jochen
2ed6264b8f
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.
346 lines
14 KiB
Go
346 lines
14 KiB
Go
package main
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// What wants, requires or triggers one unit (novox/hq issue 332), read-only. Two sources, because each misses
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// what the other sees:
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//
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// - **the manager**, asked for the unit's reverse dependencies (systemctl show's WantedBy, RequiredBy and
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// the rest, and list-dependencies --reverse for what pulls it in through another unit). It knows what is
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// loaded now, including a dependency a unit file states in its own [Unit] section;
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// - **the configuration directories**, read for an enable link naming the unit in a *.wants, *.requires or
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// *.upholds directory. A link outlives the unit file it pointed at: once the package that shipped the unit
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// is gone, the link dangles, and the manager asks for a unit it cannot find at every boot or login. That
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// is the case a failed record of a unit whose load state is not-found comes from, and the answer says
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// each link's target and whether it dangles.
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//
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// Nothing here changes anything. Clearing the record is `reset-failed`'s.
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import (
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"errors"
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"fmt"
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"io/fs"
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"os"
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"path/filepath"
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"sort"
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"strconv"
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"strings"
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)
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// reverseProperties are the unit's properties that name a unit depending on it.
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var reverseProperties = []string{"WantedBy", "RequiredBy", "RequisiteOf", "BoundBy", "UpheldBy", "ConsistsOf", "TriggeredBy", "PartOf"}
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// stateProperties say what the manager knows of the unit itself, so a not-found unit is recognised.
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var stateProperties = []string{"LoadState", "ActiveState", "SubState", "UnitFileState", "FragmentPath"}
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// dependencyDirs are the suffixes of the directories an enable link sits in, and the dependency each makes.
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var dependencyDirs = map[string]string{".wants": "Wants", ".requires": "Requires", ".upholds": "Upholds"}
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// Entry is one name in a directory as lstat sees it: a link is never followed to say what it is.
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type Entry struct {
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Name string
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// Dir is whether the name is itself a directory; a link to one is not.
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Dir bool
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// Link is where a symbolic link points, as written; empty when the name is not a link.
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Link string
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// Dangles is whether a link points at nothing: what it names does not exist.
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Dangles bool
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// Error is why a link's target could not be looked at, when that is anything but its not existing.
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Error string
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}
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// ConfigDir is one directory a manager reads units and enable links from, and whose it is.
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type ConfigDir struct {
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Path string `json:"path"`
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Whose string `json:"whose"`
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// Removable is whether a dangling link here is a person's or an administrator's to remove: their own
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// configuration, not a package's, a generator's or the runtime's, which put theirs back.
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Removable bool `json:"-"`
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}
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// EnableLink is one link in a dependency directory that names the unit.
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type EnableLink struct {
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Path string `json:"path"`
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// Of is the unit that wants (or requires, or upholds) this one: the directory's name less its suffix.
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Of string `json:"of"`
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Dependency string `json:"dependency"`
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Target string `json:"target,omitempty"`
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Dangles bool `json:"dangles"`
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// Error is why the target could not be looked at, other than its not existing: neither dangling nor not.
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Error string `json:"error,omitempty"`
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// Link is false for a plain file in a dependency directory, which the manager reads the same way.
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Link bool `json:"link"`
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Whose string `json:"whose"`
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removable bool
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}
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// configDirs are the directories a scope's manager reads unit files and enable links from, in its own order
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// of precedence (systemd.unit(5), "Unit File Load Path"). The account's own are left out, and said, when its
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// home is not known.
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func (m *Manager) configDirs(scope Scope) []ConfigDir {
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if scope == User {
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account := "the operator account's own configuration"
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dirs := []ConfigDir{}
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if m.Home != "" {
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dirs = append(dirs, ConfigDir{filepath.Join(m.Home, ".config", "systemd", "user.control"), account + " (set by a program through the manager)", true})
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}
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dirs = append(dirs, ConfigDir{fmt.Sprintf("/run/user/%d/systemd/user", m.UID), "made at runtime, gone at the next login", false})
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if m.Home != "" {
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dirs = append(dirs, ConfigDir{filepath.Join(m.Home, ".config", "systemd", "user"), account, true})
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}
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dirs = append(dirs,
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ConfigDir{"/etc/systemd/user", "the machine's configuration, for every account", true},
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ConfigDir{"/etc/xdg/systemd/user", "the machine's configuration, for every account", true})
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if m.Home != "" {
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dirs = append(dirs, ConfigDir{filepath.Join(m.Home, ".local", "share", "systemd", "user"), "a program installed in the account's own home", false})
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}
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return append(dirs,
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ConfigDir{"/usr/local/lib/systemd/user", "a program installed by hand, for every account", false},
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ConfigDir{"/usr/lib/systemd/user", "a package's", false})
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}
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return []ConfigDir{
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{"/etc/systemd/system.control", "the machine's configuration (set by a program through the manager)", true},
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{"/run/systemd/transient", "made at runtime, gone at the next boot", false},
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{"/run/systemd/generator.early", "a generator's, made again at every boot and reload", false},
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{"/etc/systemd/system", "the machine's configuration", true},
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{"/run/systemd/system", "made at runtime, gone at the next boot", false},
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{"/run/systemd/generator", "a generator's, made again at every boot and reload", false},
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{"/usr/local/lib/systemd/system", "a program installed by hand", false},
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{"/usr/lib/systemd/system", "a package's", false},
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{"/run/systemd/generator.late", "a generator's, made again at every boot and reload", false},
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}
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}
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// within is whether a path lies in one of the directories.
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func within(path string, dirs []ConfigDir) bool {
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path = filepath.Clean(path)
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for _, d := range dirs {
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if path == d.Path || strings.HasPrefix(path, d.Path+string(filepath.Separator)) {
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return true
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}
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}
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return false
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}
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// links finds every enable link naming the unit under the scope's configuration directories: by its own
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// name, or by the name of the file it points at. A directory that cannot be read is said, never skipped as
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// empty; one that does not exist is the ordinary case and is not. **A dependency directory that is itself a
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// link is followed only when it leads into the searched directories**: elsewhere it is said, and not read,
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// so a link cannot point the search, or a removal after it, at any directory on the machine.
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func (m *Manager) links(scope Scope, unit string) ([]EnableLink, []string) {
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found, unread := []EnableLink{}, []string{}
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dirs := m.configDirs(scope)
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for _, dir := range dirs {
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entries, err := m.ReadDir(dir.Path)
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if err != nil {
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if !errors.Is(err, fs.ErrNotExist) {
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unread = append(unread, dir.Path+": "+err.Error())
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}
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continue
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}
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for _, e := range entries {
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dependency, of := "", ""
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for suffix, dep := range dependencyDirs {
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if strings.HasSuffix(e.Name, suffix) {
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dependency, of = dep, strings.TrimSuffix(e.Name, suffix)
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}
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}
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if dependency == "" || (!e.Dir && e.Link == "") {
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continue
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}
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sub := filepath.Join(dir.Path, e.Name)
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read := sub
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if e.Link != "" {
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target := e.Link
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if !filepath.IsAbs(target) {
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target = filepath.Join(dir.Path, target)
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}
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if !within(target, dirs) {
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unread = append(unread, sub+": a link to "+e.Link+", outside the directories searched, not followed")
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continue
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}
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read = filepath.Clean(target)
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}
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inside, err := m.ReadDir(read)
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if err != nil {
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if !errors.Is(err, fs.ErrNotExist) {
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unread = append(unread, sub+": "+err.Error())
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}
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continue
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}
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for _, l := range inside {
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if l.Name != unit && (l.Link == "" || filepath.Base(l.Link) != unit) {
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continue
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}
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found = append(found, EnableLink{Path: filepath.Join(sub, l.Name), Of: of, Dependency: dependency,
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Target: l.Link, Dangles: l.Link != "" && l.Dangles, Error: l.Error, Link: l.Link != "",
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Whose: dir.Whose, removable: dir.Removable && e.Link == ""})
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}
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}
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}
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sort.Slice(found, func(i, j int) bool { return found[i].Path < found[j].Path })
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return found, unread
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}
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// WantedBy is what wants, requires or triggers one unit: the manager's reverse dependencies and the enable
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// links naming it, with a finding in words. A manager that does not answer is said beside the links, which
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// are read from disk and do not need it.
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func (m *Manager) WantedBy(scope Scope, unit string) (map[string]any, error) {
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if err := unitArg(unit); err != nil {
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return nil, err
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}
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answer := map[string]any{"unit": unit, "scope": string(scope)}
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manager := map[string]any{}
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args := []string{"show", "--no-pager"}
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for _, p := range append(append([]string{}, stateProperties...), reverseProperties...) {
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args = append(args, "--property="+p)
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}
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loadState := ""
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dependents := 0
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if out, err := m.call(scope, "systemctl", append(args, "--", unit)...); err != nil {
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manager["error"] = err.Error()
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} else {
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for _, line := range strings.Split(out, "\n") {
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k, v, ok := strings.Cut(line, "=")
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if !ok || k == "" {
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continue
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}
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if isReverse(k) {
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if names := strings.Fields(v); len(names) > 0 {
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manager[k] = names
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dependents += len(names)
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}
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continue
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}
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manager[k] = v
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}
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loadState, _ = manager["LoadState"].(string)
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}
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// Through other units: list-dependencies --reverse follows the same edges from the units that pull in
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// those that pull this one in. Its first line is the unit itself.
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if out, err := m.call(scope, "systemctl", "list-dependencies", "--reverse", "--plain", "--no-legend", "--no-pager", "--", unit); err != nil {
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manager["reverse_error"] = err.Error()
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} else {
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chain := []string{}
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for i, line := range strings.Split(out, "\n") {
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name := strings.TrimSpace(strings.TrimLeft(line, " │├└─●○×*"))
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if i == 0 || name == "" || name == unit {
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continue
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}
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chain = append(chain, name)
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}
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if len(chain) > 0 {
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manager["reverse"] = chain
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}
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}
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answer["manager"] = manager
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links, unread := m.links(scope, unit)
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answer["links"] = links
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answer["searched"] = m.configDirs(scope)
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if len(unread) > 0 {
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answer["unread"] = unread
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}
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answer["findings"] = findings(scope, unit, loadState, dependents, links, unread, manager["error"] != nil, m.Home == "")
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return answer, nil
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}
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func isReverse(property string) bool {
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for _, p := range reverseProperties {
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if p == property {
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return true
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}
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}
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return false
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}
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// findings say what the answer means, so a caller does not have to put the parts together.
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func findings(scope Scope, unit, loadState string, dependents int, links []EnableLink, unread []string, managerFailed, noHome bool) []string {
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out := []string{}
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dangling, removable, unknown := 0, 0, 0
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for _, l := range links {
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switch {
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case l.Dangles:
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dangling++
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if l.removable {
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removable++
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}
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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+")")
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case l.Error != "":
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unknown++
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out = append(out, l.Path+" points at "+l.Target+", which could not be looked at: "+l.Error)
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}
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}
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if loadState == "not-found" && len(links) > 0 && dangling == 0 && unknown == 0 {
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out = append(out, "the unit's file is not found, and "+plural(len(links), "enable link")+" still name it")
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}
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if removable > 0 {
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out = append(out, "`disable` does not remove a link whose unit file is gone, and no verb of this seat removes one yet "+
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"(novox/hq issue 332); once it is gone, `reset-failed` clears the unit's failed record")
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} else if dangling > 0 {
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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")
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}
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incomplete := managerFailed || len(unread) > 0 || unknown > 0 || (scope == User && noHome)
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if len(links) == 0 && dependents == 0 {
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where := "in the directories searched"
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if incomplete {
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where += ", which are not all of them (below)"
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}
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if loadState == "not-found" {
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out = append(out, "nothing names "+unit+" "+where+": a failed record of it is stale, and `reset-failed` clears it")
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} else if !managerFailed {
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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")
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}
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}
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if managerFailed {
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out = append(out, "the manager did not answer, so only the links on disk are known")
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}
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if scope == User && noHome {
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out = append(out, "the account's home is not known to this process, so its own directories were not searched")
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}
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if len(unread) > 0 {
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out = append(out, "some directories could not be read, so a link may be missing from this answer")
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}
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return out
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}
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func plural(n int, what string) string {
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if n == 1 {
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return "1 " + what
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}
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return strconv.Itoa(n) + " " + what + "s"
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}
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// readDir lists a directory as enable links need it, by lstat: each name, whether it is itself a directory,
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// where a link points, and whether what it points at does not exist — any other failure to look is said as
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// the error it was, never as dangling.
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func readDir(dir string) ([]Entry, error) {
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entries, err := os.ReadDir(dir)
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if err != nil {
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return nil, err
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}
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out := make([]Entry, 0, len(entries))
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for _, e := range entries {
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out = append(out, entryOf(filepath.Join(dir, e.Name()), e.Name(), e.Type()))
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}
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return out, nil
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}
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func entryOf(full, name string, mode fs.FileMode) Entry {
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entry := Entry{Name: name, Dir: mode.IsDir()}
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if mode&fs.ModeSymlink == 0 {
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return entry
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}
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target, err := os.Readlink(full)
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if err != nil {
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target, entry.Error = "(unreadable)", err.Error()
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}
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entry.Link = target
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if _, err := os.Stat(full); errors.Is(err, fs.ErrNotExist) {
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entry.Dangles = true
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} else if err != nil {
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entry.Error = err.Error()
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}
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return entry
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}
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