As on newer debian systems /run or /usr/run is now tmpvfs based and allocated to 10% of memory the jenkins startup fails on low-memory systems (512MB ram).

[Winstone 2011/10/16 13:38:21] - Beginning extraction from war file
[Winstone 2011/10/16 13:38:23] - Error initializing web application: prefix []
java.io.IOException: No space left on device
at java.io.FileOutputStream.writeBytes(Native Method)
at java.io.FileOutputStream.write(FileOutputStream.java:282)
at winstone.HostConfiguration.getWebRoot(HostConfiguration.java:273)
at winstone.HostConfiguration.<init>(HostConfiguration.java:73)
at winstone.HostGroup.initHost(HostGroup.java:85)
at winstone.HostGroup.<init>(HostGroup.java:45)
at winstone.Launcher.<init>(Launcher.java:197)
at winstone.Launcher.main(Launcher.java:398)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at Main._main(Main.java:268)
at Main.main(Main.java:96)

The mount command returns this:
none on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755)

The df command returns this:
none 50M 50M 0 100% /run

I'm not sure about the best solution but jenkins seems by far the biggest user of /run, all other services together use about 10MB. Maybe jenkins could use a different folder to store it's extracted war?

As a temporary fix I change /etc/default/jenkins this way:
#JENKINS_ARGS="--webroot=/var/run/jenkins/war --httpPort=$HTTP_PORT --ajp13Port=$AJP_PORT"
JENKINS_ARGS="--webroot=$JENKINS_HOME/war --httpPort=$HTTP_PORT --ajp13Port=$AJP_PORT"