The nix store more-or-less requires o+rx on all parent directories.
This is primarily because nix runs builders in a uid/gid mapped
user-namespace, and those builders have to be able to operate on the nix
store.
This check is especially helpful because nix does not produce a helpful
error on its own (rather, creating directories and such works, it's not
until 'mount --bind' that it gets an EACCES).
Helps users who run into this opaque error, such as in #67465.
Possibly fixes that issue if bad permissions were the only cause.
This should have been done initially, as otherwise it gets awfully
awkward to boot into new generations by default.
This system-specific image wasn't expected to be long-lived, thus why it
didn't end up being polished much.
Reality shows us we may be stuck with it for a bit longer, so let's make
it easier to use for new users.
'nix build' is an experimental command so we shouldn't use it
yet. (nixos-rebuild also uses 'nix', but only when using flakes, which
are themselves an experimental feature.)
nix build should store it's temporary files on target filesystem.
This should fix 'No space left on device' on systems
with low amount of RAM when there is a need to build something
like Linux kernel
For imports, it is better to use ‘modulesPath’ than rely on <nixpkgs>
being correctly set. Some users may not have <nixpkgs> set correctly.
In addition, when ‘pure-eval=true’, <nixpkgs> is unset.
When trying to build a VM using `nixos-build-vms` with a configuration
that doesn't evaluate, an error "at `<unknown-file>`" is usually shown.
This happens since the `build-vms.nix` creates a VM-network of
NixOS-configurations that are attr-sets or functions and don't contain
any file information. This patch manually adds the `_file`-attribute to
tell the module-system which file contained broken configuration:
```
$ cat vm.nix
{ vm.invalid-option = 1; }
$ nixos-build-vms vm.nix
error: The option `invalid-option' defined in `/home/ma27/Projects/nixpkgs/vm.nix@node-vm' does not exist.
(use '--show-trace' to show detailed location information)
```
we use stdenv.hostPlatform.uname.processor, which I believe is just like
`uname -p`.
Example values:
```
(import <nixpkgs> { system = "x86_64-linux"; }).stdenv.hostPlatform.uname.processor
"x86_64"
(import <nixpkgs> { system = "aarch64-linux"; }).stdenv.hostPlatform.uname.processor
aarch64
(import <nixpkgs> { system = "armv7l-linux"; }).stdenv.hostPlatform.uname.processor
"armv7l"
```
Instead of making the configuration less portable by hard coding the number of
jobs equal to the cores we can also let nix set the same number at runtime.
The volumeID will now be in the format of:
nixos-$EDITON-$RELEASE-$ARCH
an example for the minimal image would look like:
nixos-minimal-20.09-x86-64-linux
Note we're not using wayland default in the graphical media because it
could cause headaches for Nvidia users. But the session is still available
if someone logs out.
