src/site/xdoc/jsvc.xml (311 lines of code) (raw):
<?xml version="1.0"?>
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<document xmlns="http://maven.apache.org/XDOC/2.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 https://maven.apache.org/xsd/xdoc-2.0.xsd">
<properties>
<title>Daemon : Java Service</title>
<author email="jfrederic.clere@fujitsu-siemens.con">Jean-Frederic Clere</author>
</properties>
<body>
<section name="Introduction">
<p>
Jsvc is a set of libraries and applications for making Java
applications run on UNIX more easily.
<br/>
Jsvc allows the application (e.g. Tomcat) to perform some privileged operations as root
(e.g. bind to a port < 1024), and then switch identity to a non-privileged user.
<br/>
It can run on Win32 via the Cygwin emulation layer (see
<a href="http://www.cygwin.com/"> Cygwin</a> for more information),
however Win32 users may prefer to use <a href="procrun.html"> procrun</a>
instead, which allows the application to run as a Windows Service.
</p>
<p>
The sources are located in the src/native/unix subdirectory.
</p>
<p>
In the future <a href="http://apr.apache.org/"> APR </a> may be used
to provide more portable platform support.
</p>
</section>
<section name="Building from source">
<p>
To build under a UNIX operating system you will need:
</p>
<ul>
<li>GNU AutoConf (at least version 2.53)</li>
<li>An ANSI-C compliant compiler (GCC is good)</li>
<li>GNU Make</li>
<li>A Java Platform 2 compliant SDK</li>
</ul>
<p>
You need to build the "configure" program with:
</p>
<source>
sh support/buildconf.sh
</source>
<p>
(Note it is possible to replace sh by any compatible shell like bash, ksh).
The result should be something like:
<source>
support/buildconf.sh
support/buildconf.sh: configure script generated successfully
</source>
Once the configure script is generated, follow the next section.
</p>
</section>
<section name="Building from a release tarball">
<p>
To build the binary under a UNIX operating system you will need:
</p>
<ul>
<li>An ANSI-C compliant compiler (GCC is good)</li>
<li>GNU Make</li>
<li>A Java Platform 2 compliant SDK</li>
</ul>
<p>
You have to specify the <code>JAVA_HOME</code> of the SDK
either with the <code>--with-java=<dir></code> parameter or set the <code>JAVA_HOME</code> environment
to point to your SDK installation. For example:
<source>
./configure --with-java=/usr/java
</source>
or
<source>
export JAVA_HOME
./configure
</source>
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:
<source>
make
</source>
This will generate the executable file <code>jsvc</code>.
</p>
</section>
<section name="Starting jsvc">
<p>
To check the allowed parameters for the jsvc binary simply do:
<source>
./jsvc -help
Usage: jsvc [-options] class [args...]
Where options include:
-help | --help | -?
show this help page (implies -nodetach)
-jvm <JVM name>
use a specific Java Virtual Machine. Available JVMs:
'client' 'server'
-client
use a client Java Virtual Machine.
-server
use a server Java Virtual Machine.
-cp / -classpath <directories and zip/jar files>
set search path for service classes and resouces
-home <directory>
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>
user used to run the daemon (defaults to current user)
-verbose[:class|gc|jni]
enable verbose output
-cwd </full/path>
set working directory to given location (defaults to /)
-outfile </full/path/to/file>
Location for output from stdout (defaults to /dev/null)
Use the value '&2' to simulate '1>&2'
-errfile </full/path/to/file>
Location for output from stderr (defaults to /dev/null)
Use the value '&1' to simulate '2>&1'
-pidfile </full/path/to/file>
Location for output from the file containing the pid of jsvc
(defaults to /var/run/jsvc.pid)
-D<name>=<value>
set a Java system property
-X<option>
set Virtual Machine specific option
-ea[:<packagename>...|:<classname>]
-enableassertions[:<packagename>...|:<classname>]
enable assertions
-da[:<packagename>...|:<classname>]
-disableassertions[:<packagename>...|:<classname>]
disable assertions
-esa | -enablesystemassertions
enable system assertions
-dsa | -disablesystemassertions
disable system assertions
-agentlib:<libname>[=<options>]
load native agent library <libname>, e.g. -agentlib:hprof
-agentpath:<pathname>[=<options>]
load native agent library by full pathname
-javaagent:<jarpath>[=<options>]
load Java programming language agent, see java.lang.instrument
-procname <procname>
use the specified process name (works only for Linux)
-wait <waittime>
wait waittime seconds for the service to start
waittime should multiple of 10 (min=10)
-restarts <maxrestarts>
maximum automatic restarts (integer)
-1=infinite (default), 0=none, 1..(INT_MAX-1)=fixed restart count
-stop
stop the service using the file given in the -pidfile option
-keepstdin
does not redirect stdin to /dev/null
--add-modules=<module name>
Java 9 --add-modules option. Passed as it is to JVM
--module-path=<module path>
Java 9 --module-path option. Passed as it is to JVM
--upgrade-module-path=<module path>
Java 9 --upgrade-module-path option. Passed as it is to JVM
--add-reads=<module name>
Java 9 --add-reads option. Passed as it is to JVM
--add-exports=<module name>
Java 9 --add-exports option. Passed as it is to JVM
--add-opens=<module name>
Java 9 --add-opens option. Passed as it is to JVM
--limit-modules=<module name>
Java 9 --limit-modules option. Passed as it is to JVM
--patch-module=<module name>
Java 9 --patch-module option. Passed as it is to JVM
--illegal-access=<value>
Java 9 --illegal-access option. Passed as it is to JVM. Refer java help for possible values.
--enable-preview
Java 11 --enable-preview option. Passed as it is to JVM
--enable-native-access=<module name>
Java 21 --enable-native-access option. Passed as it is to JVM
</source>
</p>
<subsection name="Mac OS X universal binaries">
<p>
If jsvc was build with universal binary support the proper way of
starting <code>jsvc</code> is by using Mac OS X <code>arch</code> command:
</p>
<source>
arch -arch i386 ./jsvc -jvm server <original jsvc parameters>
for running 64-bit JVM use the:
arch -arch x86_64 ./jsvc -jvm server <original jsvc parameters>
</source>
<p>
Use <code>-jvm server</code> because default <code>client</code> JVM is
not present for all architectures.
</p>
</subsection>
</section>
<section name="Using jsvc">
<p>
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.
</p>
<subsection name="Via Daemon interface">
<p>
Do the following:
</p>
<ul>
<li>Write a Class that implements the Daemon interface (MyClass).</li>
<li>Put it in a jarfile (my.jar).</li>
<li>Call jsvc like:
<source>
./jsvc -cp commons-daemon.jar:my.jar MyClass
</source>
</li>
</ul>
</subsection>
<subsection name="Directly">
<p>
Write a Class (MyClass) that implements the following methods:
</p>
<ul>
<li>void init(String[] arguments): Here open configuration files, create a trace file, create
ServerSockets, Threads</li>
<li>void start(): Start the Thread, accept incoming connections</li>
<li>void stop(): Inform the Thread to terminate the run(), close the ServerSockets</li>
<li><code>void destroy()</code>: Destroy any object created in init()</li>
</ul>
<p>
Store it in a jarfile and use as above:
<source>
./jsvc -cp my.jar MyClass
</source>
</p>
</subsection>
</section>
<section name="How jsvc works">
<p>
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 <code>-user</code> parameter
allows to downgrade to an unprivilegded user.
When the <code>-wait</code> parameter is used, the launcher process waits until the controller says
"I am ready", otherwise it returns after creating the controller process.
</p>
<subsection name="Forks in commons-daemon">
<p>
Launcher process:
<source>
main()
{
fork()
parent: wait_child(), wait until JAVA service started when the child says "I am ready".
child: controller process.
}
</source>
Controller process:
<source>
while (fork()) {
parent: wait_for_child.
if exited and restart needed continue
else exit.
child: exit(child()). controlled process.
}
</source>
Controlled process:
<source>
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).
</source>
Note: The controller process uses signals to stop the controlled process.
</p>
</subsection>
<subsection name="Downgrading user">
<p>
On Linux <code>setuid()</code>/<code>setgid()</code> + capabilities are used. On other Unix <code>setgid</code>/<code>initgroups</code> are used.
We have something like:
<source>
/* 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 */
</source>
</p>
</subsection>
</section>
</body>
</document>