winsw: Windows service wrapper in less restrictive license
Now, I think the first question that people would ask is, why another, when there's Java Service Wrapper project already available. The main reason for writing my own was the license — Java Service Wrapper project is in GPL (so that they can sell their commercial version in a different license), and that made it difficult for Jenkins (which is under the MIT license) to use it.
Functionality-wise, there's really not much that's worth noting; the problem of wrapping a process as a Windows service is so well defined that there aren't really any room for substantial innovation. You basically write a configuration file specifying how you'd like your process to be launched, and we provide programmatic means to install/uninstall/start/stop services. Another notable different is that winsw can host any executable, whereas Java Service Wrapper can only host Java apps. Whether you like this or not depends on your taste, so I wouldn't claim mine is better. It's just different.
As the name implies, this is for Windows only. Unix systems have their own conventions for daemons, so a good behaving Unix daemon should just be using launchd/upstart/SMF/etc, instead of custom service wrapper.
You write the configuration file that defines your service. This is the one I use for Jenkins:
<service> <id>jenkins</id> <name>Jenkins</name> <description>This service runs Jenkins continuous integration system.</description> <env name="JENKINS_HOME" value="%BASE%"/> <executable>java</executable> <arguments>-Xrs -Xmx256m -jar "%BASE%\jenkins.war" --httpPort=8080</arguments> <logmode>rotate</logmode> </service>
winsw.exe into something like
jenkins.exe, then you put this XML file as
jenkins.xml. The executable locates the configuration file via this file name convention. You can then install the service like:
... and you can use the exit code from these processes to determine whether the operation was successful. There are other commands to perform other operations, like
stop, and so on.
Once the service is installed, you can start it from Windows service manager. Windows will start
jenkins.exe will launch the executable specified in the configuration file (Java in this case.) If this process dies, winsw will exit itself, and the service will be considered stopped.
winsw.exe accepts the following commands:
installto install the service to Windows Service Controller
uninstallto uninstall the service. The opposite operation of above.
startto start the service. The service must have already been installed.
stopto stop the service.
restartto restart the service. If the service is not currently running, this command acts like
statusto check the current status of the service. This command prints one line to the console.
NonExistentto indicate the service is not currently installed,
Startedto indicate the service is currently running, and
Stoppedto indicate that the service is installed but not currently running.
Winsw uses WMI underneath, and as such it uses its error code as the exit code. See MSDN article for the complete list of exit code.
When winsw is running as a service, more detailed error information is reported to the Windows event log.
Deferred file operations
To support self updating services, winsw offers a mechanism to perform file operations before the process you specified in the configuration file gets launched. This is often necessary because Windows prevents files from overwritten while it's in use.
To perform file operations, write a text file (in the UTF-8 encoding) at
myapp.copies (that is, it's in the same directory as
myapp.exe but with a different file extension), and for each operation add one line:
- To move a file, write a line
src>dst. If the
dstfile already exists it will be overwritten.
The success or failure of these operations will be recorded in the event log.
<download> element in the configuration file also provides an useful building block for a self updating services.
Winsw supports several different ways to capture stdout and stderr from the process you launch.
<logpath> element specifies the directory in which the log files are created. If this element is absent, it'll default to the same directory where the configuration file resides.
Append mode (default)
In this mode,
myapp is the base name of the executable and the configuration file) are created and outputs are simply appended to these files. Note that the file can get quite big.
Works like the append mode, except that every time the service starts, the old log files are truncated.
Works like the append mode, but in addition, if the log file gets bigger than a set size, it gets rotated to
myapp.2.out.log and so on. The nested
<sizeThreshold> element specifies the rotation threshold in KB (defaults to 10MB), and the nested
<keepFiles> element specifies the number of rotated files to keep (defaults to 8.)
<log mode="roll-by-size"> <sizeThreshold>10240</sizeThreshold> <keepFiles>8</keepFiles> </log>
Rotate by time mode
Works like the rotate mode, except that instead of using the size as a threshold, use the time period as the threshold.
This configuration must accompany a nested
<pattern> element, which specifies the timestamp pattern used as the log file name.
<log mode="roll-by-time"> <pattern>yyyyMMdd</pattern> </log>
The syntax of the pattern string is specified by DateTime.ToString(). For example, in the above example, the log of Jan 1, 2013 gets written to
Configuration file syntax
The behaviour of the service is controlled by the XML configuration file. The root element of this XML file must be
<service>, and it supports the following child element.
Specifies the ID that Windows uses internally to identify the service. This has to be unique among all the services installed in a system, and (while I haven't verified this) this must consist entirely out of alpha-numeric characters.
Short display name of the service, which can contain spaces and other characters. This shouldn't be too long, like
<id>, and this also needs to be unique among all the services in a given system.
Long human-readable description of the service. This gets displayed in Windows service manager when the service is selected.
This element specifies the executable to be launched. It can be either absolute path, or you can just specify the executable name and let it be searched from
PATH (although note that the services often run in a different user account and therefore it might have different
PATH than your shell does.)
Specify IDs of other services that this service depends on. When service X depends on service Y, X can only run if Y is running.
Multiple elements can be used to specify multiple dependencies.
Optionally set a different logging directory with and startup : reset (clear log), roll (move to *.old) or append (default).
This element specifies the arguments to be passed to the executable. Winsw will quote each argument if necessary, so do not put quotes in
<argument> to avoid double quotation.
<argument>arg1</argument> <argument>arg2</argument> <argument>arg3</argument>
For backward compatibility,
<arguments> element can be used instead to specify the whole command line in a single element.
When the service is requested to stop, winsw simply calls TerminateProcess API to kill the service instantly. However, if
<stopargument> elements are present, winsw will instead launch another process of
<stopexecutable> if that's specified) with the
<stopargument> arguments, and expects that to initiate the graceful shutdown of the service process.
Winsw will then wait for the two processes to exit on its own, before reporting back to Windows that the service has terminated.
When you use the
<stopargument>, you must use
<startargument> instead of
<argument>. See the complete example below:
<executable>catalina.sh</executable> <startargument>run</startargument> <stopexecutable>catalina.sh</stopexecutable> <stopargument>stop</stopargument>
This optional element can be specified multiple times if necessary to specify environment variables to be set for the child process. The syntax is:
<env name="HOME" value="c:\abc" />
If this optional element is specified, the service will be allowed to interact with the desktop, such as by showing a new window and dialog boxes. If your program requires GUI, set this like the following:
Note that since the introduction UAC (Windows Vista and onward), services are no longer really allowed to interact with the desktop. In those OSes, all that this does is to allow the user to switch to a separate window station to interact with the service.
This optional element is to emit simple tone when the service shuts down. This feature should be used only for debugging, as some operating systems and hardware do not support this functionality.
This optional element can be specified multiple times to have the service wrapper retrieve resources from URL and place it locally as a file. This operation runs when the service is started, before the application specified by
<executable> is launched.
<download from="http://example.com/some.dat" to="%BASE%\some.dat"/>
This is another useful building block for developing a self-updating service.
See the "Logging" section above for more details.