This adds a small, socket-activated Varlink daemon that can delegate UID
ranges for user namespaces to clients asking for it.
The primary call is AllocateUserRange() where the user passes in an
uninitialized userns fd, which is then set up.
There are other calls that allow assigning a mount fd to a userns
allocated that way, to set up permissions for a cgroup subtree, and to
allocate a veth for such a user namespace.
Since the UID assignments are supposed to be transitive, i.e. not
permanent, care is taken to ensure that users cannot create inodes owned
by these UIDs, so that persistancy cannot be acquired. This is
implemented via a BPF-LSM module that ensures that any member of a
userns allocated that way cannot create files unless the mount it
operates on is owned by the userns itself, or is explicitly
allowelisted.
BPF LSM program with contributions from Alexei Starovoitov.
This is just good style. In this particular case, if the argument is incorrect and
the function is not tested with $NOTIFY_SOCKET set, the user could not get the
proper error until running for real.
Also, remove mention of systemd. The protocol is fully generic on purpose.
F40 will be out soon, so we can update the man page already. The example should
already work.
The cloud link was dropped in fd571c9df0, so
drop the unused variable too.
Unfortunately, sd-bus-vtable.h, sd-journal.h, and sd-id128.h
have variadic macro and inline initialization of sub-object, these are
not supported in C90. So, we need to silence some errors.
I think the example should reflect the full set of lifecycle messages,
including STOPPING=1, which tells the service manager that the service
is already terminating. This is useful for reporting this information
back to the user and to suppress repeated shutdown requests.
It's not as important as the READY=1 and RELOADING=1 messages, since we
actively wait for those from the service message if the right Type= is
set. But it's still very valuable information, easy to do, and completes
the state engine.
stale HibernateLocation EFI variable
Currently, if the HibernateLocation EFI variable exists,
but we failed to resume from it, the boot carries on
without clearing the stale variable. Therefore, the subsequent
boots would still be waiting for the device timeout,
unless the variable is purged manually.
There's no point to keep trying to resume after a successful
switch-root, because the hibernation image state
would have been invalidated by then. OTOH, we don't
want to clear the variable prematurely either,
i.e. in initrd, since if the resume device is the same
as root one, the boot won't succeed and the user might
be able to try resuming again. So, let's introduce a
unit that only runs after switch-root and clears the var.
Fixes#32021
We are saying in public that the protocl is stable and can be easily
reimplemented, so provide an example doing so in the documentation,
license as MIT-0 so that it can be copied and pasted at will.
Same reason as the reload, reexec is disruptive and it requires the
same privileges, so if somebody wants to limit reloads, they'll also
want to limit reexecs, so use the same setting.
The setting is used when /sys/power/state is set to 'mem'
(common for suspend) or /sys/power/disk is set to 'suspend'
(hybrid-sleep). We default to kernel choice here, i.e.
respect what's set through 'mem_sleep_default=' kernel
cmdline option.
Today listen file descriptors created by socket unit don't get passed to
commands in Exec{Start,Stop}{Pre,Post}= socket options.
This prevents ExecXYZ= commands from accessing the created socket FDs to do
any kind of system setup which involves the socket but is not covered by
existing socket unit options.
One concrete example is to insert a socket FD into a BPF map capable of
holding socket references, such as BPF sockmap/sockhash [1] or
reuseport_sockarray [2]. Or, similarly, send the file descriptor with
SCM_RIGHTS to another process, which has access to a BPF map for storing
sockets.
To unblock this use case, pass ListenXYZ= file descriptors to ExecXYZ=
commands as listen FDs [4]. As an exception, ExecStartPre= command does not
inherit any file descriptors because it gets invoked before the listen FDs
are created.
This new behavior can potentially break existing configurations. Commands
invoked from ExecXYZ= might not expect to inherit file descriptors through
sd_listen_fds protocol.
To prevent breakage, add a new socket unit parameter,
PassFileDescriptorsToExec=, to control whether ExecXYZ= programs inherit
listen FDs.
[1] https://docs.kernel.org/bpf/map_sockmap.html
[2] https://lore.kernel.org/r/20180808075917.3009181-1-kafai@fb.com
[3] https://man.archlinux.org/man/socket.7#SO_INCOMING_CPU
[4] https://www.freedesktop.org/software/systemd/man/latest/sd_listen_fds.html
Drop connections and caches and reload config from files, to allow
for low-interruptions updates, and hook up to the usual SIGHUP and
ExecReload=. Mark servers and services configured directly via D-Bus
so that they can be kept around, and only the configuration file
settings are dropped and reloaded.
Fixes https://github.com/systemd/systemd/issues/17503
Fixes https://github.com/systemd/systemd/issues/20604
This makes it possible to update a home record (and blob directory) of a
home area that's either completely absent (i.e. on a USB stick that's
unplugged) or just inaccessible due to lack of authentication
This bypasses authentication (i.e. user_record_authenticate) if the
volume key was loaded from the keyring and no secret section is
provided.
This also changes Update() and Resize() to always try and load the
volume key from the keyring. This makes the secret section optional for
these methods while still letting them function (as long as the home
area is active)
For CI in mkosi, I want to configure systemd to log at debug level
to the journal, but not to the console. While we already have max
level settings for journald's forwarding settings, not every log line
goes to the journal, specifically during early boot and when units
are connected directly to the console (think systemd-firstboot), so
let's extend the log level options we already have to allow specifying
a comma separated list of values and lets allow prefixing values with
the log target they apply to to make this possible.
usage:
(1) get latest revocation list for your architecture
from https://uefi.org/revocationlistfile
(2) copy the file to $ESP/loader/keys/$name/dbx.auth
Naming is always a matter of preference, and the old name would certainly work,
but I think the new one has the following advantages:
- A verb is better than a noun.
- The name more similar to "the competition", i.e. 'sudo', 'pkexec', 'runas',
'doas', which generally include an action verb.
- The connection between 'systemd-run' and 'run0' is more obvious.
There has been no release yet with the old name, so we can rename without
caring for backwards compatibility.
The specified vendor UUID is not actually a UUID. This changes it to an actual UUID.
The new value matches the ones from the systemd-boot man page and [The Boot Loader Interface](https://systemd.io/BOOT_LOADER_INTERFACE/).
This new passive target is supposed to be pulled in by SSH
implementations and should be reached when remote SSH access is
possible. The idea is that this target can be used as indicator for
other components to determine if and when SSH access is possible.
One specific usecase for this is the new sd_notify() logic in PID 1 that
sends its own supervisor notifications whenever target units are
reached. This can be used to precisely schedule SSH connections from
host to VM/container, or just to identify systems where SSH is even
available.
This was lost on refactor, and only addons had a default uki
line in the .sbat. Add it back, and differentiate between the
default for UKIs vs the default for addons, so that they can
be revoked separately. These are only defaults and users are
encouraged to provide their own.
Follow-up for a8b645dec8
Then, we can read the lease file on restart, and the DHCP server will be
able to manage previously assigned addresses.
To save leases in the state directory /var/lib/systemd/network/, this
adds systemd-networkd-dhcp-server.service, and by default
systemd-networkd does not start the DHCP server without the heler
service started.
Closes#29991.
Then, this introduces systemd-networkd-persistent-storage.service.
systemd-networkd.service is an early starting service. So, at the time
it is started, the persistent storage for the service may not be ready,
and we cannot use StateDirectory=systemd/network in
systemd-networkd.service.
The newly added systemd-networkd-persistent-storage.service creates the
state directory for networkd, and notify systemd-networkd that the
directory is usable.
This brings the handling of config for kernel-install in line with most of
systemd, i.e. we search the set of paths for the main config file, and the full
set of drop-in paths for drop-ins.
This mirrors what 07f5e35fe7 did for udev.conf.
That change worked out fine, so I hope this one will too.
The update in the man page is minimal. I think we should split out a separate
page for the config file later on.
One motivating use case is to allow a drop-in to be created for temporary
config overrides and then removed after the operation is done.
This way the man pages are installed only when the corresponding binary is
installed. The conditions in man pages and man/rules/meson.build are adjusted to
match the conditions for units in units/meson.build.
Previously, we'd only freeze user.slice in the case of s2h, because we
didn't want the user session to resume while systemd was transitioning
from suspend to hibernate.
This commit extends this freezing behavior to all sleep modes.
We also have an environment variable to disable the freezing behavior
outright. This is a necessary workaround for someone that has hooks
in /usr/lib/systemd/system-sleep/ which communicate with some
process running under user.slice, or if someone is using the proprietary
NVIDIA driver which breaks when user.slice is frozen (issue #27559)
Fixes#27559
"submitted" is already used in the description of FDNAME=.
Let's use that instead of "stored" for FDPOLL= too, to make
it more clear that it's a per-submission/per-fdset setting.
This also replaces the Fedora download example with another one from
Ubuntu, since Fedora's images these days no longer qualify as DDIs, they
have no distinctive partition type UUIDs set for multiple of their
partitions, hence the images cannot be booted. A bit sad. Let's provide
a command that just works in its place.
Allow signing with an OpenSSL engine/provider, such as PKCS11. A public key is
not enough, a full certificate is needed for PKCS11, so a new parameter is
added for that too.
It turns out it's mostly PKCS11 that supports the URI format,
and other engines just take files. For example the tpm2-tss-openssl
engine just takes a sealed private key file path as the key input,
and the engine needs to be specified separately.
Add --private-key-source=file|engine:foo|provider:bar to
manually specify how to use the private key parameter.
Follow-up for 0a8264080a
These will be used by display managers to pre-select the user's
preferred desktop environment and display server type. On homed, the
display manager will also be able to set these fields to cache the
user's last selection.
`networkctl lldp` and `networkctl status INTERFACE` now use varlink
call to the networkd to query LLDP neighbors.
Then, this allows to dump LLDP neighbors in JSON format.
Co-authored-by: Tomáš Pecka <tomas.pecka@cesnet.cz>
Most of our kernel cmdline options use underscores as word separators in
kernel cmdline options, but there were some exceptions. Let's fix those,
and also use underscores.
Since our /proc/cmdline parsers don't distinguish between the two
characters anyway this should not break anything, but makes sure our own
codebase (and in particular docs and log messages) are internally
consistent.
Specify the delay, in milliseconds, between each peer
notification (gratuitous ARP and unsolicited IPv6
Neighbor Advertisement) when they are issued after
a failover event. This delay should be a multiple of
the MII link monitor interval (miimon).
The valid range is 0 - 300s. The default value is 0,
which means to match the value of the MII link monitor interval.
This effectively reverts 9175002864.
The retrans time field in RA message is for neighbor solicitation,
and the commit d4c8de21a0 makes the value
assigned to the correct sysctl property.
Let's deprecate the option, and drop the redundant functions.
Takes a list of CPU indices or ranges separated by either whitespace or commas. Alternatively,
takes the special value "all" in which will include all available CPUs in the mask.
CPU ranges are specified by the lower and upper CPU indices separated by a dash (e.g. "2-6").
This option may be specified more than once, in which case the specified CPU affinity masks are merged.
If an empty string is assigned, the mask is reset, all assignments prior to this will have no effect.
Defaults to unset and RPS CPU list is unchanged. To disable RPS when it was previously enabled, use the
special value "disable".
Currently, this will set CPU mask to all `rx` queue of matched device (if it has multiple queues).
The `/sys/class/net/<dev>/queues/rx-<n>/rps_cpus` only accept cpu bitmap mask in hexadecimal.
Fix: #30323
Let's make systemd-nspawn use our own ptyfwd logic to handle the TTY by
default.
This adds a new setting --console=, inspired by nspawn's setting of the
same name. If --console=interactive= is used, then we'll do the TTY
dance on our own via ptyfwd, and thus get tinting, our usual hotkey
handling and similar.
Since qemu's own console is useful too, let's keep it around via
--console=native.
FInally, replace the --qemu-gui switch by --console=gui.
This deprecates IPForward= setting, which unconditionally controled
the global setting, even though it is a setting in .network file.
Instead, this introduces new IPv4Forwarding= and IPv6Forwarding=
settings both in .network and networkd.conf.
If these settings are specified in a .network file, then the
per-interface forwarding setting will be configured.
If specified in networkd.conf, then the global IP forwarding setting will
be configured.
Closes#30648.
Allow to set the broadcast queueing threshold
on macvlan devices. This controls which multicast packets will be
processed in a workqueue instead of inline.
This renames a few of the switches vmspawn takes, such as --qemu-mem=
and --qemu-smp= to names without the "qemu" moniker and uses less
cryptic names (i.e. --ram= and --cpus=).
I think it's a bit unsystematic that so far we use the "qemu" prefix for
some options but not for others. At least I could not figure out a
system when we use it and when we don't. Hence let's clean it up and
just use simpler names without suffix.
After all we might want to plug other hypervisors behind vmspawn one
day, hence I think there's value in sticking to generic names for these
switches that allow us to switch out backends easily. In particular for
--ram= and --cpus= which are probably the most fundamental of VM settings
there are.
The old switches are support for compat, but not advertised in man page
or --help text anymore.
I left "--qemu-gui" under its current name, since it fundamentally is a
a qemu concept, exposing a qemu specific graphical UI.
If specified we'll not try to find a free V, but instead just output
directly to the specified TTY. This is particularly useful for
debugging, as it means "systemd-bsod --tty=/dev/tty" just works.
The command will refuse to write to a TTY, so give a strong hint
that redirecting to a file is recommended. This makes the synopsis,
man page text, and --help output consistent.
Also drop the space after the redirection operator everywhere.
Let's bring the credentials into a better order, in order of relevance.
Also, let's clarify what the generic LUKS PIN is about.
Finally, list the credentials in system-credentials(7) too, after all
people might want to unlock a disk with this via SMBIOS Type 11 or so.
Precedence for example in ac63c8df30/rules.d/99-systemd.rules.in (L75).
Add ENV to the list of keys where string substitutions can be used.
While I'm at it, also sort the list in that paragraph alphabetically.
This makes it possible to edit blob directories using homectl. The
following syntax is available:
* `--blob-directory=/path/somewhere`: Replaces the entire blob directory
with the contents of /path/somewhere
* `--blob-directory=foobar=/path/somewhere`: Replaces just the file
foobar in the blob directory with the contents of /path/somewhere
* `--blob-directory=foobar=`: Deletes the file foobar from the blob
directory
* `--blob-directory=`: Resets all previous flags
* `--avatar=`, etc: Shortcuts for `--blob-directory=FILENAME=` for the
known files in the blob directory
Introduces new extended variants of the various incarnations of
Create and Update, which take a map of filenames to FDs. This map is
then used to populate the bulk directory.
FDs are used to prevent the client from abusing homed's blob directory
permissions (everything is made world-readable by homed) to open files
that they normally aren't allowed to open. Passing along an FD ensures
that the client has read access to the file it wants homed to make
world-readable.
Internally, homework uses the map to overwrite the system blob dir.
Later, homework's existing blob dir reconciliation logic will propagate
the new contents from the system blob dir into the embedded blob
dir
This ensures that a user-specific blob directory exists in
/var/cache/systemd/homed for as long as the user exists, and gets
deleted if the user gets deleted.
It also advertises this blob directory via the user record, so that
clients can find and use it.
Allows to configure bond arp_missed_max is the maximum number of arp_interval monitor cycle
for missed ARP replies. If this number is exceeded, link is reported as
down.
In case the D-Bus policy is not set up correctly the example just
loops forever. Check the return of sd_bus_request_name_async() in
a callback and exit if the error is not temporary.
Follow-up for 34bbda18a5
This commit adds a new way of forwarding journal messages - forwarding
over a socket.
The socket can be any of AF_INET, AF_INET6, AF_UNIUX or AF_VSOCK.
The address to connect to is retrieved from the "journald.forward_address" credential.
It can also be specified in systemd-journald's unit file with ForwardAddress=
owneridmap bind option will map the target directory owner from inside the
container to the owner of the directory bound from the host filesystem.
This will ensure files and directories created in the container will be owned
by the directory owner of the host filesystem. All other users will remain
unmapped. Files to be written as other users in the container will not be
allowed.
Resolves: #27037
This field is like preferredLanguage, but takes a priority list of
languages instead. If an app isn't translated into a user's primary
language, it can fall back to one of the other languages in the list
thus making the app more accessible to the user.
For instance: in my experience, many Ukrainians are fluent in Russian,
often significantly better than English (especially if they are of a
generation that grew up during the USSR). Such a person might set this
new variable to ["uk_UA.UTF-8", "ru_UA.UTF-8"] so that software that
lacks Ukrainian translations will first try Russian translations before
defaulting to English.
Fixes#31290
cryptsetup 2.7.0 adds feature to link effective volume key in custom
kernel keyring during device activation. It can be used later to pass
linked volume key to other services.
For example: kdump enabled systems installed on LUKS2 device.
This feature allows it to store volume key linked in a kernel keyring
to the kdump reserved memory and reuse it to reactivate LUKS2 device
in case of kernel crash.
OOMPolicy in scope units is separately supported in
version v253, so I think it cannot be directly used
in the manpage with the version from the service.
fix:#30836
The idea is simple: skip the final operation that creates or removes things
or changes the attributes, but otherwise go through the rest of the code.
This results in quite a lot of fairly repetitive conditions in the low-level
code. Another approach would be to print earlier, at a higher level, but then
we'd have less precise information about what is about to happen.
It exposes the varlink_collect() call we internally provide: it collects
all responses of a method call that is issued with the "more" method
call flag. It then returns the result as a single JSON array.
The setting currently puts limits on connections per IP address and
AF_UNIX CID. Let's extend it to cover AF_UNIX too, where it puts a limit
on connections per UID.
This is particularly useful for the various Accept=yes Varlink services
we now have, as it means, the number of per-user instance services
cannot grow without bounds.
Looking for the ESP node is useful to shortcut things but if we're told that
the node is not referenced in fstab that doesn't necessarily mean that ESP is
not mounted via fstab. Indeed the check is not reliable in all cases. Firstly
because it assumes that udev already set the symlinks up. This is not the case
for initrd-less boots. Secondly the devname of the ESP partition can be wrongly
constructed by the dissect code. For example, the approach which consists in
appending "p<partnum>" suffix to construct the partition devname from the disk
devname doesn't work for DM devices.
Hence this patch makes the logic more defensive and do not mount neither ESP
nor XBOOTLDR automatically if any path in paths that starts with /efi or /boot
exists.
I think this was just overlooked in #13754, which removed
the restriction of Restart= on Type=oneshot services.
There's no reason to prevent RestartForceExitStatus=
now that Restart= has been allowed.
Closes#31148
These can be used along with two new settings MountPoint= and
EncryptedVolume= to write fstab and crypttab entries to the given
paths respectively in the root directory that repart is operating on.
This is useful to cover scenarios that aren't covered by the
Discoverable Partitions Spec. For example when one wants to mount
/home as a separate btrfs subvolume. Because multiple btrfs subvolumes
can be mounted from the same partition, we allow specifying MountPoint=
multiple times to add multiple entries for the same partition.
... i.e. apply nested config (exclusions and such) when executing R and D.
This fixes a long-standing RFE. The existing logic seems to have been an
accident of implementation. After all, if somebody specifies a config with
'R /foo; x /tmp/bar', then probably the goal is to remove stuff from under /foo,
but keep /tmp/bar. If they just wanted to nuke everything, then would not specify
the second item.
This also makes R and D use O_NOATIME, i.e. the access times of the directories
that are accessed will not be changed by the cleanup.
Obviously, we'll have to add this to NEWS and such.
Looking at the whole tmpfiles.d config in Fedora, this change has no effect.
The test cases are adjusted as appropriate. I also added another test case for
'R'/'D' with a file, just to test this code path more.
Replaces #20641.
Fixes#1633.
One of the three must always be specified, but they buried in a long list of
options in the output of --help. Make them more visible to draw the eye.
Also, drop "marked" from the description. It's supposed to mean "configured",
but it's a strange way to say that, and also it's generally obvious that the
program does what its configuration tells it to, and it's not going to remove
all files found on the system.
Previously, if given an absolute path, we would open the file, but when given a
relative path, we'd attempt to search the directories. If the user wants to open
a file from the search path, allowing paths is very confusing. E.g. with a path
like 'sysusers/foo.conf', we'd try to open '/etc/sysusers.d/sysusers/foo.conf',
'/run/sysusers.d/sysusers/foo.conf', …, and with '../foo.conf', we'd try to open
'/etc/sysusers.d/../foo.conf', '/run/sysusers.d/../foo.conf', …. This just isn't
useful, and in fact for a scheme like sysusers.d and tmpfiles.d where there we
have a flat directory with config files, only searching for plain names can
result in success. When a user specifies a relative path, it's more likely that
they wanted to open some local file. OTOH, to correctly open a local file, e.g.
one that they're just writing, this interface is also awkward, because something
like '$PWD/file.conf' has to be used to open a file with a relative path.
This patch changes the interface so that any path (i.e. an argument with "/") is
used to open a file directly, and only plain basenames are used for searching.
(Note that tpmfiles and sysusers are somewhat special here: their "config files"
make sense without the other config and users are likely to want to test them
without the other config. I was trying to do just that when writing a spec file
for a package and attempting to convert the existing scripts to sysusers and
tmpfiles. The same logic wouldn't apply for example to units or udev rules,
because they generally can only be interpreted with the whole rest of config
also available.)
The provider API which is new requires providers, which are not
widely available and don't work very well yet, so also use a
fallback with the legacy engine API.
Let's allow configuring the debug tty independently of enabling/disabling
the debug shell. This allows mkosi to configure the correct tty while
leaving enabling/disabling the debug tty to the user.
This new mode copies resources provided by the client, so that they
remain available for inspect/detach even if the original images are
deleted, but symlinks the profile as that is owned by the OS, so that
updates are automatically applied.
The intro of systemd-firstboot is rewritten to make it clearer how it fits into
the big picture. Systemd does some machine-id and presets and
systemd-firstboot.service is used to interactively fill in the blanks.
Closes#22225.
Common sense says that to "try" something means "to not fail if
something turns out not to be possible", thus do not make this
combination a hard error.
The actual implementation ignores any --link-journal= setting when
--ephemeral is in effect, so the semantics are upheld.
It's easy to add. Let's do so.
This only covers record lookups, i.e. with the --type= switch.
The higher level lookups are not covered, I opted instead to print a
message there to use --type= instead.
I am a bit reluctant to defining a new JSON format for the high-level
lookups, hence I figured for now a helpful error is good enough, that
points people to the right use.
Fixes: #29755
This returns an FD that can be used to temporarily inhibit the automatic
locking on system suspend behavior of homed. As long as the FD is open,
LockAllHomes() won't lock that home directory on suspend. This allows
desktop environments to implement custom more complicated behavior
Let's recommend that config files and drop-ins in /usr use the range
0-49 and config files in /etc and /run use the range 50-99 so that
files in /run and /etc will generally always override files from
/usr.
The documentation for `RestartPreventExitStatus=` differs from that for `SuccessExitStatus=` in ways that are sometimes confusing (e.g. using `numeric exit codes` instead of `numeric termination statuses`), and other times plain incorrect (e.g. not mentioning `termination status names`, which I've just confirmed to work in systemd 255).
This patch modifies the documentation to be as similar as possible, so as to reduce the reader's cognitive load.
`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>
Since signals can take arguments, let's suffix them with () as we
already do with functions. To make sure we remain consistent, make the
`update-dbus-docs.py` script check & fix any occurrences where this is
not the case.
Resolves: #31002
The RA's Retransmission Timer field was being ignored. This resolves the IPv6
Core Conformance test, v6LC.2.1.5 [1].
Retransmission Timer is a 32-bit unsigned integer. The time, in milliseconds,
between retransmitted Neighbor Solicitation messages. Used by the Address
Resolution and Neighbor Unreachability Detection (NUD) algorithm.
Support setting a default value for the neighbour retransmission timer value with:
[Network]
IPv6RetransmissionTimeSec=<int>
By default, upon receiving a Router Advertisement with the Retransmission Timer
field set to a non-zero value, it will update the kernel's retransmit timer value.
To disable this behaviour, configure the UseIPv6RetransmissionTime= under the
[IPv6AcceptRA] section.
[IPv6AcceptRA]
UseIPv6RetransmissionTime=<bool>
RFC4861: Neighbor Discovery in IPv6
* Section 4.2 RA Message Format.
* Section 6.3.4 Processing Received Router Advertisements
A Router Advertisement field (e.g., Cur Hop Limit, Reachable Time,
and Retrans Timer) may contain a value denoting that it is
unspecified. In such cases, the parameter should be ignored and the
host should continue using whatever value it is already using. In
particular, a host MUST NOT interpret the unspecified value as
meaning change back to the default value that was in use before the
first Router Advertisement was received.
The RetransTimer variable SHOULD be copied from the Retrans Timer
field, if the received value is non-zero.
References
[1] IPv6 Core Conformance Spec (PDF)
Let's make the firmware file to choose configurable, and enumeratable.
This adds --firmware= to select the formare, and in particular
--firmware=list to show available options.
We already support -j as shortcut for JSON mode in various tools. Let's
add one more. We probably should add this systematically (at least where
it doesn't conflict with an existing -j switch with other purpose). But
I am too lazy to add that now.
