260 lines
9.0 KiB
Nix
260 lines
9.0 KiB
Nix
/*
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Declares what makes the nix-daemon work on systemd.
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See also
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- nixos/modules/config/nix.nix: the nix.conf
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- nixos/modules/config/nix-remote-build.nix: the nix.conf
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*/
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{ config, lib, pkgs, ... }:
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with lib;
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let
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cfg = config.nix;
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nixPackage = cfg.package.out;
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isNixAtLeast = versionAtLeast (getVersion nixPackage);
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makeNixBuildUser = nr: {
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name = "nixbld${toString nr}";
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value = {
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description = "Nix build user ${toString nr}";
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/*
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For consistency with the setgid(2), setuid(2), and setgroups(2)
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calls in `libstore/build.cc', don't add any supplementary group
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here except "nixbld".
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*/
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uid = builtins.add config.ids.uids.nixbld nr;
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isSystemUser = true;
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group = "nixbld";
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extraGroups = [ "nixbld" ];
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};
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};
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nixbldUsers = listToAttrs (map makeNixBuildUser (range 1 cfg.nrBuildUsers));
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in
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{
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imports = [
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(mkRenamedOptionModuleWith { sinceRelease = 2205; from = [ "nix" "daemonIONiceLevel" ]; to = [ "nix" "daemonIOSchedPriority" ]; })
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(mkRenamedOptionModuleWith { sinceRelease = 2211; from = [ "nix" "readOnlyStore" ]; to = [ "boot" "readOnlyNixStore" ]; })
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(mkRemovedOptionModule [ "nix" "daemonNiceLevel" ] "Consider nix.daemonCPUSchedPolicy instead.")
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];
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###### interface
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options = {
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nix = {
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enable = mkOption {
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type = types.bool;
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default = true;
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description = lib.mdDoc ''
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Whether to enable Nix.
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Disabling Nix makes the system hard to modify and the Nix programs and configuration will not be made available by NixOS itself.
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'';
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};
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package = mkOption {
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type = types.package;
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default = pkgs.nix;
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defaultText = literalExpression "pkgs.nix";
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description = lib.mdDoc ''
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This option specifies the Nix package instance to use throughout the system.
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'';
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};
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daemonCPUSchedPolicy = mkOption {
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type = types.enum [ "other" "batch" "idle" ];
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default = "other";
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example = "batch";
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description = lib.mdDoc ''
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Nix daemon process CPU scheduling policy. This policy propagates to
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build processes. `other` is the default scheduling
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policy for regular tasks. The `batch` policy is
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similar to `other`, but optimised for
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non-interactive tasks. `idle` is for extremely
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low-priority tasks that should only be run when no other task
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requires CPU time.
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Please note that while using the `idle` policy may
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greatly improve responsiveness of a system performing expensive
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builds, it may also slow down and potentially starve crucial
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configuration updates during load.
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`idle` may therefore be a sensible policy for
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systems that experience only intermittent phases of high CPU load,
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such as desktop or portable computers used interactively. Other
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systems should use the `other` or
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`batch` policy instead.
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For more fine-grained resource control, please refer to
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{manpage}`systemd.resource-control(5)` and adjust
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{option}`systemd.services.nix-daemon` directly.
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'';
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};
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daemonIOSchedClass = mkOption {
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type = types.enum [ "best-effort" "idle" ];
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default = "best-effort";
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example = "idle";
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description = lib.mdDoc ''
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Nix daemon process I/O scheduling class. This class propagates to
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build processes. `best-effort` is the default
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class for regular tasks. The `idle` class is for
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extremely low-priority tasks that should only perform I/O when no
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other task does.
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Please note that while using the `idle` scheduling
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class can improve responsiveness of a system performing expensive
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builds, it might also slow down or starve crucial configuration
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updates during load.
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`idle` may therefore be a sensible class for
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systems that experience only intermittent phases of high I/O load,
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such as desktop or portable computers used interactively. Other
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systems should use the `best-effort` class.
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'';
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};
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daemonIOSchedPriority = mkOption {
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type = types.int;
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default = 4;
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example = 1;
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description = lib.mdDoc ''
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Nix daemon process I/O scheduling priority. This priority propagates
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to build processes. The supported priorities depend on the
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scheduling policy: With idle, priorities are not used in scheduling
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decisions. best-effort supports values in the range 0 (high) to 7
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(low).
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'';
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};
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# Environment variables for running Nix.
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envVars = mkOption {
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type = types.attrs;
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internal = true;
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default = { };
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description = lib.mdDoc "Environment variables used by Nix.";
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};
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nrBuildUsers = mkOption {
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type = types.int;
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description = lib.mdDoc ''
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Number of `nixbld` user accounts created to
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perform secure concurrent builds. If you receive an error
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message saying that “all build users are currently in use”,
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you should increase this value.
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'';
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};
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};
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};
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###### implementation
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config = mkIf cfg.enable {
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environment.systemPackages =
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[
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nixPackage
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pkgs.nix-info
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]
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++ optional (config.programs.bash.enableCompletion) pkgs.nix-bash-completions;
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systemd.packages = [ nixPackage ];
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systemd.tmpfiles = mkMerge [
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(mkIf (isNixAtLeast "2.8") {
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packages = [ nixPackage ];
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})
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(mkIf (!isNixAtLeast "2.8") {
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rules = [
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"d /nix/var/nix/daemon-socket 0755 root root - -"
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];
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})
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];
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systemd.sockets.nix-daemon.wantedBy = [ "sockets.target" ];
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systemd.services.nix-daemon =
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{
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path = [ nixPackage pkgs.util-linux config.programs.ssh.package ]
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++ optionals cfg.distributedBuilds [ pkgs.gzip ];
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environment = cfg.envVars
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// { CURL_CA_BUNDLE = "/etc/ssl/certs/ca-certificates.crt"; }
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// config.networking.proxy.envVars;
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unitConfig.RequiresMountsFor = "/nix/store";
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serviceConfig =
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{
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CPUSchedulingPolicy = cfg.daemonCPUSchedPolicy;
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IOSchedulingClass = cfg.daemonIOSchedClass;
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IOSchedulingPriority = cfg.daemonIOSchedPriority;
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LimitNOFILE = 1048576;
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};
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restartTriggers = [ config.environment.etc."nix/nix.conf".source ];
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# `stopIfChanged = false` changes to switch behavior
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# from stop -> update units -> start
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# to update units -> restart
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#
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# The `stopIfChanged` setting therefore controls a trade-off between a
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# more predictable lifecycle, which runs the correct "version" of
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# the `ExecStop` line, and on the other hand the availability of
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# sockets during the switch, as the effectiveness of the stop operation
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# depends on the socket being stopped as well.
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#
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# As `nix-daemon.service` does not make use of `ExecStop`, we prefer
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# to keep the socket up and available. This is important for machines
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# that run Nix-based services, such as automated build, test, and deploy
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# services, that expect the daemon socket to be available at all times.
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#
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# Notably, the Nix client does not retry on failure to connect to the
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# daemon socket, and the in-process RemoteStore instance will disable
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# itself. This makes retries infeasible even for services that are
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# aware of the issue. Failure to connect can affect not only new client
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# processes, but also new RemoteStore instances in existing processes,
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# as well as existing RemoteStore instances that have not saturated
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# their connection pool.
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#
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# Also note that `stopIfChanged = true` does not kill existing
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# connection handling daemons, as one might wish to happen before a
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# breaking Nix upgrade (which is rare). The daemon forks that handle
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# the individual connections split off into their own sessions, causing
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# them not to be stopped by systemd.
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# If a Nix upgrade does require all existing daemon processes to stop,
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# nix-daemon must do so on its own accord, and only when the new version
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# starts and detects that Nix's persistent state needs an upgrade.
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stopIfChanged = false;
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};
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# Set up the environment variables for running Nix.
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environment.sessionVariables = cfg.envVars;
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nix.nrBuildUsers = mkDefault (
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if cfg.settings.auto-allocate-uids or false then 0
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else max 32 (if cfg.settings.max-jobs == "auto" then 0 else cfg.settings.max-jobs)
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);
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users.users = nixbldUsers;
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services.displayManager.hiddenUsers = attrNames nixbldUsers;
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# Legacy configuration conversion.
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nix.settings = mkMerge [
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(mkIf (isNixAtLeast "2.3pre") { sandbox-fallback = false; })
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];
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};
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}
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