I am running Eclipse Kepler (4.3.2.M20140221-1700) (64 bit) in Ubuntu 12.04 (64 bit) with openjdk-jdk/jre (7u51-2.4.4-0ubuntu0.12.04.2) installed.
I installed PyDev for Eclipse (3.3.3.201401272249) through the Eclipse Marketplace, but it does not seem to appear when Eclipse restarted. Additionally, though i can see the plugin installed under 'installed software' in my installation details, it is not listed under 'plug-ins'.
This initially sounds like a duplicate of an extremely common issue that happens when eclipse is not run with Java 7 (PyDev.org, PyDev not showing up in eclipse, ...Python doesn't appear in preferences window, Pydev not recognized in eclipse), yet I've ruled out the possibility by using the numerous methods these other questions outline.
I verified that my installation is using Java 7 by checking both my java alternatives and my eclipse configuration information.
$ update-java-alternatives -l
java-1.7.0-openjdk-amd64 1051 /usr/lib/jvm/java-1.7.0-openjdk-amd64
I examined my 'Eclipse Installation Details->Configuration' tab to see what version of java was being used (as a sanity check against a bundled JRE, though that seemed highly unlikely for stock Kepler). The following lines lead me to believe that the System java was in use (and consequently, the single alternative above):
java.home=/usr/lib/jvm/java-7-openjdk-amd64/jre
java.io.tmpdir=/tmp
java.library.path=/usr/java/packages/lib/amd64:/usr/lib/x86_64-linux-gnu/jni:/lib/x86_64-linux-gnu:/usr/lib/x86_64-linux-gnu:/usr/lib/jni:/lib:/usr/lib
java.runtime.name=OpenJDK Runtime Environment
java.runtime.version=1.7.0_51-b00
Other applicable suggestions in these other questions (ie: "...must have a JDK...") seem to have already been addressed in this current setup wherever possible. This question is not a duplicate of the existing ones, so please do not duplicate answers from existing questions. Existing answers have already been attempted.
EDIT 1 In an attempt to diagnose the plugin itself, I have attempted to use the OSGI console in order to identify the status of the plugin as per this answer. The plugin is not listed, so I am following steps at "Where is my Bundle" in order to attempt to resolve any status or log information that may be available.
EDIT 2 The installation is located in a user directory and was installed by simply unzipping the distribution. My user has full rights to modify the installation directory.
I am uncertain as to the actual cause, but this seemed to be part of a more generic Eclipse Plugin issue answerd in this answer to Plugins installed on Eclipse not visible, which suggests running Eclipse with the -clean argument.
I am running a user-mode instance of eclipse from a directory where my user has full access rights, but executing eclipse -clean from the command line (again, as an unprivileged user) was able to solve the problem. Upon restarting eclipse, the PyDev perspective was now available.
I hope this saves someone else the wasted time.