YARN Timeline service crashing as it couldn't

Question

I'm trying to set up Hadoop history (Timeline) service with the Advanced Configuration from Apache TimelineServer documentation. I launch the service with the following command: $ yarn-daemon.sh start historyserver. Then I see the ApplicationHistoryServer up and running but after few moments it crash with the following exception (from yarn-arbi-historyserver-annaba.log):

2014-08-28 18:34:21,974 FATAL org.apache.hadoop.yarn.server.applicationhistoryservice.ApplicationHistoryServer: Error starting ApplicationHistoryServer
org.apache.hadoop.service.ServiceStateException: org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.hdfs.server.namenode.SafeModeException): Cannot create directory /tmp/hadoop-arbi/yarn/timeline/generic-history/ApplicationHistoryDataRoot. Name node is in safe mode.
The reported blocks 56 has reached the threshold 0.9990 of total blocks 56. The number of live datanodes 1 has reached the minimum number 0. In safe mode extension. Safe mode will be turned off automatically in 29 seconds.
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.checkNameNodeSafeMode(FSNamesystem.java:1272)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.mkdirsInt(FSNamesystem.java:3761)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.mkdirs(FSNamesystem.java:3737)
at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.mkdirs(NameNodeRpcServer.java:778)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.mkdirs(ClientNamenodeProtocolServerSideTranslatorPB.java:573)
at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:585)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:928)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2013)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2009)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1614)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2007)

at org.apache.hadoop.service.ServiceStateException.convert(ServiceStateException.java:59)
at org.apache.hadoop.service.AbstractService.init(AbstractService.java:172)
at org.apache.hadoop.yarn.server.applicationhistoryservice.ApplicationHistoryManagerImpl.serviceInit(ApplicationHistoryManagerImpl.java:63)
at org.apache.hadoop.service.AbstractService.init(AbstractService.java:163)
at org.apache.hadoop.service.CompositeService.serviceInit(CompositeService.java:107)
at org.apache.hadoop.yarn.server.applicationhistoryservice.ApplicationHistoryServer.serviceInit(ApplicationHistoryServer.java:88)
at org.apache.hadoop.service.AbstractService.init(AbstractService.java:163)
at org.apache.hadoop.yarn.server.applicationhistoryservice.ApplicationHistoryServer.launchAppHistoryServer(ApplicationHistoryServer.java:145)
at org.apache.hadoop.yarn.server.applicationhistoryservice.ApplicationHistoryServer.main(ApplicationHistoryServer.java:155)
Caused by: org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.hdfs.server.namenode.SafeModeException): Cannot create directory /tmp/hadoop-arbi/yarn/timeline/generic-history/ApplicationHistoryDataRoot. Name node is in safe mode.
The reported blocks 56 has reached the threshold 0.9990 of total blocks 56. The number of live datanodes 1 has reached the minimum number 0. In safe mode extension. Safe mode will be turned off automatically in 29 seconds.
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.checkNameNodeSafeMode(FSNamesystem.java:1272)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.mkdirsInt(FSNamesystem.java:3761)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.mkdirs(FSNamesystem.java:3737)
at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.mkdirs(NameNodeRpcServer.java:778)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.mkdirs(ClientNamenodeProtocolServerSideTranslatorPB.java:573)
at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:585)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:928)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2013)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2009)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1614)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2007)

at org.apache.hadoop.ipc.Client.call(Client.java:1411)
at org.apache.hadoop.ipc.Client.call(Client.java:1364)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:206)
at com.sun.proxy.$Proxy14.mkdirs(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:187)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:102)
at com.sun.proxy.$Proxy14.mkdirs(Unknown Source)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.mkdirs(ClientNamenodeProtocolTranslatorPB.java:508)
at org.apache.hadoop.hdfs.DFSClient.primitiveMkdir(DFSClient.java:2587)
at org.apache.hadoop.hdfs.DFSClient.mkdirs(DFSClient.java:2558)
at org.apache.hadoop.hdfs.DistributedFileSystem$16.doCall(DistributedFileSystem.java:820)
at org.apache.hadoop.hdfs.DistributedFileSystem$16.doCall(DistributedFileSystem.java:816)
at org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:81)
at org.apache.hadoop.hdfs.DistributedFileSystem.mkdirsInternal(DistributedFileSystem.java:816)
at org.apache.hadoop.hdfs.DistributedFileSystem.mkdirs(DistributedFileSystem.java:809)
at org.apache.hadoop.fs.FileSystem.mkdirs(FileSystem.java:1815)
at org.apache.hadoop.yarn.server.applicationhistoryservice.FileSystemApplicationHistoryStore.serviceInit(FileSystemApplicationHistoryStore.java:120)
at org.apache.hadoop.service.AbstractService.init(AbstractService.java:163)
... 7 more
2014-08-28 18:34:21,975 INFO org.apache.hadoop.util.ExitUtil: Exiting with status -1
2014-08-28 18:34:21,986 INFO org.apache.hadoop.yarn.server.applicationhistoryservice.ApplicationHistoryServer: SHUTDOWN_MSG: 
/************************************************************
SHUTDOWN_MSG: Shutting down ApplicationHistoryServer at Annaba/192.168.2.206
************************************************************/

It sounds like it failed to create direcotry /tmp/hadoop-arbi/yarn/timeline/generic-history/ApplicationHistoryDataRoot which is the default value for the yarn.timeline-service.generic-application-history.fs-history-store.uri property. But wonder why this services failed while other Hadoop services successfully created things under /tmp/:

arbi@Annaba:~$ tree /tmp/
/tmp/
├── hadoop-arbi
│   └── nm-local-dir
│       ├── filecache
│       ├── nmPrivate
│       └── usercache
├── hadoop-arbi-datanode.pid
├── hadoop-arbi-namenode.pid
├── hsperfdata_arbi
│   ├── 2929
│   ├── 2983
│   ├── 3048
│   └── 3103
├── hsperfdata_neo4j
│   └── 1029
├── Jetty_0_0_0_0_50070_hdfs____w2cu08
│   └── jsp
├── Jetty_0_0_0_0_50075_datanode____hwtdwq
│   └── jsp
├── jetty-0.0.0.0-7474-browser-_browser-any-
├── jetty-0.0.0.0-7474-webadmin-html-_webadmin-any-
├── Jetty_0_0_0_0_8042_node____19tj0x
│   ├── jsp
│   └── webapp
│       └── webapps
│           └── node
├── Jetty_Annaba_8088_cluster____n49mx9
│   ├── jsp
│   └── webapp
│       └── webapps
│           └── cluster
├── pulse-PKdhtXMmr18n [error opening dir]
├── ssh-xewZNa7CcwSD
│   └── agent.1292
├── unity_support_test.1
├── yarn-arbi-historyserver.pid
├── yarn-arbi-nodemanager.pid
└── yarn-arbi-resourcemanager.pid

Also what is this name node's safe mode?