If you create a /index/solr5/start.ini with the following contents ...
# Jetty HTTP Module
--module=http
jetty.port=8982
# Jetty JMX Module
--module=jmx
# Jetty shutdown setup
STOP.PORT=7982
STOP.KEY=solrrocks
--exec
# JVM Arguments
-Duser.timezone=UTC
# Log4j Settings
-Dlog4j.configuration=file:${jetty.base}/log4j.properties
# jvm memory settings
-Xms18g
-Xmx18g
# GC settings
-verbose:gc
-Xloggc:${jetty.base}/logs/solr_gc.log
-XX:NewRatio=3
-XX:SurvivorRatio=4
-XX:TargetSurvivorRatio=90
-XX:MaxTenuringThreshold=8
-XX:+UseConcMarkSweepGC
-XX:+UseParNewGC
-XX:+CMSScavengeBeforeRemark
-XX:PretenureSizeThreshold=64m
-XX:+UseCMSInitiatingOccupancyOnly
-XX:CMSInitiatingOccupancyFraction=70
-XX:CMSMaxAbortablePrecleanTime=2000
-XX:+CMSParallelRemarkEnabled
-XX:+ParallelRefProcEnabled
-XX:+PrintHeapAtGC
-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-XX:+PrintGCTimeStamps
-XX:+PrintTenuringDistribution
-XX:+PrintGCApplicationStoppedTime
# OOM Setup
-XX:_OnOutOfMemoryError_=${solr.install.dir}/bin/oom_solr.sh
# JMX Configuration
-Dcom.sun.management.jmxremote
-Dcom.sun.management.jmxremote.local._only_=false
-Dcom.sun.management.jmxremote.ssl=false
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.port=18982
-Dcom.sun.management.jmxremote.rmi.port=18982
Your command line to execute jetty is now ...
And there can even be more optimizations with regards to your log4j configuration.