When I tried to deploy Hudson on Tomcat 5.5 on Ubuntu 7.04 (feisty) it failed to
start and this was logged:

May 3, 2007 10:16:25 PM org.apache.catalina.startup.HostConfig deployWAR
INFO: Deploying web application archive hudson.war
May 3, 2007 10:16:31 PM hudson.PluginManager <init>
SEVERE: Hudson is unable to create /usr/share/tomcat5.5/.hudson/plugins
Perhaps its security privilege is insufficient
May 3, 2007 10:16:31 PM hudson.TcpSlaveAgentListener <init>
INFO: JNLP slave agent listener started on TCP port 3130
May 3, 2007 10:16:31 PM org.apache.catalina.core.StandardContext start
SEVERE: Error listenerStart
May 3, 2007 10:16:31 PM org.apache.catalina.core.StandardContext start
SEVERE: Context [/hudson] startup failed due to previous errors
May 3, 2007 10:16:32 PM hudson.model.Queue save
WARNING: Failed to write out the queue file /usr/share/tomcat5.5/.hudson/queue.t
xt
java.io.FileNotFoundException: /usr/share/tomcat5.5/.hudson/queue.txt (No such f
ile or directory)
at java.io.FileOutputStream.open(Native Method)
at java.io.FileOutputStream.<init>(FileOutputStream.java:179)
at java.io.FileOutputStream.<init>(FileOutputStream.java:131)
at hudson.model.Queue.save(Queue.java:139)
at hudson.model.Hudson.cleanUp(Hudson.java:893)
at hudson.WebAppMain.contextDestroyed(WebAppMain.java:170)
[rest of stacktrace omitted]

Only after manually creating /usr/share/tomcat5.5/.hudson and changing the owner
and group to tomcat55:nogroup Hudson could be started.