【Problem】rake db:migrate提示SQLite3::BusyException: database is locked: commit transaction

rails tuturial p226执行了$ rake db:migrate 后报错：

reddevil@reddevil-Lenovo:~/railsProject/demo_app/sample_app$ rake db:migrate
==  AddEmailUniquenessIndex: migrating ========================================
-- add_index(:users, :email, {:unique=>true})
   -> 0.0006s
==  AddEmailUniquenessIndex: migrated (0.0006s) ===============================

rake aborted!
An error has occurred, this and all later migrations canceled:

SQLite3::BusyException: database is locked: commit transaction

Tasks: TOP => db:migrate
(See full trace by running task with --trace)

报错信息提示数据库被锁，想到还有一个终端打开了rails console --sandbox，试了下退出了sandbox

1.9.3p194 :005 > exit
   (0.1ms)  rollback transaction

再次rake db:migrate就可以了

reddevil@reddevil-Lenovo:~/railsProject/demo_app/sample_app$ rake db:migrate
==  AddEmailUniquenessIndex: migrating ========================================
-- add_index(:users, :email, {:unique=>true})
   -> 0.0006s
==  AddEmailUniquenessIndex: migrated (0.0006s) ===============================