peer_connect panicked for 'too many open files"

[garyyu]

20191120 23:43:29.740 DEBUG gotts_p2p::handshake - Connected! Cumulative 7254@146 offered from PeerAddr(V4(45.118.135.254:13514)) "MW/Gotts 0.0.3" HEADER_HIST | TXHASHSET_HIST | PEER_LIST | TX_KERNEL_HASH | FULL_NODE
20191120 23:43:29.743 ERROR gotts_util::logger -
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
   0: backtrace::backtrace::trace
   1: backtrace::capture::Backtrace::new
   2: gotts_util::logger::send_panic_to_log::{{closure}}
   3: std::panicking::rust_panic_with_hook
   4: std::panicking::continue_panic_fmt
   5: rust_begin_unwind
   6: core::panicking::panic_fmt
   7: core::result::unwrap_failed
   8: gotts_p2p::conn::listen
   9: gotts_p2p::peer::Peer::new
  10: gotts_p2p::peer::Peer::connect
  11: gotts_p2p::serv::Server::connect
  12: std::sys_common::backtrace::__rust_begin_short_backtrace
  13: std::panicking::try::do_call
  14: __rust_maybe_catch_panic
  15: core::ops::function::FnOnce::call_once{{vtable.shim}}
  16: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  17: std::sys::unix::thread::Thread::new::thread_start
  18: _pthread_body
  19: _pthread_start

This log repeated for multiple times:

$ grep -B 1 "panicked" gotts-server.log

20191120 23:05:10.364 ERROR gotts_util::logger - 
thread 'peer_read' panicked at 'failed to open /dev/urandom: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:35:18.941 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:37:23.715 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:38:04.004 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:40:08.595 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:40:48.976 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:42:50.169 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:43:29.743 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:46:11.731 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:49:25.035 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace:
--
20191120 23:49:36.470 ERROR gotts_util::logger - 
thread 'peer_connect' panicked at 'clone conn for reader failed: Os { code: 24, kind: Other, message: "Too many open files" }': src/libcore/result.rs:1165stack backtrace: