HI,

I got this error when i wanted to install tortlebot:

sudo apt-get install ros-indigo-turtlebot ros-indigo-turtlebot-apps ros-indigo-turtlebot-interactions ros-indigo-turtlebot-simulator ros-indigo-kobuki-ftdi ros-indigo-rocon-remocon ros-indigo-rocon-qt-library ros-indigo-ar-track-alvar-msgs
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package ros-indigo-turtlebot
E: Unable to locate package ros-indigo-turtlebot-apps
E: Unable to locate package ros-indigo-turtlebot-interactions
E: Unable to locate package ros-indigo-turtlebot-simulator
E: Unable to locate package ros-indigo-kobuki-ftdi
E: Unable to locate package ros-indigo-rocon-remocon
E: Unable to locate package ros-indigo-rocon-qt-library
E: Unable to locate package ros-indigo-ar-track-alvar-msgs

I checked my ROS installation and everything looks fine. However I'm not sure why am getting this error? Also another thing might cause the issue might related to the rosdep update. When i tried to update my rosdep, again

it gives these warning:
Skip end-of-life distro "ardent"
Skip end-of-life distro "bouncy"
Skip end-of-life distro "crystal"
Add distro "dashing"
Add distro "eloquent"
Add distro "foxy"
Skip end-of-life distro "groovy"
Skip end-of-life distro "hydro"
Skip end-of-life distro "indigo"
Skip end-of-life distro "jade"
Add distro "kinetic"
Skip end-of-life distro "lunar"
Add distro "melodic"

As you can see it scaped updating and installing several other packages. Maybe this caused the issue?