[Pkg-matrix-maintainers] Bug#1128500: matrix-synapse: fails to start when python3-eventlet is installed

[Gena Byers]

On 2/20/26 4:54 PM, Andrej Shadura wrote:
> Hello,
> 
> On Fri, 20 Feb 2026, at 16:50, Gena Byers wrote:
>> Dear Maintainer,
>>
>> matrix-synapse doesn't start when python3-eventlet is installed
> 
> Can you give me more details please?
> I don’t see any mentions of this anywhere in the source.
> 

I don't know what the exact mechanism is but installing python3-eventlet 
renders matrix-synapse inoperable:

$ sudo apt-get install python3-eventlet && sudo systemctl restart 
matrix-synapse.service
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Solving dependencies... Done
The following packages were automatically installed and are no longer 
required:
   linux-doc-6.16 linux-doc-6.17 linux-image-6.16.12+deb14+1-rt-amd64 
linux-image-6.17.11+deb14-rt-amd64 linux-image-6.17.12+deb14-rt-amd64
   linux-image-6.17.13+deb14-rt-amd64 linux-image-6.17.8+deb14-rt-amd64
Use 'sudo apt autoremove' to remove them.
Suggested packages:
   python-eventlet-doc
The following NEW packages will be installed:
   python3-eventlet
0 upgraded, 1 newly installed, 0 to remove and 4 not upgraded.
Need to get 311 kB of archives.
After this operation, 987 kB of additional disk space will be used.
Get:1 http://deb.debian.org/debian testing/main all python3-eventlet all 
0.40.3-2 [311 kB]
Fetched 311 kB in 0s (1,948 kB/s)
Selecting previously unselected package python3-eventlet.
(Reading database… 1820926 files and directories currently installed.)
Preparing to unpack …/python3-eventlet_0.40.3-2_all.deb…
Unpacking python3-eventlet (0.40.3-2)…
Setting up python3-eventlet (0.40.3-2)…
Scanning processes... 

Scanning candidates... 

Scanning processor microcode... 

Scanning linux images... 


The processor microcode seems to be up-to-date.

Restarting services...
Service restarts being deferred:
  /etc/needrestart/restart.d/dbus.service
  systemctl restart nodm.service
  systemctl restart unattended-upgrades.service

No containers need to be restarted.

User sessions running outdated binaries:
  user @ session #2: bash[969641,2416463,2918488], 
chromium[2918522,2918602], crashhelper[3589], firefox[3360], 
forkserver[4282],
   glycin-svg[984474,984532], obsidian[3334,3482,3926], sh[2946], 
urxvtd[3114,3115], x-session-manag[2982]
  user @ user manager: chromium[2918499], (sd-pam)[2625]
  user @ user service: at-spi-dbus-bus.service[3161], 
blueman-applet.service[969792,969802], dbus.service[2947,4381,2070721],
   dirmngr.service[4002], dunst.service[3801], 
filter-chain.service[3018], gvfs-udisks2-volume-monitor.service[3736],
   pipewire-pulse.service[3019], pipewire.service[2953], 
wireplumber.service[3015], xdg-desktop-portal-gtk.service[3594],
   xdg-desktop-portal.service[3574]

No VM guests are running outdated hypervisor (qemu) binaries on this host.
Job for matrix-synapse.service failed because the control process exited 
with error code.
See "systemctl status matrix-synapse.service" and "journalctl -xeu 
matrix-synapse.service" for details.

$ journalctl -xeu matrix-synapse
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/sentry_sdk/utils.py", line 1346, in 
_get_contextvars
Feb 20 16:59:17 nexus python3[2979902]:     if not _is_contextvars_broken():
Feb 20 16:59:17 nexus python3[2979902]:            ~~~~~~~~~~~~~~~~~~~~~~^^
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/sentry_sdk/utils.py", line 1287, in 
_is_contextvars_broken
Feb 20 16:59:17 nexus python3[2979902]:     from eventlet.patcher import 
is_monkey_patched  # type: ignore
Feb 20 16:59:17 nexus python3[2979902]: 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/eventlet/__init__.py", line 6, in <module>
Feb 20 16:59:17 nexus python3[2979902]:     from eventlet import convenience
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/eventlet/convenience.py", line 7, in 
<module>
Feb 20 16:59:17 nexus python3[2979902]:     from eventlet.green import 
socket
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/eventlet/green/socket.py", line 21, in 
<module>
Feb 20 16:59:17 nexus python3[2979902]:     from eventlet.support import 
greendns
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/eventlet/support/greendns.py", line 78, 
in <module>
Feb 20 16:59:17 nexus python3[2979902]:     setattr(dns, pkg, 
import_patched('dns.' + pkg))
Feb 20 16:59:17 nexus python3[2979902]: 
~~~~~~~~~~~~~~^^^^^^^^^^^^^^
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/eventlet/support/greendns.py", line 60, 
in import_patched
Feb 20 16:59:17 nexus python3[2979902]:     return 
patcher.import_patched(module_name, **modules)
Feb 20 16:59:17 nexus python3[2979902]: 
~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/eventlet/patcher.py", line 136, in 
import_patched
Feb 20 16:59:17 nexus python3[2979902]:     return inject(
Feb 20 16:59:17 nexus python3[2979902]:         module_name, None, 
*additional_modules + tuple(kw_additional_modules.items())
Feb 20 16:59:17 nexus python3[2979902]:     )
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/eventlet/patcher.py", line 113, in inject
Feb 20 16:59:17 nexus python3[2979902]:     module = 
__import__(module_name, {}, {}, module_name.split(".")[:-1])
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/dns/asyncquery.py", line 34, in <module>
Feb 20 16:59:17 nexus python3[2979902]:     import dns.quic
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/dns/quic/__init__.py", line 39, in <module>
Feb 20 16:59:17 nexus python3[2979902]:     import trio
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/trio/__init__.py", line 25, in <module>
Feb 20 16:59:17 nexus python3[2979902]:     from . import abc, 
from_thread, lowlevel, socket, to_thread
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/trio/socket.py", line 16, in <module>
Feb 20 16:59:17 nexus python3[2979902]:     from . import _socket
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/trio/_socket.py", line 546, in <module>
Feb 20 16:59:17 nexus python3[2979902]:     class SocketType:
Feb 20 16:59:17 nexus python3[2979902]:     ...<221 lines>...
Feb 20 16:59:17 nexus python3[2979902]:                 raise 
NotImplementedError
Feb 20 16:59:17 nexus python3[2979902]:   File 
"/usr/lib/python3/dist-packages/trio/_socket.py", line 759, in SocketType
Feb 20 16:59:17 nexus python3[2979902]: 
@_wraps(_stdlib_socket.socket.sendmsg, assigned=(), updated=())
Feb 20 16:59:17 nexus python3[2979902]: 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Feb 20 16:59:17 nexus python3[2979902]: AttributeError: type object 
'GreenSocket' has no attribute 'sendmsg'
Feb 20 16:59:17 nexus systemd[1]: matrix-synapse.service: Control 
process exited, code=exited, status=1/FAILURE
░░ Subject: Unit process exited
░░ Defined-By: systemd
░░ Support: https://www.debian.org/support
░░
░░ An ExecStartPre= process belonging to unit matrix-synapse.service has 
exited.
░░
░░ The process' exit code is 'exited' and its exit status is 1.
Feb 20 16:59:17 nexus systemd[1]: matrix-synapse.service: Failed with 
result 'exit-code'.
░░ Subject: Unit failed
░░ Defined-By: systemd
░░ Support: https://www.debian.org/support
░░
░░ The unit matrix-synapse.service has entered the 'failed' state with 
result 'exit-code'.
Feb 20 16:59:17 nexus systemd[1]: Failed to start matrix-synapse.service 
- Synapse Matrix homeserver.
░░ Subject: A start job for unit matrix-synapse.service has failed
░░ Defined-By: systemd
░░ Support: https://www.debian.org/support
░░
░░ A start job for unit matrix-synapse.service has finished with a failure.
░░
░░ The job identifier is 230940 and the job result is failed.
Feb 20 16:59:17 nexus systemd[1]: matrix-synapse.service: Consumed 
1.643s CPU time over 4.812s wall clock time, 69.8M memory peak.
░░ Subject: Resources consumed by unit runtime
░░ Defined-By: systemd
░░ Support: https://www.debian.org/support
░░
░░ The unit matrix-synapse.service completed and consumed the indicated 
resources.
Feb 20 16:59:20 nexus systemd[1]: matrix-synapse.service: Scheduled 
restart job, restart counter is at 10.
░░ Subject: Automatic restarting of a unit has been scheduled
░░ Defined-By: systemd
░░ Support: https://www.debian.org/support
░░
░░ Automatic restarting of the unit matrix-synapse.service has been 
scheduled, as the result for
░░ the configured Restart= setting for the unit.
Feb 20 16:59:20 nexus systemd[1]: Starting matrix-synapse.service - 
Synapse Matrix homeserver...
░░ Subject: A start job for unit matrix-synapse.service has begun execution
░░ Defined-By: systemd
░░ Support: https://www.debian.org/support
░░
░░ A start job for unit matrix-synapse.service has begun execution.
░░
░░ The job identifier is 231070.

removing python3-eventlet makes matrix-synapse work again:

$ sudo apt-get purge python3-eventlet && sudo systemctl restart 
matrix-synapse.service
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Solving dependencies... Done
The following packages were automatically installed and are no longer 
required:
   linux-doc-6.16 linux-doc-6.17 linux-image-6.16.12+deb14+1-rt-amd64 
linux-image-6.17.11+deb14-rt-amd64 linux-image-6.17.12+deb14-rt-amd64
   linux-image-6.17.13+deb14-rt-amd64 linux-image-6.17.8+deb14-rt-amd64
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED:
   python3-eventlet*
0 upgraded, 0 newly installed, 1 to remove and 4 not upgraded.
After this operation, 987 kB disk space will be freed.
Do you want to continue? [Y/n]
(Reading database… 1821035 files and directories currently installed.)
Removing python3-eventlet (0.40.3-2)…

$ sudo systemctl status matrix-synapse.service
● matrix-synapse.service - Synapse Matrix homeserver
      Loaded: loaded (/etc/systemd/system/matrix-synapse.service; 
enabled; preset: enabled)
      Active: active (running) since Fri 2026-02-20 17:14:01 CET; 24s ago
  Invocation: b60ad88a34d04dc180f7609a665f5e0b
        Docs: file:/usr/share/doc/matrix-synapse/README.rst
     Process: 2985474 ExecStartPre=/usr/bin/python3 -m 
synapse.app.homeserver --config-path=/etc/matrix-synapse/homeserver.yaml 
--config-path=>
    Main PID: 2985525 (python3)
       Tasks: 12 (limit: 76824)
      Memory: 124.4M (peak: 125.5M)
         CPU: 6.230s
      CGroup: /system.slice/matrix-synapse.service
              └─2985525 /usr/bin/python3 -m synapse.app.homeserver 
--config-path=/etc/matrix-synapse/homeserver.yaml --config-path=/etc/matrix>

Feb 20 17:13:55 nexus systemd[1]: Starting matrix-synapse.service - 
Synapse Matrix homeserver...
Feb 20 17:14:00 nexus synapse[2985525]: synapse.config.logger: [main] 
***** STARTING SERVER *****
Feb 20 17:14:00 nexus synapse[2985525]: synapse.config.logger: [main] 
Server /usr/lib/python3/dist-packages/synapse/app/homeserver.py version>
Feb 20 17:14:00 nexus synapse[2985525]: synapse.config.logger: [main] 
Copyright (c) 2023 New Vector, Inc
Feb 20 17:14:00 nexus synapse[2985525]: synapse.config.logger: [main] 
Licensed under the AGPL 3.0 license. Website: https://github.com/elemen>
Feb 20 17:14:01 nexus systemd[1]: Started matrix-synapse.service - 
Synapse Matrix homeserver.