What is NFS?
A Network File System (NFS) allows remote hosts to mount
file systems over a network and interact with those file systems as though they
are mounted locally. This enables system administrators to consolidate
resources onto centralized servers on the network.
How many NFS versions?
Currently,
there are four versions of NFS.
1. nfsv2 ( nfs version 2 )
2. nfsv3 ( “ “ 3 )
3. nfsv4.0 ( “
“ 4.0 )
4. nfsv4.1 ( “
“ 4.1 )
* NFS version 2 (NFSv2) is no longer supported by Red
Hat.
* NFS
version 3 (NFSv3) supports safe asynchronous writes and is more robust at error
handling than the previous NFSv2; it also supports 64-bit file sizes and
offsets, allowing clients to access more than 2 GB of file data.
* NFSv4
works through firewalls and on the Internet, no longer requires an rpcbind service, supports ACLs, and utilizes
stateful operations.
* Recently
Red Hat Enterprise Linux 7 adds support for NFS version 4.1
(NFSv4.1), which provides a number of performance and security enhancements,
including client-side support for Parallel NFS (pNFS).
NOTE:
Red Hat
Enterprise Linux 7 supports NFSv3, NFSv4.0, and NVSv4.1 clients. NFS
clients attempt to mount using NFSv4.0 by default, and fall back to NFSv3 if
the mount operation is not successful.
All versions
of NFS can use Transmission Control Protocol (TCP) running over an IP network,
with NFSv4 requiring it.
NFSv3 can
use the User Datagram Protocol (UDP)
running over an IP network to provide a stateless network connection between
the client and server.
In order for
NFS to work with a default installation of Red Hat Enterprise Linux with a
firewall enabled, configure IPTables with the default TCP port 2049. Without
proper IPTables configuration, NFS will not function properly.
How to Configure NFS Server:
There are
two ways to configure an NFS server:
1.
Through the manually editing the NFS
configuration file ( /etc/exports )
If NFS
package is not installed then install it:
#yum
install nfs* -y
the /etc/exports file only specifies the exported
directory and the hosts permitted to access it, as in the following example:
#vim
/etc/exports
Write it on
blank file:
/directory system1.example.com
in this example
you have a directory named “directory” and you want to share it with “system1.example.com”.
Change the permission of shared directory:
#chmod 777 /directory
Same as you
can share multiple file with multiple hosts.
After modified
the configuration file execute this command for maintain the table of exported
NFS file system:
#exportfs -r
NFS requires the rpcbind service to be running. Start it with the following command:
#service rpcbind restart
Restart the NFS service:
In RHEL6:
#service nfs restart
In RHEL7:
#systemctl restart nfs
For verify
or see the NFS server's export list execute following command:
#showmount –e
Same example of NFS with default
settings:
Each default
for every exported file system must be explicitly overridden. For example, if
the rw option is not specified, then the exported file system is shared as
read-only. The following is a sample line from /etc/exports which overrides two
default options:
/directory system1.example.com(rw,async)
Like this (in blue color)
you can use following default settings:
ro (Read Only):
The exported
file system is read-only. Remote hosts cannot change the data shared on the
file system. To allow hosts to make changes to the file system (that is,
read/write), specify the rw option.
sync
:
The NFS server will not reply to requests before
changes made by previous requests are written to disk. To enable asynchronous
writes instead, specify the option async.
wdelay
:
The NFS server will delay writing to the disk if it
suspects another write request is imminent. This can improve performance as it
reduces the number of times the disk must be accesses by separate write
commands, thereby reducing write overhead. To disable this, specify the no_wdelay. no_wdelay is only available
if the default sync option is also specified.
root_squash
:
This prevents root users connected remotely (as
opposed to locally) from having root privileges; instead, the NFS server will
assign them the user ID nfsnobody. This effectively "squashes" the
power of the remote root user to the lowest local user, preventing possible
unauthorized writes on the remote server. To disable root squashing, specify no_root_squash.
2.
By the Command Line, By the using of “exportfs” command.
For more details read the man page of “exportfs”
