Recipe 2.5 Configuring Solaris 8 to Read Aliases from a NIS Server

Problem

You must configure a Solaris 8 system to read aliases from a NIS server.

Solution

Edit the aliases entry in the /etc/nsswitch.conf file, changing it to the following:

 aliases:    nis files 

Discussion

No m4 configuration commands are needed to use the nsswitch.conf file on a Solaris system. The basic sendmail configuration already installed on your system should work. If your system is not yet configured to run sendmail, use the generic-solaris.mc file as a starting point to get your Solaris server running.

Both the Linux system and the Solaris system have a system-wide service switch file named /etc/nsswitch.conf . The difference is that the Red Hat Linux 7.3 system does not use the aliases entry in that file, and the Solaris system does. When the system has an active system service switch file, sendmail uses that file and ignores the file identified by the confSERVICE_SWITCH_FILE define. The correct solution for the Solaris system is to identify the sources of alias information in the nsswitch.conf file. Any source that is compatible with the nsswitch.conf syntax and with sendmail can be specified. See the nsswitch.conf manpage for information about the syntax supported on your computer.

Recipe 2.3 and Recipe 2.4 also show aliases being read from an external server. But Recipe Recipe 2.2 and most examples in this book assume the aliases database is a local file located directly on the sendmail system. This is a common design, and there are some good reasons why.

Aliases are only searched for mailers that have the A flag set. On most systems, only the local mailer has this flag set, which means that aliases only apply to inbound mail that has been accepted for delivery through the local mailer. A centralized database that includes aliases for all of the users in the organization is needed only by a server that will accept mail for all of the users in the organization. For most Unix workstations, the bulk of the entries in a centralized database are unused ”only those users who actually receive their mail at the workstation are looked up.

Placing the aliases file directly on the system that needs it improves performance and reduces network overhead. It also enhances security ”data that passes over the network is subject to corruption and spoofing, and adding another protocol to the mix, in this case NIS, makes the system vulnerable to any bugs that might appear in that protocol.

Security, performance, and applicability limit the demand for a centralized aliases database accessible through the network. Think hard about why you want to put the aliases database on an external NIS or LDAP server before you proceed. However, if you decide to read aliases from an external server, sendmail can be configured to do so.

See Also

Recipe 2.4 provides a solution to the same problem for different operating systems. The nsswitch.conf file is covered in the books TCP/IP Network Administration , Third Edition, by Craig Hunt (O'Reilly), and Managing NFS and NIS , Second Edition, by Stern, Eisler, and Labiaga (O'Reilly).