Refuse a glob as a unit, and make wanted-by say only what it saw

systemctl expands *, ? and [ in a unit argument, so reset-failed or stop
of "*" would have acted on every unit. wanted-by called a link dangling on
any stat error, followed a linked .wants anywhere, and missed most of the
manager's load path; it now says each of these, and says nothing names a
unit only of the directories it searched.

modules/systemd/cmd/systemd-tools/client.go

@@ -244,11 +244,11 @@ func (m *Manager) Status(scope Scope, unit string) (map[string]any, error) {
 		return nil, err
 	}
 	props := []string{"LoadState", "ActiveState", "SubState", "UnitFileState", "MainPID", "ExecMainStatus", "Description", "FragmentPath"}
-	args := []string{"show", unit, "--no-pager"}
+	args := []string{"show", "--no-pager"}
 	for _, p := range props {
 		args = append(args, "--property="+p)
 	}
-	out, err := m.call(scope, "systemctl", args...)
+	out, err := m.call(scope, "systemctl", append(args, "--", unit)...)
 	if err != nil {
 		return nil, err
 	}
@@ -277,7 +277,7 @@ func (m *Manager) Act(scope Scope, verb, unit string) (map[string]any, error) {
 	if err := unitArg(unit); err != nil {
 		return nil, err
 	}
-	if _, err := m.call(scope, "systemctl", verb, unit); err != nil {
+	if _, err := m.call(scope, "systemctl", verb, "--", unit); err != nil {
 		return nil, err
 	}
 	after, err := m.Status(scope, unit)
@@ -368,7 +368,7 @@ func (m *Manager) Journal(scope Scope, unit string, q JournalQuery) (map[string]
 // unitSecrets are the values of the unit's own Environment= that must not be answered. Read with
 // systemctl show, which needs no escalation; a unit that does not exist has none.
 func (m *Manager) unitSecrets(scope Scope, unit string) ([]knownSecret, error) {
-	out, err := m.call(scope, "systemctl", "show", unit, "--no-pager", "--property=Environment", "--value")
+	out, err := m.call(scope, "systemctl", "show", "--no-pager", "--property=Environment", "--value", "--", unit)
 	if err != nil {
 		return nil, err
 	}
@@ -402,11 +402,16 @@ func (m *Manager) Failed(scopes ...Scope) map[string]any {
 }
 
 // unitArg refuses a unit name systemctl or journalctl would read as an option — which under sudo would be
-// root's option.
+// root's option — and **a glob** (novox/hq issue 332): systemctl expands *, ? and [ in a unit argument to
+// every loaded unit matching it, so `stop` or `reset-failed` of "*" would act on all of them. Every verb
+// names one unit; `units` alone takes a pattern, as its own argument. The name is also given after "--".
 func unitArg(unit string) error {
 	if unit == "" || strings.HasPrefix(unit, "-") || strings.ContainsAny(unit, " \t\n\r\x00") {
 		return fmt.Errorf("%q is not a unit's name", unit)
 	}
+	if strings.ContainsAny(unit, "*?[") {
+		return fmt.Errorf("%q is a pattern, not one unit's name: the service manager would act on every unit it matches", unit)
+	}
 	return nil
 }
 

modules/systemd/cmd/systemd-tools/client_test.go

@@ -139,7 +139,7 @@ func TestASystemActEscalatesAndAnswersTheStateAfter(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if got := append([]string{calls[0].cmd}, calls[0].args...); !reflect.DeepEqual(got, []string{"sudo", "-n", "systemctl", "restart", "sshd.service"}) {
+	if got := append([]string{calls[0].cmd}, calls[0].args...); !reflect.DeepEqual(got, []string{"sudo", "-n", "systemctl", "restart", "--", "sshd.service"}) {
 		t.Fatalf("%v", got)
 	}
 	if r["ok"] != true || r["active"] != "active" || r["mesh_declared"] != false || r["note"] != nil {

modules/systemd/cmd/systemd-tools/wanted.go

@@ -12,10 +12,11 @@ package main
 //     is the case a failed record of a unit whose load state is not-found comes from, and the answer says
 //     each link's target and whether it dangles.
 //
-// Nothing here changes anything. Removing a link is `disable`'s; clearing the record is `reset-failed`'s.
+// Nothing here changes anything. Clearing the record is `reset-failed`'s.
 
 import (
 	"errors"
+	"fmt"
 	"io/fs"
 	"os"
 	"path/filepath"
@@ -33,21 +34,26 @@ var stateProperties = []string{"LoadState", "ActiveState", "SubState", "UnitFile
 // dependencyDirs are the suffixes of the directories an enable link sits in, and the dependency each makes.
 var dependencyDirs = map[string]string{".wants": "Wants", ".requires": "Requires", ".upholds": "Upholds"}
 
-// Entry is one name in a directory, as much of it as an enable link needs.
+// Entry is one name in a directory as lstat sees it: a link is never followed to say what it is.
 type Entry struct {
 	Name string
-	// Dir is whether the name is a directory (followed, when it is a link to one).
+	// Dir is whether the name is itself a directory; a link to one is not.
 	Dir bool
 	// Link is where a symbolic link points, as written; empty when the name is not a link.
 	Link string
-	// Dangles is whether a link points at nothing that exists.
+	// Dangles is whether a link points at nothing: what it names does not exist.
 	Dangles bool
+	// Error is why a link's target could not be looked at, when that is anything but its not existing.
+	Error string
 }
 
 // ConfigDir is one directory a manager reads units and enable links from, and whose it is.
 type ConfigDir struct {
 	Path  string `json:"path"`
 	Whose string `json:"whose"`
+	// Removable is whether a dangling link here is a person's or an administrator's to remove: their own
+	// configuration, not a package's, a generator's or the runtime's, which put theirs back.
+	Removable bool `json:"-"`
 }
 
 // EnableLink is one link in a dependency directory that names the unit.
@@ -58,36 +64,72 @@ type EnableLink struct {
 	Dependency string `json:"dependency"`
 	Target     string `json:"target,omitempty"`
 	Dangles    bool   `json:"dangles"`
+	// Error is why the target could not be looked at, other than its not existing: neither dangling nor not.
+	Error string `json:"error,omitempty"`
 	// Link is false for a plain file in a dependency directory, which the manager reads the same way.
 	Link  bool   `json:"link"`
 	Whose string `json:"whose"`
+
+	removable bool
 }
 
-// configDirs are the directories a scope's manager reads enable links from, the person's first: the
+// configDirs are the directories a scope's manager reads unit files and enable links from, in its own order
-// account's own configuration in user scope, the machine's administrator's, the runtime's and the packages'.
+// of precedence (systemd.unit(5), "Unit File Load Path"). The account's own are left out, and said, when its
+// home is not known.
 func (m *Manager) configDirs(scope Scope) []ConfigDir {
 	if scope == User {
+		account := "the operator account's own configuration"
 		dirs := []ConfigDir{}
 		if m.Home != "" {
-			dirs = append(dirs, ConfigDir{filepath.Join(m.Home, ".config", "systemd", "user"), "the operator account's own configuration"})
+			dirs = append(dirs, ConfigDir{filepath.Join(m.Home, ".config", "systemd", "user.control"), account + " (set by a program through the manager)", true})
+		}
+		dirs = append(dirs, ConfigDir{fmt.Sprintf("/run/user/%d/systemd/user", m.UID), "made at runtime, gone at the next login", false})
+		if m.Home != "" {
+			dirs = append(dirs, ConfigDir{filepath.Join(m.Home, ".config", "systemd", "user"), account, true})
+		}
+		dirs = append(dirs,
+			ConfigDir{"/etc/systemd/user", "the machine's configuration, for every account", true},
+			ConfigDir{"/etc/xdg/systemd/user", "the machine's configuration, for every account", true})
+		if m.Home != "" {
+			dirs = append(dirs, ConfigDir{filepath.Join(m.Home, ".local", "share", "systemd", "user"), "a program installed in the account's own home", false})
 		}
 		return append(dirs,
-			ConfigDir{"/etc/systemd/user", "the machine's configuration, for every account"},
+			ConfigDir{"/usr/local/lib/systemd/user", "a program installed by hand, for every account", false},
-			ConfigDir{"/usr/lib/systemd/user", "a package's"})
+			ConfigDir{"/usr/lib/systemd/user", "a package's", false})
 	}
 	return []ConfigDir{
-		{"/etc/systemd/system", "the machine's configuration"},
+		{"/etc/systemd/system.control", "the machine's configuration (set by a program through the manager)", true},
-		{"/run/systemd/system", "made at runtime, gone at the next boot"},
+		{"/run/systemd/transient", "made at runtime, gone at the next boot", false},
-		{"/usr/lib/systemd/system", "a package's"},
+		{"/run/systemd/generator.early", "a generator's, made again at every boot and reload", false},
+		{"/etc/systemd/system", "the machine's configuration", true},
+		{"/run/systemd/system", "made at runtime, gone at the next boot", false},
+		{"/run/systemd/generator", "a generator's, made again at every boot and reload", false},
+		{"/usr/local/lib/systemd/system", "a program installed by hand", false},
+		{"/usr/lib/systemd/system", "a package's", false},
+		{"/run/systemd/generator.late", "a generator's, made again at every boot and reload", false},
 	}
 }
 
+// within is whether a path lies in one of the directories.
+func within(path string, dirs []ConfigDir) bool {
+	path = filepath.Clean(path)
+	for _, d := range dirs {
+		if path == d.Path || strings.HasPrefix(path, d.Path+string(filepath.Separator)) {
+			return true
+		}
+	}
+	return false
+}
+
 // links finds every enable link naming the unit under the scope's configuration directories: by its own
 // name, or by the name of the file it points at. A directory that cannot be read is said, never skipped as
-// empty; one that does not exist is the ordinary case and is not.
+// empty; one that does not exist is the ordinary case and is not. **A dependency directory that is itself a
+// link is followed only when it leads into the searched directories**: elsewhere it is said, and not read,
+// so a link cannot point the search, or a removal after it, at any directory on the machine.
 func (m *Manager) links(scope Scope, unit string) ([]EnableLink, []string) {
 	found, unread := []EnableLink{}, []string{}
-	for _, dir := range m.configDirs(scope) {
+	dirs := m.configDirs(scope)
+	for _, dir := range dirs {
 		entries, err := m.ReadDir(dir.Path)
 		if err != nil {
 			if !errors.Is(err, fs.ErrNotExist) {
@@ -96,21 +138,29 @@ func (m *Manager) links(scope Scope, unit string) ([]EnableLink, []string) {
 			continue
 		}
 		for _, e := range entries {
-			if !e.Dir {
+			dependency, of := "", ""
-				continue
-			}
-			dependency := ""
-			of := ""
 			for suffix, dep := range dependencyDirs {
 				if strings.HasSuffix(e.Name, suffix) {
 					dependency, of = dep, strings.TrimSuffix(e.Name, suffix)
 				}
 			}
-			if dependency == "" {
+			if dependency == "" || (!e.Dir && e.Link == "") {
 				continue
 			}
 			sub := filepath.Join(dir.Path, e.Name)
-			inside, err := m.ReadDir(sub)
+			read := sub
+			if e.Link != "" {
+				target := e.Link
+				if !filepath.IsAbs(target) {
+					target = filepath.Join(dir.Path, target)
+				}
+				if !within(target, dirs) {
+					unread = append(unread, sub+": a link to "+e.Link+", outside the directories searched, not followed")
+					continue
+				}
+				read = filepath.Clean(target)
+			}
+			inside, err := m.ReadDir(read)
 			if err != nil {
 				if !errors.Is(err, fs.ErrNotExist) {
 					unread = append(unread, sub+": "+err.Error())
@@ -122,7 +172,8 @@ func (m *Manager) links(scope Scope, unit string) ([]EnableLink, []string) {
 					continue
 				}
 				found = append(found, EnableLink{Path: filepath.Join(sub, l.Name), Of: of, Dependency: dependency,
-					Target: l.Link, Dangles: l.Link != "" && l.Dangles, Link: l.Link != "", Whose: dir.Whose})
+					Target: l.Link, Dangles: l.Link != "" && l.Dangles, Error: l.Error, Link: l.Link != "",
+					Whose: dir.Whose, removable: dir.Removable && e.Link == ""})
 			}
 		}
 	}
@@ -140,13 +191,13 @@ func (m *Manager) WantedBy(scope Scope, unit string) (map[string]any, error) {
 	answer := map[string]any{"unit": unit, "scope": string(scope)}
 
 	manager := map[string]any{}
-	args := []string{"show", unit, "--no-pager"}
+	args := []string{"show", "--no-pager"}
 	for _, p := range append(append([]string{}, stateProperties...), reverseProperties...) {
 		args = append(args, "--property="+p)
 	}
 	loadState := ""
 	dependents := 0
-	if out, err := m.call(scope, "systemctl", args...); err != nil {
+	if out, err := m.call(scope, "systemctl", append(args, "--", unit)...); err != nil {
 		manager["error"] = err.Error()
 	} else {
 		for _, line := range strings.Split(out, "\n") {
@@ -190,7 +241,7 @@ func (m *Manager) WantedBy(scope Scope, unit string) (map[string]any, error) {
 	if len(unread) > 0 {
 		answer["unread"] = unread
 	}
-	answer["findings"] = findings(unit, loadState, dependents, links, unread, manager["error"] != nil)
+	answer["findings"] = findings(scope, unit, loadState, dependents, links, unread, manager["error"] != nil, m.Home == "")
 	return answer, nil
 }
 
@@ -204,31 +255,49 @@ func isReverse(property string) bool {
 }
 
 // findings say what the answer means, so a caller does not have to put the parts together.
-func findings(unit, loadState string, dependents int, links []EnableLink, unread []string, managerFailed bool) []string {
+func findings(scope Scope, unit, loadState string, dependents int, links []EnableLink, unread []string, managerFailed, noHome bool) []string {
 	out := []string{}
-	dangling := 0
+	dangling, removable, unknown := 0, 0, 0
 	for _, l := range links {
-		if l.Dangles {
+		switch {
+		case l.Dangles:
 			dangling++
-			out = append(out, l.Path+" makes "+l.Of+" want "+unit+" and points at "+l.Target+", which does not exist ("+l.Whose+")")
+			if l.removable {
+				removable++
+			}
+			out = append(out, l.Path+" makes "+l.Of+" "+strings.TrimSuffix(strings.ToLower(l.Dependency), "s")+" "+unit+" and points at "+l.Target+", which does not exist ("+l.Whose+")")
+		case l.Error != "":
+			unknown++
+			out = append(out, l.Path+" points at "+l.Target+", which could not be looked at: "+l.Error)
 		}
 	}
-	if loadState == "not-found" && len(links) > 0 && dangling == 0 {
+	if loadState == "not-found" && len(links) > 0 && dangling == 0 && unknown == 0 {
 		out = append(out, "the unit's file is not found, and "+plural(len(links), "enable link")+" still name it")
 	}
-	if dangling > 0 {
+	if removable > 0 {
-		out = append(out, "a dangling link is the manager's configuration, not the mesh's: `disable` in this scope removes the links naming the unit where the manager still accepts its name — ask this verb again to see that it is gone — and `reset-failed` then clears the unit's failed record")
+		out = append(out, "`disable` does not remove a link whose unit file is gone, and no verb of this seat removes one yet "+
+			"(novox/hq issue 332); once it is gone, `reset-failed` clears the unit's failed record")
+	} else if dangling > 0 {
+		out = append(out, "the dangling links are in a package's, a generator's or the runtime's directory, which puts them back: they are not the person's to remove")
 	}
-	if len(links) == 0 && dependents == 0 && !managerFailed && len(unread) == 0 {
+	incomplete := managerFailed || len(unread) > 0 || unknown > 0 || (scope == User && noHome)
+	if len(links) == 0 && dependents == 0 {
+		where := "in the directories searched"
+		if incomplete {
+			where += ", which are not all of them (below)"
+		}
 		if loadState == "not-found" {
-			out = append(out, "nothing names "+unit+" any more: a failed record of it is stale, and `reset-failed` clears it")
+			out = append(out, "nothing names "+unit+" "+where+": a failed record of it is stale, and `reset-failed` clears it")
-		} else {
+		} else if !managerFailed {
-			out = append(out, "no unit and no enable link pulls "+unit+" in: it starts only when asked by name, by a timer, socket or path unit the manager does not list, or by a program")
+			out = append(out, "no unit and no enable link pulls "+unit+" in "+where+": it starts only when asked by name, by a timer, socket or path unit the manager does not list, or by a program")
 		}
 	}
 	if managerFailed {
 		out = append(out, "the manager did not answer, so only the links on disk are known")
 	}
+	if scope == User && noHome {
+		out = append(out, "the account's home is not known to this process, so its own directories were not searched")
+	}
 	if len(unread) > 0 {
 		out = append(out, "some directories could not be read, so a link may be missing from this answer")
 	}
@@ -242,8 +311,9 @@ func plural(n int, what string) string {
 	return strconv.Itoa(n) + " " + what + "s"
 }
 
-// readDir lists a directory as enable links need it: each name, whether it is a directory (a link to one
+// readDir lists a directory as enable links need it, by lstat: each name, whether it is itself a directory,
-// followed), where a link points and whether that exists.
+// where a link points, and whether what it points at does not exist — any other failure to look is said as
+// the error it was, never as dangling.
 func readDir(dir string) ([]Entry, error) {
 	entries, err := os.ReadDir(dir)
 	if err != nil {
@@ -251,17 +321,25 @@ func readDir(dir string) ([]Entry, error) {
 	}
 	out := make([]Entry, 0, len(entries))
 	for _, e := range entries {
-		entry := Entry{Name: e.Name(), Dir: e.IsDir()}
+		out = append(out, entryOf(filepath.Join(dir, e.Name()), e.Name(), e.Type()))
-		if e.Type()&fs.ModeSymlink != 0 {
-			full := filepath.Join(dir, e.Name())
-			if target, err := os.Readlink(full); err == nil {
-				entry.Link = target
-			}
-			info, err := os.Stat(full)
-			entry.Dangles = err != nil
-			entry.Dir = err == nil && info.IsDir()
-		}
-		out = append(out, entry)
 	}
 	return out, nil
 }
+
+func entryOf(full, name string, mode fs.FileMode) Entry {
+	entry := Entry{Name: name, Dir: mode.IsDir()}
+	if mode&fs.ModeSymlink == 0 {
+		return entry
+	}
+	target, err := os.Readlink(full)
+	if err != nil {
+		target, entry.Error = "(unreadable)", err.Error()
+	}
+	entry.Link = target
+	if _, err := os.Stat(full); errors.Is(err, fs.ErrNotExist) {
+		entry.Dangles = true
+	} else if err != nil {
+		entry.Error = err.Error()
+	}
+	return entry
+}

modules/systemd/cmd/systemd-tools/wanted_test.go

@@ -1,10 +1,14 @@
 package main
 
 // What wants a unit, and a failed record cleared (novox/hq issue 332): over a fake runner and a fake
-// directory listing, so no link is made to test them.
+// directory listing, so no link is made to test them (the mesh makes no symbolic links, its tests
+// included); the real listing is tested on what a temporary directory holds without one.
 
 import (
+	"errors"
 	"io/fs"
+	"os"
+	"path/filepath"
 	"reflect"
 	"strings"
 	"testing"
@@ -72,7 +76,7 @@ func TestWantedByFindsADanglingEnableLinkInTheAccountsOwnConfiguration(t *testin
 	links := answer["links"].([]EnableLink)
 	want := []EnableLink{{Path: home + "/.config/systemd/user/default.target.wants/greenclip.service", Of: "default.target",
 		Dependency: "Wants", Target: "/usr/lib/systemd/user/greenclip.service", Dangles: true, Link: true,
-		Whose: "the operator account's own configuration"}}
+		Whose: "the operator account's own configuration", removable: true}}
 	if !reflect.DeepEqual(links, want) {
 		t.Fatalf("links %+v", links)
 	}
@@ -135,7 +139,7 @@ func TestWantedBySaysWhenNothingNamesTheUnit(t *testing.T) {
 		t.Fatalf("%v", answer["links"])
 	}
 	said := strings.Join(answer["findings"].([]string), "\n")
-	if !strings.Contains(said, "nothing names gone.service any more") {
+	if !strings.Contains(said, "nothing names gone.service in the directories searched:") {
 		t.Fatalf("%q", said)
 	}
 }
@@ -229,7 +233,7 @@ func TestResetFailedClearsOneUnitEscalatedOnlyInTheSystemScope(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if !reflect.DeepEqual(calls[0].args, []string{"--user", "reset-failed", "greenclip.service"}) || calls[0].cmd != "systemctl" {
+	if !reflect.DeepEqual(calls[0].args, []string{"--user", "reset-failed", "--", "greenclip.service"}) || calls[0].cmd != "systemctl" {
 		t.Fatalf("%s %v", calls[0].cmd, calls[0].args)
 	}
 	answer := out.(map[string]any)
@@ -247,3 +251,194 @@ func TestResetFailedClearsOneUnitEscalatedOnlyInTheSystemScope(t *testing.T) {
 type stdioTool struct {
 	run func(map[string]any) (any, error)
 }
+
+// **A glob is not a unit** (the review of mesh-catalog #137): systemctl expands it to every loaded unit it
+// matches, so `reset-failed` or `stop` of "*" would act on all of them. Refused before anything runs, for
+// every verb taking a unit.
+func TestAGlobIsRefusedAsAUnitByEveryVerb(t *testing.T) {
+	for _, bad := range []string{"*", "*.service", "foo?.service", "a[bc].mount"} {
+		if unitArg(bad) == nil {
+			t.Errorf("%q accepted", bad)
+		}
+	}
+	var calls []call
+	m := withTree(operator(fake(func(call) Ran { return Ran{} }, &calls)), tree{})
+	for _, tool := range tools(m) {
+		verb := strings.TrimPrefix(tool.Name, seat+".")
+		if verb == "units" || verb == "failed" {
+			continue // a pattern, and no unit
+		}
+		_, err := tool.Run(map[string]any{"unit": "*", "scope": "user", "why": "test"})
+		if err == nil {
+			t.Errorf("%s accepted {\"unit\":\"*\"}", verb)
+		}
+	}
+	if len(calls) != 0 {
+		t.Fatalf("a glob reached the manager: %v", calls)
+	}
+}
+
+// The unit is given after "--" to show as well as to an act, so nothing after it is read as an option.
+func TestTheUnitComesAfterTheEndOfOptions(t *testing.T) {
+	var calls []call
+	m := operator(fake(func(call) Ran { return Ran{Stdout: "LoadState=loaded\n"} }, &calls))
+	if _, err := m.Status(System, "sshd.service"); err != nil {
+		t.Fatal(err)
+	}
+	a := calls[0].args
+	if a[0] != "show" || a[len(a)-2] != "--" || a[len(a)-1] != "sshd.service" {
+		t.Fatalf("%v", a)
+	}
+}
+
+// A target that could not be looked at, for any reason but its not existing, is neither dangling nor not:
+// it is said as the error it was, and the answer does not say nothing names the unit.
+func TestALinkWhoseTargetCannotBeLookedAtIsNotSaidToDangle(t *testing.T) {
+	user := home + "/.config/systemd/user"
+	fsys := tree{
+		user:                           {{Name: "default.target.wants", Dir: true}},
+		user + "/default.target.wants": {{Name: "x.service", Link: "/mnt/away/x.service", Error: "stat /mnt/away/x.service: permission denied"}},
+	}
+	answer, err := withTree(operator(fake(showAndReverse("LoadState=loaded\n", "x.service\n"), nil)), fsys).WantedBy(User, "x.service")
+	if err != nil {
+		t.Fatal(err)
+	}
+	links := answer["links"].([]EnableLink)
+	if len(links) != 1 || links[0].Dangles || links[0].Error == "" {
+		t.Fatalf("%+v", links)
+	}
+	said := strings.Join(answer["findings"].([]string), "\n")
+	if !strings.Contains(said, "could not be looked at: stat /mnt/away/x.service: permission denied") || strings.Contains(said, "does not exist") {
+		t.Fatalf("%q", said)
+	}
+}
+
+// A *.wants directory that is itself a link is followed only into the directories searched: one leading
+// elsewhere is said and not read, so neither the search nor a removal after it can be pointed anywhere.
+func TestALinkedDependencyDirectoryIsFollowedOnlyIntoTheSearchedDirectories(t *testing.T) {
+	user := home + "/.config/systemd/user"
+	fsys := tree{
+		user: {
+			{Name: "default.target.wants", Link: "/srv/elsewhere"},
+			{Name: "graphical-session.target.wants", Link: "/etc/systemd/user/shared.wants"},
+		},
+		"/srv/elsewhere":                 {{Name: "x.service", Link: "/gone/x.service", Dangles: true}},
+		"/etc/systemd/user/shared.wants": {{Name: "x.service", Link: "/gone/x.service", Dangles: true}},
+	}
+	read := []string{}
+	m := withTree(operator(fake(showAndReverse("LoadState=not-found\n", "x.service\n"), nil)), fsys)
+	inner := m.ReadDir
+	m.ReadDir = func(dir string) ([]Entry, error) { read = append(read, dir); return inner(dir) }
+	answer, err := m.WantedBy(User, "x.service")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, d := range read {
+		if d == "/srv/elsewhere" {
+			t.Fatal("a linked .wants outside the searched directories was followed")
+		}
+	}
+	links := answer["links"].([]EnableLink)
+	if len(links) != 1 || links[0].Path != user+"/graphical-session.target.wants/x.service" || links[0].removable {
+		t.Fatalf("%+v", links)
+	}
+	unread, _ := answer["unread"].([]string)
+	if len(unread) != 1 || !strings.Contains(unread[0], "outside the directories searched, not followed") {
+		t.Fatalf("%v", unread)
+	}
+}
+
+// "Nothing names it" is only ever said of the directories searched, and the account's own are not among
+// them when its home is not known — which is said.
+func TestNothingNamesItIsSaidOfTheDirectoriesSearchedAndTheHomeWhenUnknown(t *testing.T) {
+	m := withTree(operator(fake(showAndReverse("LoadState=not-found\n", "x.service\n"), nil)), tree{})
+	m.Home = ""
+	answer, err := m.WantedBy(User, "x.service")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, d := range answer["searched"].([]ConfigDir) {
+		if strings.Contains(d.Path, ".config") || strings.Contains(d.Path, ".local") || d.Path == "" {
+			t.Fatalf("searched %q without a home", d.Path)
+		}
+	}
+	said := strings.Join(answer["findings"].([]string), "\n")
+	if !strings.Contains(said, "nothing names x.service in the directories searched, which are not all of them") ||
+		!strings.Contains(said, "the account's home is not known") {
+		t.Fatalf("%q", said)
+	}
+	m.Home = home
+	answer, _ = m.WantedBy(User, "x.service")
+	said = strings.Join(answer["findings"].([]string), "\n")
+	if !strings.Contains(said, "nothing names x.service in the directories searched:") {
+		t.Fatalf("%q", said)
+	}
+}
+
+// Every directory systemd reads units from, in both scopes (systemd.unit(5)).
+func TestTheSearchedDirectoriesAreTheManagersLoadPath(t *testing.T) {
+	m := withTree(operator(nil), tree{})
+	paths := func(s Scope) string {
+		var out []string
+		for _, d := range m.configDirs(s) {
+			out = append(out, d.Path)
+		}
+		return strings.Join(out, "\n")
+	}
+	for _, want := range []string{"/etc/systemd/system.control", "/run/systemd/transient", "/run/systemd/generator.early",
+		"/etc/systemd/system", "/run/systemd/system", "/run/systemd/generator", "/usr/local/lib/systemd/system",
+		"/usr/lib/systemd/system", "/run/systemd/generator.late"} {
+		if !strings.Contains(paths(System)+"\n", want+"\n") {
+			t.Errorf("system scope does not search %s", want)
+		}
+	}
+	for _, want := range []string{home + "/.config/systemd/user.control", "/run/user/1000/systemd/user", home + "/.config/systemd/user",
+		"/etc/systemd/user", "/etc/xdg/systemd/user", home + "/.local/share/systemd/user", "/usr/local/lib/systemd/user", "/usr/lib/systemd/user"} {
+		if !strings.Contains(paths(User)+"\n", want+"\n") {
+			t.Errorf("user scope does not search %s", want)
+		}
+	}
+}
+
+// The real listing, by lstat, on what a temporary directory holds: a directory, a file, and a directory
+// that does not exist or cannot be read.
+func TestReadDirListsByLstat(t *testing.T) {
+	dir := t.TempDir()
+	if err := os.Mkdir(filepath.Join(dir, "default.target.wants"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, "x.service"), []byte("[Unit]\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	entries, err := readDir(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []Entry{{Name: "default.target.wants", Dir: true}, {Name: "x.service"}}
+	if !reflect.DeepEqual(entries, want) {
+		t.Fatalf("%+v", entries)
+	}
+	if _, err := readDir(filepath.Join(dir, "absent")); !errors.Is(err, fs.ErrNotExist) {
+		t.Fatalf("a missing directory: %v", err)
+	}
+	if os.Getuid() != 0 {
+		locked := filepath.Join(dir, "locked")
+		if err := os.Mkdir(locked, 0o000); err != nil {
+			t.Fatal(err)
+		}
+		defer os.Chmod(locked, 0o755)
+		if _, err := readDir(locked); err == nil || errors.Is(err, fs.ErrNotExist) {
+			t.Fatalf("an unreadable directory read as %v", err)
+		}
+	}
+	// And through the search: a real tree with no link in it names nothing, and says so.
+	m := operator(fake(showAndReverse("LoadState=not-found\n", "x.service\n"), nil))
+	m.Home, m.ReadDir = dir, readDir
+	answer, err := m.WantedBy(User, "x.service")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(answer["links"].([]EnableLink)) != 0 {
+		t.Fatalf("%v", answer["links"])
+	}
+}