Книга: Fedora™ Unleashed, 2008 edition

Configure User Information

Configure User Information

Providing users with information about the server and its use is a good practice for any administrator of a public FTP server. Adequate user information can help prevent user problems and eliminate tech support calls. You also can use this information to inform users of restrictions governing the use of your FTP server. User information gives you an excellent way to document how your FTP server should be used.

You can use the commands detailed in the following sections to display messages to users as they log in to the server and as they perform specific actions. The following commands enable messages to be displayed to users when logging in to the server and when an action is performed.

This command is a reference to a file that is displayed before the user receives a login prompt from the FTP server:

banner <path>

This file generally contains information to identify the server. The path is an absolute pathname relative to the system root (/), not the base of the anonymous FTP user's home. The entry might look like this:

banner /etc/rh8ftp.banner

This example uses the file named rh8ftp.banner under the /etc directory. The file can contain one or more lines of text, such as:

Welcome to Widget, Inc.'s Red Hat Linux FTP server.
This server is only for use of authorized users.
Third-party developers should use a mirror site.

When an FTP user attempts to log in, the banner is displayed like so:

$ ftp shuttle2
Connected to shuttle2.home.org.
220-Welcome to Widget, Inc.'s Red Hat Linux FTP server.
220-This server is only for use of authorized users.
220-Third-party developers should use a mirror site.
220-
220-
220 shuttle2 FTP server (Version wu-2.6.2-8) ready.
504 AUTH GSSAPI not supported.
504 AUTH KERBEROS_V4 not supported.
KERBEROS_V4 rejected as an authentication type
Name (shuttle2:phudson):

This line specifies a text file to be displayed to the user during login and when the user issues the cd command:

message <path> {<when> {<class> ...}}

The optional when clause can be LOGIN or CWD=(dir), where dir is the name of a directory that is current. The optional class parameter enables messages to be shown to only a given class or classes of users.

Using messages is a good way to give information about where things are on your site as well as information that is system dependent, such as alternative sites, general policies regarding available data, server availability times, and so on.

You can use magic cookies to breathe life into your displayed messages. Magic cookies are symbolic constants that are replaced by system information. Table 20.1 lists the message command's valid magic cookies and their representations.

TABLE 20.1 Magic Cookies and Their Descriptions

To understand how this command works, imagine that you want to display a welcome message to everyone who logs in to the FTP server. An entry of:

message /home/ftp/welcome.msg login
message /welcome.msg          login

shows the contents of the welcome.msg file to all authenticated users who log in to the server. The second entry shows the same message to the anonymous user.

The welcome.msg file is not created with the installation of the RPM, but you can create it using a text editor. Type the following:

Welcome to the anonymous ftp service on %L!
There are %N out of %M users logged in.
Current system time is %T
Please send email to %E if there are any problems with this service.
Your current working directory is %C

Save this file as /var/ftp/welcome.msg. Verify that it works by connecting to the FTP server:

220 FTP server ready.
504 AUTH GSSAPI not supported.
504 AUTH KERBEROS_V4 not supported.
KERBEROS_V4 rejected as an authentication type
Name (shuttle:phudson): anonymous
331 Guest login ok, send your complete e-mail address as password.
Password:
230-Welcome to the anonymous ftp service on shuttle.home.org!
230-
230-There are 1 out of unlimited users logged in.
230-
230-Current system time is Mon Nov 3 10:57:06 2003
230-
230-Please send email to root@localhost if there are
230-any problems with this service.
230-Your current working directory is /

This line sets the email address for the FTP administrator:

email <name>

This string is printed whenever the %E magic cookie is specified. This magic cookie is used in the message line or in the shutdown file. You should display this string to users in the login banner message so that they know how to contact you (the administrator) in case of problems with the FTP server.

The readme line tells the server whether a notification should be displayed to the user when a specific file was last modified. Here's the command:

readme <path> {<when {<class>}}

The path parameter is any valid path for the user. The optional when parameter is exactly as seen in the message line. class can be one or more classes as defined in the class file. The path is absolute for real users. For the anonymous user, the path is relative to the anonymous home directory, which is /var/ftp by default.

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