze
 
-  LINUX_CI_OS_VERSION = "Ubuntu 16.04"
-  LINUX_GLIBC_CI_VERSION = "2.23"
-  LINUX_GCC_CI_VERSION = "5.0"
-  LINUX_PREFERRED_GCC_FORMULA = "gcc@5"
-
-  # Ubuntu 22.04 (see Linux-CI.md)
+  # See Linux-CI.md
+  LINUX_CI_OS_VERSION = "Ubuntu 22.04"
+  LINUX_GLIBC_CI_VERSION = "2.35"
   LINUX_GLIBC_NEXT_CI_VERSION = "2.35"
-  # LINUX_GCC_CI_VERSION = "11.0"
-  # LINUX_PREFERRED_GCC_FORMULA = "gcc@11"
+  LINUX_GCC_CI_VERSION = "11.0"
+  LINUX_PREFERRED_GCC_FORMULA = "gcc@11"
 
   if OS.mac?
     require "os/mac"
diff --git a/Library/Homebrew/test/compiler_selector_spec.rb b/Library/Homebrew/test/compiler_selector_spec.rb
index 5ee6d0c2eb..afedc9d8b1 100644
--- a/Library/Homebrew/test/compiler_selector_spec.rb
+++ b/Library/Homebrew/test/compiler_selector_spec.rb
@@ -52,7 +52,7 @@ describe CompilerSelector do
 
     it "returns gcc-5 if gcc formula offers gcc-5 on linux", :needs_linux do
       software_spec.fails_with(:clang)
-      allow(Formulary).to receive(:factory).with("gcc@5").and_return(double(version: Version.new("5.0")))
+      allow(Formulary).to receive(:factory).with("gcc@11").and_return(double(version: Version.new("5.0")))
       expect(selector.compiler).to eq("gcc-5")
     end
 
@@ -60,14 +60,14 @@ describe CompilerSelector do
       software_spec.fails_with(:clang)
       software_spec.fails_with(gcc: "5")
       software_spec.fails_with(gcc: "7")
-      allow(Formulary).to receive(:factory).with("gcc@5").and_return(double(version: Version.new("5.0")))
+      allow(Formulary).to receive(:factory).with("gcc@11").and_return(double(version: Version.new("5.0")))
       expect(selector.compiler).to eq("gcc-6")
     end
 
     it "returns gcc-7 if gcc formula offers gcc-5 and fails with gcc <= 6 on linux", :needs_linux do
       software_spec.fails_with(:clang)
       software_spec.fails_with(:gcc) { version "6" }
-      allow(Formulary).to receive(:factory).with("gcc@5").and_return(double(version: Version.new("5.0")))
+      allow(Formulary).to receive(:factory).with("gcc@11").and_return(double(version: Version.new("5.0")))
       expect(selector.compiler).to eq("gcc-7")
     end
 
diff --git a/Library/Homebrew/test/formula_installer_bottle_spec.rb b/Library/Homebrew/test/formula_installer_bottle_spec.rb
index 143fc03dcf..1cc7037b93 100644
--- a/Library/Homebrew/test/formula_installer_bottle_spec.rb
+++ b/Library/Homebrew/test/formula_installer_bottle_spec.rb
@@ -24,7 +24,7 @@ describe FormulaInstaller do
 
     stub_formula_loader formula
     stub_formula_loader formula("gcc") { url "gcc-1.0" }
-    stub_formula_loader formula("gcc@5") { url "gcc-5.0" }
+    stub_formula_loader formula("gcc@11") { url "gcc-11.0" }
 
     fi = FormulaInstaller.new(formula)
     fi.fetch
diff --git a/Library/Homebrew/test/formulary_spec.rb b/Library/Homebrew/test/formulary_spec.rb
index 0fc043fe6b..03fe46e6ab 100644
--- a/Library/Homebrew/test/formulary_spec.rb
+++ b/Library/Homebrew/test/formulary_spec.rb
@@ -142,7 +142,7 @@ describe Formulary do
       before do
         allow(described_class).to receive(:loader_for).and_call_original
         stub_formula_loader formula("gcc") { url "gcc-1.0" }
-        stub_formula_loader formula("gcc@5") { url "gcc-5.0" }
+        stub_formula_loader formula("gcc@11") { url "gcc-11.0" }
       end
 
       let(:installed_formula) { described_class.factory(formula_path) }
diff --git a/Library/Homebrew/test/unpack_strategy/zstd_spec.rb b/Library/Homebrew/test/unpack_strategy/zstd_spec.rb
index 6e9198b996..270db9ce40 100644
--- a/Library/Homebrew/test/unpack_strategy/zstd_spec.rb
+++ b/Library/Homebrew/test/unpack_strategy/zstd_spec.rb
@@ -6,5 +6,12 @@ require_relative "shared_examples"
 describe UnpackStrategy::Zstd do
   let(:path) { TEST_FIXTURE_DIR/"cask/container.tar.zst" }
 
-  include_examples "UnpackStrategy::detect"
+  it "is correctly detected" do
+    # UnpackStrategy.detect(path) for a .tar.XXX file returns either UnpackStrategy::Tar if
+    # the host's tar is able to extract that compressed file or UnpackStrategy::XXX otherwise,
+    # such as UnpackStrategy::Zstd. On macOS UnpackStrategy.detect("container.tar.zst")
+    # returns UnpackStrategy::Zstd, and on ubuntu-22.04 it returns UnpackStrategy::Tar,
+    # because the host's version of tar is recent enough and zstd is installed.
+    expect(UnpackStrategy.detect(path)).to(be_a(described_class).or(be_a(UnpackStrategy::Tar)))
+  end
 end