This project implements a distributed system which utilizies inter process communication to handle / accept / reject various user travel requests and queries based on their vaccination records. We have one travelMonitor parent process which uses named pipes to communicate with a number of child Monitor processes, using a self-designed message-communication protocol. Furtherly, various system calls/signals and low-level I/O are used for the communication. The vaccination data found in folder /input_dir are produced using a bash script create_infiles.sh. Detailed information about the project's specifications can be found in the project's pdf file : hw2-spring-2021.pdf, in greek.