安装calibre后转换pdf报错

[mamacmm]

安装参考https://www.bookstack.cn/read/help/Ubuntu.md 安装完calibre，使用命令ebook-convert test.txt test.pdf 测试发现;

1% 将输入转换为HTML中...
InputFormatPlugin: TXT Input running
on /home/bookstack/workspace/test.txt
Language not specified
Creator not specified
Building file list...
Normalizing filename cases
Rewriting HTML links
flow is too short, not running heuristics
Forcing index-1.html into XHTML namespace
34% 正在对电子书进行转换...
Merging user specified metadata...
Detecting structure...
Auto generated TOC with 0 entries.
Flattening CSS and remapping font sizes...
Source base font size is 12.00000pt
Removing fake margins...
Cleaning up manifest...
Trimming unused files from manifest...
Creating PDF Output...
67% 正在运行 PDF Output 插件
Traceback (most recent call last):
  File "site.py", line 77, in main
  File "site-packages/calibre/ebooks/conversion/cli.py", line 391, in main
  File "site-packages/calibre/ebooks/conversion/plumber.py", line 1270, in run
  File "site-packages/calibre/ebooks/conversion/plugins/pdf_output.py", line 163, in convert
  File "site-packages/calibre/gui2/__init__.py", line 13, in <module>
ImportError: cannot import name QApplication

然后，只生成了一个 index-1.html ，没有生成 pdf 文件