First try restarting the system and then execute this command.
If it does not work then try make a new npm project and keep the dependencies local. To do it, you run the following commands:
$ run npm init
$ run npm i truffle
$ run ./node_modules/.bin/truffle init
If both the above solutions do not work, then it should be some problem with the version. So, install the latest
version of npm and node. You can do it by running the following command:
$ npm install -g truffle