git如何忽略部分不想备份的文件

git如何忽略部分不想备份的文件
ubuntu@VM-0-2-ubuntu:~/Projects/microblog$ git status
On branch master
Your branch is up-to-date with 'origin/master'.
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git checkout -- <file>..." to discard changes in working directory)

modified: app.db

Untracked files:
(use "git add <file>..." to include in what will be committed)

__pycache__/
logs/
migrations/versions/045455cbbc13_new_fields_in_user_model.py
migrations/versions/0bdbe14f07ca_posts_table.py
migrations/versions/__pycache__/045455cbbc13_new_fields_in_user_model.cpython-37.pyc
migrations/versions/__pycache__/0bdbe14f07ca_posts_table.cpython-37.pyc
venv/

no changes added to commit (use "git add" and/or "git commit -a")

git设置忽略文件和目录
1.进入本地git库目录
2.创建.gitignore
vi .gitignore
/logs
/migrations
/venv
__pycache__/
app.db
保存退出
3.修改文件，添加忽略正则

git status查看状态
On branch master
Your branch is up-to-date with 'origin/master'.
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git checkout -- <file>..." to discard changes in working directory)

modified: app.db

no changes added to commit (use "git add" and/or "git commit -a")
还剩下app.db，不知怎么回事。