rospack is too slow
Sometimes old defunct packages - "zombies" - that have had their manifests moved removed or deleted may be making it time-consuming to crawl the directory structure.
Solution: Try running
$ rospack profile
This will tell you the time required to crawl your directory structure and will describe your directory structure, including any zombies that may be in the structure. These will be indicated with an asterisk.
Getting rid of the zombies may improve your system performance - running the command
rospack profile --zombie-only
will list these zombies. From this point you can either manually remove the zombies, or, if it looks to you like the entire list can be safely deleted, you can run the command (be very careful!):
rospack profile --zombie-only | xargs rm -r
This will remove all of the zombie directories, and can potentially may it quicker to navigate or build your ros directory structure.
rospack is unable to find packages that are added recently
The same command as "rospack too slow" section forces full crawl of package directories and might work for addressing this issue.
After running the above, try again rospack find or any command failed.