Configure Commands Directed Toward the cdpath
This alias command allows the administrator to provide another name for a directory other than its standard name:
alias <string> <dir>
The alias line applies to only the cd command. This line is particularly useful if a popular directory is buried deep within the anonymous FTP user's directory tree. The following is a sample entry:
alias linux-386 /pub/redhat/7.3/en/i386/
This line would allow the user to type cd linux-386 and be automatically taken to the /pub/redhat/7.3/en/i386 directory.
The cdpath <dir> line specifies the order in which the cd command looks for a given user-entered string. The search is performed in the order in which the cdpath lines are entered in the ftpacess file.
For example, if the following cdpath entries are in the ftpaccess file,
cdpath /pub/redhat/
cdpath /pub/linux/
and the user types cd i386, the server searches for an entry in any defined aliases, first in the /pub/redhat directory and then in the /pub/linux directory. If a large number of aliases are defined, it is recommended that symbolic links to the directories be created instead of aliases. Doing so reduces the amount of work on the FTP server and decreases the wait time for the user.
Structure of the shutdown File
The shutdown command tells the server where to look for the shutdown message generated by the ftpshut command or by the user. The shutdown command is used with a pathname to a shutdown file, such as:
shutdown /etc/rh8ftpshutdown
If this file exists, the server checks the file to see when the server should shut down. The syntax of this file is as follows:
<year> <month> <day> <hour> <minute> <deny_offset> <disc_offset> <text>
year can be any year after 1970 (called the epoch), month is from 0-11, hour is 0-23, and minute is 0-59. deny_offset is the number of minutes before shutdown in which the server disallows new connections. disc_offset is the number of minutes before connected users are disconnected, and text is the message displayed to the users at login. In addition to the valid magic cookies defined in the messages section, those listed in Table 20.2 are also available.
TABLE 20.2 Magic Cookies for the shutdown File
| Cookie | Description |
|---|---|
%s |
The time the system will be shut down |
%r |
The time new connections will be denied |
%d |
The time current connections will be dropped |
Configuring FTP Server File-Conversion Actions
The FTP server can convert files during transfer to compress and uncompress files automatically. Suppose that the user is transferring a file to his Microsoft Windows machine that was TARed and GZIPed on a Linux machine. If the user does not have an archive utility installed to uncompress these files, he cannot access or use the files.
As the FTP server administrator, you can configure the FTP server to automatically unarchive these files before download if the site supports users who do not have unarchive capabilities. Additionally, you can configure an upload area for the users, and then configure the FTP server to automatically compress any files transferred to the server.
The structure of the format of the ftpconversions file is:
1:2:3:4:5:6:7:8
where 1 is the strip prefix, 2 is the strip postfix, 3 is the add-on prefix, 4 is the add-on postfix, 5 is the external command, 6 is the types, 7 is the options, and 8 is the description.
Strip Prefix
The strip prefix is one or more characters at the beginning of a filename that should be automatically removed by the server when the file is requested. By specifying a given prefix to strip in a conversions rule, such as devel, the user can request the file devel_procman.tar.gz by the command get procman.tar.gz, and the FTP server performs any other rules that apply to that file and retrieve it from the server. Although this feature is documented, as of version 2.6.2, it has yet to be implemented.
Strip Postfix
The strip postfix works much the same as the strip prefix, except that one or more characters are taken from the end of the filename. This feature is typically used to strip the .gz extension from a file that was TARed and GZIPed when the server performed automatic decompression before sending the file to the client.
Add-On Prefix
The add-on prefix conversion instructs the server to insert one or more characters to a filename before it is transferred to the server or client. For example, assume that a user requests the file procman.tar.gz. The server has a conversion rule to add a prefix of gnome to all .tar.gz files; therefore the server would append this string to the file before sending it to the client. The user would receive a file called gnome_procman.tar.gz. Keywords such as uppercase and lowercase can be used in this function to change the case of the filename for those operating systems in which case makes a difference. As with the strip prefix conversion, this feature is not yet implemented in version 2.6.2.
Add-On Postfix
An add-on postfix instructs the server to append one or more characters to the end of a filename during the transfer or reception of a file. A server can contain TARed packages of applications that are uncompressed. If an add-on postfix conversion is configured on the server, the server could compress the file, append a .gz extension after the file was compressed, and then send that file to the client. The server could also perform the same action for uncompressed files sent to the server. This would have the effect of conserving disk space on the server.
External Command
The external command entries in the ftpconversions file contain the bulk of the FTP server conversion rules. The external command entry tells the server what should be done with a file after it is transferred to the server. The specified conversion utility can be any command on the server, although generally it is a compression utility. As the file is sent, the server passes the file through the external command. If the file is being uploaded to the server, the command needs to send the result to standard in, whereas a download sends the result to standard out. For example, here is an entry specifying the tar command: