Alias Database Problems

Alias Database Problems

Problems can occur with the alias database, especially if a sendmail process accesses the DBM version before it is completely rebuilt. Two circumstances can cause this problem:

One process accesses the database while another process is rebuilding it.
The process rebuilding the database dies because it has been killed, or a station crash has occurred before completing the rebuild.

sendmail has two techniques for trying to relieve these problems. First, to avoid the problem of a partially rebuilt database, sendmail ignores interrupts while rebuilding the database. Second, at the end of the rebuild it adds an alias of the following form (which is not normally legal):

@: @

Before sendmail accesses the database, it ensures that this entry exists. For this action to occur, the configuration file must contain the -a option.

If the @:@ entry does not exist, sendmail waits for it to appear. After the specified waiting period elapses, sendmail itself forces a rebuild. For this action to occur, the configuration file must include the D option. If the D option is not specified, a warning message is generated and sendmail continues.

Another alias problem can arise for stations incorporating the NIS alias database in /etc/aliases through the use of the +:+ alias. If the NIS alias server goes down or is otherwise nonresponsive to NIS queries, sendmail will not see the aliases normally obtained from the NIS server. This situation may result in mail being returned, marked User unknown.