diff --git a/Library/Homebrew/diagnostic.rb b/Library/Homebrew/diagnostic.rb
index 736f35ff19..807c9024b6 100644
--- a/Library/Homebrew/diagnostic.rb
+++ b/Library/Homebrew/diagnostic.rb
@@ -480,60 +480,6 @@ module Homebrew
         EOS
       end
 
-      def check_for_gettext
-        find_relative_paths("lib/libgettextlib.dylib",
-                            "lib/libintl.dylib",
-                            "include/libintl.h")
-        return if @found.empty?
-
-        # Our gettext formula will be caught by check_linked_keg_only_brews
-        gettext = begin
-          Formulary.factory("gettext")
-        rescue
-          nil
-        end
-        homebrew_owned = @found.all? do |path|
-          Pathname.new(path).realpath.to_s.start_with? "#{HOMEBREW_CELLAR}/gettext"
-        end
-        return if gettext&.linked_keg&.directory? && homebrew_owned
-
-        inject_file_list @found, <<~EOS
-          gettext files detected at a system prefix.
-          These files can cause compilation and link failures, especially if they
-          are compiled with improper architectures. Consider removing these files:
-        EOS
-      end
-
-      def check_for_iconv
-        find_relative_paths("lib/libiconv.dylib", "include/iconv.h")
-        return if @found.empty?
-
-        libiconv = begin
-          Formulary.factory("libiconv")
-        rescue
-          nil
-        end
-        if libiconv&.linked_keg&.directory?
-          unless libiconv.keg_only?
-            <<~EOS
-              A libiconv formula is installed and linked.
-              This will break stuff. For serious. Unlink it.
-            EOS
-          end
-        else
-          inject_file_list @found, <<~EOS
-            libiconv files detected at a system prefix other than /usr.
-            Homebrew doesn't provide a libiconv formula, and expects to link against
-            the system version in /usr. libiconv in other prefixes can cause
-            compile or link failure, especially if compiled with improper
-            architectures. macOS itself never installs anything to /usr/local so
-            it was either installed by a user or some other third party software.
-
-            tl;dr: delete these files:
-          EOS
-        end
-      end
-
       def check_for_config_scripts
         return unless HOMEBREW_CELLAR.exist?
         real_cellar = HOMEBREW_CELLAR.realpath
@@ -571,17 +517,17 @@ module Homebrew
         EOS
       end
 
-      def check_dyld_vars
-        dyld_vars = ENV.keys.grep(/^DYLD_/)
-        return if dyld_vars.empty?
+      def check_ld_vars
+        ld_vars = ENV.keys.grep(/^(|DY)LD_/)
+        return if ld_vars.empty?
 
-        values = dyld_vars.map { |var| "#{var}: #{ENV.fetch(var)}" }
+        values = ld_vars.map { |var| "#{var}: #{ENV.fetch(var)}" }
         message = inject_file_list values, <<~EOS
-          Setting DYLD_* vars can break dynamic linking.
+          Setting DYLD_* or LD_* variables can break dynamic linking.
           Set variables:
         EOS
 
-        if dyld_vars.include? "DYLD_INSERT_LIBRARIES"
+        if ld_vars.include? "DYLD_INSERT_LIBRARIES"
           message += <<~EOS
 
             Setting DYLD_INSERT_LIBRARIES can cause Go builds to fail.
@@ -612,38 +558,6 @@ module Homebrew
         EOS
       end
 
-      def check_for_multiple_volumes
-        return unless HOMEBREW_CELLAR.exist?
-        volumes = Volumes.new
-
-        # Find the volumes for the TMP folder & HOMEBREW_CELLAR
-        real_cellar = HOMEBREW_CELLAR.realpath
-        where_cellar = volumes.which real_cellar
-
-        begin
-          tmp = Pathname.new(Dir.mktmpdir("doctor", HOMEBREW_TEMP))
-          begin
-            real_tmp = tmp.realpath.parent
-            where_tmp = volumes.which real_tmp
-          ensure
-            Dir.delete tmp
-          end
-        rescue
-          return
-        end
-
-        return if where_cellar == where_tmp
-
-        <<~EOS
-          Your Cellar and TEMP directories are on different volumes.
-          macOS won't move relative symlinks across volumes unless the target file already
-          exists. Brews known to be affected by this are Git and Narwhal.
-
-          You should set the "HOMEBREW_TEMP" environmental variable to a suitable
-          directory on the same volume as your Cellar.
-        EOS
-      end
-
       def check_git_version
         # https://help.github.com/articles/https-cloning-errors
         return unless Utils.git_available?
@@ -859,21 +773,6 @@ module Homebrew
         nil
       end
 
-      def check_for_non_prefixed_findutils
-        findutils = Formula["findutils"]
-        return unless findutils.any_version_installed?
-
-        gnubin = %W[#{findutils.opt_libexec}/gnubin #{findutils.libexec}/gnubin]
-        default_names = Tab.for_name("findutils").with? "default-names"
-        return if !default_names && (paths & gnubin).empty?
-
-        <<~EOS
-          Putting non-prefixed findutils in your path can cause python builds to fail.
-        EOS
-      rescue FormulaUnavailableError
-        nil
-      end
-
       def check_for_pydistutils_cfg_in_home
         return unless File.exist? "#{ENV["HOME"]}/.pydistutils.cfg"
 
diff --git a/Library/Homebrew/extend/os/diagnostic.rb b/Library/Homebrew/extend/os/diagnostic.rb
index 3e0d104fc4..34d09f9614 100644
--- a/Library/Homebrew/extend/os/diagnostic.rb
+++ b/Library/Homebrew/extend/os/diagnostic.rb
@@ -1 +1,5 @@
-require "extend/os/mac/diagnostic" if OS.mac?
+if OS.mac?
+  require "extend/os/mac/diagnostic"
+elsif OS.linux?
+  require "extend/os/linux/diagnostic"
+end
diff --git a/Library/Homebrew/extend/os/linux/diagnostic.rb b/Library/Homebrew/extend/os/linux/diagnostic.rb
new file mode 100644
index 0000000000..63f8d7b479
--- /dev/null
+++ b/Library/Homebrew/extend/os/linux/diagnostic.rb
@@ -0,0 +1,33 @@
+require "tempfile"
+require "utils/shell"
+require "os/linux/diagnostic"
+
+module Homebrew
+  module Diagnostic
+    class Checks
+      def check_tmpdir_sticky_bit
+        message = generic_check_tmpdir_sticky_bit
+        return if message.nil?
+        message + <<~EOS
+          If you don't have administrative privileges on this machine,
+          create a directory and set the HOMEBREW_TEMP environment variable,
+          for example:
+            install -d -m 1755 ~/tmp
+            #{Utils::Shell.set_variable_in_profile("HOMEBREW_TEMP", "~/tmp")}
+        EOS
+      end
+
+      def check_xdg_data_dirs
+        return if ENV["XDG_DATA_DIRS"].to_s.empty?
+        return if ENV["XDG_DATA_DIRS"].split("/").include?(HOMEBREW_PREFIX/"share")
+        <<~EOS
+          Homebrew's share was not found in your XDG_DATA_DIRS but you have
+          this variable set to include other locations.
+          Some programs like `vapigen` may not work correctly.
+          Consider adding Homebrew's share directory to XDG_DATA_DIRS like so:
+            #{Utils::Shell.prepend_variable_in_profile("XDG_DATA_DIRS", HOMEBREW_PREFIX/"share")}
+        EOS
+      end
+    end
+  end
+end
diff --git a/Library/Homebrew/extend/os/mac/diagnostic.rb b/Library/Homebrew/extend/os/mac/diagnostic.rb
index 92fb3f315f..cef36ac8f9 100644
--- a/Library/Homebrew/extend/os/mac/diagnostic.rb
+++ b/Library/Homebrew/extend/os/mac/diagnostic.rb
@@ -29,6 +29,21 @@ module Homebrew
         ]).freeze
       end
 
+      def check_for_non_prefixed_findutils
+        findutils = Formula["findutils"]
+        return unless findutils.any_version_installed?
+
+        gnubin = %W[#{findutils.opt_libexec}/gnubin #{findutils.libexec}/gnubin]
+        default_names = Tab.for_name("findutils").with? "default-names"
+        return if !default_names && (paths & gnubin).empty?
+
+        <<~EOS
+          Putting non-prefixed findutils in your path can cause python builds to fail.
+        EOS
+      rescue FormulaUnavailableError
+        nil
+      end
+
       def check_for_unsupported_macos
         return if ARGV.homebrew_developer?
 
@@ -275,6 +290,95 @@ module Homebrew
           may not build correctly with a non-/usr/local prefix.
         EOS
       end
+
+      def check_for_gettext
+        find_relative_paths("lib/libgettextlib.dylib",
+                            "lib/libintl.dylib",
+                            "include/libintl.h")
+        return if @found.empty?
+
+        # Our gettext formula will be caught by check_linked_keg_only_brews
+        gettext = begin
+          Formulary.factory("gettext")
+        rescue
+          nil
+        end
+
+        if gettext&.linked_keg&.directory?
+          homebrew_owned = @found.all? do |path|
+            Pathname.new(path).realpath.to_s.start_with? "#{HOMEBREW_CELLAR}/gettext"
+          end
+          return if homebrew_owned
+        end
+
+        inject_file_list @found, <<~EOS
+          gettext files detected at a system prefix.
+          These files can cause compilation and link failures, especially if they
+          are compiled with improper architectures. Consider removing these files:
+        EOS
+      end
+
+      def check_for_iconv
+        find_relative_paths("lib/libiconv.dylib", "include/iconv.h")
+        return if @found.empty?
+
+        libiconv = begin
+          Formulary.factory("libiconv")
+        rescue
+          nil
+        end
+        if libiconv&.linked_keg&.directory?
+          unless libiconv.keg_only?
+            <<~EOS
+              A libiconv formula is installed and linked.
+              This will break stuff. For serious. Unlink it.
+            EOS
+          end
+        else
+          inject_file_list @found, <<~EOS
+            libiconv files detected at a system prefix other than /usr.
+            Homebrew doesn't provide a libiconv formula, and expects to link against
+            the system version in /usr. libiconv in other prefixes can cause
+            compile or link failure, especially if compiled with improper
+            architectures. macOS itself never installs anything to /usr/local so
+            it was either installed by a user or some other third party software.
+
+            tl;dr: delete these files:
+          EOS
+        end
+      end
+
+      def check_for_multiple_volumes
+        return unless HOMEBREW_CELLAR.exist?
+        volumes = Volumes.new
+
+        # Find the volumes for the TMP folder & HOMEBREW_CELLAR
+        real_cellar = HOMEBREW_CELLAR.realpath
+        where_cellar = volumes.which real_cellar
+
+        begin
+          tmp = Pathname.new(Dir.mktmpdir("doctor", HOMEBREW_TEMP))
+          begin
+            real_tmp = tmp.realpath.parent
+            where_tmp = volumes.which real_tmp
+          ensure
+            Dir.delete tmp
+          end
+        rescue
+          return
+        end
+
+        return if where_cellar == where_tmp
+
+        <<~EOS
+          Your Cellar and TEMP directories are on different volumes.
+          macOS won't move relative symlinks across volumes unless the target file already
+          exists. Brews known to be affected by this are Git and Narwhal.
+
+          You should set the "HOMEBREW_TEMP" environmental variable to a suitable
+          directory on the same volume as your Cellar.
+        EOS
+      end
     end
   end
 end
diff --git a/Library/Homebrew/os/linux/diagnostic.rb b/Library/Homebrew/os/linux/diagnostic.rb
new file mode 100644
index 0000000000..66cd7fe8af
--- /dev/null
+++ b/Library/Homebrew/os/linux/diagnostic.rb
@@ -0,0 +1,7 @@
+module Homebrew
+  module Diagnostic
+    class Checks
+      alias generic_check_tmpdir_sticky_bit check_tmpdir_sticky_bit
+    end
+  end
+end
diff --git a/Library/Homebrew/test/diagnostic_spec.rb b/Library/Homebrew/test/diagnostic_spec.rb
index 52e7d3a392..0ac855ab75 100644
--- a/Library/Homebrew/test/diagnostic_spec.rb
+++ b/Library/Homebrew/test/diagnostic_spec.rb
@@ -145,11 +145,6 @@ describe Homebrew::Diagnostic::Checks do
     end
   end
 
-  specify "#check_dyld_vars" do
-    ENV["DYLD_INSERT_LIBRARIES"] = "foo"
-    expect(subject.check_dyld_vars).to match("Setting DYLD_INSERT_LIBRARIES")
-  end
-
   specify "#check_for_symlinked_cellar" do
     begin
       HOMEBREW_CELLAR.rmtree
@@ -165,6 +160,26 @@ describe Homebrew::Diagnostic::Checks do
     end
   end
 
+  specify "#check_ld_vars catches LD vars" do
+    ENV["LD_LIBRARY_PATH"] = "foo"
+    expect(subject.check_ld_vars).to match("Setting DYLD_\\* or LD_\\* variables")
+  end
+
+  specify "#check_ld_vars catches DYLD vars" do
+    ENV["DYLD_LIBRARY_PATH"] = "foo"
+    expect(subject.check_ld_vars).to match("Setting DYLD_\\* or LD_\\* variables")
+  end
+
+  specify "#check_ld_vars catches LD and DYLD vars" do
+    ENV["LD_LIBRARY_PATH"] = "foo"
+    ENV["DYLD_LIBRARY_PATH"] = "foo"
+    expect(subject.check_ld_vars).to match("Setting DYLD_\\* or LD_\\* variables")
+  end
+
+  specify "#check_ld_vars returns success when neither LD nor DYLD vars are set" do
+    expect(subject.check_ld_vars).to be nil
+  end
+
   specify "#check_tmpdir" do
     ENV["TMPDIR"] = "/i/don/t/exis/t"
     expect(subject.check_tmpdir).to match("doesn't exist")
diff --git a/Library/Homebrew/test/os/mac/diagnostic_spec.rb b/Library/Homebrew/test/os/mac/diagnostic_spec.rb
index ffa4ebca9e..22cbd158f1 100644
--- a/Library/Homebrew/test/os/mac/diagnostic_spec.rb
+++ b/Library/Homebrew/test/os/mac/diagnostic_spec.rb
@@ -45,4 +45,9 @@ describe Homebrew::Diagnostic::Checks do
     expect(subject.check_ruby_version)
       .to match "Ruby version 1.8.6 is unsupported on 10.12"
   end
+
+  specify "#check_dyld_insert" do
+    ENV["DYLD_INSERT_LIBRARIES"] = "foo"
+    expect(subject.check_ld_vars).to match("Setting DYLD_INSERT_LIBRARIES")
+  end
 end
diff --git a/Library/Homebrew/test/utils/shell_spec.rb b/Library/Homebrew/test/utils/shell_spec.rb
index d32f9928fd..a9456ae117 100644
--- a/Library/Homebrew/test/utils/shell_spec.rb
+++ b/Library/Homebrew/test/utils/shell_spec.rb
@@ -75,19 +75,20 @@ describe Utils::Shell do
     it "supports Tcsh" do
       ENV["SHELL"] = "/bin/tcsh"
       expect(subject.prepend_path_in_profile(path))
-        .to start_with("echo 'setenv PATH #{path}:$")
+        .to eq("echo 'setenv PATH #{path}:$PATH' >> #{shell_profile}")
     end
 
     it "supports Bash" do
       ENV["SHELL"] = "/bin/bash"
       expect(subject.prepend_path_in_profile(path))
-        .to start_with("echo 'export PATH=\"#{path}:$")
+        .to eq("echo 'export PATH=\"#{path}:$PATH\"' >> #{shell_profile}")
     end
 
     it "supports Fish" do
       ENV["SHELL"] = "/usr/local/bin/fish"
+      ENV["fish_user_paths"] = "/some/path"
       expect(subject.prepend_path_in_profile(path))
-        .to start_with("echo 'set -g fish_user_paths \"#{path}\" $fish_user_paths' >>")
+        .to eq("echo 'set -g fish_user_paths \"#{path}\" $fish_user_paths' >> #{shell_profile}")
     end
   end
 end
diff --git a/Library/Homebrew/utils/shell.rb b/Library/Homebrew/utils/shell.rb
index 8c1c5f984b..56ea7fd1e6 100644
--- a/Library/Homebrew/utils/shell.rb
+++ b/Library/Homebrew/utils/shell.rb
@@ -40,6 +40,17 @@ module Utils
       SHELL_PROFILE_MAP.fetch(preferred, "~/.bash_profile")
     end
 
+    def set_variable_in_profile(variable, value)
+      case preferred
+      when :bash, :ksh, :sh, :zsh, nil
+        "echo 'export #{variable}=#{sh_quote(value)}' >> #{profile}"
+      when :csh, :tcsh
+        "echo 'setenv #{variable} #{csh_quote(value)}' >> #{profile}"
+      when :fish
+        "echo 'set -gx #{variable} #{sh_quote(value)}' >> #{profile}"
+      end
+    end
+
     def prepend_path_in_profile(path)
       case preferred
       when :bash, :ksh, :sh, :zsh, nil