The general idea is that users should be able to figure out if some option
that they see in a config file or on some internet page is something that
systemd knows about. Once users know that, yes, this was an option but has
been deprecated and removed from the documentation, it's much easier for them
to find any docs in old versions if they want to. Or to switch to something
different.
This imports credentials also via SMBIOS' "OEM vendor string" section,
similar to the existing import logic from fw_cfg.
Functionality-wise this is very similar to the existing fw_cfg logic,
both of which are easily settable on the qemu command line.
Pros and cons of each:
SMBIOS OEM vendor strings:
- pro: fast, because memory mapped
- pro: somewhat VMM independent, at least in theory
- pro: qemu upstream sees this as the future
- pro: no additional kernel module needed
- con: strings only, thus binary data is base64 encoded
fw_cfg:
- pro: has been supported for longer in qemu
- pro: supports binary data
- con: slow, because IO port based
- con: only qemu
- con: requires qemu_fw_cfg.ko kernel module
- con: qemu upstream sees this as legacy
Let's merge the footnote with the overall explanation of where systemd
parses its options from and reword the section a bit to hopefully make
things a bit more clear.
Before this patch, there was no way to request all running user instances for
reexecuting. However this can be useful especially during package updates
otherwise user instances are never updated and keep running a potentially very
old version of the binaries.
Now assuming that we have enough priviledge, it's possible to request
reexecution of all user instances:
systemctl kill --signal=SIGRTMIN+25 "user@*.service"
Note that this request is obviously asynchronous as it relies on a
signal. Keeping "systemctl kill" as the only interface should be good enough to
make this obvious and that's the reason why another interface, such as
"systemctl --global daemon-reexec" has not been considered.
PID1 already uses SIGTERM for reexecuting hence sending it SIGRTMIN+25 is a
nop.
* Fixed typo
Before, the file claimed that some systemd units are created "from other
configuration". It should have read "from other configuration files".
Co-authored-by: Nozz <nozolo90@gmail.com>
Some extra safety when invoked via "sudo". With this we address a
genuine design flaw of sudo, and we shouldn't need to deal with this.
But it's still a good idea to disable this surface given how exotic it
is.
Prompted by #5666
