I faced same issue but fix it by the changing the package file section command. The whole step that i followed was:
At first try with this command: sudo apt-get install -y mongodb
This is the unofficial mongodb package provided by Ubuntu and it is not maintained by MongoDB and conflict with MongoDB’s offically supported packages.
If the above command not working then you can fix the issue by one of the bellow procedure:
#Step 1: Import the MongoDB public key
#In Ubuntu 18.*+, you may get invalid signatures. --recv value may need to be updated to EA312927.
#See here for more details on the invalid signature issue: [https://stackoverflow.com/questions/34733340/mongodb-gpg-invalid-signatures][1]
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
#Step 2: Generate a file with the MongoDB repository url
echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' | sudo tee /etc/apt/sources.list.d/mongodb.list
#Step 3: Refresh the local database with the packages
sudo apt-get update
#Step 4: Install the last stable MongoDB version and all the necessary packages on our system
sudo apt-get install mongodb-org
#Or
# The unofficial mongodb package provided by Ubuntu is not maintained by MongoDB and conflict with MongoDB’s offically supported packages. Use the official MongoDB mongodb-org packages, which are kept up-to-date with the most recent major and minor MongoDB releases.
sudo apt-get install -y mongodb
Hope this will work for you also. You can follow this MongoDB
Update The above instruction will install mongodb 2.6 version, if you want to install latest version for Uubuntu 12.04 then just replace above step 2 and follow bellow instruction instead of that:
#Step 2: Generate a file with the MongoDB repository url echo "deb http://repo.mongodb.org/apt/ubuntu trusty/mongodb-org/3.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb.list
If you are using Ubuntu 14.04 then use bellow step instead of above step 2
#Step 2: Generate a file with the MongoDB repository url echo "deb http://repo.mongodb.org/apt/ubuntu trusty/mongodb-org/3.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.0.list