I'm running Ubuntu 12.04's packaged Jetty in which I installed solr 4.3.1 (by copying the war file to /var/lib/jetty/webapps. When I start Jetty, I get this error:

failed SolrRequestFilter: org.apache.solr.common.SolrException: Could not find necessary SLF4j logging jars. If using Jetty, the SLF4j logging jars need to go in the jetty lib/ext directory.

The package libslf4j-java is installed, and the jars are in /usr/share/java:

/usr/share/java/log4j-over-slf4j.jar
/usr/share/java/slf4j-api.jar
/usr/share/java/slf4j-jcl.jar
/usr/share/java/slf4j-jdk14.jar
/usr/share/java/slf4j-log4j12.jar
/usr/share/java/slf4j-migrator.jar
/usr/share/java/slf4j-nop.jar
/usr/share/java/slf4j-simple.jar

but somehow, Jetty and/or Solr are not finding them. How do I make them find them? or how do I install some other jars where jetty/solr would find them?

The full error is:

88 [main] INFO org.mortbay.log - jetty-6.1.24
443 [main] INFO org.mortbay.log - Deploy /etc/jetty/contexts/javadoc.xml -> org.mortbay.jetty.handler.ContextHandler@cec0c5{/javadoc,file:/usr/share/jetty/javadoc}
522 [main] INFO org.mortbay.log - Extract file:/var/lib/jetty/webapps/solr.war to /var/cache/jetty/data/Jetty__8080_solr.war__solr__zdafkg/webapp
1501 [main] WARN org.mortbay.log - failed SolrRequestFilter: org.apache.solr.common.SolrException: Could not find necessary SLF4j logging jars. If using Jetty, the SLF4j logging jars need to go in the jetty lib/ext directory. For other containers, the corresponding directory should be used. For more information, see: http://wiki.apache.org/solr/SolrLogging
1501 [main] ERROR org.mortbay.log - Failed startup of context org.mortbay.jetty.webapp.WebAppContext@5329c5{/solr,file:/var/lib/jetty/webapps/solr.war}
org.apache.solr.common.SolrException: Could not find necessary SLF4j logging jars. If using Jetty, the SLF4j logging jars need to go in the jetty lib/ext directory. For other containers, the corresponding directory should be used. For more information, see: http://wiki.apache.org/solr/SolrLogging
    at org.apache.solr.servlet.SolrDispatchFilter.<init>(SolrDispatchFilter.java:105)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
    at java.lang.Class.newInstance0(Class.java:374)
    at java.lang.Class.newInstance(Class.java:327)
    at org.mortbay.jetty.servlet.Holder.newInstance(Holder.java:153)
    at org.mortbay.jetty.servlet.FilterHolder.doStart(FilterHolder.java:92)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:662)
    at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)
    at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250)
    at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:518)
    at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.handler.HandlerCollection.doStart(HandlerCollection.java:152)
    at org.mortbay.jetty.handler.ContextHandlerCollection.doStart(ContextHandlerCollection.java:156)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.handler.HandlerCollection.doStart(HandlerCollection.java:152)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:130)
    at org.mortbay.jetty.Server.doStart(Server.java:224)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.xml.XmlConfiguration.main(XmlConfiguration.java:985)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:616)
    at org.mortbay.start.Main.invokeMain(Main.java:194)
    at org.mortbay.start.Main.start(Main.java:534)
    at org.mortbay.jetty.start.daemon.Bootstrap.start(Bootstrap.java:30)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:616)
    at org.apache.commons.daemon.support.DaemonLoader.start(DaemonLoader.java:243)
Caused by: java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
    at org.apache.solr.servlet.SolrDispatchFilter.<init>(SolrDispatchFilter.java:103)
    ... 36 more
Caused by: java.lang.ClassNotFoundException: org.slf4j.LoggerFactory
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at org.mortbay.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:392)
    at org.mortbay.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:363)
    ... 37 more
1505 [main] WARN org.mortbay.log - failed org.mortbay.jetty.webapp.WebAppContext@5329c5{/solr,file:/var/lib/jetty/webapps/solr.war}: java.lang.NoClassDefFoundError: org/slf4j/Logger
1579 [main] WARN org.mortbay.log - failed ContextHandlerCollection@19d0a1: java.lang.NoClassDefFoundError: org/slf4j/Logger
1582 [main] INFO org.mortbay.log - Opened /var/log/jetty/2013_06_27.request.log
1582 [main] WARN org.mortbay.log - failed HandlerCollection@cbf30e: java.lang.NoClassDefFoundError: org/slf4j/Logger
1582 [main] ERROR org.mortbay.log - Error starting handlers
java.lang.NoClassDefFoundError: org/slf4j/Logger
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2454)
    at java.lang.Class.getMethod0(Class.java:2697)
    at java.lang.Class.getMethod(Class.java:1622)
    at org.mortbay.log.Log.unwind(Log.java:228)
    at org.mortbay.log.Log.warn(Log.java:197)
    at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:475)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.handler.HandlerCollection.doStart(HandlerCollection.java:152)
    at org.mortbay.jetty.handler.ContextHandlerCollection.doStart(ContextHandlerCollection.java:156)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.handler.HandlerCollection.doStart(HandlerCollection.java:152)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:130)
    at org.mortbay.jetty.Server.doStart(Server.java:224)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.xml.XmlConfiguration.main(XmlConfiguration.java:985)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:616)
    at org.mortbay.start.Main.invokeMain(Main.java:194)
    at org.mortbay.start.Main.start(Main.java:534)
    at org.mortbay.jetty.start.daemon.Bootstrap.start(Bootstrap.java:30)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:616)
    at org.apache.commons.daemon.support.DaemonLoader.start(DaemonLoader.java:243)
Caused by: java.lang.ClassNotFoundException: org.slf4j.Logger
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at org.mortbay.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:392)
    at org.mortbay.jetty.webapp.WebAppClassLoader.loadClass(WebAppClassLoader.java:363)
    ... 29 more