If you used Aptitude (apt-get) to install Jenkins on Ubuntu 12.04, uncomment the JAVA_ARGS
line in the top few lines of /etc/default/jenkins
:
# arguments to pass to java
#JAVA_ARGS="-Xmx256m" # <--default value
JAVA_ARGS="-Xmx2048m"
#JAVA_ARGS="-Djava.net.preferIPv4Stack=true" # make jenkins listen on IPv4 address