Using NFS to Share CentOS 6 Folders with Remote Linux and UNIX Systems
CentOS 6 provides two mechanisms for sharing files and folders with other systems on a network. One approach is to use technology called Samba. Samba is based on Microsoft Windows Folder Sharing and allows CentOS 6 systems to make folders accessible to Windows systems, and also to access Windows based folder shares from CentOS 6. This approach can also be used to share folders between other Linux and UNIX based systems as long as they too have Samba support installed and configured. This is by far the most popular approach to sharing folders in heterogeneous network environments. The topic of folder sharing using Samba is covered in Sharing CentOS 6 Folders with Remote Windows Systems.
Another option, which is targeted specifically at sharing folders between Linux and UNIX based systems, uses technology called Network File System (NFS). NFS allows the file system on one Linux computer to be accessed over a network connection by another Linux or UNIX system. NFS was originally developed by Sun Microsystems (now part of Oracle Corporation) in the 1980s and remains the standard mechanism for sharing of remote Linux/UNIX file systems to this day.
NFS is very different to the Windows SMB resource sharing technology used by Samba. In this chapter we will be looking at network based sharing of folders between CentOS 6 and other UNIX/Linux based systems using NFS.
Ensuring NFS Services are running on CentOS 6
The first task is to verify that the NFS services are installed and running on your CentOS 6 system. This can be achieved either from the command line, or using the graphical services tool.
Begin by confirming that the NFS service is installed by running the following command from a terminal window:
rpm –q nfs-utils
If the rpm command reports that the package is not yet installed, it may be installed using the yum command:
su – yum install nfs-utils
To verify that the NFS services are running from the command-line, run the following command from a terminal window:
su - /sbin/service nfs status
If the services are running you will see output similar to the following:
rpc.mountd (pid 3617) is running... nfsd (pid 3614 3613 3612 3611 3610 3609 3608 3607) is running... rpc.rquotad (pid 3601) is running...
If the service is not running, invoke it using the following command:
/sbin/service nfs start
Configuring the CentOS 6 Firewall to Allow NFS Traffic
Next, the firewall needs to be configured to allow NFS traffic. To achieve this, run the Firewall Configuration tool by selecting the System -> Administration -> Firewall menu option. If the firewall is enabled, make sure that the check box next to NFS4 is set and then click on Apply and OK.
Now that NFS is running and the firewall has been configured, we need to specify which parts of the CentOS 6 file system may be accessed by remote Linux or UNIX systems. Whilst previous versions of CentOS included a graphical tool called system-config-nfs, unfortunately this tool has been removed in CentOS 6. The good news is that this task can still be easily achieved by manually editing the appropriate configuration file. The file that needs to be edited is /etc/exports, which will need to be created and modified to export directories for access by remote systems via NFS. The syntax for an export line in this file is as follows:
<export> <host1>(<options>) <host2>(<options>)...
In the above line, <export> is replaced by the directory to be exported, <host1> is the name or IP address of the system to which access is being granted and <options> represents the restrictions that are to be imposed on that access (read only, read write etc). Multiple host and options entries may be placed on the same line if required. For example, the following line grants read only permission to /datafiles to a host with the IP address of 192.168.2.38:
The use of wildcards in permitted in order to apply an export to multiple hosts. For example, the following line permits read write access to /home/demo to all external hosts:
A full list of options supported by the exports file may be found by reading the exports man page:
</pre> man exports </pre>
For the purposes of this chapter, we will configure the /etc/exports file as follows:
/tmp *(rw,sync) /vol1 192.168.2.21(ro,sync)
Once configured, the directories must first be exported using the exportfs command:
It is also possible to view the current share settings from the command-line using the exportfs tool:
The above command will generate the following output:
/vol1 192.168.2.21 /tmp <world>
The shared folders may be accessed from a remote system either by mounting them manually from the command-line, or browsing to them using the Nautilus File Browser. Keep in mind that it may also be necessary to configure the firewall on the remote system to allow NFS traffic.
To mount a remote folder from the command line, open a terminal window and create a folder where you would like the remote folder to be mounted:
Next enter the command to mount to the remote folder (in this example we use CentOS6 as the remote hostname and /tmp as the remote path - modify these to match your environment):
su - mount CentOS6:/tmp /home/demo/demo-folder
The remote /tmp folder will then be mounted on the local system. Once mounted, the /home/demo/demo-folder will contain the remote folder and all its contents.
Mounting an NFS Filesystem on System Startup
It is also possible to configure a CentOS system to automatically mount a remote file system each time the system starts up. This is achieved by editing the /etc/fstab file. To do this load the /etc/fstab file into your favorite editor as super user:
su - gedit /etc/fstab
When loaded, it will likely look something like the following:
/dev/mapper/vg_CentOS6-lv_root / ext4 defaults 1 1 UUID=4a9886f5-9545-406a-a694-04a60b24df84 /boot ext4 defaults 1 2 /dev/mapper/vg_CentOS6-lv_swap swap swap defaults 0 0 tmpfs /dev/shm tmpfs defaults 0 0 devpts /dev/pts devpts gid=5,mode=620 0 0 sysfs /sys sysfs defaults 0 0 proc /proc proc defaults 0 0
To mount, for example, a folder with the path /tmp which resides on a system with the IP address 192.168.2.21 in the local folder with the path /nfsmount (note that this folder must already exist) add the following line to the fstab file:
192.168.2.21:/tmp /nfsmount nfs
Next time the system reboots the /tmp folder located on the remote CentOS system will be mounted on the local /nfsmount mount point. All the files in the remote folder can then be accessed as if they reside on the local hard disk drive.
Unmounting an NFS Mount Point
Once a remote file system is mounted using NFS it can be unmounted using the unmount command with the local mount point as the command-line argument. For example, to unmount our example filesystem mount point requires the use of the following command:
su - umount /nfsmount