章 9. 列印

儘管很多人試圖淘汰列印功能,但列印資訊到紙上仍是一個重要的功能。列印由兩個基本元件組成,包含了資料傳送到印表機的方式以及印表機可以理解的資料形式。

9.1. 快速開始

基本的列印功能可以快速設定完成,列印機必須能夠列印純 ASCII 文字。若要列印其他類型的檔案,請參考 過濾器

  1. 建立一個目錄來儲存要被列印的檔案:

    # mkdir -p /var/spool/lpd/lp
    # chown daemon:daemon /var/spool/lpd/lp
    # chmod 770 /var/spool/lpd/lp
  2. root 建立 /etc/printcap 內容如下:

    lp:\
    	:lp=/dev/unlpt0:\  (1)
    	:sh:\
    	:mx#0:\
    	:sd=/var/spool/lpd/lp:\
    	:lf=/var/log/lpd-errs:
    1此行是針對連接到 USB 埠的印表機。連接到並列或 "印表器 (Printer)" 埠的印表機要使用:直接連接到網路的印表機要使用:替換 network-printer-name 為網路印表機的 DNS 主機名稱。
  3. 編輯 /etc/rc.conf 加入下行來開啟 lpd

    lpd_enable="YES"

    啟動服務:

    # service lpd start
    Starting lpd.
  4. 測試列印:

    # printf "1. This printer can print.\n2. This is the second line.\n" | lpr

    若列印的兩行未從左邊界開始,而是呈現 "階梯狀 (Stairstep)",請參考 避免在純文字印表機階梯狀列印

    現在可以使用 lpr 來列印文字檔,只要在指令列給序檔案名稱,或者將輸出使用管線符號 (Pipe) 傳送給 lpr

    % lpr textfile.txt
    % ls -lh | lpr

9.2. 印表機連線

印表機有許多方式可以連接到電腦,小型的桌面印表機會直接連接到電腦的 USB 埠,舊式的印表機會連接到並列 (Parallel) 或 "印表機 (Printer)" 埠,而有一部份印表機則是直接連接網路,讓印表機能夠給多台電腦共享使用,還有少部分印表機則是連接到較罕見的序列 (Serial) 埠。

FreeBSD 可以與這些類型的印表機溝通。

USB

USB 印表機可以連接到電腦上任何可用的 USB 埠。

當 FreeBSD 偵測到 USB 印表機,會建立兩個裝置項目:/dev/ulpt0 以及 /dev/unlpt0,傳送到兩者任一裝置的資料都會被轉發到印表機。在每個列印工作完成後 ulpt0 便會重設 USB 埠,重設 USB 埠可能會在部份印表機造成問題,因此通常可以改使用 unlpt0 裝置。unlpt0 不會重設 USB 埠。

並列 (IEEE-1284)

並列埠裝置使用 /dev/lpt0,此裝置不論印表機是否連接上都會存在,它並不會自動偵測。

供應商已不再採用這種 "舊式" 連接埠,且有許多電腦甚至已沒有這種連接埠。可以用轉接器來連接並列印表機到 USB 埠,有了轉接器,並列印表機可以被當作 USB 印表機使用。有另一種稱作 列印伺服器 (Print server) 的裝置也可用來連接並列印表機到網路。

序列 (RS-232)

序列埠也是另一種舊式連接埠,已很少用在印表機上,除了某些特殊的應用外,纜線、接頭與需要的佈線方式依需求變化性很大。

內建在主機板的序列埠的序列裝置名稱為 /dev/cuau0/dev/cuau1。也有序列 USB 轉接器可使用,而裝置的的名稱則會是 /dev/cuaU0

要與序列印表機通訊必須知道數個通訊參數,其中最重要的是 傳輸速率 (Baud rate) 或 BPS (Bits Per Second) 以及 同位檢查 (Parity)。數值有數種,但一般序列印表機會使用 的傳輸速率是 9600 且無同位檢查。

網路

網路印表機可直接連接到區域網路。

若印表機透過 DHCP 分配動態位址,則必須要知道 DNS 主機名稱,DNS 應動態更新來讓主機名稱能夠對應到正確的 IP 位址。指定網路印表機一個靜態的 IP 位址可避免這個問題。

大多數網路印表機可以認得使用 LPD 通訊協定所送出的列印工作,列印佇列 (Print queue) 的名稱也會在這時指定。部份印表機會依據使用的佇列來決定處理資料的方式,例如 raw 佇列會列印原始資料,而 text 佇列則會在純文字上增加換行符號 (Carriage return)。

大部份網路印表機也可列印直接傳送到埠號 9100 的資料。

9.2.1. 摘要

有線網路連線通常是安裝最簡單的方式,且可以提供快速的列印。若要直接連接到電腦,較建議使用 USB,由於較快速、簡單。並列連線仍然可以使用,但有纜線長度與速度上的限制。而序列連線則比較難設定,不同型號的纜線佈線方式不同,且通訊參數如傳輸速率及同位檢查增加了複雜性,所幸序列印表機並不多。

9.3. 常見的頁面描述語言

傳送給印表機的資料必須使用印表機能夠理解的語言,這些語言稱為頁面描述語言 (Page Description Languages) 或 PDL。

Port 套件集與 FreeBSD 工具集有許多可以處理 PostScript™ 輸出的應用程式,此表整理出了可轉換 PostScript™ 成其他常用 PDL 的工具:

要可以列印最簡單的方式就是選擇支援 PostScript™ 的印表機,再來是支援 PCL 的印表機,有了 print/ghostscript9-base 這些印表機也可像原生支援 PostScript™ 的印表機一般使用。有直接支援 PostScript™ 或 PCL 的印表機通常也會直接支援純 ASCII 文字檔案。

行列式印表機如同典型的噴墨式印表機通常不支援 PostScript™ 或 PCL,這種印表機通常可以列印純 ASCII 文字檔案。print/ghostscript9-base 支援部份這種印表機使用的 PDL,不過要在這種印表機上列印完全以圖型為基礎的頁面通常會非常緩慢,由於需要傳送大量的資料並列印。

以主機為基礎的印表機通常較難設定,有些會因為用了專用的 PDL 而無法使用,盡可能避免使用這類的印表機。

有關各種 PDL 的介紹可至 http://www.undocprint.org/formats/page_description_languages。各種型號印表機所使用的特定 PDL 可至 http://www.openprinting.org/printers 查詢。

9.4. 直接列印

對於偶爾列印,檔案可以直接傳送到印表機裝置,無需做任何設定。例如,要傳送一個名稱為 sample.txt 的檔案到 USB 印表機:

# cp sample.txt /dev/unlpt0

要直接使用網路印表機列印需看該印表機支援的功能,但大多數會接受埠號 9100 的列印作業,可使用 nc(1) 來完成。要使用 DNS 主機名稱為 netlaser 的印表機列印與上述相同的檔案可:

# nc netlaser 9100 < sample.txt

9.5. LPD (行列式印表機 Daemon)

在背景列印一個檔案稱作 Spooling,緩衝程式 (Spooler) 讓使用者能夠繼續執行電腦的其他程式而不需要等候印表機緩慢的完成列印工作。

FreeBSD 內含的緩衝程式 (Spooler) 稱作 lpd(8),而列印工作會使用 lpr(1) 來提交。

9.5.1. 初始設定

建立要用來儲存列印工作的目錄、設定擁有關係以及權限來避免其他使用者可以檢視這些檔案的內容:

# mkdir -p /var/spool/lpd/lp
# chown daemon:daemon /var/spool/lpd/lp
# chmod 770 /var/spool/lpd/lp

印表機會定義在 /etc/printcap,每台印表機項目所包含的詳細資料有名稱、連接的接頭以及各種其他設定。建立 /etc/printcap 使用以下內容:

lp:\				(1)
	:lp=/dev/unlpt0:\	(2)
	:sh:\			(3)
	:mx#0:\			(4)
	:sd=/var/spool/lpd/lp:\	(5)
	:lf=/var/log/lpd-errs:	(6)
1印表機的名稱。 lpr(1) 會傳送列印工作到 lp 印表機,除非有使用 -P 來指定其他印表機,所以預的印表機名稱應使用 lp
2印表機所連接到裝置。替換此行為正確的連線類型,如此處所示。
3在列印工作開始時不列印首頁。
4不限制列印工作的最大尺寸。
5此印表機的緩衝 (Spooling) 目錄路徑,每台印表機會自己使用一個獨立的緩衝 (Spooling) 目錄。
6回報此印表機的錯誤的日誌檔。

在建立 /etc/printcap 之後,使用 chkprintcap(8) 測試印表機是否有錯誤:

# chkprintcap

在繼續之前修正任何回報的問題。

開啟 /etc/rc.conf 中的 lpd(8)

lpd_enable="YES"

啟動服務:

# service lpd start

9.5.2. 使用 lpr(1) 列印

Documents are sent to the printer with lpr. A file to be printed can be named on the command line or piped into lpr. These two commands are equivalent, sending the contents of doc.txt to the default printer:

% lpr doc.txt
% cat doc.txt | lpr

Printers can be selected with -P. To print to a printer called laser:

% lpr -Plaser doc.txt

9.5.3. 過濾器

The examples shown so far have sent the contents of a text file directly to the printer. As long as the printer understands the content of those files, output will be printed correctly.

Some printers are not capable of printing plain text, and the input file might not even be plain text.

Filters allow files to be translated or processed. The typical use is to translate one type of input, like plain text, into a form that the printer can understand, like PostScript™ or PCL. Filters can also be used to provide additional features, like adding page numbers or highlighting source code to make it easier to read.

The filters discussed here are input filters or text filters. These filters convert the incoming file into different forms. Use su(1) to become root before creating the files.

Filters are specified in /etc/printcap with the if= identifier. To use /usr/local/libexec/lf2crlf as a filter, modify /etc/printcap like this:

lp:\
	:lp=/dev/unlpt0:\
	:sh:\
	:mx#0:\
	:sd=/var/spool/lpd/lp:\
	:if=/usr/local/libexec/lf2crlf:\   (1)
	:lf=/var/log/lpd-errs:
1if= identifies the input filter that will be used on incoming text.

The backslash line continuation characters at the end of the lines in printcap entries reveal that an entry for a printer is really just one long line with entries delimited by colon characters. An earlier example can be rewritten as a single less-readable line:

lp:lp=/dev/unlpt0:sh:mx#0:sd=/var/spool/lpd/lp:if=/usr/local/libexec/lf2crlf:lf=/var/log/lpd-errs:

9.5.3.1. 避免在純文字印表機階梯狀列印

Typical FreeBSD text files contain only a single line feed character at the end of each line. These lines will "stairstep" on a standard printer:

A printed file looks
                    like the steps of a staircase
                                                 scattered by the wind

A filter can convert the newline characters into carriage returns and newlines. The carriage returns make the printer return to the left after each line. Create /usr/local/libexec/lf2crlf with these contents:

#!/bin/sh
CR=$'\r'
/usr/bin/sed -e "s/$/${CR}/g"

Set the permissions and make it executable:

# chmod 555 /usr/local/libexec/lf2crlf

Modify /etc/printcap to use the new filter:

:if=/usr/local/libexec/lf2crlf:\

Test the filter by printing the same plain text file. The carriage returns will cause each line to start at the left side of the page.

9.5.3.2. 使用 print/enscript 在 PostScript™ 印表機美化純文字內容

GNUEnscript converts plain text files into nicely-formatted PostScript™ for printing on PostScript™ printers. It adds page numbers, wraps long lines, and provides numerous other features to make printed text files easier to read. Depending on the local paper size, install either print/enscript-letter or print/enscript-a4 from the Ports Collection.

Create /usr/local/libexec/enscript with these contents:

#!/bin/sh
/usr/local/bin/enscript -o -

Set the permissions and make it executable:

# chmod 555 /usr/local/libexec/enscript

Modify /etc/printcap to use the new filter:

:if=/usr/local/libexec/enscript:\

Test the filter by printing a plain text file.

9.5.3.3. 列印 PostScript™ 到 PCL 印表機

Many programs produce PostScript™ documents. However, inexpensive printers often only understand plain text or PCL. This filter converts PostScript™ files to PCL before sending them to the printer.

由 Port 套件集安裝 Ghostscript PostScript™ 直譯器,print/ghostscript9-base

Create /usr/local/libexec/ps2pcl with these contents:

#!/bin/sh
/usr/local/bin/gs -dSAFER -dNOPAUSE -dBATCH -q -sDEVICE=ljet4 -sOutputFile=- -

Set the permissions and make it executable:

# chmod 555 /usr/local/libexec/ps2pcl

PostScript™ input sent to this script will be rendered and converted to PCL before being sent on to the printer.

Modify /etc/printcap to use this new input filter:

:if=/usr/local/libexec/ps2pcl:\

Test the filter by sending a small PostScript™ program to it:

% printf "%%\!PS \n /Helvetica findfont 18 scalefont setfont \
72 432 moveto (PostScript printing successful.) show showpage \004" | lpr

9.5.3.4. 智慧過濾器

A filter that detects the type of input and automatically converts it to the correct format for the printer can be very convenient. The first two characters of a PostScript™ file are usually %!. A filter can detect those two characters. PostScript™ files can be sent on to a PostScript™ printer unchanged. Text files can be converted to PostScript™ with Enscript as shown earlier. Create /usr/local/libexec/psif with these contents:

#!/bin/sh
#
#  psif - Print PostScript or plain text on a PostScript printer
#
IFS="" read -r first_line
first_two_chars=`expr "$first_line" : '\(..\)'`

case "$first_two_chars" in
%!)
    # %! : PostScript job, print it.
    echo "$first_line" && cat && exit 0
    exit 2
    ;;
*)
    # otherwise, format with enscript
    ( echo "$first_line"; cat ) | /usr/local/bin/enscript -o - && exit 0
    exit 2
    ;;
esac

Set the permissions and make it executable:

# chmod 555 /usr/local/libexec/psif

Modify /etc/printcap to use this new input filter:

:if=/usr/local/libexec/psif:\

Test the filter by printing PostScript™ and plain text files.

9.5.3.5. 其他智慧過濾器

Writing a filter that detects many different types of input and formats them correctly is challenging. print/apsfilter from the Ports Collection is a smart "magic" filter that detects dozens of file types and automatically converts them to the PDL understood by the printer. See http://www.apsfilter.org for more details.

9.5.4. 多序列

The entries in /etc/printcap are really definitions of queues. There can be more than one queue for a single printer. When combined with filters, multiple queues provide users more control over how their jobs are printed.

As an example, consider a networked PostScript™ laser printer in an office. Most users want to print plain text, but a few advanced users want to be able to print PostScript™ files directly. Two entries can be created for the same printer in /etc/printcap:

textprinter:\
	:lp=9100@officelaser:\
	:sh:\
	:mx#0:\
	:sd=/var/spool/lpd/textprinter:\
	:if=/usr/local/libexec/enscript:\
	:lf=/var/log/lpd-errs:

psprinter:\
	:lp=9100@officelaser:\
	:sh:\
	:mx#0:\
	:sd=/var/spool/lpd/psprinter:\
	:lf=/var/log/lpd-errs:

Documents sent to textprinter will be formatted by the /usr/local/libexec/enscript filter shown in an earlier example. Advanced users can print PostScript™ files on psprinter, where no filtering is done.

This multiple queue technique can be used to provide direct access to all kinds of printer features. A printer with a duplexer could use two queues, one for ordinary single-sided printing, and one with a filter that sends the command sequence to enable double-sided printing and then sends the incoming file.

9.5.5. 監視與控制列印

Several utilities are available to monitor print jobs and check and control printer operation.

9.5.5.1. lpq(1)

lpq(1) shows the status of a user’s print jobs. Print jobs from other users are not shown.

Show the current user’s pending jobs on a single printer:

% lpq -Plp
Rank   Owner      Job  Files                                 Total Size
1st    jsmith     0    (standard input)                      12792 bytes

Show the current user’s pending jobs on all printers:

% lpq -a
lp:
Rank   Owner      Job  Files                                 Total Size
1st    jsmith     1    (standard input)                      27320 bytes

laser:
Rank   Owner      Job  Files                                 Total Size
1st    jsmith     287  (standard input)                      22443 bytes

9.5.5.2. lprm(1)

lprm(1) is used to remove print jobs. Normal users are only allowed to remove their own jobs. root can remove any or all jobs.

Remove all pending jobs from a printer:

# lprm -Plp -
dfA002smithy dequeued
cfA002smithy dequeued
dfA003smithy dequeued
cfA003smithy dequeued
dfA004smithy dequeued
cfA004smithy dequeued

Remove a single job from a printer. lpq(1) is used to find the job number.

% lpq
Rank   Owner      Job  Files                                 Total Size
1st    jsmith     5    (standard input)                      12188 bytes
% lprm -Plp 5
dfA005smithy dequeued
cfA005smithy dequeued

9.5.5.3. lpc(8)

lpc(8) is used to check and modify printer status. lpc is followed by a command and an optional printer name. all can be used instead of a specific printer name, and the command will be applied to all printers. Normal users can view status with lpc(8). Only root can use commands which modify printer status.

Show the status of all printers:

% lpc status all
lp:
	queuing is enabled
	printing is enabled
	1 entry in spool area
	printer idle
laser:
	queuing is enabled
	printing is enabled
	1 entry in spool area
	waiting for laser to come up

Prevent a printer from accepting new jobs, then begin accepting new jobs again:

# lpc disable lp
lp:
	queuing disabled
# lpc enable lp
lp:
	queuing enabled

Stop printing, but continue to accept new jobs. Then begin printing again:

# lpc stop lp
lp:
	printing disabled
# lpc start lp
lp:
	printing enabled
	daemon started

Restart a printer after some error condition:

# lpc restart lp
lp:
	no daemon to abort
	printing enabled
	daemon restarted

Turn the print queue off and disable printing, with a message to explain the problem to users:

# lpc down lp Repair parts will arrive on Monday
lp:
	printer and queuing disabled
	status message is now: Repair parts will arrive on Monday

Re-enable a printer that is down:

# lpc up lp
lp:
	printing enabled
	daemon started

See lpc(8) for more commands and options.

9.5.6. 分享印表機

Printers are often shared by multiple users in businesses and schools. Additional features are provided to make sharing printers more convenient.

9.5.6.1. 別名

The printer name is set in the first line of the entry in /etc/printcap. Additional names, or aliases, can be added after that name. Aliases are separated from the name and each other by vertical bars:

lp|repairsprinter|salesprinter:\

Aliases can be used in place of the printer name. For example, users in the Sales department print to their printer with

% lpr -Psalesprinter sales-report.txt

Users in the Repairs department print to their printer with

% lpr -Prepairsprinter repairs-report.txt

All of the documents print on that single printer. When the Sales department grows enough to need their own printer, the alias can be removed from the shared printer entry and used as the name of a new printer. Users in both departments continue to use the same commands, but the Sales documents are sent to the new printer.

9.5.6.2. 頁首

It can be difficult for users to locate their documents in the stack of pages produced by a busy shared printer. Header pages were created to solve this problem. A header page with the user name and document name is printed before each print job. These pages are also sometimes called banner or separator pages.

Enabling header pages differs depending on whether the printer is connected directly to the computer with a USB, parallel, or serial cable, or is connected remotely over a network.

Header pages on directly-connected printers are enabled by removing the :sh:\ (Suppress Header) line from the entry in /etc/printcap. These header pages only use line feed characters for new lines. Some printers will need the /usr/shared/examples/printing/hpif filter to prevent stairstepped text. The filter configures PCL printers to print both carriage returns and line feeds when a line feed is received.

Header pages for network printers must be configured on the printer itself. Header page entries in /etc/printcap are ignored. Settings are usually available from the printer front panel or a configuration web page accessible with a web browser.

9.5.7. 參考文獻

Example files: /usr/shared/examples/printing/.

The 4.3BSD Line Printer Spooler Manual, /usr/shared/doc/smm/07.lpd/paper.ascii.gz.

9.6. 其他列印系統

Several other printing systems are available in addition to the built-in lpd(8). These systems offer support for other protocols or additional features.

9.6.1. CUPS (Common UNIX™ Printing System)

CUPS is a popular printing system available on many operating systems. Using CUPS on FreeBSD is documented in a separate article: CUPS

9.6.2. HPLIP

Hewlett Packard provides a printing system that supports many of their inkjet and laser printers. The port is print/hplip. The main web page is at http://hplipopensource.com/hplip-web/index.html. The port handles all the installation details on FreeBSD. Configuration information is shown at http://hplipopensource.com/hplip-web/install/manual/hp_setup.html.

9.6.3. LPRng

LPRng was developed as an enhanced alternative to lpd(8). The port is sysutils/LPRng. For details and documentation, see http://www.lprng.com/.


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