What is the meaning of the error that started mongodb on the server

  mongodb, question 
2017-05-02T16:16:31.190+0800 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'.
 2017-05-02T16:16:31.190+0800 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
 2017-05-02T16:16:31.190+0800 I CONTROL  [initandlisten]
 2017-05-02T16:16:31.190+0800 I CONTROL  [initandlisten] ** WARNING: soft rlimits too low. rlimits set to 3901 processes,   1000000 files. Number of processes should be at least 500000 : 0.5 times number of files.
 2017-05-02T16:16:31.190+0800 I CONTROL  [initandlisten]
 2017-05-02T16:16:31.265+0800 I FTDC     [initandlisten] Initializing full-time diagnostic data capture with directory '/var/mongodb/data/diagnostic.data'
 2017-05-02T16:16:31.279+0800 I NETWORK  [HostnameCanonicalizationWorker] Starting hostname canonicalization worker
 2017-05-02T16:16:31.282+0800 I NETWORK  [initandlisten] waiting for connections on port 27017
 2017-05-02T17:13:19.617+0800 I NETWORK  [initandlisten] connection accepted from 127.0.0.1:52260 #1 (1 connection now open)
 2017-05-02T17:13:48.843+0800 I NETWORK  [conn1] end connection 127.0.0.1:52260 (0 connections now open)
 2017-05-02T17:26:19.310+0800 I CONTROL  [signalProcessingThread] got signal 15 (Terminated), will terminate after current cmd ends
 2017-05-02T17:26:19.310+0800 I FTDC     [signalProcessingThread] Shutting down full-time diagnostic data capture
 2017-05-02T17:26:19.312+0800 I CONTROL  [signalProcessingThread] now exiting
 2017-05-02T17:26:19.312+0800 I NETWORK  [signalProcessingThread] shutdown: going to close listening sockets  ...
 2017-05-02T17:26:19.312+0800 I NETWORK  [signalProcessingThread] closing listening socket: 6
 2017-05-02T17:26:19.312+0800 I NETWORK  [signalProcessingThread] closing listening socket: 7
 2017-05-02T17:26:19.312+0800 I NETWORK  [signalProcessingThread] removing socket file: /tmp/mongodb-27017.sock
 2017-05-02T17:26:19.313+0800 I NETWORK  [signalProcessingThread] shutdown: going to flush diaglog  ...
 2017-05-02T17:26:19.313+0800 I NETWORK  [signalProcessingThread] shutdown: going to close sockets  ...
 2017-05-02T17:26:19.313+0800 I STORAGE  [signalProcessingThread] WiredTigerKVEngine shutting down
 2017-05-02T17:26:19.547+0800 I STORAGE  [signalProcessingThread] shutdown: removing fs lock  ...
 2017-05-02T17:26:19.547+0800 I CONTROL  [signalProcessingThread] dbexit:  rc: 0

The list here is just WARNING and will not cause the server to quit. If these two WARNING are of interest, check the documentation:
Disable Transparent Huge Pages (THP)
UNIX ulimit Settings
The reason the server exited was:

2017-05-02T17:26:19.310+0800 I CONTROL [signalProcessingThread] got signal 15 (Terminated), will terminate after current cmd ends

In fact, this is a normal end, may bekillOr other similar orders are overmongod.