How to configure NFS Server in RHEL 6
Network File System (NFS) protocol allow Linux client to mount remote file systems and interact with those file systems as they are mounted locally.
- NFS was developed by Sun Microsystems in 1980
- NFS stand for Network File System
- NFS is used to share files and printer between Linux / Unix systems
- Red Hat Enterprise Linux 6 supports NFSv2, NFSv3, and NFSv4 clients.
- By default RHEL6 use NFSv4 if the server supports it.
NFSv1
NFSv1 was the development stage of NFS protocol. It was used only for in house experimental purpose. When a stable version of NFS was ready, Developers decided to release it as the new version of NFS known as NFSv2.
NFSv2
- NFSv2 supports only 32 bit.
- NFSv2 only allowed the first 2 GB of a file to be read
- NFSv2 operated only over UDP
NFSv3
- NFSv3 supports 64 bit file system.
- NFSv3 can handle files larger than 2 GB.
- NFSv3 supports asynchronous writes on the server. asynchronous writes improve write performance.
- NFSv3 supports additional file attributes in many replies, to avoid the need to re-fetch them.
- NFSv3 supports READDIRPLUS operation. READDIRPLUS operation get file handles and attributes along with file names when scanning a directory.
- NFSv3 supports TCP. Using TCP as a transport made NFS over a WAN more feasible.
NFSv4
- NFSv4 retains all NFSv3 advantages.
- NFSv4 supports ACLs.
- NFSv4 uses the virtual file system to present the server's export.
- NFSv4 supports Pseudo file system. Pseudo File System provide maximum flexibility. Exports Pathname on servers can be changed transparently to clients.
- NFSv4 have locking operations as the part of protocol which keep track of open files and delegations.
- NFSv4 works through firewalls and on the Internet.
RHCE 6 Exam objectives cover in this article
- Provide network shares to specific clients
- Provide network shares suitable for group collaboration
In this tutorial I will use two systems Server and linuxclient from our LAB environment. I will configure NFS Server on Server system and NFS client on linuxclient system. If you want to check the network topology used in this article please check following article. Lab set up for RHCE 6 practice
Configure NFS Server in RHEL6
Our first task is to install the necessary RPM. Two RPM are required for NFS server
- nfs-utils
- rpcbind
nfs-utils
This is the main RPM which provide nfs service.
rpcbind
NFS depends on Remote Procedure Calls(RPC) service which is controlled by rpcbind service. In earlier version of RHEL portmap service was used to map RPC program numbers to IP address port number combinations. This service is now replaced by rpcbind to enable IPv6 support.
If you do not have above RPM installed, than first install them. You can use any method to install RPM.
"NFS file server" is the primary group associated with NFS. So if you have configured yum repository than following command will install the mandatory packages[nfs-utils and nfs4-acl-tools] from that group.
#yum groupinstall " NFS file server"
Or alternatively you can use
# yum install nfs* -y
If you do not have yum repository use RPM command to install these packages. Go in the folder which contain RPM (In installation disk of RHEL6, Package folder contains all RPM ) and run following command.
#rpm -ivh nfs* --nodeps --force #rpm -ivh rpcbind* --nodeps --force
Our second task is to verify that the NFS services are installed. This can be done form following command.
rpm –qa nfs-utils
Verify that rpcbind package is installed.
rpm –qa rpcbind
For this article I assume that you have both packages installed.
Following services are associated with NFS daemons. Each service have its script file stored in init.d directory.
| /etc/init.d/nfs | Main control script for NFS Daemons which control NFS services. |
| /etc/init.d/nfslock | Script for lock files and the statd daemon, which locks and provides status of files those are currently in use. |
| /etc/init.d/portreserve | Replacement script for the portmap which used to set up ports for RPC services. |
| /etc/init.d/rpcbind | RPC program number converter. |
| /etc/init.d/rpcgssd | Script for RPC-related security services. |
| /etc/init.d/rpcidmapd | Configuration script used for mapping of NFS user ID to LDAP and Kerberos systems. |
| /etc/init.d/rpcsvcgssd | Control script for the server side of RPC-related general security services. |
You can start each script directly by following command
#/etc/init.d/[script name]
For example to start nfs service
#/etc/init.d/nfs
Or you can use service command to start / stop /restart the service
#service nfs start
nfs and rpcbind are the compulsory services for nfs daemons.
Make sure nfs and rpcbind scripts are active before you configure NFS server.
Start the services
Make sure that services remain on after reboot
Check the status to services it must be running
How to configure NFS client on RHEL6
Check necessary RPM
Install if you are missing them
Start the necessary services and Verify the status of services it must be running
Make sure service remain on after reboot
Check connectivity form server
How to create NFS Share
So far we have setup NFS Server and NFS client with basic configurations. Now create a NFS Share on NFS Server and mount it from NFS Client.
On Server system make a directory /nfs_share and create a test file in it
On Server /etc/exportfs defines what resources will be available for clients. /etc/exports file use following syntax to share resources
[mountpoint] [host][permissions/options]
Remember there is no space between the [host] field and the [permissions/options] field. If you include a space, you receive a syntax error.
Common Mount permission options
| rw | read/write permissions |
| ro | Sread-only permissions |
| insecure | Allows the use of ports over 1024 |
| sync | Specifies that all changes must be written to disk before a command completes |
| no_wdelay | Forces the writing of changes immediately |
| root_squash | Prevents root users |
NFS Host Entries
/etc/exportfs supports conventional wildcards which provide flexibility when specifying hosts.
- you can use the hostname for hosts within your domain.
- you need fully qualified domain name for outside hosts.
- you can reference all the hosts within a specific domain.
- You can use the * for the host segment, followed by the domain name for the network, such as *.example.com for all the hosts in the example.com network.
- Instead of host name, You can also use single host's ip address.
- you can use IP network addresses with a CNDR format
- You can also use an NIS netgroup name to reference a collection of hosts. The NIS netgroup name is preceded by an @ sign.
For example following are the valid example for hosts entries
directory host(options) /nfs_share *(rw,sync) /nfs_share *.example.com(rw,sync) /nfs_share 192.168.1.10(rw,sync) /nfs_share 192.168.1.0/255.255.255.0(rw,sync) /nfs_share 192.168.1.0/24(rw,sync) /nfs_share @netgroup(rw,sync)
We will share it globally with read / write options. Open /etc/exports file
add following line and save the file
Restart the NFS service
showmount
showmount command with -e option will display shared NFS directories locally and remotely. To review the export list for a NFS server, add the name / IP address of NFS server. If this command doesn't work, communication may be blocked with a firewall.
During the exam you may face two common errors as the output of showmount -e command
on NfS server
clnt_create: RPC: Program not registered
on NFS client
clnt_create: RPC: Port mapper failure - Unable to receive: errno 113 (No route to host)
On server this is generated due to order of services. In exam always start /restart rpcbind service before nfs.
On client this is generated due to firewall configured on NFS server. On linuxclient system use showmount to list all NFS Share
clnt_create: RPC: Port mapper failure - Unable to receive: errno 113 (No route to host)
showmount -e command returns above error on NFS client if firewall is not properly configured on NFS Server.
Configure IPTABLES rules for NFS Server.
During the RHCE6 exam you may have a iptable firewall enabled system. You should know how to allow nfs through firewall.
NFS port range
In order to allow NFS through iptable firewall we need to open following ports
- TCP and UDP port 2049 for NFS.
- TCP and UDP port 111 (rpcbind/sunrpc).
- TCP and UDP port specified with MOUNTD_PORT="port"
- TCP and UDP port specified with STATD_PORT="port"
- TCP port specified with LOCKD_TCPPORT="port"
- UDP port specified with LOCKD_UDPPORT="port"
NFS requires rpcbind, which dynamically assigns ports for RPC services at startup time. Dynamic ports could not be protected by iptables as these ports might change on reboot and make changes obsolete.
So you need to configure NFS services to use fixed ports.
Open /etc/sysconfig/nfs
Uncomment following directives to use default port, Or change them with desired TCP / UDP unused ports and save the file.
# TCP port rpc.lockd should listen on. LOCKD_TCPPORT=[port-number] # UDP port rpc.lockd should listen on. LOCKD_UDPPORT=[port-number] # Port rpc.mountd should listen on. MOUNTD_PORT=[port-number] # Port rquotad should listen on. RQUOTAD_PORT=[port-number] # Port rpc.statd should listen on. STATD_PORT=[port-number] # Outgoing port statd should used. The default is port is random STATD_OUTGOING_PORT=[port-number]
Here is the sample listing with default port number
LOCKD_TCPPORT=32803 LOCKD_UDPPORT=32769 MOUNTD_PORT=892 RQUOTAD_PORT=875 STATD_PORT=662 STATD_OUTGOING_PORT=2020
So far we have configured fix port for nfs server now let's configure firewall to allow nfs traffic.
Run setup command
Select firewall configuration
Select Customize [Make sure firewall option remain selected ]
Select NFS4
Select Forward and press enter
Select eth+ and press enter on close button
Select ok and press enter
Select Yes and press enter
Select Quit and press enter
Now open /etc/sysconfig/iptables file
Add following iptable rules
-A INPUT -m state --state NEW -m udp -p udp --dport 111 -j ACCEPT -A INPUT -m state --state NEW -m tcp -p tcp --dport 111 -j ACCEPT -A INPUT -m state --state NEW -m tcp -p tcp --dport 32803 -j ACCEPT -A INPUT -m state --state NEW -m udp -p udp --dport 32769 -j ACCEPT -A INPUT -m state --state NEW -m tcp -p tcp --dport 892 -j ACCEPT -A INPUT -m state --state NEW -m udp -p udp --dport 892 -j ACCEPT -A INPUT -m state --state NEW -m tcp -p tcp --dport 875 -j ACCEPT -A INPUT -m state --state NEW -m udp -p udp --dport 875 -j ACCEPT -A INPUT -m state --state NEW -m tcp -p tcp --dport 662 -j ACCEPT -A INPUT -m state --state NEW -m udp -p udp --dport 662 -j ACCEPT
under the rule for port 2049 and save file
NFS and SELinux
SELinux is the integral part of RHEL6 and directories shared via NFS would not work without proper changes to SELinux.
Important SELinux Booleans for NFS
| nfs_export_all_ro | Allows NFS to share files and directories as read-only |
| nfs_export_all_rw | Allows NFS to share files and directories as read/write |
| httpd_use_nfs | Allows httpd to access NFS file systems |
| use_nfs_home_dirs | Supports NFS home directories |
| samba_share_nfs | Allows Samba to export NFS volumes |
| allow_nfsd_anon_write | Allows NFS servers to modify public files |
| allow_ftpd_usr_nfs | Allows FTP servers to use NFS for public file transfer services |
During the exam Make sure the SELinux booleans are compatible, specifically nfs_export_all_ro and nfs_export_all_rw are set to on
If nfs_export_all_ro and nfs_export_all_rw Booleans are set to off change the value
Verify that the Booleans have been changed:
Restart the iptables , rpcbind, and nfs service
Now try again to run showmount -e command on NFS client
Create a /nfs_tmp directory to mount NFS share locally
Mount /nfs_share to local /nfs_tmp directory
Perform read and write operations, You can read but write will be denied.
We shared with write permission still we are getting permission denied message because default Linux file permission always over ride NFS share permission. To fix it
On Server system change file permission
On client try again to write this time it will be permitted
Now we have full file permission on nfs_share directory open /etc/exportfs file
Change rw [Read, Write] share option to ro[Read only] and save the file
Restart the nfs service
Or use the exportfs command to manually export any new resources added to the /etc/exports file.
| -a | Exports directories |
| -r | Reexports directories |
| -u | Unexports directories |
| -v | Show verbose output |
In real world I would recommended to use exportfs to manually export the directories rather than restart the service because while you restart the nfs service, you also disconnect your nfs clients as well.
On client remount the nfs_share
Try to perform write operation, This time you will get NFS share error message.
NFS Tools
During the exam following commands could be helpful for troubleshooting
| mountstats | Shows information about mounted NFS shares |
| nfsstat | Shows statistics of exported resources |
| nfsiostat | Shows statistics of NFS mounted shares |
source : http://computernetworkingnotes.com/network-administration/how-to-configure-nfs-server-in-rhel-6.html
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