title: MongoDB can not start by the command `service mongod start`
body: <p>when i run the command <code>sudo service mongod start</code> the MongoDB cannot start and when i run the service mongod status it shows it has not been started, and the log shows:</p>
  
  <pre><code>2018-07-05T14:32:03.595+0800 I CONTROL  [main] ***** SERVER RESTARTED *****
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten] MongoDB starting : pid=15656 port=27017 dbpath=/var/lib/mongodb 64-bit host=iZbp1ik57sceo226yjpivxZ
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten] db version v4.0.0-rc7
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten] git version: 7230641bb09b1ceb04c3135cf83a5044c4838906
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten] OpenSSL version: OpenSSL 1.0.2g  1 Mar 2016
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten] allocator: tcmalloc
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten] modules: none
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten] build environment:
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten]     distmod: ubuntu1604
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten]     distarch: x86_64
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten]     target_arch: x86_64
  2018-07-05T14:32:03.605+0800 I CONTROL  [initandlisten] options: { config: "/etc/mongod.conf", net: { bindIp: "0.0.0.0", port: 27017 }, processManagement: { timeZoneInfo: "/usr/share/zoneinfo" }, security: { authorization: "enabled" }, storage: { dbPath: "/var/lib/mongodb", journal: { enabled: true } }, systemLog: { destination: "file", logAppend: true, path: "/var/log/mongodb/mongod.log" } }
  2018-07-05T14:32:03.605+0800 I STORAGE  [initandlisten] Detected data files in /var/lib/mongodb created by the 'wiredTiger' storage engine, so setting the active storage engine to 'wiredTiger'.
  2018-07-05T14:32:03.605+0800 I STORAGE  [initandlisten]
  2018-07-05T14:32:03.605+0800 I STORAGE  [initandlisten] ** WARNING: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine
  2018-07-05T14:32:03.605+0800 I STORAGE  [initandlisten] **          See http://dochub.mongodb.org/core/prodnotes-filesystem
  2018-07-05T14:32:03.605+0800 I STORAGE  [initandlisten] wiredtiger_open config: create,cache_size=488M,session_max=20000,eviction=(threads_min=4,threads_max=4),config_base=false,statistics=(fast),log=(enabled=true,archive=true,path=journal,compressor=snappy),file_manager=(close_idle_time=100000),statistics_log=(wait=0),verbose=(recovery_progress),
  2018-07-05T14:32:04.204+0800 E STORAGE  [initandlisten] WiredTiger error (13) [1530772324:204155][15656:0x7fb5cb734a00], wiredtiger_open: /var/lib/mongodb/WiredTiger.turtle: handle-open: open: Permission denied Raw: [1530772324:204155][15656:0x7fb5cb734a00], wiredtiger_open: /var/lib/mongodb/WiredTiger.turtle: handle-open: open: Permission denied
  2018-07-05T14:32:04.204+0800 E STORAGE  [initandlisten] WiredTiger error (13) [1530772324:204458][15656:0x7fb5cb734a00], wiredtiger_open: /var/lib/mongodb/WiredTiger.turtle: handle-open: open: Permission denied Raw: [1530772324:204458][15656:0x7fb5cb734a00], wiredtiger_open: /var/lib/mongodb/WiredTiger.turtle: handle-open: open: Permission denied
  2018-07-05T14:32:04.204+0800 E STORAGE  [initandlisten] WiredTiger error (13) [1530772324:204610][15656:0x7fb5cb734a00], wiredtiger_open: /var/lib/mongodb/WiredTiger.turtle: handle-open: open: Permission denied Raw: [1530772324:204610][15656:0x7fb5cb734a00], wiredtiger_open: /var/lib/mongodb/WiredTiger.turtle: handle-open: open: Permission denied
  2018-07-05T14:32:04.204+0800 F STORAGE  [initandlisten] Failed to start up WiredTiger under any compatibility version.
  2018-07-05T14:32:04.204+0800 F STORAGE  [initandlisten] 13: Permission denied
  2018-07-05T14:32:04.204+0800 F -        [initandlisten] Fatal Assertion 28595 at src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp 194
  2018-07-05T14:32:04.204+0800 F -        [initandlisten]
  ***aborting after fassert() failure
  </code></pre>
  
  <p>but when i tried <code>mongod --auth -f /etc/mongod.conf</code> the server can start and when visit the log file it shows that:</p>
  
  <pre><code>2018-07-05T14:35:34.228+0800 I CONTROL  [main] ***** SERVER RESTARTED *****
  2018-07-05T14:35:34.239+0800 I CONTROL  [initandlisten] MongoDB starting : pid=15665 port=27017 dbpath=/var/lib/mongodb 64-bit host=iZbp1ik57sceo226yjpivxZ
  2018-07-05T14:35:34.239+0800 I CONTROL  [initandlisten] db version v4.0.0-rc7
  2018-07-05T14:35:34.239+0800 I CONTROL  [initandlisten] git version: 7230641bb09b1ceb04c3135cf83a5044c4838906
  2018-07-05T14:35:34.240+0800 I CONTROL  [initandlisten] OpenSSL version: OpenSSL 1.0.2g  1 Mar 2016
  2018-07-05T14:35:34.240+0800 I CONTROL  [initandlisten] allocator: tcmalloc
  2018-07-05T14:35:34.240+0800 I CONTROL  [initandlisten] modules: none
  2018-07-05T14:35:34.240+0800 I CONTROL  [initandlisten] build environment:
  2018-07-05T14:35:34.240+0800 I CONTROL  [initandlisten]     distmod: ubuntu1604
  2018-07-05T14:35:34.240+0800 I CONTROL  [initandlisten]     distarch: x86_64
  2018-07-05T14:35:34.240+0800 I CONTROL  [initandlisten]     target_arch: x86_64
  2018-07-05T14:35:34.240+0800 I CONTROL  [initandlisten] options: { config: "/etc/mongod.conf", net: { bindIp: "0.0.0.0", port: 27017 }, processManagement: { timeZoneInfo: "/usr/share/zoneinfo" }, security: { authorization: "enabled" }, storage: { dbPath: "/var/lib/mongodb", journal: { enabled: true } }, systemLog: { destination: "file", logAppend: true, path: "/var/log/mongodb/mongod.log" } }
  2018-07-05T14:35:34.240+0800 I STORAGE  [initandlisten] Detected data files in /var/lib/mongodb created by the 'wiredTiger' storage engine, so setting the active storage engine to 'wiredTiger'.
  2018-07-05T14:35:34.240+0800 I STORAGE  [initandlisten]
  2018-07-05T14:35:34.240+0800 I STORAGE  [initandlisten] ** WARNING: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine
  2018-07-05T14:35:34.240+0800 I STORAGE  [initandlisten] **          See http://dochub.mongodb.org/core/prodnotes-filesystem
  2018-07-05T14:35:34.240+0800 I STORAGE  [initandlisten] wiredtiger_open config: create,cache_size=488M,session_max=20000,eviction=(threads_min=4,threads_max=4),config_base=false,statistics=(fast),log=(enabled=true,archive=true,path=journal,compressor=snappy),file_manager=(close_idle_time=100000),statistics_log=(wait=0),verbose=(recovery_progress),
  2018-07-05T14:35:35.005+0800 I STORAGE  [initandlisten] WiredTiger message [1530772535:5560][15665:0x7f0ab9512a00], txn-recover: Main recovery loop: starting at 18/8960
  2018-07-05T14:35:35.113+0800 I STORAGE  [initandlisten] WiredTiger message [1530772535:113878][15665:0x7f0ab9512a00], txn-recover: Recovering log 18 through 19
  2018-07-05T14:35:35.179+0800 I STORAGE  [initandlisten] WiredTiger message [1530772535:179582][15665:0x7f0ab9512a00], txn-recover: Recovering log 19 through 19
  2018-07-05T14:35:35.248+0800 I STORAGE  [initandlisten] WiredTiger message [1530772535:248647][15665:0x7f0ab9512a00], txn-recover: Set global recovery timestamp: 0
  2018-07-05T14:35:35.283+0800 I RECOVERY [initandlisten] WiredTiger recoveryTimestamp. Ts: Timestamp(0, 0)
  2018-07-05T14:35:35.311+0800 I CONTROL  [initandlisten] ** WARNING: You are running this process as the root user, which is not recommended.
  2018-07-05T14:35:35.311+0800 I CONTROL  [initandlisten]
  2018-07-05T14:35:35.312+0800 I CONTROL  [initandlisten]
  2018-07-05T14:35:35.312+0800 I CONTROL  [initandlisten] ** WARNING: /sys/kernel/mm/transparent_hugepage/defrag is 'always'.
  2018-07-05T14:35:35.312+0800 I CONTROL  [initandlisten] **        We suggest setting it to 'never'
  2018-07-05T14:35:35.312+0800 I CONTROL  [initandlisten]
  2018-07-05T14:35:35.312+0800 I CONTROL  [initandlisten] ** WARNING: soft rlimits too low. rlimits set to 7856 processes, 65535 files. Number of processes should be at least 32767.5 : 0.5 times number of files.
  2018-07-05T14:35:35.312+0800 I CONTROL  [initandlisten]
  2018-07-05T14:35:35.336+0800 I FTDC     [initandlisten] Initializing full-time diagnostic data capture with directory '/var/lib/mongodb/diagnostic.data'
  2018-07-05T14:35:35.337+0800 I NETWORK  [initandlisten] waiting for connections on port 27017
  </code></pre>
  
  <p>and the whole config file is as below:</p>
  
  <pre><code># mongod.conf
  # 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: 0.0.0.0
  
  # how the process runs
  processManagement:
    timeZoneInfo: /usr/share/zoneinfo
  
  #security:
  security:
    authorization: enabled
  
  #operationProfiling:
  
  #replication:
  
  #sharding:
  
  ## Enterprise-Only Options:
  
  #auditLog:
  
  #snmp:
  </code></pre>
  
  <p>So, what is the matter with it? why the first method can not run it but the second method can start it?</p>