I installed mongodb following the instructions on my site. To open a shell, I have to go to the mongodb installation directory and then type
./bin/mongo
I don't know the default directory. where could it be?
Late to the party, but this might help others: I installed mongodb 3.4.10 for Ubuntu 16.4
I found a mongo file to start a shell in
/usr/bin/mongo
I found it using the following commands
sudo updatedb locate -b '\mongo'
Windows: c:\Program Files\MongoDB\Server\3.4.7\bin\mongod
c:\Program Files\MongoDB\Server\3.4.7\bin\mongod
Mac: /usr/local/Cellar/mongodb/3.4.7/bin/mongod
/usr/local/Cellar/mongodb/3.4.7/bin/mongod
Replacing 3.4.7 with your Mongodb version
Use the command which mongo to find the location of the mongo executable.
which mongo