Klaus Knopper answers your Linux questions

Ask Klaus

Article from Issue 153/2013

Klaus Knopper is the creator of Knoppix and co-founder of LinuxTag expo. He works as a teacher, programmer, and consultant. If you have a configuration problem, or if you just want to learn more about how Linux works, send your questions to: klaus@linux-magazine.com

Blind-Friendly Browsing

Hello Klaus: I installed Knoppix 7.0 to a USB stick for a blind user on a different continent. There have been problems in getting it to consistently boot into the Adriane audio desktop, which is necessary, with no visual-only prompting. The user is also diabetic; hence, a braille output device is not usable.

I would appreciate some pointers. I have also just received a cover DVD with Knoppix 7.0.4, which I will try shortly. There is also a matter of a secure login with a different username and password.

It was very interesting to read of [the user's] current websurfing with Microsoft Windows, Internet Explorer, and the "Jaws" screen reader software. It "reads" the whole page, including all the HTML tags. He finds most pages grossly unusable, especially when unduly padded with the Facebook and Twitter buttons, and poorly placed adverts with graphics and no descriptive text.

Many thanks for the excellent work in making Knoppix available.


Modifying boot options for a USB flash disk-installed version of Knoppix is easy and can be done even without booting Knoppix.

Open the file boot/syslinux/syslinux.cfg from the flash disk in your favorite text editor (Leafpad under GNU/Linux; Notepad++ under Windows would be sufficient). The start of the file will look like Listing 1.

Listing 1

Beginning of Knoppix syslinux.cfg


The lines starting with LABEL each define a new section containing a KERNEL (or, in general, a static executable for running an operating system) and an APPEND line. The latter defines variables and options that influence behavior and hardware support, as well as controlling the parameters of scripts that are run at bootup.

The relevant option for the ADRIANE talking desktop is adriane, which activates speech and console menus in Knoppix when the boot scripts detect this option. To make it easier, I added a LABEL for this, so you can just type adriane at the boot: prompt instead of knoppix adriane.

Now, of course, it is difficult to type anything at a boot prompt if the screen is not visible to you, which is where the DEFAULT keyword right at the top of the file comes in handy. DEFAULT defines which LABEL line should be used when you start the system without typing anything, so if you exchange

DEFAULT knoppix

which would start the 32-bit Linux kernel with standard options, with

DEFAULT adriane

which starts the 32-bit Linux kernel with the additional option adriane, then after saving the file, your computer will automatically start the ADRIANE system on next boot. To reduce the delay time that I had set for being able to change boot options, you can change TIMEOUT 100 to TIMEOUT 10 (the number is tenths of a second), which gives you a faster startup.

For changing language and other options, have a look at the APPEND line after the chosen LABEL (adriane); for example, you could make the system boot and translate menus in German by changing lang=en to lang=de.

Some more information about blind-friendly browsers: ADRIANE uses ELinks, which is compiled with (non-graphical) JavaScript support, so self-modifying web pages, which are sometimes used to determine the user's location or display different menu structures, depending on the local computer's settings, have a good chance to work in console mode. ELinks does not read the entire page at once but allows you to jump from link to link using the arrow keys, so you can navigate to the information you are searching for easily and then hit Return to enter the page.

In ADRIANE's Screenreader SBL (i.e., Screenreader for Blind Linux users), you use control keys to access the displayed text (Table 1). ADRIANE also supports starting the graphical environment, employing speech and magnification with graphical programs using the Orca screen reader, which interfaces with the console screen reader, sharing speech and braille support. LibreOffice works pretty well with Orca, but since migration to Gtk3, it became difficult to find a working combination of Orca and Iceweasel (Firefox). I'm unsure whether I can get this fixed for Knoppix 7.2, so I would recommend staying with the console-based ELinks for accessible browsing in ADRIANE for now.

Table 1

Adriane Control Keys



CapsLock Space

Read the current line of text

CapsLock PageUp

Read from top of screen to current position

CapsLock PageDown

Read from current position to end of screen

PageUp/PageDown (no CapsLock)

Previous/Next screen page

CapsLock ArrowUp

Change reading position to one line up

CapsLock ArrowDown

Change reading position to one line down

CapsLock ArrowLeft

Spell character to the left of cursor

CapsLock ArrowRight

Spell character to the right of cursor

CapsLock F1 or F2

Slower or faster speech

CapsLock F3 or F4

Tune voice pitch lower or higher

CapsLock F5 or F6

Decrease or increase volume of voice

CapsLock F7 or F8

Select previous or next speech language/accent; these are predefined in SBL's configuration file /etc/sbl/spk/speechd

CapsLock Pos1 or End

Read first or last line of screen

Alt+F1… Alt+F10

Switch to virtual console 1 … 10; a separate ADRIANE menu is on each virtual console, so you can run programs in parallel and switch between them with the associated Alt+Fn key

Live Browsing

Hello Klaus: I have the Knoppix 7.04 disks from Linux Pro magazine for both December 2012 and February 2013, and in both disks, the Remove disk and Hit return feature don't work. Additionally, the Konqueror browser has server authentication issues, and the browsers do not work. Does this mean that if I were to install Knoppix 7.04 onto my computers from these disks, Knoppix would behave incorrectly?

Thanks, Steve

Knoppix installed on a hard disk should behave just the same as it did when running from a Live system, which also means that the same fix or workaround that works for the Live system should also work for a hard disk-installed version.

I always recommend the install on flash disk variant, however, because Knoppix is designed to run from mobile data storage and detect hardware, so it can run on many computers. Installing Knoppix on a hard disk, and thus decompressing the data, will not give you much advantage compared with a plain Debian or Ubuntu hard disk installation.

I'll start with the browsers: For Iceweasel (Firefox) and Chromium, I have configured the browsers so they block "active" content like plugins and certain JavaScript constructs by default, to allow safe browsing.

Konqueror is basically installed "as is," and would only be started in combination with KDE programs; otherwise, Iceweasel is the default browser. Konqueror, Iceweasel, and Chromium all have different ways of storing authentication data, and the settings to handle special characters like umlauts might have different presets.

If you decide to use Konqueror, you will have to go through its settings and check to see whether needed cookies are enabled, whether JavaScript (if needed for the authenticated website in question) is enabled, and whether the correct character set is being used (otherwise, non-ASCII characters could arrive scrambled at the server with which you are trying to authenticate).

The please remove CD and hit return at the end of your Knoppix session only appears in the DVD or CD version. At this time, all programs should have ended and there should be no more references to the CD-ROM, which would keep it from unmounting and being ejected. Apparently, if your CD tray refuses to return the CD, something might have crashed or a process might be keeping your CD drive busy. It would be interesting for me to find out how this happened: Maybe you have a clue that a program refuses to start when running from CD or just sits there and waits for something?

Also, crashing kernel modules can halt a program, especially network drive mounts or access to Internet services. If they are stalled for some reason, the corresponding process cannot be terminated; therefore, the CD cannot be ejected.

If you just hit Return, as the shutdown message tells you, your computer should switch off anyway. If it doesn't, the ACPI or APM power management functions might be disabled; thus, the computer cannot be switched off by software alone. In this case, another message should appear saying you can now turn off your computer.

Internal Hard Disks and PCManFM

Klaus: Hello, I got a strange problem after creating a new account and setting the default session to lxsession. PCManFM, the file manager in LXDE, will only display new devices like USB flash disks or CD-ROMs, but not devices that are already there. Is this a bug?

The default setting for PCManFM is to display only removable devices (i.e., devices that have the removable flag set in /sys/block/sd*/removable. I changed this setting for Knoppix to allow internal hard disks and partitions to display as well.

The setting lives in file $HOME/.config/libfm/libfm.conf in the section marked [config]:


Depending on the version of PCManFM you use, a checkbox for this could be missing in the PCManFM Preferences GUI, so using a text editor for enabling internal hard disks in the file browser is the easiest way. You might have to restart PCManFM for the new setting to take effect.

The Author

Klaus Knopper is the creator of Knoppix and co-founder of LinuxTag expo. He currently works as a teacher, programmer, and consultant. If you have a configuration problem, or if you just want to learn more about how Linux works, send your questions to: mailto:klaus@linux-magazine.com

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