kumod: raise soft rlimit nofile -> hard limit on startup

crates/kumod/Cargo.toml

@@ -37,7 +37,7 @@ minijinja = {version="0.30",features=["source"]}
 mlua = {version="0.8", features=["vendored", "lua54", "async", "send", "serialize"]}
 mod-redis = {path="../mod-redis"}
 mod-sqlite = {path="../mod-sqlite"}
-nix = "0.26"
+nix = {version="0.26", features=["resource"]}
 once_cell = "1.17"
 ouroboros = "0.15"
 prometheus = "0.13"

crates/kumod/src/main.rs

@@ -4,6 +4,7 @@ use anyhow::Context;
 use caps::{CapSet, Capability, CapsHashSet};
 use clap::{Parser, ValueEnum};
 use metrics_prometheus::recorder::Layer;
+use nix::sys::resource::{getrlimit, setrlimit, Resource};
 use nix::unistd::{Uid, User};
 use std::path::PathBuf;
 use tracing_subscriber::fmt::writer::BoxMakeWriter;
@@ -116,6 +117,9 @@ fn main() -> anyhow::Result<()> {
     // runtime after we've called it.
     opts.drop_privs()?;
 
+    let (_no_file_soft, no_file_hard) = getrlimit(Resource::RLIMIT_NOFILE)?;
+    setrlimit(Resource::RLIMIT_NOFILE, no_file_hard, no_file_hard)?;
+
     tokio::runtime::Builder::new_multi_thread()
         .enable_all()
         .build()