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Error: mongod cannot start with error: keyFile too open permissions

Cause: Mongod key file accepts only mode 600 (read and write by owner only)

chmod 600 ./keyFile

Error: When use rs.Add():

{
“errmsg” : “exception: can’t use localhost in repl set member names except when using it for all members”,
“code” : 13393,
“ok” : 0
}

Cause:

1. Your replica set is using localhost for it members and you are adding a new member with IP/hostname other than localhost

2. Your replica set is using IP/hostname for it members and you are adding a new member with localhost as hostname

Solution: Only use localhost for replica set members if you are sure that all mongod/mongos instance are on the same local machine. Otherwise, use hostname or IP.

Error: When use coomand rs.initiate()

{ “errmsg” : “couldn’t initiate : can’t find self in the replset config”, “ok” : 0 }

Cause: a hostname(s) of a replica set member(s) cannot be resolved

Solution: Add hostname(s) in /etc/hosts

Error: addShard() command returns error:

{
“ok” : 0,
“errmsg” : “couldn’t connect to new shard socket exception [CONNECT_ERROR] for replname/hostname:27017”
}

Cause:

1. hostname:27017 cannot be reached

2. if hostname:27017 can be reached, then your replica set [replname] configuration contains members with ‘localhost‘ as host name

Solution: Unless you  are running all mongod/mongos instances on the same machine, then you can use ‘localhost’ in rs.Add() command. Otherwise, use hostname instead of localhost in all rs.Add(), sh.addShard() command. Note that when adding a host itself to replcaset/shard an usable hostname should be present in /etc/hosts, or you will get this error:

{ “errmsg” : “couldn’t initiate : can’t find self in the replset config”, “ok” : 0 }

Error: replset couldn’t find a slave with id 1, not tracking <id>

Causes: After removing and adding replica to MongoDB replica set using rs.add() and rs.remove(), the replica set member id’s don’t follow a continuous order from _id: 0, for example:

{
“_id” : “rs0”,
“version” : 1,
“members” : [
{
“_id” : 4,
“host” : “mongodb0.example.net:27017”
},
{
“_id” : 5,
“host” : “mongodb1.example.net:27017”
},
{
“_id” : 7,
“host” : “mongodb2.example.net:27017”
}
]
}

Solution: You can use rs.reconfig() to re-etablish the order:

var cfg = {
“_id” : “rs0”,
“version” : 1,
“members” : [
{
“_id” : 0,
“host” : “mongodb0.example.net:27017”
},
{
“_id” : 1,
“host” : “mongodb1.example.net:27017”
},
{
“_id” : 2,
“host” : “mongodb2.example.net:27017”
}
]
}
rs.reconfig(cfg);