Finally, another alternative is to use Apache and the HTTP protocol for serving files. Using a web server to provide data downloads can reduce the need to monitor and maintain a separate software service (or directories) on your server. This approach to serving files also reduces system resource requirements and gives remote users a bit more flexibility when downloading (such as enabling them to download multiple files at once). See Chapter 17, 'Apache Web Server Management,' for more information about using Apache.
Installing FTP Software
As part of the Workstation installation, the client software for FTP is already installed. You can verify that FTP-related software is installed on your system by using the RPM (Red Hat Package Manager), grep, and sort commands in this query:
$ rpm -qa | grep ftp | sort
The sample results might differ, depending on what software packages are installed. In your Fedora file system, the /usr/bin/pftp file is symbolically linked to /usr/bin/ftp as well as the vsftpd server under the /usr/sbin directory. The base anonymous FTP directory structure is located under the /var/ftp directory. Other installed packages include additional text- based and graphical FTP clients.
If vsftpd is not installed, you can find it under FTP Server in the Add/Remove Applications dialog.
If you host an FTP server connected to the Internet, make it a habit to always check the Fedora site, http://fedora.redhat.com, for up-to-date system errata and security and bug fixes for your server software.
Because the anonftp and wu-ftpd RPM packages are not included with Fedora, you must download and install them if you want to use the wu-ftpd server. Retrieve the most recent packages for Linux from http://www.wu-ftpd.org/ to build from the latest source code or obtain RPM packages from a reputable mirror.
The FTP User
After Fedora is installed, an FTP user is created. This user is not a normal user per se, but a name for anonymous FTP users. The FTP user entry in /etc/passwd looks like this:
ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
The FTP user, as discussed here, applies to anonymous FTP configurations and server setup.
Also, note that other Linux distributions might use a different default directory, such as /usr/local/ftp, for FTP files and anonymous users.
This entry follows the standard /etc/passwd entry: username, password, user ID, group ID, comment field, home directory, and shell. To learn more about /etc/password, see the section 'The Password File' in Chapter 10, 'Managing Users.'
Items in this entry are separated by colons. In the preceding example, you can see that the Fedora system hosting the server uses x is present in the traditional password field. The shadow password system is important because it provides Fedora an additional level of security; the shadow password system is normally installed during the Fedora installation.
The FTP server software uses this user account to assign permissions to users connecting to the server. By using a default shell of /sbin/nologin (as opposed to /bin/bash or some other standard interactive shell) for anonymous FTP users, the software renders those users unable to log in as regular users. /sbin/nologin is not a shell, but a program usually assigned to an account that has been locked. As root inspection of the /etc/shadow file shows (see Listing 20.1), it is not possible to log in to this account, denoted by the use of * as the password.
ftp User Entry# cat /etc/shadow
bin:*:11899:0:99999:7:::
daemon:*:11899:0:99999:7:::
adm:*:11899:0:99999:7:::
lp:*:11899:0:99999:7:::
...
ftp:*:12276:0:99999:7:::
...
The shadow file (only a portion of which is shown in Listing 20.1) contains additional information not found in the standard /etc/passwd file, such as account expiration, pass word expiration, whether the account is locked, and the encrypted password. The * in the password field indicates that the account is not a standard login account; thus, it does not have a password.
Although shadow passwords are in use on the system, passwords are not transmitted in a secure manner when using FTP. Because FTP was written before the necessity of encryption and security, it does not provide the mechanics necessary to send encrypted pass words. Account information is sent in plain text on FTP servers; anyone with enough technical knowledge and a network sniffer can find the password for the account to which you connect on the server. Many sites use an anonymous-only FTP server specifically to prevent normal account passwords from being transmitted over the Internet.
Figure 20.1 shows a portion of an ethereal capture of an FTP session where you can see it has caught a user's password being sent in clear text. The ethereal client is a graphical browser used to display network traffic in real time, and it can be used to watch packet data, such as an FTP login on a LAN.
FIGURE 20.1 The ethereal client can filter and sniff FTP sessions to capture usernames and passwords.
Conscientious Linux administrators take the time to carefully install, set up, and configure a production FTP server before offering public service or opening up for business on the Internet. However, you can set up a server very quickly on a secure LAN by following a few simple steps:
1. Ensure that the FTP server RPM package is installed, networking is enabled, and firewall rules on the server allow FTP access. See Chapter 14, 'Networking,' to see how to use Red Hat's system-config-securitylevel client for firewalling.
2. If anonymous access to server files is desired, populate the /var/ftp/pub directory. Do this by mounting or copying your content, such as directories and files, under this directory.
3. Edit and then save the appropriate configuration file (such as vsftpd.conf for vsftpd) to enable access.
4. If you are using wu-ftpd, you must start or restart xinetd like so: /etc/rc.d/init.d/xinetd restart. If you are using
