NFS Server

The Network File System is a TCP/IP file sharing protocol invented by Sun Microsystems. The daemons that implement the server are nfsd, mountd, and if quotas are needed rquotad. Since NFS relies on remote procedure calls, the portmapper daemon must also be running.

Shared files systems are defined in the /etc/exports file.

Each line describes a file system to export and which client machines can mount it with what permissions. By default, the user ID of the mounting user is used for file level permissions on the server machine. So, if you mount a remote file system as user "foo", then the permissions of the user "foo" on the server machine control what can be done on the mounted file system (within the limits of the /etc/exports definition). This is considered a weakness of NFS security because if a remote user gains root access, he has root permissions on NFS shared files. However, root connections can be blocked in the /etc/exports file.

Here is a simple example of /etc/exports:

        /dir1       (rw)
        /dir2       *.localdomain(ro, root_squash)
        /dir3       (rw,all_squash)

dir1 is shared read/write to all machines; dir2 is shared read-only to all machines in localdomain, and root connections are mapped to the anonymous uid/gid; dir3 is shared read/write to all machines, and all connections are mapped to the anonymous uid/gid.

 

NFS Client

To mount a remote NFS filesystem, use:
mount -t nfs servername:/exported-file-system /local-mount-point

To allow all users to mount the NFS filesystem, add this to /etc/hosts:
nfssrv:/exported /mnt/local nfs noauto,user,exec 0 0
where nfssrv:/exported is the remote NFS server and filesystem and /mnt/local is the local mount point.

NFS Utilities

Check NFS traffic on the server with nfsstat.

Show server statistics:
nfsstat -s

Show client statistics:
nfsstat -c

Show exported filesystems on a remote server:
showmount --exports nfs-server

Show all mounted filesystems:
showmount --all nfs-server

NFS Performance

The NFS HOW-TO recommends mounting all NFS shares with these options:
hard,intr,rsize=8192,wsize-8192
The read size and write size buffers will greatly increase performance in most cases. The hard option tells the system to lock an app that is using an NFS mount if communication is lost between server and client. The intr lets you kill such an app with the Interrupt signal (don't have to use kill -9).