Some useful MongoDB commands

mongo {Host}:{Port}/{DB} -u {User} -p{Password}

Sample: 
mongo localhost:27017/admin -u root -pPassword
mongo 127.0.0.1:27017/admin -u root -pPassword

db.serverStatus().connections

db.currentOp(true).inprog.reduce(
  (accumulator, connection) => {
    ipaddress = connection.client ? connection.client.split(":")[0] : "Internal";
    accumulator[ipaddress] = (accumulator[ipaddress] || 0) + 1;
    accumulator["TOTAL_CONNECTION_COUNT"]++;
    return accumulator;
  },
  { TOTAL_CONNECTION_COUNT: 0 }
)

db.serverStatus().wiredTiger.cache

db.serverStatus().wiredTiger.concurrentTransactions

rs.status()

rs.printSlaveReplicationInfo()

rs.printReplicationInfo()

rs.config()

# Run on PRIMARY Node
rs.stepDown()

# Run on SECONDARY node which need to freeze 
rs.freeze(no of seconds)

db.getProfilingStatus()

db.setProfilingLevel(1, { slowms: 100, sampleRate: 1 })

db.setProfilingLevel(0, { slowms: 100, sampleRate: 1 })

mongostat -h {HostName/IP} -u {User} -p '{Password}' --port={Port} --authenticationDatabase=admin

Sample:
mongostat -h 127.0.0.1 -u root -p 'Password' --port=27018 --authenticationDatabase=admin

mongotop -h {HostName/IP} -u {User} -p '{Password}' --port={Port} --authenticationDatabase=admin

Sample:
mongotop -h 127.0.0.1 -u root -p 'Password' --port=27018 --authenticationDatabase=admin

# Get the list of collection scan whole collections 
mlogfilter mongod.log --planSummary=COLLSCAN

# Get the list of slow queries more than 1000ms
mlogfilter mongod.log --slow 1000

# Get the list of errors, warnings 
mlogfilter mongod.log  --word assert warning errors

# Get the specific namespace queries which are running more than 1000ms
mlogfilter mongod.log --namespace admin.\$cmd --slow 1000

mloginfo mongod.log  --queries

sh.status()

sh.stopBalancer()

sh.startBalancer()