Error 1 :

This occurred after downloading ros_comm package.

sai@sai-HP-EliteBook-8460w:~$ roscore
... logging to /home/sai/.ros/log/0ac69688-0f30-11e3-889a-e4115b3c2706/roslaunch-sai-HP-EliteBook-8460w-2955.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1gb .="" p="">
started roslaunch server http://sai-HP-EliteBook-8460w:44124/
ros_comm version 1.8.11


SUMMARY
========

PARAMETERS
 * /rosdistro
 * /rosversion

NODES

auto-starting new master
process[master]: started with pid [2971]
ROS_MASTER_URI=http://sai-HP-EliteBook-8460w:11311/

setting /run_id to 0ac69688-0f30-11e3-889a-e4115b3c2706



ERROR: rosout is not built. Please run 'rosmake rosout'



failed to start core service [/rosout]
[master] killing on exit
sai@sai-HP-EliteBook-8460w:~$

Solution:

Just delete the ros_comm package