In the wiki, this was a separate page. I don't think this split is useful,
since the information about what is stable and what not seems randomly split
between the two pages.
Links are adjusted for our own pages. Some external links to gentoo and other
projects seem to be broken, but it's a chore to fix them.
Instead of saying that patches for portability are not accepted, say that this
is decided case-by-case. This is what happens in practice, and we tend to
discuss each patch on its own merits.
Some sentences are reworded a bit where they sound awkward.
Failing after a single check leads to extra sleeps scattered through
test cases, and can also lead to false failures. Instead perform a
recheck for a number of seconds until the state matches, and fail only
if the timeout is exceeded.
This allows removing all the manual sleeps in the testcases.
Interfaces may come up at any time, even during our initialization of
them, for various reasons; e.g. the kernel will raise VLAN when its
parent is raised; or we will raise an interface if configured with
BindCarrier and its associated interfaces come up.
When LinkLocalAddressing has been disabled for ipv6, we disable
addr_gen_mode in the kernel, so it will not automatically create a
ipv6ll address when the interface is raised. However, we currently
drop all foreign addresses before disabling addr_gen_mode.
If the link has been up for a long time, then its kernel-created ipv6ll
address will be correctly dropped. If the link is down, and stays
down until we raise it after finishing configuration, the addr_gen_mode
setting will be disabled when the interface is raised and the kernel
will not create any ipv6ll address.
However, if the interface is raised after dropping foreign config,
but before we have disabled addr_gen_mode, the kernel will create a
ipv6ll tentative address that will eventually finish DAD and become a
working ipv6ll address, even though we have been configured to disable
ipv6ll.
Moving our call to drop foreign addresses to after we have successfully
set addr_gen_mode closes this window; after we disable addr_gen_mode,
we can safely remove foreign ipv6ll addresses (including tentative ones)
and be sure that the kernel will not create any more.
Fixes: #13882.
The kernel will create an ipv6ll tentative address immediately when an
interface is raised if addr_gen_mode is not disabled; and, the kernel does
not notify netlink listeners about any tentative addresses. So it's
possible for an interface to contain tentative ipv6 link-local address(es)
that networkd doesn't know about when all foreign addresses are dropped.
In this case, networkd is later notified about the new ipv6ll address(es)
after they finish DAD and are no longer tentative; but since that's after
networkd has already dropped foreign addresses, they are incorrectly left
on the interface.
Similar to the link->setting_mtu flag, this delays continued configuration
until after the genmode has been successfully set; this is important
because we do not want networkd to raise the interface before the genmode
has been set, as if we're disabling the genmode, raising the interface
before we have successfully disabled the genmode will result in the kernel
creating a ipv6ll address, even though we don't want that.
There are sometimes users who put unit files in a location that is inaccessible
when systemd starts although they are not found and thus not started because
the corresponding mount units have not activated yet.
There is already a warning for such issue in man 8 systemctl:
link PATH...
...<snip>...
The file system where
the linked unit files are located must be accessible
when systemd is started (e.g. anything underneath /home
or /var is not allowed, unless those directories are
located on the root file system).
However, it looks that it's difficult to find the warning because introductory
users typically doesn't know systemctl link.
Although there is a description in UNIT FILE LOAD PATH pointing to systemctl
link, symlink is now not explicitly mentioned there and thus users doesn't
easily get aware of they should read it.
To deal with this, let's describe "symlink" and "systemctl link" more
explicitly in UNIT FILE LOAD PATH.
