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Solaris and other SVR4 versions of Unix provide file sharing through NFS and the /etc/dfs/dfstab file. The syntax of this particular file permits you to restrict file system sharing to a limited number of hosts or to share file systems with no restrictions whatsoever. Restricting file systems to a select set of hosts is particularly important if you are permitting the client hosts to access the file systems read/write and even more important if root on the clients will have the authority of root on your NFS server.
You can specify the hosts that are permitted to mount file systems by stringing them together in a colon-separated format with the share command, such as this command which can be issued on the command line or included in the dfstab file for a more or less permanent setup:
share -F nfs -o rw=mercury:venus:earth:mars:jupiter:saturn:uranus:neptune /planets
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If you include additional options or a large number of client systems, your share command can become quite long:
share -F nfs -o rw=mercury:venus:earth:mars:jupiter:saturn:uranus:neptune,anon=0 -d "planetary data" /planets
Given several dozen clients or more that need to be included in your host list, your share commands can quickly become unwieldy. One way around this problem is to convert your list of clients into a netgroup that includes all of the client systems with which your server's file systems should be shared. The netgroup definitions are set up the in /etc/netgroup file. The format of each entry in a netgroup is:
The format of each netgroup includes the netgroup name followed by a series of netgroup members:
group-name (host, user, domain) ...
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As you can see, this format is not just for creating lists of systems. For other uses, each of the fields represented in the "triplet" may be used. For NFS file sharing, only the host field is needed. To comply with the format, you would omit the user and domain fields, but include the commas as separators. An example of such an entry for the host "mercury" would look like this:
To define a group for all of the planets, therefore, you would use this syntax:
planets (mercury,,) (venus,,) (earth,,) (mars,,) (jupiter,,) (saturn,,) \
(uranus,,) (neptune,,)
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You could also use a vertical approach to setting up this list if this appeals more to you. The example below shows the planet with the continuation backslash at the end of each line.
planets \
(mercury,,) \
(venus,,) \
(earth,,) \
(mars,,) \
(jupiter,,) \
(saturn,,) \
(uranus,,) \
(neptune,,)
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Once your netgroup is set up, you need to decide how you're going to use it. Within the /etc/dfs/dfstab file, your netgroup would take the place of the client list:
share -F nfs -o rw="planets",anon=0 -d "planetary data" /planets
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I put the name of the netgroup in quotes just to differentiate it from the host names that might also appear in the file. In fact, you could mix the two if you were so inclined:
share -F nfs -o rw="planets":pluto,anon=0 -d "planetary data" /planets
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In this share command, we are sharing the /planets file system with the eight planets and pluto (Pluto was downgraded from planet status a year or more ago).
For your server to use the /etc/netgroup file to determine which hosts are included in a particular netgroup, you need to make sure that the netgroup line in the /etc/nsswitch.conf file on your NFS server contains the word "files" or set up the netgroup map on your NIS server. In the /etc/nsswitch.conf, the line might look like this:
If you're going to share file systems with the same hosts from multiple servers, you might elect to share this information through NIS instead. In this case, you would create your /etc/netgroup file, cd to /var/yp and run a "make netgroup" command to add netgroup to your NIS maps.
To view netgroups distributed via NIS, you can run this command on a client:
The -k option includes the name of the netgroup to the information displayed. The response for the planets netgroup would look like this:
planets (mercury,,) (venus,,) (earth,,) (mars,,) (jupiter,,) (saturn,,)
(uranus,,) (neptune,,)
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In other words, it looks just like the contents of the /etc/netgroup file (but flattened into a single line if you defined your netgroup vertically).
Once a netgroup is set up, it simplifies sharing additional file systems with the same group and makes it less likely than file systems will be shared without the proper host restrictions. Adding or removing share clients is also straightforward. Just update the /etc/netgroup file and push the map if you are using NIS.
