H2 DB 是一種輕量級的檔案型資料庫，還提供 Web Console 視覺化操作資料庫，支援標準的JDBC API。

因是檔案型資料庫，在使用的時候經常會遇到如下問題：

Error Message:

Database may be already in use: "Locked by another process"

Detail Stack:

Exception in thread "main" org.h2.jdbc.JdbcSQLException: Database may be already in use: "Locked by another process". Possible solutions: close all other connection(s); use the server mode [90020-161]
 

    at org.h2.message.DbException.getJdbcSQLException(DbException.java:329)
    at org.h2.message.DbException.get(DbException.java:169)
    at org.h2.message.DbException.get(DbException.java:146)
    at org.h2.store.FileLock.getExceptionAlreadyInUse(FileLock.java:435)
    at org.h2.store.FileLock.lockFile
 
(FileLock.java:332)
    at org.h2.store.FileLock.lock(FileLock.java:128)
    at org.h2.engine.Database.open(Database.java:539)
    at org.h2.engine.Database.openDatabase(Database.java:219)
    at org.h2.engine.Database.<init>(Database.java:214)
    at org.h2.engine.Engine.openSession(Engine.java
 
:56)
    at org.h2.engine.Engine.openSession(Engine.java:159)
    at org.h2.engine.Engine.createSessionAndValidate(Engine.java:138)
    at org.h2.engine.Engine.createSession(Engine.java:121)
    at org.h2.server.TcpServerThread.run(TcpServerThread.java:124)
    at java.lang.Thread.run(Unknown Source)

    at org.h2.engine.SessionRemote.done(SessionRemote.java:538)
    at org.h2.engine.SessionRemote.initTransfer(SessionRemote.java:109)
    at org.h2.engine.SessionRemote.connectServer(SessionRemote.java:373)
    at org.h2.engine.SessionRemote.connectEmbeddedOrServer(SessionRemote.java:267)
    at org.h2.jdbc.JdbcConnection.<init>(JdbcConnection.java:110)
    at org.h2.jdbc.JdbcConnection.<init>(JdbcConnection.java:94)
    at org.h2.Driver.connect(Driver.java:72)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at java.sql.DriverManager.getConnection(Unknown Source)
    at org.h2.tools.RunScript.process(RunScript.java:312)
    at org.h2.tools.RunScript.runTool(RunScript.java:140)
    at org.h2.tools.RunScript.main(RunScript.java:68)

在工程裡面會生成 “dbname.lock.db” , 怎麼刪除都刪不掉。 原因可想而知，某個程序佔用了該檔案，必須先關閉該程序。

解決辦法：

開啟“終端“ | “命令列“，輸入指令 : ps aux | grep java

找到帶有關鍵字 h2的程序，例如程序編號是：356322， 輸入命令kill 之

kill 356322

之後，就可以刪除 lock住的檔案了

rm -f dbname.lock.db

重啟 h2 db 服務就不會報錯了！