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Chapter 25 . Running a Print Server 641 Configuring Local Printers in Red Hat Add a local printer (in other words, a printer connected directly to your computer) with the Printer Configuration window using the following procedure. (See the Choosing a Printer sidebar if you don t yet have a printer.) Connect your printer before starting this procedure. This enables the printer software to autodetect the printer s location and to immediately test the printer when you have finished adding it. Tip Choosing a Printer The PostScript language is the preferred format for Linux and UNIX printing and has been for many years. Every major word-processing product that runs on Fedora, Red Hat Linux, SUSE, Debian, and UNIX systems supports PostScript printing, so a printer that natively supports PostScript printing is sure to work in Linux. If you get a PostScript printer and it is not explicitly shown in the list of supported printers, simply select the PostScript filter when you install the printer locally. No special drivers are needed. Your next best option is to choose a printer that supports PCL. In either case, make sure that the PostScript or PCL is implemented in the printer hardware and not in the Windows driver. Avoid printers that are referred to as Winprinters. These printers use nonstandard printing interfaces (those other than PostScript or PCL). Support for these low-end printers is hit or miss. For example, some low-end HP DeskJet printers use the pnm2ppa driver to print documents in Printing Performance Architecture (PPA) format. Some Lexmark printers use the pbm217k driver to print. Although drivers are available for many of these Winprinters, many of them are not fully supported. Ghostscript may also support your printer; if it does, you can use that tool to do your printing. Ghostscript (found at www.ghostscript.com) is a free PostScript-interpreter program. It can convert PostScript content to output that can be interpreted by a variety of printers. There are both GNU and Aladdin Ghostscript drivers available. Although the latest Aladdin drivers are not immediately released under the GPL, you can use older Aladdin drivers that are licensed under the GNU. You ll find an excellent list of printers supported in Linux at www.linuxprinting.org (select the Printer Listing link). I strongly recommend that you visit that site before you purchase a printer to work with Linux. In addition to showing supported printers, the site also has a page describing how to choose a printer for use with Linux (www.linuxprinting. org/suggested.html).
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640 Part V . Running Servers Figure 25-2: Print test pages or temporarily stop printing from the Printers page. Using the Red Hat Printer Configuration Window If you are using Fedora, RHEL or other Red Hat Linux systems, you can use the Printer Configuration window to set up your printers. In fact, it s recommended that you use it instead of CUPS Web administration because the resulting printer configuration files are tailored to work with Red Hat systems. To install a printer from your GNOME desktop in Fedora, start the Printer Configuration window by selecting System Setting.Printing (or as root user by typing system-config-printer). This tool lets you add and delete printers and edit printer properties. It also lets you send test pages to those printers to make sure they are working properly. The key here is that you are configuring printers that are managed by your print daemon (cupsd for the CUPS service). After a printer is configured, users on your local system can use it. Subsequently, you can refer to the Configuring Print Servers section to learn how to make the server available to users from other computers on your network. The printers that you set up can be connected directly to your computer (as on a parallel port) or to another computer on the network (for example, from another UNIX system or Windows system).
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Chapter 25 . Running a Print Server 639 From the computer at address 10.0.0.5, you would type: http://localhost:631/admin (substituting the CUPS server s name or IP address for localhost), and when prompted, enter the root username and password. Now, with the Admin screen displayed, here s how to set up a printer: 1. Click the Add Printer button. The Add New Printer screen appears. 2. Type a name, location, and description for the printer and click Continue. 3. Select the device to which the printer is connected. The printer can be connected locally to a parallel, SCSI, serial, or USB port directly on the computer. Alternatively, you can select a network connection type for Apple printers (appSocket/HP JetDirect), Internet Printing Protocol (http or ipp), or a Windows printer (using SAMBA or SMB). 4. If prompted for more information, you may need to further describe the connection to the printer. For example, you may need to enter the baud rate and parity for a serial port, or you might be asked for the network address for an IPP or Samba printer. 5. Select the make of the print driver (if you don t see the manufacturer of your printer listed, choose PostScript for a PostScript printer or HP for a PCL printer). For the make you choose, you will be able to select a specific model. 6. If the printer is added successfully, the next page you see shows a link to the description of that printer. Click on that link. From the new printer page, you can print a test page or modify the printer configuration. After you are able to print from CUPS, you can return to the CUPS Web-based administration page and do further work with your printers. Here are a few examples of what you can do: . List print jobs. Click Jobs to see what print jobs are currently active from any of the printers configured for this server. Click Show Completed Jobs to see information about jobs that are already printed. . Create a printer class. Click Classes; then click Add Class and identify a name and location for a printer class. Click Continue. Then, from the list of Printers configured on your server, select the ones to go into this class. . View printers. You can click the Printers link from the top of any of the CUPS Web-based administration pages to view the printers you have configured. For each printer that appears, you can click Stop Printer (to stop the printer from printing but still accept print jobs for the queue), Reject Jobs (to not accept any further print jobs for the moment), or Print Test Page (to print a page). Figure 25-2 shows the Printers page.
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638 Part V . Running Servers If CUPS is already running on your computer, you can immediately use CUPS Webbased administration from your Web browser. To see if CUPS is running and start setting up your printers, open a Web browser on the local computer and type the following into its location box: http://localhost:631/admin You are prompted for a valid login name and password. Type the root login name and the root user s password, and then click OK. A screen similar to the one shown in Figure 25-1 appears. Figure 25-1: CUPS provides a Web-based administration tool. By default, Web-based CUPS administration is available only from the local host. To access Web-based CUPS administration from another computer, you must change the /admin section in the /etc/cups/cupsd.conf file. As recommended in the text of this file, you should limit access to CUPS administration from the Web. The following example includes an Allow line to permit access from a host from IP address 10.0.0.5 (you must also change the Listen 127.0.0.1:631 line to listen outside your local host, as described a bit later). AuthType Basic AuthClass System Order Deny, Allow Deny from All Allow From 127.0.0.1 Allow From 10.0.0.5
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Chapter 25 . Running a Print Server 637 . CUPS offers a Web-based interface for adding and managing printers. You can access this service by typing localhost:631 from a Web browser on the computer running the CUPS service. (See the section titled Using Web-Based CUPS Administration, later in this chapter.) The KDE desktop comes with a tool for managing CUPS server features. To launch the KDE CUPS Server Configuration window, type /usr/bin/cupsdconf from a Terminal window. . You also can configure CUPS manually (that is, edit the configuration files and start the cupsd daemon manually). Configuration files for CUPS are contained in the /etc/cups directory. In particular, you might be interested in the cupsd. conf file, which identifies permission, authentication, and other information for the printer daemon, and printers.conf, which identifies addresses and options for configured printers. Use the classes.conf file to define local printer classes. You can print to CUPS from non-UNIX systems as well. For example, you can use a PostScript printer driver to print directly from Windows XP to your CUPS server. You can use CUPS without modification by configuring the XP computer with a PostScript driver that uses http://printservername:631printers/target Printer as its printing port. To use CUPS, you need to have it installed. Most Linux distributions let you choose to add CUPS during the initial system install or will simply add CUPS by default. If CUPS was not added when you first installed your Linux distribution, check your original installation medium (DVD or CD) to see if it is there for you to install now. Fedora, Slackware, SUSE, and other Linux distributions all have CUPS on the first CD or DVD of their installation sets. Setting Up Printers While it is usually best to use the printer administration tools that are specifically built for your distribution, many Linux systems simply rely on the tools that come with the CUPS software package. This section explores how to use CUPS Web-based administration tools that come with every Linux distribution and then examines the printer configuration tool system-config-printer that comes with Fedora and Red Hat Enterprise Linux systems for setting up printers. Using Web-Based CUPS Administration CUPS offers its own Web-based administrative tool for adding, deleting, and modifying printer configurations on your computer. The CUPS print service (using the cupsd daemon) listens on port 631 to provide access to the CUPS Web-based administrative interface. Note
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636 Part V . Running Servers Common UNIX Printing Service (CUPS) CUPS has become the standard for printing from Linux and other UNIX-like operating systems. It was designed to meet today s needs for standardized printer definitions and sharing on IP-based networks (as most computer networks are today). Nearly every Linux distribution today comes with CUPS as its printing service. Here are some of the service s features: . IPP At its heart, CUPS is based on the Internet Printing Protocol (www.pwg. org/ipp), a standard that was created to simplify how printers can be shared over IP networks. In the IPP model, printer servers and clients who want to print can exchange information about the model and features of a printer using HTTP (that is, Web content) protocol. A server could also broadcast the availability of a printer so a printing client could easily find a list of locally available printers. . Drivers CUPS also standardized how printer drivers are created. The idea was to have a common format that could be used by printer manufacturers so that a driver could work across all different types of UNIX systems. That way, a manufacturer only had to create the driver once to work for Linux, Mac OS X, and a variety of UNIX derivatives. . Printer classes You can use printer classes to create multiple print server entries that point to the same printer or one print server entry that points to multiple printers. In the first case, multiple entries could each allow different options (such as pointing to a particular paper tray or printing with certain character sizes or margins). In the second case, you could have a pool of printers so that printing is distributed, decreasing the occurrence of congested print queues often caused by a malfunctioning printer or a printer that is dealing with very large documents. . UNIX print commands To integrate into Linux and other UNIX environments, CUPS offers versions of standard commands for printing and managing printers that have been traditionally offered with UNIX systems. Many Linux distributions come with simplified methods of configuring CUPS printers. Here are two examples: . In Fedora and other Red Hat Linux systems, the Printer Configuration window (system-config-printer command) enables you to configure printers that use the CUPS facility. . In SUSE, the YaST facility includes a printer configuration module. From the YaST Control Center select Hardware.Printer. For distributions that don t have their own printer configuration tools, there are several ways to configure CUPS using tools that aren t specific to a Linux distribution. Here are a couple of them:
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Running a Print Server Sharing printers is a good way to save money and make your printing more efficient. Very few people need to print all the time, but when they do want to print something, they usually need it quickly. Setting up a print server can save money by eliminating the need for a printer at every workstation. Some of those savings can be used to buy printers that can output more pages per minute or have higher-quality output. You can attach printers to your Linux system to make them available to users of that system (standalone printing) or to other computers on the network as a shared printer. You can also configure your Linux printer as a remote CUPS or Samba printer. With Samba, you are emulating Windows printing services, which is pretty useful given the abundance of Windows client systems. This chapter describes configuring and using printers on Linux systems with various desktop environments in use. Some of the details may vary from one distribution to another, but the information included here should work well for the more commonly used distributions. This chapter focuses on Common UNIX Printing Service (CUPS), which is the recommended print service for the majority of Linux installations. Examples in this chapter use the Printer Configuration options in the GNOME and K Desktop environments. Once a local printer is configured, print commands such as lpr are available for carrying out the actual printing. Commands also exist for querying print queues (lpq), manipulating print queues (lpc), and removing print queues (lprm). A local printer can also be shared as a print server for users on other computers on your network. 2C H A5P5T E R . . . . In This Chapter Understanding printing in Linux Setting up printers Using printing commands Managing document printing Sharing printers . . . .
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634 Part V . Running Servers Some remote mail servers may refuse to send messages to you if you are using a certificate that is not signed by a CA that they recognize. If this happens, then you may need to remove the -o smtpd_use_tls=yes option from the smtp line. Replace smtpd_enforce_tls with smtpd_enable_tls on the port 587 line if you need to maintain support for non-TLS clients on that port due to packet filters. 9. Enable SSL/TLS in the Courier-IMAP daemon by editing /etc/courier/ imapd-ssl and replacing the values for TLS_CERTFILE and TLS_TRUSTCERTS with the following: TLS_CERTFILE=/etc/ssl/private/mail.pem TLS_TRUSTCERTS=/etc/ssl/certs/ca-certificates.pem 10. Restart Postfix and the Courier-IMAP daemons: # invoke-rc.d postfix restart # invoke-rc.d courier-imap restart # invoke-rc.d courier-imap-ssl restart 11. Configure your mail clients to use SSL. All SSL-enabled clients should support SSL/TLS when sending to port 465 and when receiving on port 993. Newer clients that support the STARTTLS extension should also be able to use SSL/TLS when sending to port 25 or 587, and when receiving from port 143. Summary Using Linux and a good Internet connection, you can set up and maintain your own mail server. Preparing your computer to become a mail server includes configuring your network connection, setting up delivery and retrieval methods, and adding required software packages. This chapter describes how to install, configure, and troubleshoot two of the most popular open source server packages: sendmail and Postfix. Those packages can be used in tandem with spam filtering software (such as SpamAssassin) and virus scanning software (such as ClamAV). Methods for securing your mail server include configuring support for SSL/TLS encryption. . . . Caution
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Chapter 24 . Running a Mail Server 633 Debconf will ask you whether you want to trust the CA certificates by default. In most cases, you will want to select Yes. 3. If you are going to be using a certificate from a CA that is not already recognized (this is generally only true if you are running your own CA), place the CA public certificate in its own file in /etc/ssl/certs/ and update the certificate database: # update-ca-certificates 4. Generate the private key and certificate signing request, as described in Chapter 23. The best location for these files is /etc/ssl/private/. Here s an example: # cd /etc/ssl/private # umask 0077 # openssl genrsa -out mail.key 1024 # openssl req -new -key mail.key -out mail.csr 5. Get your CSR (Certificate Signing Request) signed and place the certificate in /etc/mail/private/mail.crt. Or, to do a self-signed certificate, do the following: # openssl req -new -x509 -nodes -sha1 -days 365 -key mail.key -out mail.crt Many mail programs will refuse to connect to the server if they do not recognize the certificate. If you are running your own CA, you can overcome this by distributing the CA public key to all clients. 6. Concatenate the private key and certificate into a single file: # cd /etc/ssl/private # umask 0077 # cat mail.key mail.crt >> mail.pem 7. Tell Postfix where to find certificates and keys by adding the following lines to the end of /etc/postfix/main.cf: smtpd_tls_cert_file = /etc/ssl/private/mail.pem smtpd_tls_key_file = $smtpd_tls_cert_file smtpd_tls_CAfile = /etc/ssl/certs/ca-certificates.crt 8. Configure the Postfix daemons to support SSL/TLS by adding -o smtpd_ use_tls=yes to the line in /etc/postfix/master.cf that starts with smtpd. There will also be three commented-out lines at the end of the file that start with tlsmgr, smtps, and 587. Uncomment them and remove the -o smtpd_ sasl_auth_enable=yes parameters. When finished, the lines will look something like this: smtp inet n - - - - smtpd -o smtpd_use_tls=yes (there will be quite a few lines in between) # only used by postfix-tls tlsmgr fifo - - n 300 1 tlsmgr smtps inet n - n - - smtpd -o smtpd_tls_wrappermode=yes 587 inet n - n - - smtpd -o smtpd_enforce_tls=yes Caution
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