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You may not be able to log in if the system answers at a different speed from the speed at which your system is calling. This little glitch would prevent you from seeing the login prompt. For example, if you are calling at 1200 baud, and the remote system answers at 2400 baud, you need to send a BREAK twice, assuming that the related gettydefs entry says go from 2400->300->1200. Therefore, the chat script would look like this:
login:-BREAK-login:-BREAK-login: nuucp word: loginAok
The difference between the primary expect-send and the subexpect-subsend is that the subexpect-subsend will only be used if the expect strings are not received.
The uucico program stops looking at the incoming characters when a match is found for the expect text. It is common, however, to use the last text expected to ensure that the send sequence isn’t sent to the remote system too soon.
Before you can define the chat script, you need at the very least the uucp login name and password, which you will use to access the remote system. You should use the cu command to contact the remote system to find out what you need to define for the script. A sample session appears here:
chare@unilabs> cu -l tty21 Connected >send NEWLINE> login: nuucp Welcome to Unilabs Research Shere=bugs ~.
To create a chat script for the system bugs, which is directly connected to your system, describe it this way:
This would translate into a chat script that looks like this:
“” \r\c login: nuucp
The pair of double quotes means “expect nothing;” \r\c is “send newline.” These special characters are two of a number of characters used in chat scripts—table 3.3 lists the others. It is wise to avoid the use of subexpect-subsend pairs unless needed, because they can often lead to problems in establishing a connection.
When the L-devices and L.sys files have been configured, communication can then be evaluated with the uucico program’s debug option. The process uucico uses is essentially the same for Version 2 and HDB. When the call is initiated, uucico keeps track of the process by creating a status file for the machine in the /usr/spool/uucp directory. This status file is called STST. machine name. The status file contains the details of the last connection. If the status file is present when the remote system calls in, the connection is dropped after telling the remote that there is a LOCK file. If the status file is there when you want to make an outgoing call, the call is prevented, and a message is logged saying there is a status file to prevent the call. The contents of the status file look like this:
pointer to error code
|
| number of calls
| |
| | time of last call
| | |
4 1 729570390 LOGIN FAILED unilabs
| |
status |
system
The error code is explained in the status part of the entry, which eliminates the need for interpreting the error code manually.
When the status file exists, any other jobs queued for the affected system do not result in a call until the retry time period has been reached. To circumvent this, you can remove the status file.
In HDB UUCP, one file essentially controls access to commands and files on your system. Version 2 UUCP uses as many as five files; three files are used in the typical configuration:
USERFILE
USERFILE controls access to the files on your system for both remote and local users. It is highly recommended that for each entry in your /etc/passwd file, you create an entry in USERFILE. The code listing section at the end of the chapter includes genUSER, which generates a default USERFILE. The following sample USERFILE is created by genUSER:
root, /usr/spool/uucppublic / daemon, /usr/spool/uucppublic / bin, /usr/spool/uucppublic /bin sys, /usr/spool/uucppublic / adm, /usr/spool/uucppublic /usr/adm uucp, /usr/spool/uucppublic /usr/lib/uucp/uucico nuucp, /usr/spool/uucppublic /usr/lib/uucp/uucico uucpadm, /usr/spool/uucppublic /usr/lib/uucp lp, /usr/spool/uucppublic /bin tutor, /usr/spool/uucppublic install, /usr/spool/uucppublic chare, /usr/spool/uucppublic
Like the entries in the HDB Permissions files, each USERFILE entry defines a number of constraints for file transfer, including:
Not all constraints must be configured, but keep in mind that the fewer the constraints you implement, the greater the risk of a security violation.
USERFILE entries consist of:
username,system [c] pathname(s) uu101,thumper /usr/spool/uucppublic /usr/tmp uu102,bugs c /u/tmp
The username (uu101, uu102) defines the name that must be used to log in to the local system. This username must be configured in the ./etc.passwd file using a shell of /usr/lib/uucp/uucico.
The system portion defines the name of the remote system. The callback flag, shown as a single “c” separated by a space, is similar to the CALLBACK option in HDB UUCP. If the letter ‘c’ exists after the system name, then when your system answers a call from the remote system, your system will hang up the phone, and then call the remote system back. In this way you can validate the identity of the remote system.
The pathname component(s) is a space-delimited absolute pathname list of directories that are accessible by the remote machine.
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