mirror of
https://github.com/NixOS/nix.dev.git
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153 lines
4.2 KiB
Markdown
153 lines
4.2 KiB
Markdown
# Frequently Asked Questions
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## Nix
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### What to do if a binary cache is down or unreachable?
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Pass `--option substitute false` to Nix commands.
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### How do I add a new binary cache?
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Using NixOS (≥ 22.05):
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```nix
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nix.settings = {
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trusted-substituters = [ "https://cache.nixos.org" ];
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substituters = [ "https://cache.nixos.org" ];
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};
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```
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Using NixOS (≤ 21.11):
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```nix
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nix = {
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trustedBinaryCaches = [ "https://cache.nixos.org" ];
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binaryCaches = [ "https://cache.nixos.org" ];
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};
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```
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Using `Nix`:
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```shell-session
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$ echo "trusted-binary-caches = https://cache.nixos.org" >> /etc/nix/nix.conf
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$ nix-build helpers/bench.nix --option extra-binary-caches https://cache.nixos.org
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```
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### How do I force nix to re-check whether something exists at a binary cache?
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Nix caches the contents of binary caches so that it doesn't have to query them
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on every command. This includes negative answers (cache doesn't have something).
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The default timeout for that is 1 hour as of writing.
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To wipe all cache-lookup-caches:
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```shell-session
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$ rm $HOME/.cache/nix/binary-cache-v*.sqlite*
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```
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Alternatively, use the `narinfo-cache-negative-ttl` option to reduce the
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cache timeout.
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### How do I fix: error: querying path in database: database disk image is malformed
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Try:
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```shell-session
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$ sqlite3 /nix/var/nix/db/db.sqlite "pragma integrity_check"
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```
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Which will print the errors in the database. If the errors are due to missing
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references, the following may work:
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```shell-session
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$ mv /nix/var/nix/db/db.sqlite /nix/var/nix/db/db.sqlite-bkp
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$ sqlite3 /nix/var/nix/db/db.sqlite-bkp ".dump" | sqlite3 /nix/var/nix/db/db.sqlite
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```
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### How to operate between Nix paths and strings?
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<http://stackoverflow.com/a/43850372>
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### How do I fix: error: current Nix store schema is version 10, but I only support 7
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This means you have upgraded Nix sqlite schema to a newer version, but then tried
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to use older Nix.
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The solution is to dump the db and use old Nix version to initialize it:
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```shell-session
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$ /path/to/nix/unstable/bin/nix-store --dump-db > /tmp/db.dump
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$ mv /nix/var/nix/db /nix/var/nix/db.toonew
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$ mkdir /nix/var/nix/db
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$ nix-store --init # this is the old nix-store
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$ nix-store --load-db < /tmp/db.dump
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```
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### How to build reverse dependencies of a package?
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```shell-session
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$ nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
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```
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### I'm getting: writing to file: Connection reset by peer
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Too big files in src, out of resources (HDD space, memory)
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### What are channels and different branches on github?
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See <https://nixos.wiki/wiki/Nix_channels>
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### How can I manage dotfiles in \$HOME with Nix?
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<https://github.com/nix-community/home-manager>
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### Are there some known impurities in builds?
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Yes.
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- CPU (we try hard to avoid compiling native instructions, but rather hardcode supported ones)
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- current time/date
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- FileSystem (ext4 has a known bug creating [empty files on power loss](https://github.com/NixOS/nixpkgs/issues/15581))
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- Kernel
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- Timing behaviour of the build system (parallel Make not getting correct inputs in some cases)
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### What's the recommended process for building custom packages?
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> E.g. if I git clone nixpkgs how do I use the cloned repo to define new / updated packages?
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## NixOS
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### How to build my own ISO?
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<http://nixos.org/nixos/manual/index.html#sec-building-image>
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### How do I connect to any of the machines in NixOS tests?
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Apply following patch:
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```diff
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diff --git a/nixos/lib/test-driver/test-driver.pl b/nixos/lib/test-driver/test-driver.pl
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index 8ad0d67..838fbdd 100644
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--- a/nixos/lib/test-driver/test-driver.pl
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+++ b/nixos/lib/test-driver/test-driver.pl
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@@ -34,7 +34,7 @@ foreach my $vlan (split / /, $ENV{VLANS} || "") {
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if ($pid == 0) {
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dup2(fileno($pty->slave), 0);
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dup2(fileno($stdoutW), 1);
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- exec "vde_switch -s $socket" or _exit(1);
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+ exec "vde_switch -tap tap0 -s $socket" or _exit(1);
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}
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close $stdoutW;
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print $pty "version\n";
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```
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And then the vde_switch network should be accessible locally.
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### How to bootstrap NixOS inside an existing Linux installation?
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There are a couple of tools:
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- <https://github.com/jeaye/nixos-in-place>
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- <https://github.com/elitak/nixos-infect>
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- <https://github.com/cleverca22/nix-tests/tree/master/kexec>
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