HDFS NFS startup error: “ERROR mount.MountdBase: Failed to start the TCP server...ChannelException: Failed to bind..." - hadoop

Question

Attempting to use / startup HDFS NFS following the docs (ignoring the instructions to stop the rpcbind service and did not start the hadoop portmap service given that the OS is not SLES 11 and RHEL 6.2), but running into error when trying to set up the NFS service starting the hdfs nfs3 service:
[root#HW02 ~]#
[root#HW02 ~]#
[root#HW02 ~]# cat /etc/os-release
NAME="CentOS Linux"
VERSION="7 (Core)"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="7"
PRETTY_NAME="CentOS Linux 7 (Core)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:centos:centos:7"
HOME_URL="https://www.centos.org/"
BUG_REPORT_URL="https://bugs.centos.org/"
CENTOS_MANTISBT_PROJECT="CentOS-7"
CENTOS_MANTISBT_PROJECT_VERSION="7"
REDHAT_SUPPORT_PRODUCT="centos"
REDHAT_SUPPORT_PRODUCT_VERSION="7"
[root#HW02 ~]#
[root#HW02 ~]#
[root#HW02 ~]# service nfs status
Redirecting to /bin/systemctl status nfs.service
Unit nfs.service could not be found.
[root#HW02 ~]#
[root#HW02 ~]#
[root#HW02 ~]# service nfs stop
Redirecting to /bin/systemctl stop nfs.service
Failed to stop nfs.service: Unit nfs.service not loaded.
[root#HW02 ~]#
[root#HW02 ~]#
[root#HW02 ~]# service rpcbind status
Redirecting to /bin/systemctl status rpcbind.service
● rpcbind.service - RPC bind service
Loaded: loaded (/usr/lib/systemd/system/rpcbind.service; enabled; vendor preset: enabled)
Active: active (running) since Tue 2019-07-23 13:48:54 HST; 28s ago
Process: 27337 ExecStart=/sbin/rpcbind -w $RPCBIND_ARGS (code=exited, status=0/SUCCESS)
Main PID: 27338 (rpcbind)
CGroup: /system.slice/rpcbind.service
└─27338 /sbin/rpcbind -w
Jul 23 13:48:54 HW02.ucera.local systemd[1]: Starting RPC bind service...
Jul 23 13:48:54 HW02.ucera.local systemd[1]: Started RPC bind service.
[root#HW02 ~]#
[root#HW02 ~]#
[root#HW02 ~]# hdfs nfs3
19/07/23 13:49:33 INFO nfs3.Nfs3Base: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting Nfs3
STARTUP_MSG: host = HW02.ucera.local/172.18.4.47
STARTUP_MSG: args = []
STARTUP_MSG: version = 3.1.1.3.1.0.0-78
STARTUP_MSG: classpath = /usr/hdp/3.1.0.0-78/hadoop/conf:/usr/hdp/3.1.0.0-78/hadoop/lib/jersey-server-1.19.jar:/usr/hdp/3.1.0.0-78/hadoop/lib/ranger-hdfs-plugin-shim-1.2.0.3.1.0.0-78.jar:
...
<a bunch of other jars>
...
STARTUP_MSG: build = git#github.com:hortonworks/hadoop.git -r e4f82af51faec922b4804d0232a637422ec29e64; compiled by 'jenkins' on 2018-12-06T12:26Z
STARTUP_MSG: java = 1.8.0_112
************************************************************/
19/07/23 13:49:33 INFO nfs3.Nfs3Base: registered UNIX signal handlers for [TERM, HUP, INT]
19/07/23 13:49:33 INFO impl.MetricsConfig: Loaded properties from hadoop-metrics2.properties
19/07/23 13:49:33 INFO impl.MetricsSystemImpl: Scheduled Metric snapshot period at 10 second(s).
19/07/23 13:49:33 INFO impl.MetricsSystemImpl: Nfs3 metrics system started
19/07/23 13:49:33 INFO oncrpc.RpcProgram: Will accept client connections from unprivileged ports
19/07/23 13:49:33 INFO security.ShellBasedIdMapping: Not doing static UID/GID mapping because '/etc/nfs.map' does not exist.
19/07/23 13:49:33 INFO nfs3.WriteManager: Stream timeout is 600000ms.
19/07/23 13:49:33 INFO nfs3.WriteManager: Maximum open streams is 256
19/07/23 13:49:33 INFO nfs3.OpenFileCtxCache: Maximum open streams is 256
19/07/23 13:49:34 INFO nfs3.DFSClientCache: Added export: / FileSystem URI: / with namenodeId: -1408097406
19/07/23 13:49:34 INFO nfs3.RpcProgramNfs3: Configured HDFS superuser is
19/07/23 13:49:34 INFO nfs3.RpcProgramNfs3: Delete current dump directory /tmp/.hdfs-nfs
19/07/23 13:49:34 INFO nfs3.RpcProgramNfs3: Create new dump directory /tmp/.hdfs-nfs
19/07/23 13:49:34 INFO nfs3.Nfs3Base: NFS server port set to: 2049
19/07/23 13:49:34 INFO oncrpc.RpcProgram: Will accept client connections from unprivileged ports
19/07/23 13:49:34 INFO mount.RpcProgramMountd: FS:hdfs adding export Path:/ with URI: hdfs://hw01.ucera.local:8020/
19/07/23 13:49:34 INFO oncrpc.SimpleUdpServer: Started listening to UDP requests at port 4242 for Rpc program: mountd at localhost:4242 with workerCount 1
19/07/23 13:49:34 ERROR mount.MountdBase: Failed to start the TCP server.
org.jboss.netty.channel.ChannelException: Failed to bind to: 0.0.0.0/0.0.0.0:4242
at org.jboss.netty.bootstrap.ServerBootstrap.bind(ServerBootstrap.java:272)
at org.apache.hadoop.oncrpc.SimpleTcpServer.run(SimpleTcpServer.java:89)
at org.apache.hadoop.mount.MountdBase.startTCPServer(MountdBase.java:83)
at org.apache.hadoop.mount.MountdBase.start(MountdBase.java:98)
at org.apache.hadoop.hdfs.nfs.nfs3.Nfs3.startServiceInternal(Nfs3.java:56)
at org.apache.hadoop.hdfs.nfs.nfs3.Nfs3.startService(Nfs3.java:69)
at org.apache.hadoop.hdfs.nfs.nfs3.Nfs3.main(Nfs3.java:79)
Caused by: java.net.BindException: Address already in use
at sun.nio.ch.Net.bind0(Native Method)
at sun.nio.ch.Net.bind(Net.java:433)
at sun.nio.ch.Net.bind(Net.java:425)
...
...
19/07/23 13:49:34 INFO util.ExitUtil: Exiting with status 1: org.jboss.netty.channel.ChannelException: Failed to bind to: 0.0.0.0/0.0.0.0:4242
19/07/23 13:49:34 INFO nfs3.Nfs3Base: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down Nfs3 at HW02.ucera.local/172.18.4.47
************************************************************/
Not sure how to interpret any of the errors seen here (and have not installed any packages like nfs-utils, assuming that Ambari would have installed all needed packages when cluster was initially installed).
Any debugging suggestions or solutions for what to do about this?
** UPDATE:
After looking at the error, I can see
Caused by: java.net.BindException: Address already in use
and looking into what is already using it, we see...
[root#HW02 ~]# netstat -ltnp | grep 4242
tcp 0 0 0.0.0.0:4242 0.0.0.0:* LISTEN 98067/jsvc.exec
The process jsvc.exec appears to be related to running java applications. Given that hadoop runs on java, I assume it would be bad to just kill the process. Is it not supposed to be on this port (since interferes with NFS Gateway)? Not sure what to do about this.

Answer 1

TLDR: nfs gateway service was already running (by default, apparently) and the service that I thought was blocking the hadoop nfs3 service (jsvc.exec) from starting was (I'm assuming) part of that service already running.
What made me suspect this was that when shutting down the cluster, the service also stopped plus the fact that it was using the port I needed for nfs. The way that I confirmed this was just from following the verification steps in the docs and seeing that my output was similar to what should be expected.
[root#HW02 ~]# rpcinfo -p hw02
program vers proto port service
100000 4 tcp 111 portmapper
100000 3 tcp 111 portmapper
100000 2 tcp 111 portmapper
100000 4 udp 111 portmapper
100000 3 udp 111 portmapper
100000 2 udp 111 portmapper
100005 1 udp 4242 mountd
100005 2 udp 4242 mountd
100005 3 udp 4242 mountd
100005 1 tcp 4242 mountd
100005 2 tcp 4242 mountd
100005 3 tcp 4242 mountd
100003 3 tcp 2049 nfs
[root#HW02 ~]# showmount -e hw02
Export list for hw02:
/ *
Another thing that could told me that the jsvc process was part of an already running hdfs nfs service would have been checking the process info...
[root#HW02 ~]# ps -feww | grep jsvc
root 61106 59083 0 14:27 pts/2 00:00:00 grep --color=auto jsvc
root 163179 1 0 12:14 ? 00:00:00 jsvc.exec -Dproc_nfs3 -outfile /var/log/hadoop/root/hadoop-hdfs-root-nfs3-HW02.ucera.local.out -errfile /var/log/hadoop/root/privileged-root-nfs3-HW02.ucera.local.err -pidfile /var/run/hadoop/root/hadoop-hdfs-root-nfs3.pid -nodetach -user hdfs -cp /usr/hdp/3.1.0.0-78/hadoop/conf:...
...
hdfs 163193 163179 0 12:14 ? 00:00:17 jsvc.exec -Dproc_nfs3 -outfile /var/log/hadoop/root/hadoop-hdfs-root-nfs3-HW02.ucera.local.out -errfile /var/log/hadoop/root/privileged-root-nfs3-HW02.ucera.local.err -pidfile /var/run/hadoop/root/hadoop-hdfs-root-nfs3.pid -nodetach -user hdfs -cp /usr/hdp/3.1.0.0-78/hadoop/conf:...
and seeing jsvc.exec -Dproc_nfs3 ... to get the hint that jsvc (which apparently is for running java apps on linux) was being used to run the very nfs3 service I was trying to start.
And for anyone else with this problem, note that I did not stop all the services that the docs want you to stop (since using centos7)
[root#HW01 /]# service nfs status
Redirecting to /bin/systemctl status nfs.service
● nfs-server.service - NFS server and services
Loaded: loaded (/usr/lib/systemd/system/nfs-server.service; disabled; vendor preset: disabled)
Active: inactive (dead)
[root#HW01 /]# service rpcbind status
Redirecting to /bin/systemctl status rpcbind.service
● rpcbind.service - RPC bind service
Loaded: loaded (/usr/lib/systemd/system/rpcbind.service; enabled; vendor preset: enabled)
Active: active (running) since Fri 2019-07-19 15:17:02 HST; 6 days ago
Main PID: 2155 (rpcbind)
CGroup: /system.slice/rpcbind.service
└─2155 /sbin/rpcbind -w
Warning: Journal has been rotated since unit was started. Log output is incomplete or unavailable.
Also note that I did not follow any of the config file settings recommended in the docs (and that some of the properties instructed in the docs could not even be found in the Ambari-managed HDFS configs (so if anyone can explain why this is still working for me despite that, please do)).
** Update:
After talking with some people more experienced with using HDP (v3.1) than me, the docs that I linked to for setting up NFS for HDFS may not be totally up to date (when setting up NFS via Ambari mgnt. in any case)...
Can have a cluster node act as an NFS gateway by checking it off as a NFS node in the Ambari host management UI:
Needed configs can be set like so in the HDFS mgnt. UI...
Can confirm that HDFS NFS gateway is running by looking at the Host > Summary > Components section in Ambari...