MongoDB aborting when running mongod command on terminal - database

Question

when i run mongod command on ubuntu terminal i get this error:
{"t":{"$date":"2020-10-28T22:27:29.341+05:00"},"s":"I", "c":"CONTROL", "id":23285, "ctx":"main","msg":"Automatically disabling TLS 1.0, to force-enable TLS 1.0 specify --sslDisabledProtocols 'none'"}
{"t":{"$date":"2020-10-28T22:27:29.348+05:00"},"s":"W", "c":"ASIO", "id":22601, "ctx":"main","msg":"No TransportLayer configured during NetworkInterface startup"}
{"t":{"$date":"2020-10-28T22:27:29.349+05:00"},"s":"I", "c":"NETWORK", "id":4648601, "ctx":"main","msg":"Implicit TCP FastOpen unavailable. If TCP FastOpen is required, set tcpFastOpenServer, tcpFastOpenClient, and tcpFastOpenQueueSize."}
{"t":{"$date":"2020-10-28T22:27:29.349+05:00"},"s":"I", "c":"STORAGE", "id":4615611, "ctx":"initandlisten","msg":"MongoDB starting","attr":{"pid":9479,"port":27017,"dbPath":"/data/db","architecture":"64-bit","host":"E7250"}}
{"t":{"$date":"2020-10-28T22:27:29.349+05:00"},"s":"I", "c":"CONTROL", "id":23403, "ctx":"initandlisten","msg":"Build Info","attr":{"buildInfo":{"version":"4.4.1","gitVersion":"ad91a93a5a31e175f5cbf8c69561e788bbc55ce1","openSSLVersion":"OpenSSL 1.1.1f 31 Mar 2020","modules":[],"allocator":"tcmalloc","environment":{"distmod":"ubuntu2004","distarch":"x86_64","target_arch":"x86_64"}}}}
{"t":{"$date":"2020-10-28T22:27:29.349+05:00"},"s":"I", "c":"CONTROL", "id":51765, "ctx":"initandlisten","msg":"Operating System","attr":{"os":{"name":"Ubuntu","version":"20.04"}}}
{"t":{"$date":"2020-10-28T22:27:29.349+05:00"},"s":"I", "c":"CONTROL", "id":21951, "ctx":"initandlisten","msg":"Options set by command line","attr":{"options":{}}}
{"t":{"$date":"2020-10-28T22:27:29.350+05:00"},"s":"E", "c":"NETWORK", "id":23024, "ctx":"initandlisten","msg":"Failed to unlink socket file","attr":{"path":"/tmp/mongodb-27017.sock","error":"Operation not permitted"}}
{"t":{"$date":"2020-10-28T22:27:29.350+05:00"},"s":"F", "c":"-", "id":23091, "ctx":"initandlisten","msg":"Fatal assertion","attr":{"msgid":40486,"file":"src/mongo/transport/transport_layer_asio.cpp","line":919}}
{"t":{"$date":"2020-10-28T22:27:29.350+05:00"},"s":"F", "c":"-", "id":23092, "ctx":"initandlisten","msg":"\n\n***aborting after fassert() failure\n\n"}
mongod process is running when i enter command sudo systemctl status mongod
● mongod.service - MongoDB Database Server
Loaded: loaded (/lib/systemd/system/mongod.service; enabled; vendor preset: ena>
Active: active (running) since Wed 2020-10-28 22:02:55 PKT; 32min ago
Docs: https://docs.mongodb.org/manual
Main PID: 7566 (mongod)
Memory: 159.0M
CGroup: /system.slice/mongod.service
└─7566 /usr/bin/mongod --config /etc/mongod.conf
Oct 28 22:02:55 E7250 systemd[1]: Started MongoDB Database Server.
what went wrong?
etc/mongod.conf file
# mongod.conf
# for documentation of all options, see:
# http://docs.mongodb.org/manual/reference/configuration-options/
# Where and how to store data.
storage:
dbPath: /var/lib/mongodb
journal:
enabled: true
# engine:
# mmapv1:
# wiredTiger:
# where to write logging data.
systemLog:
destination: file
logAppend: true
path: /var/log/mongodb/mongod.log
# network interfaces
net:
port: 27017
bindIp: 127.0.0.1
# how the process runs
processManagement:
timeZoneInfo: /usr/share/zoneinfo
#security:
#operationProfiling:
#replication:
#sharding:
## Enterprise-Only Options:
#auditLog:
#snmp:

Answer 1

This works for me:
Stop mongod process by entering the following command in terminal: sudo systemctl stop mongod
You have to make directory for "dbPath" with following command: sudo mkdir -p /data/db and sudo chown -R `id -un` /data/db
Then run sudo mongod --port 27017
Done!
you can't run sudo systemctl start mongod and sudo mongod --port 27017 at same time. Stop mongod by sudo systemctl stop mongod then run sudo mongod --port 27017
Hope this solution works for all who have same problem.

Answer 2

When you start the mongod service with sudo systemctl start mongod then the systemd reads the service file /usr/lib/systemd/system/mongod.service.
By default it sets the user to mongod and reads the config file /etc/mongod.conf:
[Service]
User=mongod
Group=mongod
Environment="OPTIONS=-f /etc/mongod.conf"
When you start the service with sudo mongod then your mongo runs as root and no config file is read.
In the default mongod.conf file the dbPath is set to
# Where and how to store data.
storage:
dbPath: /var/lib/mongo
journal:
enabled: true
However, when dbPath is not provided then default /data/db applies.
You may start the MongoDB with sudo mongod -f /etc/mongod.conf which correspond to sudo systemctl start mongod - however your mongod is running as root rather than mongod user.
Note, usually you don't edit settings directly in /usr/lib/systemd/system/mongod.service file. Create a copy to /etc/systemd/system/mongod.service and customize this copy. See https://unix.stackexchange.com/questions/206315/whats-the-difference-between-usr-lib-systemd-system-and-etc-systemd-system