This is apparent from the service file directory in plymouth:
├── multi-user.target.wants
│ ├── plymouth-quit.service -> ../plymouth-quit.service
│ └── plymouth-quit-wait.service -> ../plymouth-quit-wait.service
Leaving it unspecified caused gdm-wayland to crash on boot, see #39615.
The change made other display managers not quit plymouth properly however. By
removing "multi-user.target" from `plymouth-quit.after` this is resolved.
The isKexecable flag treated Linux without kexec as just a normal
variant, when it really should be treated as a special case incurring
complexity debt to support.
Resolved the following conflicts (by carefully applying patches from the both
branches since the fork point):
pkgs/development/libraries/epoxy/default.nix
pkgs/development/libraries/gtk+/3.x.nix
pkgs/development/python-modules/asgiref/default.nix
pkgs/development/python-modules/daphne/default.nix
pkgs/os-specific/linux/systemd/default.nix
This can be used to fix issues where udhcpc times out before
acquiring a lease. For example of these issues, see:
https://bugs.alpinelinux.org/issues/3105#note-8
Signed-off-by: Dino A. Dai Zovi <ddz@theta44.org>
At one point in my configuration I had:
boot.kernel.sysctl = {
# https://unix.stackexchange.com/questions/13019/description-of-kernel-printk-values
"kernel.printk" = "4 4 1 7";
};
which triggered:
error: The unique option `boot.kernel.sysctl.kernel.printk' is defined multiple times, in `/home/teto/dotfiles/nixpkgs/mptcp-unstable.nix' and `/home/teto/nixpkgs/nixos/modules/system/boot/kernel.nix'.
(use ‘--show-trace’ to show detailed location information)
Traceback (most recent call last):
File "/home/teto/nixops/scripts/nixops", line 984, in <module>
args.op()
File "/home/teto/nixops/scripts/nixops", line 406, in op_deploy
max_concurrent_activate=args.max_concurrent_activate)
File "/home/teto/nixops/nixops/deployment.py", line 1045, in deploy
self.run_with_notify('deploy', lambda: self._deploy(**kwargs))
File "/home/teto/nixops/nixops/deployment.py", line 1034, in run_with_notify
f()
File "/home/teto/nixops/nixops/deployment.py", line 1045, in <lambda>
self.run_with_notify('deploy', lambda: self._deploy(**kwargs))
File "/home/teto/nixops/nixops/deployment.py", line 985, in _deploy
self.configs_path = self.build_configs(dry_run=dry_run, repair=repair, include=include, exclude=exclude)
File "/home/teto/nixops/nixops/deployment.py", line 653, in build_configs
raise Exception("unable to build all machine configurations")
Exception: unable to build all machine configurations
This simple addition allows to override it.
Fixes#28443
Fixed few invocations to `systemctl` to have an absolute path. Additionally add
LOCALE_ARCHIVE so that perl stops spewing warning messages.
This option, if set to true, enables fallbacking to an interactive
passphrase prompt when the specified keyFile is not found.
The default is false, which is compatible with previous behavior and
doesn't prevent unattended boot.
Regression introduced by 801c920e95.
Since then, the btrfsSimple subtest of the installer VM test fails with:
Btrfs did not return a path for the subvolume at /
The reason for this is that the output for "btrfs subvol show" has
changed between version 4.8.2 and 4.13.1.
For example the output of "btrfs subvol show /" in version 4.8.2 was:
/ is toplevel subvolume
In version 4.13.1, the output now is the following and thus the regular
expressions used in nixos-generate-config.pl and install-grub.pl now
match (which results in the error mentioned above):
/
Name: <FS_TREE>
UUID: -
Parent UUID: -
Received UUID: -
Creation time: -
Subvolume ID: 5
Generation: 287270
Gen at creation: 0
Parent ID: 0
Top level ID: 0
Flags: -
Snapshot(s):
In order to fix this I've changed nixos-generate-config.pl and
install-grub.pl, because both use "btrfs subvol show" in a similar vein,
so the regex for parsing the output now doesn't match anymore whenever
the volume path is "/", which should result in the same behaviour as we
had with btrfs-progs version 4.8.2.
Tested against the btrfsSimple, btrfsSubvols and btrfsSubvolDefault
subtests of the installer VM test and they all succeed now.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
* the keyboard modules in all-hardware.nix are already defaults of
boot.initrd.availableKernelModules
* ide modules, hid_lenovo_tpkbd and scsi_wait_scan have been removed
because they're not available anymore
* i8042 was a duplicate (see few lines abowe)
the systemd.unit(5) discussion of wantedBy and requiredBy is in the
[Install] section, and thus focused on stateful 'systemctl enable'.
so, clarify that in NixOS, wantedBy & requiredBy are still what most
users want, and not to be confused with enabled.
Boot fails when a keyfile is configured for all encrypted filesystems
and no other luks devices are configured. This is because luks support is only
enabled in the initrd, when boot.initrd.luks.devices has entries. When a
fileystem has a keyfile configured though, it is setup by a custom
command, not by boot.initrd.luks.
This commit adds an internal config flag to enable luks support in the
initrd file, even if there are no luks devices configured.
Grub configs include the NixOS version and date they were built, now
systemd can have fun too:
version Generation 99 NixOS 17.03.1700.51a83266d1, Linux Kernel 4.9.43, Built on 2017-08-30
version Generation 100 NixOS 17.03.1700.51a83266d1, Linux Kernel 4.9.43, Built on 2017-08-30
version Generation 101 NixOS 17.03.1700.51a83266d1, Linux Kernel 4.9.43, Built on 2017-08-31
version Generation 102 NixOS 17.03.1700.51a83266d1, Linux Kernel 4.9.43, Built on 2017-09-01
version Generation 103 NixOS 17.03.1700.51a83266d1, Linux Kernel 4.9.43, Built on 2017-09-02
version Generation 104 NixOS 17.09beta41.1b8c7786ee, Linux Kernel 4.9.46, Built on 2017-09-02
version Generation 105 NixOS 17.09.git.1b8c778, Linux Kernel 4.9.46, Built on 2017-09-02
The message buffer of the kernel lists
> Please run 'e2fsck -f /dev/disk/by-label/nixos' first.
as the output of the command `resize2fs "$device"`.
This fixesNixOS/nixpkgs#26910.
old version of blkid used to output version information including libblkid version
when invoked with --help parameter
new version does not output libblkid version when invoked with --help parameter
fix is to invoke blkid with -V parameter to output version including libblkid in both cases
* systemd-boot-builder.py: add support for profiles
This will also list the generations of other profiles than `system` in
the boot menu. See the documentation of the `--profile-name` option of
nixos-rebuild for more information on profiles.
* Fix errors introduced by previous commit
Or else `services.udev.packages = [ bcache-tools ]` cannot be used.
To not break bcache in the initrd I'm modifying this in stage-1.nix:
- --replace /bin/sh ${extraUtils}/bin/sh
+ --replace ${bash}/bin/sh ${extraUtils}/bin/sh
Reasoning behind that change:
* If not modifying the /bin/sh pattern in any way, it will also match
${bash}/bin/sh, creating a broken path like
/nix/store/HASH-bash/nix/store/HASH-bash/bin/sh in the udev rule file.
* The addition of /bin/sh was done in 775f381a9e
("stage-1: add bcache support"). It seems somewhat plausible that
no new users have appeared since then and we can take this opportunity
to back out of this change without much fear of regressions.
If there _are_ regressions, they should be in the form of build time
errors, not runtime (boot), due to how the udev rule output is checked
for invalid path references. So low risk, IMHO.
* An alternative approach could be to copy the /bin/sh substitute rule
over to the non-initrd udev rules implementation in NixOS, but I think
this way is better:
- The rules file comes with a working path out of the box.
- We can use more precise pattern matching when modifying the udev
rules for the initrd.
The default font is unreadably small on some hidpi displays. This
makes it possible to specify a TrueType or OpenType font at any point
size, and it will automatically be converted to the format the Grub
uses.
Restructure the nixos-artwork to make it easy to selectively
incorporate other components from upstream without needing to download
the full package.
Until now only the Gnome_Dark wallpaper was included. Add other
wallpapers available in the package repository.
Since fat32 provides little recovery facilities after a crash,
it can leave the system in an unbootable state, when a crash/outage
happens shortly after an update. To decrease the likelihood of this
event sync the efi filesystem after each update.
Someone on IRC wanted to boot Fedora from another disk. While I'm not
too familiar with UEFI booting in conjunction with GRUB2 it took some
time to get it to work.
So in order to safe others from frustration I'm adding this as another
example to the extraEntries option.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
This has surfaced since d990aa7163.
The "simpleUefiGummiboot" installer test fails since this commit,
because that commit introduced a small check to verify whether the store
was altered.
While installing NixOS for the first time, the store is usually in
/mnt/nix/store and without the read-only bind mount that's preventing
programs from altering the store.
So after nixos-install is done creating the system closure and setting
it as the active system profile, the bootloader is written from the
closure inside the chroot. The systemd-boot-builder is invoked during
this step, which adds .pyc files for various Python modules of the
Python 3 store path, which in turn invalidates the hash of the Python 3
store path itself.
At the time the system is booted up again, the nix-store is verified and
fails with something like this:
path /nix/store/zvm545rqc4d97caqq9h7344bnd06jhzb-python3-3.5.3 was
modified! expected hash
b2c975f4b8d197443fbb09690fb3f6545e165dd44c9309d7d6df2fce0579ebeb, got
bccca19f39c9d26d857ccf1fb72818b2b817967e6d497a25a1283e36ed0acf01
Running the interpreter with the -B argument prevents Python from
writing those byte code files:
https://docs.python.org/3/using/cmdline.html#cmdoption-B
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
This reverts commit c2b56626f1.
It broke creating the manual. I suspect the descriptions are
auto-wrapped by <para> and </para>.
We've been through this already in 3af715af90.
/cc #24978, @zraexy, @Mic92.
The LUKS header can be on another device (e.g. a USB stick). In my case
it can take up to two seconds until the partition on my USB stick is
available (i.e. the decryption fails without this patch). This will also
remove some redundancy by providing the shell function `wait_target` and
slightly improve the output (one "." per second and a success/failure
indication after 10 seconds instead of always printing "ok").
Restarting them is useless since the filesystem is already
checked. Worse, restarting them causes the filesystem to be unmounted.
Also remove an override for systemd-rkill@.service which no longer
exists.
We only care about /nix/store because its contents might be out of
sync with /nix/var/nix/db. Syncing other filesystems might cause
unnecessary delays or hangs (e.g. I encountered a case where an NFS
mount was taking a very long time to sync).
When dhcpcd instead of networkd is used, the network-online.target behaved
the same as network.target, resulting in broken services that need a working
network connectivity when being started.
This commit makes dhcpcd wait for a lease and makes it wanted by
network-online.target. In turn, network-online.target is now wanted by
multi-user.target, so it will be activated at every boot.
Using toJSON on a string value works because the allowed JSON escape
sequences is almost a subset of the systemd allowed escape sequences.
The only exception is `\/` which JSON allows but systemd doesn't.
Luckily this sequence isn't required and toJSON don't produce it making
the result valid for systemd consumption.
Examples of things that this fixes are environment variables with double
quotes or newlines.
Since systemd version 232 the install subcommand of bootctl opens the
loader.conf with fopen() modes "wxe", where the "e" stands for
exclusive, so the call will fail if the file exists.
For installing the boot loader just once this is fine, but if we're
using NIXOS_INSTALL_BOOTLOADER on a systemd where the bootloader is
already present this will fail.
Exactly this is done within the simpleUefiGummiboot installer test,
where nixos-install is called twice and thus the bootloader is also
installed twice, resulting in an error during the fopen call:
Failed to open loader.conf for writing: File exists
Removing the file prior to calling bootctl should fix this.
I've tested this using the installer.simpleUefiGummiboot test and it now
succeeds.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Cc: @edolstra, @shlevy, @mic92
Fixes: #22925
This leads to the following error when trying to install a new machine
where the machine ID wasn't yet initialized during boot:
Failed to get machine did: No such file or directory
In addition this was also detected by the simpleUefiGummiboot installer
test.
So let's generate a fallback machine ID by using
systemd-machine-id-setup before actually running bootctl.
Tested this by running the installer.simpleUefiGummiboot test, it still
fails but not because of the machine ID.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Cc: @edolstra, @shlevy, @mic92
Fixes: #22561
Since the bonds interface changed to a lot more possible values we create a
mapping of kernel bond attribute names and values to networkd attributes.
Those match for the most part, but have to transformed slightly.
There is also an assert that unknown options won’t slip through silently.
The Raspberry Pi boot loader was deleting all xx-initrd text files
(which simply contain the path to the actual initrd files) just after
having created them. The code was actually trying to delete real,
obsolete initrd files, which are named <hash>-initrd-initrd (after path
cleaning), but the glob was catching the other files as well.
This reverts commit 712e62c260.
This commit broke NixOS containers. Systemd wouldn't detect if a container
started successfully and would kill it again after a grace period.
Additionally this prints mount errors due to already mounted filesystems
at boot.
This code in amazon-image.nix:
if mountFS "$device" "$mp" "" auto; then
if [ -z "$diskForUnionfs" ]; then diskForUnionfs="$mp"; fi
fi
relies on mountFS to return a zero exit status if mounting
succeeds. But the lustrateRoot check in mountFS was causing a non-zero
exit status. As a result /disk0 would be mounted, but not used for
/tmp.
(cherry picked from commit d082ed8c35dec48aee2afd1303b3c8b2a1b242b0)
networkd options are always correct or up to date. This option allows to by
pass type checking. It is also easier to write because examples can be just copy
and paste from manpages.
Networkd units can contain secrets. In future also wireguard vpn will be supported by
networkd. To avoid leakage of private keys, those could be then also put outside
of the /nix/store
Having a writeable /etc/systemd/network also allows to quick fix network issues,
when upgrading `nixos-rebuild switch` would require network on its own (due
updates).
This reverts commit 656cc3acaf because it
causes building the manual to fail:
$ nixos-rebuild build
...
building path(s) ‘/nix/store/s9y5z78z5pssvmixcmv9ix13gs8xj87f-manual-olinkdb’
Writing /nix/store/s9y5z78z5pssvmixcmv9ix13gs8xj87f-manual-olinkdb/manual.db for book(book-nixos-manual)
./man-pages.xml:625: element para: Relax-NG validity error : Did not expect element para there
./man-pages.xml:3: element variablelist: Relax-NG validity error : Element refsection has extra content: variablelist
./man-pages.xml:29: element refsection: Relax-NG validity error : Element refentry has extra content: refsection
./man-pages.xml:3: element reference: Relax-NG validity error : Element reference failed to validate content
./man-pages.xml fails to validate
CC @cleverca22, @Mic92
- most nixos user only require time synchronisation,
while ntpd implements a battery-included ntp server (1,215 LOCs of C-Code vs 64,302)
- timesyncd support ntp server per interface (if configured through dhcp for instance)
- timesyncd is already included in the systemd package, switching to it would
save a little disk space (1,5M)
Using the --force option on GRUB isn't recommended, but there are very
specific instances where it makes sense. One example is installing on a
partitionless disk.
Thanks to @NeQuissimus in a5c1985fef for
updating busybox, which since version 1.25 doesn't allow local variables
outside of functions anymore (which is the desired behaviour).
See the following upstream commit of busybox which is the change that
let's this problem surface:
https://git.busybox.net/busybox/commit/?id=ef2386b80abfb22ccb697ddbdd4047aacc395c50
So this has been an error I've made on my end in
67223ee205, because I originally had a
function for killing the processes but desired to inline it because it's
only used in one place.
This fixes the boot-stage1 NixOS test.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
For some reason, between Linux 4.4.19 and 4.4.20, the atkbd and libps2
kernel modules lost their dependency on i8042 in modules.dep, causing
i8042 not to be included in the initrd. This breaks keyboard in the
initrd, in turn breaking LUKS.
This only happens on the 16.03 branch; on 16.09, it appears i8042 is
pulled into the initrd anyway (through some other dependency,
presumably). But let's include it explicitly.
http://hydra.nixos.org/build/40468431
This makes it easy to specify kernel patches:
boot.kernelPatches = [ pkgs.kernelPatches.ubuntu_fan_4_4 ];
To make the `boot.kernelPatches` option possible, this also makes it
easy to extend and/or modify the kernel packages within a linuxPackages
set. For example:
pkgs.linuxPackages.extend (self: super: {
kernel = super.kernel.override {
kernelPatches = super.kernel.kernelPatches ++ [
pkgs.kernelPatches.ubuntu_fan_4_4
];
};
});
Closes#15095
This fixes two bugs:
* When socket activation is detected, the service itself is added to stop-start list instead of its sockets.
* When service is marked to restart instead of stop (`StopIfChanged = no`) we don't need to restart sockets.
This ensures that most "trivial" derivations used to build NixOS
configurations no longer depend on GCC. For commands that do invoke
gcc, there is runCommandCC.
This is a standard environment that doesn't contain a C/C++
compiler. This is mostly to prevent trivial builders like runCommand
and substituteAll from pulling in gcc for simple configuration changes
on NixOS.
This allows us to define system user targets in addition to the existing
services, timers and sockets.
Furthermore, we add a top-level configuration keyword:
- Documentation
Using "tmpfs" as a script part for system.activationScripts is a bit
misleading since 6efcfe03ae.
We no longer solely mount tmpfs within this script, so using "specialfs"
fits more nicely in terms of naming.
Tested against the "simple" NixOS installer test.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Regression introduced by 79d4636d50.
The mentioned commit moves /run/keys from stage 2 to
boot.specialFileSystems, the latter being remounted during system
activation.
Unfortunately, the specialMount function in the activation script does
this unconditionally and thus will fail if it can't be remounted because
the mount point simply doesn't exist.
We now check the mount point for existance and only remount if it exists
but mkdir + mount it if it doesn't.
Tested against the "simple" NixOS installer test.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
When Grub is to be used with UEFI, it is not going to write to any MBR
of any disk. As such, it is safe to use multiple "nodev" device entries
when mirroring the ESP partition to multiple disks.
E.g.:
```
boot.loader.grub = {
enable = true;
version = 2;
zfsSupport = true;
efiSupport = true;
mirroredBoots = [
{ devices = [ "nodev" ]; path = "/boot1"; efiSysMountPoint = "/boot1"; }
{ devices = [ "nodev" ]; path = "/boot2"; efiSysMountPoint = "/boot2"; }
{ devices = [ "nodev" ]; path = "/boot3"; efiSysMountPoint = "/boot3"; }
];
};
boot.loader.efi.canTouchEfiVariables = true;
```
Fixes#18584
All swap device option sets "have" a label, it's just that sometimes it's
undefined. Because we set a `device` attribute when we have a label anyway it's
ok to just check device prefix.
Fixes#18891.
See #18319 for details. Starting network-online.target manually does not
work as it hangs indefinitely.
Additionally, don't treat avahi and dhcpcd special and sync their systemd units
with the respective upstream suggestion.
Systemd upstream provides targets for networking. This also includes a target network-online.target.
In this PR I remove / replace most occurrences since some of them were even wrong and could delay startup.
This partially reverts commit ab9537ca22.
From the manpage of systemd-nspawn(1):
Note that systemd-nspawn will mount file systems private to the
container to /dev, /run and similar.
Testing this in a shell turns out:
$ sudo systemd-nspawn --bind-ro=/nix/store "$(readlink "$(which ls)")" /proc
Spawning container aszlig on /home/aszlig.
Press ^] three times within 1s to kill container.
/etc/localtime does not point into /usr/share/zoneinfo/, not updating
container timezone.
1 execdomains kpageflags stat
acpi fb loadavg swaps
asound filesystems locks sys
buddyinfo fs meminfo sysrq-trigger
bus interrupts misc sysvipc
cgroups iomem modules thread-self
cmdline ioports mounts timer_list
config.gz irq mtrr timer_stats
consoles kallsyms net tty
cpuinfo kcore pagetypeinfo uptime
crypto key-users partitions version
devices keys scsi vmallocinfo
diskstats kmsg self vmstat
dma kpagecgroup slabinfo zoneinfo
driver kpagecount softirqs
Container aszlig exited successfully.
So the test on whether PID 1 exists in /proc is enough, because if we
use PID namespaces there actually _is_ a PID 1 (as shown above) and the
special file systems are already mounted. A test on the $containers
variable actually mounts them twice.
This unbreaks NixOS containers and I've tested this against the
containers-imperative NixOS test.
Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Cc: @rickynils, @shlevy, @edolstra
Before this commit updating /var/setuid-wrappers/ folder introduced
a small window where NixOS activation scripts could be terminated
and resulted into empty /var/setuid-wrappers/ folder.
That's very unfortunate because one might lose sudo binary.
Instead we use two atomic operations mv and ln (as described in
https://axialcorps.com/2013/07/03/atomically-replacing-files-and-directories/)
to achieve atomicity.
Since /var/setuid-wrappers is not a directory anymore, tmpfs mountpoints
were removed in installation scripts and in boot process.
Tested:
- upgrade /var/setuid-wrappers/ from folder to a symlink
- make sure /run/setuid-wrappers-dirs/ legacy symlink is really deleted
Both btrfs-progs and utillinux are ~5MB, we may discuss in future
to handle this better but I see no better way at the moment than
increaing purity in the install process.
OnCalendar entrys can be specified multiple times in a systemd timer, to
make more complex scheduling possible.
Tested by manually checking the timer generated by the following:
systemd = {
services.huhu = {
description = "meh";
wantedBy = [ "default.target" ];
serviceConfig.ExecStart = "/bin/sh -c 'printf HUHU!'";
startAt = [ "*:*:0/30" "*:0/1:15" ];
};
};
It prints HUHU to the log at seconds 0, 15 and 30 of each minute.
A new internal config option `fileSystems.<name>.early` is added to indicate
that the filesystem needs to be loaded very early (i.e. in initrd). They are
transformed to a shell script in `system.build.earlyMountScript` with calls to
an undefined `specialMount` function, which is expected to be caller-specific.
This option is used by stage-1, stage-2 and activation script to set up and
remount those filesystems. Options for them are updated according to systemd
defaults.
lustrate /ˈlʌstreɪt/ verb.
purify by expiatory sacrifice, ceremonial washing, or some other
ritual action.
- sudo touch /etc/NIXOS_LUSTRATE
⇒ on next reboot, during stage 1, everything but /nix and /boot
is moved to /old-root
- echo "etc/passwd" | sudo tee -a /etc/NIXOS_LUSTRATE
⇒ on next reboot, during stage 1, everything but /nix and /boot
is moved to /old-root; except /etc/passwd is copied back.
Useful for installing NixOS in place on another distro. For instance:
$ nix-env -iE '_: with import <nixpkgs/nixos> { configuration = {}; }; with config.system.build; [ nixos-generate-config manual.manpages ]'
$ sudo mkdir /etc/nixos
$ sudo `which nixos-generate-config`
… edit the configuration files in /etc/nixos using man configuration.nix
if needed
maybe add: users.extraUsers.root.initialHashedPassword = "" ?
… Build the entire NixOS system and link it to the system profile:
$ nix-env -p /nix/var/nix/profiles/system -f '<nixpkgs/nixos>' -A system --set
… If you were using a single user install:
$ sudo chown -R 0.0 /nix
… NixOS is about to take over
$ sudo touch /etc/NIXOS
$ sudo touch /etc/NIXOS_LUSTRATE
… Let's keep the configuration files we just created
$ echo etc/nixos | sudo tee -a /etc/NIXOS_LUSTRATE
$ sudo mv -v /boot /boot.bak &&
sudo /nix/var/nix/profiles/system/bin/switch-to-configuration boot
$ sudo reboot
… NixOS boots, Stage 1 moves all the old distro stuff in /old-root.
The builder has this convoluted `while` loop which just replicates
`readlink -e`. I'm sure there was a reason at one point, because the
loop has been there since time immemorial. It kept getting copied
around, I suspect because nobody bothered to understand what it actually
did.
Incidentally, this fixes#17513, but I have no idea why.
This patch adds handling of a directory becoming a symlink in
/etc. Before this patch, the directory wasn't removed and then
symlinking failed, which caused directory not being updated at all.
The idea for the patch goes to @abbradar at
https://github.com/NixOS/nixpkgs/issues/16978#issuecomment-232921903:
> A heuristic idea for this -- a function `isStatic :: Path -> Bool`:
>
> * if path `/etc/foo` is a file, return True iff it's a symlink to `/etc/static/foo`.
> * if path is a directory, return True iff for all items in it `isStatic` is True.
>
> On any conflicts, if old path is static, it's safe to replace and/or
> delete stale. Otherwise make a backup and notify the user via a
> journal entry and console output.
The only difference here -- it will not replace user configs.
This also fixes https://github.com/NixOS/nixpkgs/issues/16978.
We currently only allow upstream's default of "reboot.target" due to the
way the symlinks are initialized. I made this configurable similar to the
default unit.
