I've had two instances recently. I've found the "immediately" needed
information, but they are samples of more generic problems.
1. Today's problem was easily solved. I had seen a post discussing an
application of the "tree" command. When I tried it, I got "command not
found". In _this_ case it was easily solved by using Synaptic's search
function -- there is a package named "tree".
However that is not always the case. Some months ago I got a "command
not found" message for a command that had a man page (do not recall the
specific command). It turned out it was one utility command among many
provided by a package with an unrelated name.
Is there a general way to find such a package?
2. There are many commands whose man pages point to using the "info"
command. I personally find that format more annoying than useful. I
would prefer to access the TeXInfo formatted document and convert it
locally to desired format - usually HTML.
If the command is on my machine (i.e. GRUB), I can generally find the
associated TeXInfo formatted file (usually concealed in a tarred or
zipped file). How to search for all TeXInfo files on debian.org?