Can't start mongodb service

Just a simple reinstall worked.

sudo apt purge mongodb-org*
sudo rm -r /var/log/mongodb
sudo rm -r /var/lib/mongodb
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv EA312927
echo "deb http://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/3.2 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.2.list
sudo apt update
sudo apt-get install -y mongodb-org

and double-check the config file:

sudo nano /etc/systemd/system/mongodb.service

paste this:

[Unit]
Description=High-performance, schema-free document-oriented >database
After=network.target

[Service]
User=mongodb
ExecStart=/usr/bin/mongod --quiet --config /etc/mongod.conf

[Install]
WantedBy=multi-user.target

finally

sudo systemctl start mongodb
sudo systemctl enable mongodb

also I think I changed the permissions of the log file to 777

This Worked for me.

sudo chown -R mongodb:mongodb /var/lib/mongodb 
sudo chown mongodb:mongodb /tmp/mongodb-27017.sock

I am using Linux Mint 20.

chown -R mongodb:mongodb /var/lib/mongodb
chown mongodb:mongodb /tmp/mongodb-27017.sock

sudo systemctl restart mongod
sudo systemctl status mongod

these permission commands work for me on ubuntu 20.04