Lawrence Carr
NT1430
Unit 7 Sharing Files with NFS
Network File System (NFS) is a distributed file system protocol originally developed by Sun Microsystems in 1984, allowing a user on a client computer to access files over a network much like local storage is accessed. NFS, like many other protocols, builds on the Open Network Computing Remote Procedure Call (ONC RPC) system. The Network File System is an open standard defined in RFCs, allowing anyone to implement the protocol. NFS is the most-known service using remote procedure call (RPC). It is an excellent way of sharing files between Linux and other UNIX systems. NFS also allows for machines to mount without authentication, at boot, which is great if you have a cluster of systems or if you want to use a centralized home directory system (using an NFS-mounted directory for home directories to keep your configurations and files identical on multiple systems). The computer where directory located is called the server and computers or devices connecting to that server are called clients. Clients usually 'mount' the shared directory to make it a part of their own directory structure. NFS is perhaps best for more 'permanent' network mounted directories such as /home directories or regularly accessed shared resources. If you want a network share that guest users can easily connect to, Samba is more suited. This is because tools exist more readily across old and proprietary operating systems to temporarily mount and detach from Samba shares. NFS is also very easy to set up. To begin, you need to install the NFS package, so on Fedora or Red Hat Enterprise Linux and other similar systems, install the nfs-utils package, # yum install nfs-utils. Next, you will need to edit /etc/exports which are where we define what filesystems can be remotely accessed. What this /etc/exports does is export the /srv directory on the server to the hosta.domain.com computer as read/write and to hostb.domain.com as read-only. It also exports /home as read/write to any computer in the network. There are other options you can supply on a per-host or per-network basis, including the no_root_squash option which will not prevent root on a client machine from writing files to the server as root; by default, NFS will map any requests from root on the client to the 'nobody' user on the server. Next, check /etc/hosts.allow and /etc/hosts.deny. NFS will check these files for access controls to the server. This is particularly necessary if you are using wildcards or broad network specifications in /etc/exports; using hosts.allow and hosts.deny you can fine-tune which clients do and don't have access. Finally, to start NFS sharing, on the server you need to start a few services as follows; # service portmap start, # service nfs start, # service nfslock start, # service rpcbind, start, and # service rpcidmapd start. To see what filesystems are exported, use the exportfs command; if you've made changes to /etc/exports, use exportfs -ra to force NFS to re-read the configuration. To make sure that NFS is running, use the rpcinfo command; if it returns a list of services and addresses being listened to, you know it is running. Finally, if you are running iptables on the server as a firewall, you will need to change what ports the NFS services listen to. By default, these are random unused ports, with portreserve/portmap letting requesting services know what ports to connect to. This is a major difference between NFSv3, where this is true, and NFSv4 which solely uses TCP port 2049, so this largely depends on which version of NFS you plan to use or enforce. On Fedora or Red Hat Enterprise Linux, this can be done by editing /etc/sysconfig/nfs. The next step is to open the firewall on these ports, which can be done by editing /etc/sysconfig/iptables (again keeping in mind this is on a RHEL system). After the changes are made, restart the firewall and the NFS services. At this point, your NFS server is set up and ready to accept connections from remote clients, which can be tested by mounting one of the exported filesystems on the client.