jvsc文档

./configure --with-java=/usr/java

or

export JAVA_HOME ./configure

If your operating system is supported, configure will go through cleanly, otherwise it will report an error (please send us the details of your OS/JDK, or a patch against the sources). To build the binaries and libraries simply do:

make

This will generate the executable file jsvc. Starting jsvc

To check the allowed parameters for the jsvc binary simply do:

./jsvc -help Usage: jsvc [-options] class [args...]

Where options include:

-help | --help | -? show this help page (implies -nodetach) -jvm use a specific Java Virtual Machine. Available JVMs: 'client' 'server' -cp / -classpath set search path for service classes and resouces -home set the path of your JDK or JRE installation (or set the JAVA_HOME environment variable) -version show the current Java environment version (to check correctness of -home and -jvm. Implies -nodetach) -showversion show the current Java environment version (to check correctness of -home and -jvm) and continue execution. -nodetach don't detach from parent process and become a daemon -debug verbosely print debugging information -check only check service (implies -nodetach) -user user used to run the daemon (defaults to current user) -verbose[:class|gc|jni] enable verbose output -outfile Location for output from stdout (defaults to /dev/null) Use the value '&2' to simulate '1>&2' -errfile Location for output from stderr (defaults to /dev/null) Use the value '&1' to simulate '2>&1' -pidfile Location for output from the file containing the pid of jsvc (defaults to /var/run/jsvc.pid) -D= set a Java system property -X set Virtual Machine specific option -ea[:...|:] -enableassertions[:...|:] enable assertions -da[:...|:] -disableassertions[:...|:] disable assertions -esa | -enablesystemassertions enable system assertions -dsa | -disablesystemassertions disable system assertions -agentlib:[=] load native agent library , e.g. -agentlib:hprof -agentpath:[=] load native agent library by full pathname -javaagent:[=] load Java programming language agent, see java.lang.instrument -procname use the specified process name (works only for Linux) -wait wait waittime seconds for the service to start waittime should multiple of 10 (min=10) -stop stop the service using the file given in the -pidfile option -keepstdin does not redirect stdin to /dev/null

Using jsvc

There two ways to use jsvc: via a Class that implements the Daemon interface or via calling a Class that has the required methods. For example Tomcat-4.1.x uses the Daemon interface whereas Tomcat-5.0.x provides a Class whose methods are called by jsvc directly. Via Daemon interface

Do the following:

* Write a Class that implements the Daemon interface (MyClass). * Put it in a jarfile (my.jar). * Call jsvc like:

./jsvc -cp commons-daemon.jar:my.jar MyClass

Directly

Write a Class (MyClass) that implements the following methods:

* void init(String[] arguments): Here open configuration files, create a trace file, create ServerSockets, Threads * void start(): Start the Thread, accept incoming connections * void stop(): Inform the Thread to terminate the run(), close the ServerSockets * void destroy(): Destroy any object created in init()

Store it in a jarfile and use as above:

./jsvc -cp my.jar MyClass

How jsvc works

Jsvc uses 3 processes: a launcher process, a controller process and a controlled process. The controlled process is also the main java thread, if the JVM crashes the controller will restart it in the next minute. Jsvc is a daemon process so it should be started as root and the -user parameter allows to downgrade to an unprivilegded user. When the -wait parameter is used, the launcher process waits until the controller says "I am ready", otherwise it returns after creating the controller process. Forks in commons-daemon

Launcher process:

main() { fork() parent: wait_child(), wait until JAVA service started when the child says "I am ready". child: controller process. }

Controller process:

while (fork()) { parent: wait_for_child. if exited and restart needed continue else exit. child: exit(child()). controlled process. }

Controlled process:

In child(): controlled process. init_JVM(). load_service(). start_service(). say "I am ready" wait for signal or poll for stop stop_service(). destroy_service(). destroy_JVM(). exit (with different codes so that parent knows if it has to restart us).

Note: The controller process uses signals to stop the controlled process. Downgrading user

On Linux setuid()/setgid() + capabilities are used. On other unix setgid/initgroups are used. We have something like:

/* as root */ init_JVM(). load_service. /*  java_load() calls the load method */ downgrade user (set_caps() or set_user_group()) /* as the user $USER (from -user $USER parameter) */ umask() start_service. /* java_start() calls the start method */

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