Jsvc is a set of libraries and applications for making Java
applications run on UNIX more easily.
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.
It can run on Win32 via the Cygwin emulation layer (see
Cygwin for more information),
however Win32 users may prefer to use procrun
instead, which allows the application to run as a Windows Service.
The sources are located in the src/native/unix subdirectory.
In the future APR may be used to provide more portable platform support.
To build under a UNIX operating system you will need:
sh support/buildconf.sh
support/buildconf.sh support/buildconf.sh: configure script generated successfully
To build the binary under a UNIX operating system you will need:
./configure --with-java=/usr/java
export JAVA_HOME ./configure
make
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 <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)
-stop
stop the service using the file given in the -pidfile option
-keepstdin
does not redirect stdin to /dev/null
If jsvc was build with universal binary support the proper way of starting jsvc is by using Mac OS X arch command:
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>
Use -jvm server because default client JVM is not present for all architectures.
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.
Do the following:
./jsvc -cp commons-daemon.jar:my.jar MyClass
Write a Class (MyClass) that implements the following methods:
./jsvc -cp my.jar MyClass
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.
Launcher process:
main()
{
fork()
parent: wait_child(), wait until JAVA service started when the child says "I am ready".
child: controller process.
}
while (fork()) {
parent: wait_for_child.
if exited and restart needed continue
else exit.
child: exit(child()). 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).
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 */