SSH远程Ubuntu机器按住按键时IPython崩溃问题求助

问题现象 #

• 通过SSH连接到Ubuntu 18.04.2 LTS机器，启动IPython会话后，只要长按按键（比如退格键）约半秒，IPython就会直接崩溃
• 崩溃后进入异常bash环境：按键输入无法显示，但能正常执行ls、man、pwd、ipython等命令，只能通过先按Ctrl+D再按Ctrl+C来终止会话，根本没法执行%tb这类调试命令

崩溃时的错误堆栈 #

File "/home/zach/local/anaconda3/bin/ipython", line 11, in <module> sys.exit(start_ipython())
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/__init__.py", line 125, in start_ipython return launch_new_instance(argv=argv, **kwargs)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/traitlets/config/application.py", line 658, in launch_instance app.start()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/terminal/ipapp.py", line 356, in start self.shell.mainloop()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/terminal/interactiveshell.py", line 498, in mainloop self.interact()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/terminal/interactiveshell.py", line 481, in interact code = self.prompt_for_code()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/IPython/terminal/interactiveshell.py", line 410, in prompt_for_code **self._extra_prompt_options())
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 738, in prompt return run_sync()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/shortcuts/prompt.py", line 727, in run_sync return self.app.run(inputhook=self.inputhook, pre_run=pre_run2)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/application/application.py", line 709, in run return run()
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/application/application.py", line 682, in run run_until_complete(f, inputhook=inputhook)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/eventloop/defaults.py", line 123, in run_until_complete return get_event_loop().run_until_complete(future, inputhook=inputhook)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/eventloop/posix.py", line 66, in run_until_complete self._run_once(inputhook)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/eventloop/posix.py", line 85, in _run_once self._inputhook_context.call_inputhook(ready, inputhook)
File "/home/zach/local/anaconda3/lib/python3.7/site-packages/prompt_toolkit/eventloop/inputhook.py", line 78, in call_inputhook threading.Thread(target=thread).start()
File "/home/zach/local/anaconda3/lib/python3.7/threading.py", line 847, in start _start_new_thread(self._bootstrap, ())
RuntimeError: can't start new thread

已排查的情况 #

• 不是Python本身的问题：直接启动Python交互环境，长按按键完全正常
• 换IPython版本/安装源没用：不管用Anaconda自带的IPython，还是系统的/usr/bin/ipython，问题都存在；重装Anaconda也解决不了，但同版本Ubuntu的另一台全新安装Anaconda的机器完全没这个问题
• 初步怀疑：从报错看是线程创建耗尽，推测IPython的事件循环可能给每个按键事件都创建新线程，长按按键时短时间生成大量线程，超出系统限制；这个问题和IPython文档里提到的OS X下按方向键崩溃的情况很类似
• 确认过没有其他程序占用大量线程

解决思路 #

我给你几个可以尝试的方案，按顺序试就行：

1. 禁用IPython的inputhook：启动IPython时加上--no-inputhook参数，也就是执行ipython --no-inputhook，这个参数可以禁用prompt_toolkit的输入钩子，避免它创建过多线程
2. 调整终端环境变量：试试修改TERM变量，比如先执行export TERM=xterm-256color，再启动IPython；有些时候SSH连接的终端类型不兼容会导致按键事件处理异常
3. 调整prompt_toolkit版本：报错出在prompt_toolkit的线程创建部分，你可以试试安装和IPython 7.5.0兼容的旧版本prompt_toolkit，比如执行pip install prompt_toolkit==2.0.10，或者升级到最新的兼容版本
4. 检查系统线程限制：执行ulimit -u查看当前用户的最大进程/线程数，如果数值比较低（比如1024），可以临时调高试试：ulimit -u 4096，再启动IPython测试
5. 收集信息提交bug：如果上面的方法都没用，你可以启动IPython时加上--Application.verbose_crash=True参数，获取更详细的崩溃日志，然后提交给IPython的官方团队

内容的提问来源于stack exchange，提问作者Zach Boyd