序本文主要研究一下openjdk的jvm.cfg文件jdk8/Library/Java/JavaVirtualMachines/jdk1.8.0_151.jdk/Contents/Home/jre/lib/jvm.cfg# List of JVMs that can be used as an option to java, javac, etc.# Order is important – first in this list is the default JVM.# NOTE that this both this file and its format are UNSUPPORTED and# WILL GO AWAY in a future release.## You may also select a JVM in an arbitrary location with the# “-XXaltjvm=<jvm_dir>” option, but that too is unsupported# and may not be available in a future release.#-server KNOWN-client IGNORE对于jdk8该文件在JAVA_HOME/jre/lib/目录下；其注释显示该配置文件用于配置java、javac能够使用的option，其中配置顺序非常重要，第一个为default JVM(不管其是KNOWN还是IGNORE；IGNORE仅仅是禁用VM option；ERROR则报错显示not supported)；可以看到这里-server是默认的，而-client则被忽略jdk9-12/Library/Java/JavaVirtualMachines/jdk-12.jdk/Contents/Home/lib/jvm.cfg-server KNOWN-client IGNORE对于jdk9、10、11、12该文件在JAVA_HOME/lib/目录下设置-client为default对于jdk12，把-client移到前面-client IGNORE-server KNOWN执行java -version显示如下java -versionError: missing client' JVM at /Library/Java/JavaVirtualMachines/jdk-12.jdk/Contents/Home/lib/client/libjvm.dylib’.Please install or use the JRE or JDK that contains these missing components.可以看到对于mac的jdk12，把client设置为default则报错禁用client-server KNOWN-client ERROR执行java -client -version显示如下java -client -versionError: client VM not supported可以看到设置-client为ERROR，则报错显示not supported删除jvm.cfgjava -versionError: could not open `/Library/Java/JavaVirtualMachines/jdk-12.jdk/Contents/Home/lib/jvm.cfg’可以看到删除jvm.cfg，执行java -version则会报错小结jvm.cfg文件用于配置java、javac能够使用的option，其中配置顺序非常重要，第一个为default JVM(不管其是KNOWN还是IGNORE；IGNORE仅仅是禁用VM option；ERROR则报错显示not supported)对于jdk8该文件在JAVA_HOME/jre/lib/目录下；对于jdk9、10、11、12该文件在JAVA_HOME/lib/目录下；删除jvm.cfg文件的话，则执行java命令会报错可以看到对于mac来说其open jdk的jvm.cfg中-server位于-client前面，-server是default JVM，而-client则被忽略docThe Java HotSpot VM Architecture OverviewWhat is the purpose of jvm.cfg file in relation to Java?Running the JVM in server modeServer-Class Machine DetectionChange Default Java VM to ClientOpenJDK default options to always use the server VM