Not able to access the CUPS Printer Manager in Firefox when, or after, using a proxy server

Just a quick tip if you are trying to use the CUPS Printer Manager in a Firefox browser window (http://localhost:631/) to add a printer, manage a printer or view print jobs but the brower displays a message such as ‘Connecting to…’ and eventually times out and displays the following message:

 Network Error (tcp_error)

A communication error occurred: “Operation timed out”
The Web Server may be down, too busy, or experiencing other problems preventing it from responding to requests. You may wish to try again at a later time.

For assistance, contact your network support team.

or the following message:

Unable to connect

Firefox can’t establish a connection to the server at

    The site could be temporarily unavailable or too busy. Try again in a few moments.
    If you are unable to load any pages, check your computer’s network connection.
    If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web.

    Try Again

This sometimes happens to me when my laptop is connected to a corporate network and the browser is, or recently was, configured to use a proxy server. Anyway, in Firefox I select ‘Open menu’ > ‘Preferences’ > ‘Network’ > ‘Settings…’ and make sure ‘No proxy’ is selected, then I select ‘Open menu’ > ‘Preferences’ and click on the ‘Clear Now’ button for ‘Cached Web Content’ (I have to click twice to clear the cache, for some reason) and the ‘Clear Now’ button for ‘Offline Web Content and User Data’. After doing this, I can access all the CUPS Printer Manager pages in the browser again.

Installing and configuring the CUPS-PDF virtual printer driver

Some applications, such as LibreOffice, have built-in support for exporting their output to PDF files. For applications without built-in support for creating PDF files there may already be an installed ‘Print to File (PDF)’ driver in your installation that you can use. However, the Print to File (PDF) option does not appear in the list of available printers in all applications. Fortunately, CUPS has a driver named CUPS-PDF which you can install to create a virtual printer that will produce PDF files.

I install the package net-print/cups-pdf and use the CUPS Printer Manager in a browser to set up a virtual printer to ‘print’ PDF files. I use the driver in conjunction with a shell script that calls a utility to display a ‘Save As’ dialogue box so the user can specify the directory and name of the PDF file.

KDialog (KDE/Qt) and Zenity (GTK+) are two well-known dialogue box tools for use in shell scripts (see, for example, the Linux Magazine article Adding graphic elements to your scripts with Zenity and KDialog). However, although I use KDE on my main laptop, I was unable to get KDialog working properly in a shell script launched by the CUPS PDF driver, so I resorted to using Zenity, which I found simple to use and reliable. My shell script using Zenity is listed further down.

Although Zenity has performed this job perfectly for me in all releases of KDE since 2007, it rankled that I could not get KDialog to do the job. However, a couple of Gentoo users were able to use KDialog successfully with the CUPS PDF driver, each with a different approach to the other, but their approaches both consisted of two shell scripts. In contrast, a solution using Zenity uses only one shell script. You can see the KDialog solutions by the two users (Havin_it and sicvolo) in Gentoo Forums thread [TIP] CUPS-PDF “Save As” with kdialog. I was determined to have a single shell script using KDialog, and was able to conflate sicvolo‘s two-script solution. My thanks go to him for his clever code in his two shell scripts, as I would never have worked it out myself. My single shell script using KDialog is listed further down.

First I will explain how to install the CUPS PDF driver package, then how to use the CUPS Printer Manager to install the virtual printer, and finally how to use a shell script with either Zenity or KDialog in order to display a graphical dialogue box prompting you to specify the directory and file name for the PDF file to be created. I use Gentoo Linux, but the procedure will be similar in other distributions (package manager commands excepted).

1.0  Installation of the cups-pdf driver and virtual printer

1.1  Install the cups-pdf package:

# emerge cups-pdf

1.2  Launch a Web browser and enter http://localhost:631/ in the Address bar to display the CUPS Printer Manager.

1.3  Click on ‘Administration’ to call up the Administration page, then click ‘Add Printer’. If prompted, enter the username ‘root’ (without the quotes) and the root user’s password.

1.4  Select ‘CUPS-PDF (Virtual PDF Printer)’ in the list of local printers, and click ‘Continue’.

1.5  Enter a name, decription and location for the virtual printer. For example, I entered ‘Virtual_PDF_Printer’, ‘Virtual PDF Printer’ and ‘Mesh Edge DX’ (without the quotes), respectively. Then click ‘Continue’.

1.6  Select ‘Generic’ in the ‘Make:’ box, and click ‘Continue’.

1.7  Select ‘Generic CUPS-PDF Printer (w/ options) (en)’ in the ‘Model:’ box, and click ‘Add Printer’. The virtual printer should now be available for you to use.

1.8  When you come to print from an application, if you select Virtual_PDF_Printer from the list of available printers the PDF file will be saved in the directory /var/spool/cups-pdf/<your username>/. Note that the directory will be created automatically the first time you ‘print’ to PDF.

1.9  Optionally, you could create a shortcut (Desktop Config File) on your Desktop to open the directory mentioned in Step 1.8 above.

1.10 Optionally, instead of Step 1.9 you could edit the file /etc/cups/cups-pdf.conf as root user to get cups-pdf to ‘print’ PDF documents to your Desktop instead of in /var/spool/cups-pdf/<your username>/, by changing the line:

#Out /var/spool/cups-pdf/${USER}


Out ${HOME}/Desktop

2.0  How to display a dialog box prompting for the directory and file name of the PDF file

If you prefer to be prompted for a file name so that you can save the PDF file wherever you want and give it any name you want, perform the steps below instead of Steps 1.9 or 1.10 above. Either perform the steps in 2.1 (Zenity) or the steps in 2.2 (KDialog). Then perform the steps in 2.3, which apply in both cases.

2.1   Zenity (GTK+)

2.1.1   Install Zenity:

# emerge zenity

2.1.2   Check it is installed:

# eix -I zenity
[I] gnome-extra/zenity
Available versions: 3.12.1 {debug libnotify test +webkit}
Installed versions: 3.12.1(13:49:47 04/12/14)(libnotify webkit -debug -test)
Description: Tool to display dialogs from the commandline and shell scripts

2.1.3   Using a text editor, create the following shell script in your home directory and give it a meaningful name, such as

export DISPLAY
PDFNAME=$(zenity --file-selection --save --confirm-overwrite)

2.2   KDialog (KDE/Qt)

2.2.1   Install KDialog:

# emerge kde-base/kdialog

2.2.2   Check it is installed:

# eix -I kde-base/kdialog
[I] kde-base/kdialog
Available versions: (4) 4.12.5(4/4.12) (~)4.14.2(4/4.14) (~)4.14.3(4/4.14)
{aqua debug}
Installed versions: 4.14.3(4)(00:56:36 04/12/14)(-aqua -debug)
Description: KDialog can be used to show nice dialog boxes from shell scripts

2.2.3   Using a text editor, create the following shell script in your home directory and give it a meaningful name such as


if [ -z $1 ]; then
    echo "specify user" >> $HOME/cups-pdf_script.log
    return 1
# Search these processes for the session variable (they are run as the current user and have the DBUS session variable set)
compatiblePrograms=( kdeinit kded4 pulseaudio trackerd )

# Attempt to get a program pid
for index in ${compatiblePrograms[@]}; do
   PID=$(ps -ef | grep $1 | grep ${index} | head -1 | awk '{print $2}')
   if [[ "${PID}" != "" ]]; then
if [[ "${PID}" == "" ]]; then
   echo "Could not detect active login session" >> $HOME/cups-pdf_script.log
   return 1
QUERY_ENVIRON="$(tr '\0' '\n' < /proc/${PID}/environ | grep "DBUS_SESSION_BUS_ADDRESS" | cut -d "=" -f 2-)"
if [[ "${QUERY_ENVIRON}" != "" ]]; then
#   echo ${QUERY_ENVIRON} >> $HOME/cups-pdf_script.log
   return 0
   echo "Could not find dbus session ID in user environment." >> $HOME/cups-pdf_script.log
   return 1


export DISPLAY=:0
export XAUTHORITY=/home/${CURRENT_USER}/.Xauthority
export HOME=/home/${CURRENT_USER}/

date > $HOME/cups-pdf_script.log

get_dbus ${CURRENT_USER}
if [ $? -eq 0 ]; then
   while [ True ]; do
      CURDATE=$(/bin/date +%Y%m%d)
      CURNAME=$(/bin/cat "$CONFIG_FILE")
      BASENAME=$(basename $CURRENT_PDF)
      FILENAME=$(/usr/bin/kdialog --getsavefilename "$CURNAME$CURDATE-" "*.pdf" --title="Save PDF")
      if [ $? -eq 1 ]; then
      echo $FILENAME
      if [ ! "$FILENAME" = "" ]; then
         if [ -e "$FILENAME" ]; then
            /usr/bin/kdialog --warningcontinuecancel "File already exists"
            if [ $? -eq 1 ]; then
         FILENAME=$(echo $FILENAME.pdf | sed -re "s/(\.pdf)+$/.pdf/g")
         /usr/bin/kdialog --error "You must select a file or hit Cancel."
   if [ "${CANCELLED}" == "No" ]; then
      /bin/cp "${CURRENT_PDF}" "${FILENAME}"
      okular "${FILENAME}" &
   /bin/rm "${CURRENT_PDF}"
   echo "No errors encountered." >> $HOME/cups-pdf_script.log
   exit 0
   /bin/rm "${CURRENT_PDF}"
   echo "Errors encountered." >> $HOME/cups-pdf_script.log
   exit 1

2.3   Whichever of the above two options (Zenity or KDialog) you chose, do the following:

2.3.1   Make the shell script file executable:

# chmod +x /home/<your username>/

2.3.2   Edit the file /etc/cups/cups-pdf.conf, find the line starting with ‘#PostProcessing‘, and change it to:

PostProcessing /home/<your username>/

2.3.3   Restart CUPS:

# /etc/init.d/cupsd restart # If your installation uses OpenRC.

# systemctl restart cups.service # If your installation uses systemd.

Now, when you select Virtual_PDF_Printer from your applications’ list of available printers and click ‘Print’, a pop-up window should appear, allowing you to select the target directory for the PDF file and enter a file name of your choice.