It seems like MongoDB 3.6 isn't automatically configured to restart if it crashes. Looking at the systemd service that is bundled with the latest .deb package for Ubuntu 16.04LTS it doesn't seem to have restarts configured:
$ sudo systemctl cat mongod # /lib/systemd/system/mongod.service [Unit] Description=High-performance, schema-free document-oriented database After=network.target Documentation=https://docs.mongodb.org/manual [Service] User=mongodb Group=mongodb ExecStart=/usr/bin/mongod --config /etc/mongod.conf PIDFile=/var/run/mongodb/mongod.pid # file size LimitFSIZE=infinity # cpu time LimitCPU=infinity # virtual memory size LimitAS=infinity # open files LimitNOFILE=64000 # processes/threads LimitNPROC=64000 # locked memory LimitMEMLOCK=infinity # total threads (user+kernel) TasksMax=infinity TasksAccounting=false # Recommended limits for for mongod as specified in # http://docs.mongodb.org/manual/reference/ulimit/#recommended-settings [Install] WantedBy=multi-user.target
Sending SIGKILL and SIGSEGV both kill the process and it isn't restarted. I'm not sure if those are "caught" by systemd and not just restarted however.
So a few questions: Is this crucial for a high availability service like a database? It sure seems like it. Is there any reason MongoDB wouldn't have this configured out of the box?