1, error description:

ming@ming:~$ rosdep update

reading sources in the list data from/etc/ros/rosdep/sources list. D
ERROR: unable to process the source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml] :
& lt; urlopen error [Errno 111] Connection refused> (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml)
ERROR: Unable to process the source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml] :
& lt; urlopen error [Errno 111] Connection refused> (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml)
ERROR: unable to process the source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml] :
& lt; urlopen error [Errno 111] Connection refused> (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml)
ERROR: unable to process the source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml] :
& lt; urlopen error [Errno 111] Connection refused> (https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml)
Hit https://raw.githubusercontent.com/ros/rosdistro/master/releases/fuerte.yaml
Query rosdistro index https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml
Add distro “ardent”
ERROR: ERROR loading sources list:
& lt; urlopen error < urlopen error [Errno 111] Connection refused> (https://raw.githubusercontent.com/ros/rosdistro/master/ardent/distribution.yaml)>

solution:

sudo gedit /etc/resolv.conf

comments the old nameserver line, and adds the following two lines:

Nameserver 8.8.8.8 # Google nameserver

Nameserver 8.8.4.4 # Google nameserver

save exit, execute

sudo apt to get the update

and then

rosdep update

occurs:

is OK!

2. Error description:
Ming @ming:~$sudo rosdep init
ERROR: default sources list file already exists:
/etc/ros/rosdep/sources.list.d/20-default.list
Please delete if you wish to re-initialize

solution:

deletes the existing initialization file by issuing the following command:

sudo rm /etc/ros/rosdep/sources.list.d/20-default.list

and then rerun

sudo rosdep init

problem solved.