Kyle Isom
47b4e533ff
Rootless podman deeply caches the UID in storage, subuid mappings, and systemd sessions. Changing it destroys all container state. Reference: log/2026-04-03-uid-incident.md Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
64 lines
2.0 KiB
Nix
64 lines
2.0 KiB
Nix
# MCP (Metacircular Control Plane) agent user and configuration.
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#
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# Creates a dedicated 'mcp' system user with rootless podman support
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# and a systemd service for the agent daemon.
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{ pkgs, ... }:
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{
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users.users.mcp = {
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isSystemUser = true;
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uid = 850; # NEVER CHANGE. Rootless podman caches the UID in storage, subuid mappings,
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# and systemd sessions. Changing it destroys all container state.
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# See log/2026-04-03-uid-incident.md.
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group = "mcp";
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home = "/srv/mcp";
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shell = pkgs.shadow; # nologin equivalent
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subUidRanges = [{ startUid = 100000; count = 65536; }];
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subGidRanges = [{ startGid = 100000; count = 65536; }];
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extraGroups = [ "systemd-journal" ];
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linger = true;
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};
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users.groups.mcp = { gid = 850; };
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# MCP Master runs as an MCP-managed container (not a systemd service).
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# Deployed via: mcp deploy mcp-master --direct
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# See ~/.config/mcp/services/mcp-master.toml
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systemd.services.mcp-agent = {
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description = "MCP Agent";
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after = [ "network-online.target" ];
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wants = [ "network-online.target" ];
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wantedBy = [ "multi-user.target" ];
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serviceConfig = {
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Type = "simple";
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ExecStart = "/srv/mcp/mcp-agent server --config /srv/mcp/mcp-agent.toml";
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Restart = "on-failure";
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RestartSec = 5;
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User = "mcp";
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Group = "mcp";
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Environment = [
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"HOME=/srv/mcp"
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"XDG_RUNTIME_DIR=/run/user/850"
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"PATH=/run/current-system/sw/bin:/usr/local/bin"
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];
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NoNewPrivileges = true;
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ProtectSystem = "full"; # "strict" blocks /run/user; "full" protects /usr and /boot
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# ProtectHome makes /run/user inaccessible, which breaks rootless podman.
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# The agent's home is /srv/mcp (not /home), so this is acceptable.
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ProtectHome = false;
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PrivateTmp = true;
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PrivateDevices = true;
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ProtectKernelTunables = true;
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ProtectKernelModules = true;
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RestrictSUIDSGID = true;
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LockPersonality = true;
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RestrictRealtime = true;
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ReadWritePaths = [ "/srv" ];
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};
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};
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}
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