flm serve crash on linux

[jeremyfowers]

(base) jfowers@hp-omni-1:~$ flm serve lfm2.5-it:1.2b
[FLM]  Using environment-specified port: 52625
[FLM]  Loading model: /home/jfowers/.config/flm/models/LFM2.5-1.2B-NPU2
[FLM]  Starting server on port 52625...
[FLM]  WebServer started on port 52625 with 10 I/O threads
[FLM]  Enter 'exit' to stop the server: 
[🔗 ]  TCP connection established - Remote: 127.0.0.1:35286
[TCP]  Read 687 bytes from socket
================================================
[⬇️ ]  Incoming Request: GET
[LOG]  Time stamp: 07:50:25 02:28:2026
[LOG]  Target: /
[LOG]  Version: 11
[LOG]  Keep-Alive: 1
================================================
[🔒 ]  TCP connection closed - Remote: 127.0.0.1:35286
[🔗 ]  TCP connection established - Remote: 127.0.0.1:38592
[TCP]  Read 505 bytes from socket
[✈️ ]  Handling Preflight (OPTIONS) request
Segmentation fault (core dumped)

Crash info:

 ⎿  === ExecutablePath ===
     /opt/fastflowlm/bin/flm
     === Date ===
     Sat Feb 28 07:51:55 2026
     === Title ===
     flm crashed with SIGSEGV in boost::beast::buffers_suffix<boost::beast::detail::buffers_ref<boost::beast::buffers_cat_view<boost::asio::const_buffer, boost::asio::const_buffer, boost::asio::const_buffer,
     boost::beast::http::basic_fields<std::allocator<char> >::writer::field_range, boost::beast::http::chunk_crlf> > >::consume()
     === Signal ===
     11
     === SignalName ===
     SIGSEGV
     === SegvReason ===
     reading unknown VMA
     === SegvAnalysis ===
     Segfault happened at: 0x5f406f0bb3dc <_ZN5boost5beast14buffers_suffixINS0_6detail11buffers_refINS0_16buffers_cat_viewIJNS_4asio12const_bufferES6_S6_NS0_4http12basic_fieldsISaIcEE6writer11field_rangeENS7_1
     0chunk_crlfEEEEEEE7consumeEm+204>: movzwl 0x30(%rax),%edx
     PC (0x5f406f0bb3dc) ok
     source "0x30(%rax)" (0x7ec13c031) not located in a known VMA region (needed readable region)!
     destination "%edx" ok
     Stack memory exhausted (SP below stack segment)
     === ProcCmdline ===
     flm serve lfm2.5-it:1.2b
     === StacktraceTop ===
     boost::beast::buffers_suffix<boost::beast::detail::buffers_ref<boost::beast::buffers_cat_view<boost::asio::const_buffer, boost::asio::const_buffer, boost::asio::const_buffer,
     boost::beast::http::basic_fields<std::allocator<char> >::writer::field_range, boost::beast::http::chunk_crlf> > >::consume (this=this@entry=0x7ec13c0017b0, amount=148) at
     /usr/include/boost/beast/http/impl/fields.hpp:285
     boost::beast::http::serializer<false, boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >::consume (this=0x7ec13c001730, n=<optimized out>) at
     /usr/include/c++/15/new:232
     boost::beast::http::detail::write_some_op<boost::beast::http::detail::write_op<boost::beast::http::detail::write_msg_op<HttpSession::handle_request(bool)::<lambda(boost::beast::error_code, std::size_t)>,
     boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, false, boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >,
     boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, boost::beast::http::detail::serializer_is_done, false, boost::beast::http::empty_body,
     boost::beast::http::basic_fields<std::allocator<char> > >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, false, boost::beast::http::empty_body,
     boost::beast::http::basic_fields<std::allocator<char> > >::operator() (this=0x7ec151bf58a0, ec=..., bytes_transferred=197) at /usr/include/boost/beast/http/impl/write.hpp:131
     boost::asio::detail::binder2<boost::beast::http::detail::write_some_op<boost::beast::http::detail::write_op<boost::beast::http::detail::write_msg_op<HttpSession::handle_request(bool)::<lambda(boost::beast
     ::error_code, std::size_t)>, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, false, boost::beast::http::empty_body,
     boost::beast::http::basic_fields<std::allocator<char> > >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, boost::beast::http::detail::serializer_is_done, false,
     boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, false,
     boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >, boost::system::error_code, long unsigned int>::operator() (this=0x7ec151bf58a0) at
     /usr/include/boost/asio/detail/bind_handler.hpp:181
     boost::asio::detail::binder0<boost::asio::detail::binder2<boost::beast::http::detail::write_some_op<boost::beast::http::detail::write_op<boost::beast::http::detail::write_msg_op<HttpSession::handle_reques
     t(bool)::<lambda(boost::beast::error_code, std::size_t)>, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, false, boost::beast::http::empty_body,
     boost::beast::http::basic_fields<std::allocator<char> > >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, boost::beast::http::detail::serializer_is_done, false,
     boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::any_io_executor>, false,
     boost::beast::http::empty_body, boost::beast::http::basic_fields<std::allocator<char> > >, boost::system::error_code, long unsigned int> >::operator() (this=0x7ec151bf58a0) at
     /usr/include/boost/asio/detail/bind_handler.hpp:56

cc @superm1

[jeremyfowers]

This is reproducible by pressing the "Verify models" button in Open WebUI

[ZaneNi]

@jeremyfowers Thanks for you feedback.

May I ask where is the "Verify models" button?

This is reproducible by pressing the "Verify models" button in Open WebUI

[rudifus-ppy]

some CORS preflight issue - workaround
sudo apt install nginx

and

sudo tee /etc/nginx/sites-available/flm-proxy > /dev/null << 'EOF'
server {
    listen 52626;
    location / {
        if ($request_method = OPTIONS) {
            add_header Access-Control-Allow-Origin *;
            add_header Access-Control-Allow-Methods "GET, POST, OPTIONS";
            add_header Access-Control-Allow-Headers "Content-Type, Authorization";
            return 200;
        }
        add_header Access-Control-Allow-Origin *;
        proxy_pass http://127.0.0.1:52625;
        proxy_set_header Host $host;
    }
}
EOF
sudo ln -s /etc/nginx/sites-available/flm-proxy /etc/nginx/sites-enabled/
sudo nginx -t && sudo systemctl reload nginx

tested on Gorgon Point HX 470 AI, FastFlowLm v v0.9.35 Linux ubuntu 24.04 LTS

flm validate
[Linux]  Kernel: 6.17.0-14-generic
[Linux]  NPU: /dev/accel/accel0 with 8 columns
[Linux]  NPU FW Version: 1.1.2.64
[Linux]  amdxdna version: 0.6
[Linux]  Memlock Limit: infinity

interestingly - no NPU actiivty shown by the Resources monitor for NPU there

[eimsbush]

(Sorry for reediting)

$ sudo flm validate
[Linux]  Kernel: 6.17.0-1025-oem
[Linux]  NPU: /dev/accel/accel0 with 8 columns
[Linux]  NPU FW Version: 1.1.2.64
[Linux]  amdxdna version: 0.6
[Linux]  Memlock Limit: 10008 MB


$ sudo flm --version
FLM v0.9.43

Maybe these additional info can help. But i see there is a pull request already sent.

[FLM]  Qwen3.5 pre-resize image height to 720 pixels if larger than that
[FLM]  Loading model: /root/.config/flm/models/Qwen3.5-4B-NPU2
[FLM]  Start generating...
[FLM]  Total images: 0
[FLM]  Prefill chunk 1/1 with 32 tokens
[FLM]  Creating checkpoint at context length %d32, general_token_idx 32
[FLM]  Total images: 0
Speicherzugriffsfehler

sudo dmesg -T | tail -n 50


[Sa, 13. Jun 2026, 22:45:42] flm[8540]: segfault at 0 ip 00005fa8ae6a6b80 sp 00007cda8f3fa140 error 4 in flm[1cab80,5fa8ae57d000+52a000] likely on CPU 2 (core 2, socket 0)
[Sa, 13. Jun 2026, 22:45:42] Code: 60 8b 7f 18 64 48 8b 04 25 28 00 00 00 48 89 45 c8 31 c0 85 ff 7e 27 4c 8b 46 10 48 8b 33 48 63 cf 31 d2 0f 1f 80 00 00 00 00 <41> 0f b7 04 50 c1 e0 10 89 04 96 48 83 c2 01 48 39 d1 75 ec 48 83```