In one of the next commits we'd like to introduce a concept of
optionally hashing the hostname from the machine ID. For that we we need
to optionally back gethostname_full() by code involving sd-id128, hence
let's move it from src/basic/ to src/shared/, since only there we are
allowed to use our public APIs.
once we decided on a hostname, let's tell the supervisor about it. This
is useful for example in order to recognize the system via mDNS/LLMNR or
in a DHCP lease.
`system.hostname` credential is treated similarly to the pre-existing
`system.machine_id` credential. It is considered after /etc/hostname,
but prior to the kernel defaults or os-release defaults.
Fixes#30667.
Signed-off-by: Ivan Shapovalov <intelfx@intelfx.name>
Previously, sethostname_idempotent_full() calls gethostname_full() with
GET_HOSTNAME_ALLOW_NONE and GET_HOSTNAME_ALLOW_LOCALHOST flags. That
intended to get any values set by kernel. But, that does not work, as
the hostname may be empty.
Let's simplify the logic. The function sethostname_idempotent_full()
intends to set the requested hostname only when the current hostname
is different from the requested one. So, no check in getostname_full()
is required. Hence, simply use the result of uname() here.
Fixes#21896.
This follows the addition of DEFAULT_HOSTNAME= in os-release.
The distinction between the value from os-release or the env var and
the compile-time setting is not made in the api: HostnameSource is
"default" is all cases. I think that this level of detail is not needed,
because the users of this mostly care whether the hostname was set by
user configuration or not.
See https://bugzilla.redhat.com/show_bug.cgi?id=1893417 for the back story:
the fallback hostname matters a lot in certain environments. Right now the only
way to configure the fallback hostname is by recompiling systemd, which is
obviously problematic in case when the fallback hostname shall differ between
different editions of the same distro that share a single compiled rpm.
By making this overridable through an envvar, we're providing an escape hatch
without making this a top-level api. Later on a way to set this through
os-release is added, but I think the approach with the variable is still
useful. It it very convenient for testing, or to override settings only in a
particular service, etc.
In hostnamed this is exposed as a dbus property, and in the logs in both
places.
This is of interest to network management software and such: if the fallback
hostname is used, it's not as useful as the real configured thing. Right now
various programs try to guess the source of hostname by looking at the string.
E.g. "localhost" is assumed to be not the real hostname, but "fedora" is. Any
such attempts are bound to fail, because we cannot distinguish "fedora" (a
fallback value set by a distro), from "fedora" (received from reverse dns),
from "fedora" read from /etc/hostname.
/run/systemd/fallback-hostname is written with the fallback hostname when
either pid1 or hostnamed sets the kernel hostname to the fallback value. Why
remember the fallback value and not the transient hostname in /run/hostname
instead?
We have three hostname types: "static", "transient", fallback".
– Distinguishing "static" is easy: the hostname that is set matches what
is in /etc/hostname.
– Distingiushing "transient" and "fallback" is not easy. And the
"transient" hostname may be set outside of pid1+hostnamed. In particular,
it may be set by container manager, some non-systemd tool in the initramfs,
or even by a direct call. All those mechanisms count as "transient". Trying
to get those cases to write /run/hostname is futile. It is much easier to
isolate the "fallback" case which is mostly under our control.
And since the file is only used as a flag to mark the hostname as fallback,
it can be hidden inside of our /run/systemd directory.
For https://bugzilla.redhat.com/show_bug.cgi?id=1892235.
gethostname(3) says it's unspecified whether the string is properly terminated
when the hostname is too long. We created a buffer with one extra byte, and it
seems the intent was to let that byte serve as terminator even if we get an
unterminated string from gethostname().
No functional change, just moving a bunch of things around. Before
we needed a rather complicated setup to test hostname_setup(), because
the code was in src/core/. When things are moved to src/shared/
we can just test it as any function.
The test is still "unsafe" because hostname_setup() may modify the
hostname.
Daan De Meyer
Yu Watanabe
Lennart Poettering
Ivan Shapovalov
Zbigniew Jędrzejewski-Szmek
Kay Sievers