Files
nix-config-ryan4yin/hosts/12kingdoms-youko/homelab-services/transmission.nix
T
Ryan Yin 4470b3d014 docs: centralize documentation under docs/
Move standalone repository docs from the root into docs/ and add a documentation index that links the moved docs and the code-local runbooks.

Update Markdown links, source comments, and the root entry points to the new locations. Keep README.md and AGENTS.md at the root as required entry points.

Assisted-by: DeepSeek Harness (deepseek-flash)
2026-11-02 17:48:57 +08:00

275 lines
12 KiB
Nix

{
config,
lib,
myvars,
pkgs,
...
}:
let
dataDir = "/data/fileshare/public/transmission";
name = "transmission";
# Transmission runs in its own network namespace with a direct path to the
# main router: the default host gateway is suzi, a transparent proxy that
# hijacks DNS to fake IPs (which only resolve on the proxied path) and has no
# UPnP/NAT-PMP. In the namespace it gets its own address, a real resolver, and
# a default route at the main router, so peers can reach it and it can resolve
# real addresses without going through the proxy.
netns = "transmission";
nsIp = "192.168.5.118";
hostVeth = "tr-hveth";
nsVeth = "tr-nveth";
# Real resolvers for the namespace (v4 first; the host's resolver is suzi).
resolvConf = pkgs.writeText "transmission-resolv.conf" (
lib.concatMapStrings (ns: "nameserver ${ns}\n") myvars.networking.nameservers
);
# Drop nss-resolve from the host's nsswitch for this service only: it talks to
# the host's resolved over a unix socket, which would resolve through suzi and
# return fake IPs again, bypassing the resolvers above.
nsswitchConf = pkgs.runCommand "transmission-nsswitch.conf" { } ''
sed -E 's/ resolve \[!UNAVAIL=return\]//' ${config.environment.etc."nsswitch.conf".source} > $out
'';
ip = "${pkgs.iproute2}/bin/ip";
sysctl = "${pkgs.procps}/bin/sysctl";
nft = "${pkgs.nftables}/bin/nft";
# The namespace is a first-class host on br0, so once the router's IPv6
# firewall is relaxed it is reachable from the Internet with no host firewall
# in front of it. Keep the peer port open (that is the point) and the RPC
# LAN-only; drop everything else.
netnsFirewall = pkgs.writeText "transmission-netns.nft" ''
table inet transmission-fw {
chain input {
type filter hook input priority filter; policy drop;
iif "lo" accept
ct state established,related accept
meta l4proto icmp accept
meta l4proto ipv6-icmp accept
tcp dport 51413 accept
udp dport 51413 accept
udp dport 6771 accept
ip saddr ${myvars.networking.lanCidr} tcp dport 9091 accept
}
}
'';
in
{
# transmission 4.1.4 takes an fcntl lock on its config-dir lock file, but the
# AppArmor profile shipped by nixpkgs grants rw without k (lock), so the
# daemon exits with "Another process is already using". See docs/WORKAROUNDS.md.
security.apparmor.includes."local/bin.transmission-daemon" = ''
/var/lib/transmission/.config/transmission-daemon/lock rwk,
'';
# Join the shared fileshare group so transmission can read/write files
# created by sftpgo, and vice versa (via setgid directories).
users.users.${name}.extraGroups = [ "fileshare" ];
# Set up transmission's home dir with setgid + fileshare group ownership.
# The setgid bit (2) causes all files created here to inherit the group
# 'fileshare', regardless of which service creates them.
systemd.tmpfiles.rules = [
# Keep shared parent owned by root to avoid tmpfiles "unsafe path transition"
# when another service creates subdirectories under /data/fileshare/public.
"d /data/fileshare 2775 root fileshare -"
"d ${dataDir} 2775 ${name} fileshare -"
"d ${dataDir}/incomplete 2775 ${name} fileshare -"
"d ${dataDir}/downloads 2775 ${name} fileshare -"
"d ${dataDir}/watch 2775 ${name} fileshare -"
];
# the headless Transmission BitTorrent daemon
# https://github.com/NixOS/nixpkgs/blob/nixos-26.05/nixos/modules/services/torrent/transmission.nix
# https://wiki.archlinux.org/title/transmission
services.transmission = {
enable = true;
package = pkgs.transmission_4;
user = name;
group = name;
# 2775: setgid preserves fileshare group on download/incomplete dirs.
downloadDirPermissions = "2775";
# Whether to enable tweaking of kernel parameters to open many more connections at the same time.
# Note that you may also want to increase peer-limit-global.
# And be aware that these settings are quite aggressive and might not suite your regular desktop use.
# For instance, SSH sessions may time out more easily.
performanceNetParameters = true;
# Path to a JSON file to be merged with the settings.
# Useful to merge a file which is better kept out of the Nix store to set secret config parameters like `rpc-password`.
credentialsFile = config.age.secrets."transmission-credentials.json".path;
# Whether to open the RPC port in the firewall.
openRPCPort = false;
openPeerPorts = true;
# https://github.com/transmission/transmission/blob/main/docs/Editing-Configuration-Files.md
settings = {
# 0 = None, 1 = Critical, 2 = Error, 3 = Warn, 4 = Info, 5 = Debug, 6 = Trace;
message-level = 3;
# Encryption may help get around some ISP filtering,
# but at the cost of slightly higher CPU use.
# 0 = Prefer unencrypted connections,
# 1 = Prefer encrypted connections,
# 2 = Require encrypted connections; default = 1)
# Keep it at "prefer": forcing encryption drops peers that cannot do
# MSE, which costs upload opportunities on public swarms.
encryption = 1;
# rpc = Web Interface
rpc-port = 9091;
# The netns has its own loopback, so caddy (on the host) reaches the RPC
# over the namespace address instead of 127.0.0.1. Plain HTTP on the LAN;
# the RPC auth and whitelists below still apply.
rpc-bind-address = nsIp;
anti-brute-force-enabled = true;
# After this amount of failed authentication attempts is surpassed,
# the RPC server will deny any further authentication attempts until it is restarted.
# This is not tracked per IP but in total.
# Health-check probes (homepage/uptime-kuma) hit the authenticated RPC
# gateway and each 401 counts, so keep this well above a 401 burst.
anti-brute-force-threshold = 100;
rpc-authentication-required = true;
# Comma-delimited list of IP addresses.
# Wildcards allowed using '*'. Example: "127.0.0.*,192.168.*.*",
rpc-whitelist-enabled = true;
rpc-whitelist = "127.0.0.*,192.168.*.*";
# Comma-delimited list of domain names.
# Wildcards allowed using '*'. Example: "*.foo.org,example.com",
rpc-host-whitelist-enabled = true;
rpc-host-whitelist = "*.writefor.fun,localhost,192.168.5.*";
rpc-user = myvars.username;
rpc-username = myvars.username;
# rpc-password = "test"; # you'd better use the credentialsFile for this.
incomplete-dir-enabled = true;
incomplete-dir = "${dataDir}/incomplete";
download-dir = "${dataDir}/downloads";
# Watch a directory for torrent files and add them to transmission.
watch-dir-enabled = false;
watch-dir = "${dataDir}/watch";
# Whether to enable Micro Transport Protocol (µTP).
utp-enabled = true;
# Executable to be run at torrent completion.
script-torrent-done-enabled = false;
# script-torrent-done-filename = "/path/to/script";
# Enable Local Peer Discovery (LPD).
lpd-enabled = true;
# The peer port to listen for incoming connections.
peer-port = 51413;
# Bind peer sockets to the namespace address, so the listener, outgoing
# source, and UPnP/NAT-PMP advertisement all use the address the main
# router forwards 51413 to.
bind-address-ipv4 = nsIp;
# Enable UPnP or NAT-PMP to forward a port through your firewall(NAT).
# https://github.com/transmission/transmission/blob/main/docs/Port-Forwarding-Guide.md
port-forwarding-enabled = true;
# "normal" speed limits
speed-limit-down-enabled = true;
speed-limit-down = 30000; # KB/s
# Keep seeding under the 50 Mbps uplink (~20 Mbps).
speed-limit-up-enabled = true;
speed-limit-up = 2500; # KB/s
upload-slots-per-torrent = 16;
# Start torrents as soon as they are added
start-added-torrents = true;
# Queuing
# When true, Transmission will only download
# download-queue-size non-stalled torrents at once.
download-queue-enabled = true;
download-queue-size = 10;
# When true, torrents that have not shared data for
# queue-stalled-minutes are treated as 'stalled'
# and are not counted against the queue-download-size
# and seed-queue-size limits.
queue-stalled-enabled = true;
queue-stalled-minutes = 60;
# When true. Transmission will only seed seed-queue-size
# non-stalled torrents at once.
seed-queue-enabled = true;
# With 30+ torrents, 10 was leaving most seeds queued (never uploading).
seed-queue-size = 50;
};
};
# Create the namespace and its veth (the host end becomes another port on
# br0), so the service below can join it and appear as its own LAN host.
systemd.services.transmission-netns = {
description = "Network namespace for transmission";
wantedBy = [ "multi-user.target" ];
bindsTo = [ "sys-subsystem-net-devices-br0.device" ];
after = [ "sys-subsystem-net-devices-br0.device" ];
serviceConfig = {
Type = "oneshot";
RemainAfterExit = true;
ExecStop = "${ip} netns del ${netns}";
};
script = ''
set -euo pipefail
# idempotent: clean up leftovers from an unclean stop
${ip} netns del ${netns} 2>/dev/null || true
${ip} link del ${hostVeth} 2>/dev/null || true
${ip} netns add ${netns}
${ip} link add ${hostVeth} type veth peer name ${nsVeth}
${ip} link set ${hostVeth} master br0
${ip} link set ${hostVeth} up
${ip} link set ${nsVeth} netns ${netns}
${ip} -n ${netns} link set lo up
# Pin the MAC so the SLAAC-based IPv6 address is stable across reboots.
${ip} -n ${netns} link set ${nsVeth} address 02:00:00:00:76:01
# Keep a stable address: temporary addresses rotate and would not match
# what transmission listens on and advertises.
${ip} netns exec ${netns} ${sysctl} -q -w net.ipv6.conf.${nsVeth}.use_tempaddr=0 || true
${ip} -n ${netns} link set ${nsVeth} up
${ip} -n ${netns} addr add ${nsIp}/24 dev ${nsVeth}
${ip} -n ${netns} route add default via ${myvars.networking.mainGateway}
# Apply the namespace firewall after the interface is up.
${ip} netns exec ${netns} ${nft} -f ${netnsFirewall}
'';
};
# Join the namespace and resolve through real resolvers instead of suzi.
systemd.services.transmission = {
after = [ "transmission-netns.service" ];
requires = [ "transmission-netns.service" ];
# restart together with the namespace; otherwise the service would stay in
# the deleted namespace after the netns unit is recreated
partOf = [ "transmission-netns.service" ];
serviceConfig = {
NetworkNamespacePath = "/run/netns/${netns}";
# Joining a namespace owned by the host is incompatible with the module's
# default PrivateUsers=; the rest of the sandbox stays in place.
PrivateUsers = false;
# Resolve directly instead of through the host's systemd-resolved (suzi).
BindReadOnlyPaths = [
"${resolvConf}:/etc/resolv.conf"
"${nsswitchConf}:/etc/nsswitch.conf"
];
# glibc's resolver uses netlink to pick source addresses; the module's
# default set does not include it.
RestrictAddressFamilies = [ "AF_NETLINK" ];
};
};
# The /data mounts are `nofail`, so nothing orders transmission after them;
# without this the unit can start before /data/fileshare/public is mounted and
# fail its mount-namespace setup (seen on the host, where the tasks race).
systemd.services.transmission.unitConfig.RequiresMountsFor = "/data/fileshare/public";
}