Struct LinuxHostIdFile 

pub struct LinuxHostIdFile { /* private fields */ }

/etc/hostid — the glibc 4-byte binary hostid file read by gethostid(3) and hostid(1).

Opt-in only: not part of crate::sources::default_chain or [crate::sources::network_default_chain]. On stock Linux distros the file is absent (no sethostid has run), so defaulting it would cost every caller a syscall for a near-universal miss. Ship it as a constructible type so operators who know they have /etc/hostid (OpenZFS hosts, minimal non-systemd images, Red Hat containers that bind-mount machine-id but not hostid) can push it explicitly.

File format

glibc stores the hostid as four raw bytes in native byte order (sethostid(2)). Decoded with u32::from_ne_bytes(...) and formatted as 8-digit lowercase hex to match hostid(1) output.

Why we don’t call gethostid(3)

When /etc/hostid is absent glibc fabricates a value from gethostname() → IPv4 lookup. That value is neither stable nor unique and would flow through as identity — actively harmful. This source reads the file directly; absence yields Ok(None) so the resolver falls through.

Probe behaviour

• File absent / PermissionDenied → Ok(None).
• File size ≠ 4 bytes → Ok(None) with a log::debug! entry (defensive: sheared reads, FreeBSD text-UUID /etc/hostid mistakenly placed on Linux).
• Value 0x00000000 or 0xffffffff → Ok(None) with a log::debug! entry (unset or known-garbage sentinels).
• Other I/O error → Err(Error::Io).
• Otherwise → Ok(Some(Probe::new(SourceKind::LinuxHostId, "<hex>"))).

Implementations

impl LinuxHostIdFile

pub fn new() -> Self

Read from the standard path (/etc/hostid).

pub fn at(path: impl Into<PathBuf>) -> Self

Read from a caller-supplied path. Useful for tests and unusual image layouts.

pub fn path(&self) -> &Path

The configured path.

Trait Implementations

impl Clone for LinuxHostIdFile

fn clone(&self) -> LinuxHostIdFile

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for LinuxHostIdFile

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for LinuxHostIdFile

fn default() -> Self

Returns the “default value” for a type.

impl Source for LinuxHostIdFile

fn kind(&self) -> SourceKind

Provenance label for this source. Shown in error messages and the resolved crate::HostId.

fn probe(&self) -> Result<Option<Probe>, Error>

Attempt to produce a raw identifier.