Shallow Thoughts : : linux

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Thu, 01 Mar 2018

Re-enabling PHP when a Debian system upgrade disables it

I updated my Debian Testing system via apt-get upgrade, as one does during the normal course of running a Debian system. The next time I went to a locally hosted website, I discovered PHP didn't work. One of my websites gave an error, due to a directive in .htaccess; another one presented pages that were full of PHP code interspersed with the HTML of the page. Ick!

In theory, Debian updates aren't supposed to change configuration files without asking first, but in practice, silent and unexpected Apache bustage is fairly common. But for this one, I couldn't find anything in a web search, so maybe this will help.

The problem turned out to be that /etc/apache2/mods-available/ includes four files:

$ ls /etc/apache2/mods-available/*php*

The appropriate files are supposed to be linked from there into /etc/apache2/mods-enabled. Presumably, I previously had a link to ../mods-available/php7.0.* (or perhaps 7.1?); the upgrade to PHP 7.2 must have removed that existing link without replacing it with a link to the new ../mods-available/php7.2.*.

The solution is to restore those links, either with ln -s or with the approved apache2 commands (as root, of course):

# a2enmod php7.2
# systemctl restart apache2

Whew! Easy fix, but it took a while to realize what was broken, and would have been nice if it didn't break in the first place. Why is the link version-specific anyway? Why isn't there a file called /etc/apache2/mods-available/php.* for the latest version? Does PHP really change enough between minor releases to break websites? Doesn't it break a website more to disable PHP entirely than to swap in a newer version of it?

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[ 10:31 Mar 01, 2018    More linux | permalink to this entry | comments ]

Fri, 02 Feb 2018

Raspberry Pi Console over USB: Configuring an Ethernet Gadget

When I work with a Raspberry Pi from anywhere other than home, I want to make sure I can do what I need to do without a network.

With a Pi model B, you can use an ethernet cable. But that doesn't work with a Pi Zero, at least not without an adapter. The lowest common denominator is a serial cable, and I always recommend that people working with headless Pis get one of these; but there are a lot of things that are difficult or impossible over a serial cable, like file transfer, X forwarding, and running any sort of browser or other network-aware application on the Pi.

Recently I learned how to configure a Pi Zero as a USB ethernet gadget, which lets you network between the Pi and your laptop using only a USB cable. It requires a bit of setup, but it's definitely worth it. (This apparently only works with Zero and Zero W, not with a Pi 3.)

The Cable

The first step is getting the cable. For a Pi Zero or Zero W, you can use a standard micro-USB cable: you probably have a bunch of them for charging phones (if you're not an Apple person) and other devices.

Set up the Pi

Setting up the Raspberry Pi end requires editing two files in /boot, which you can do either on the Pi itself, or by mounting the first SD card partition on another machine.

In /boot/config.txt add this at the end:


In /boot/cmdline.txt, at the end of the long list of options but on the same line, add a space, followed by: modules-load=dwc2,g_ether

Set a static IP address

This step is optional. In theory you're supposed to use some kind of .local address that Bonjour (the Apple protocol that used to be called zeroconf, and before that was called Rendezvous, and on Linux machines is called Avahi). That doesn't work on my Linux machine. If you don't use Bonjour, finding the Pi over the ethernet link will be much easier if you set it up to use a static IP address. And since there will be nobody else on your USB network besides the Pi and the computer on the other end of the cable, there's no reason not to have a static address: you're not going to collide with anybody else.

You could configure a static IP in /etc/network/interfaces, but that interferes with the way Raspbian handles wi-fi via wpa_supplicant and dhcpcd; so you'd have USB networking but your wi-fi won't work any more.

Instead, configure your address in Raspbian via dhcpcd. Edit /etc/dhcpcd.conf and add this:

interface usb0
static ip_address=
static routers=
static domain_name_servers=

This will tell Raspbian to use address for its USB interface. You'll set up your other computer to use

Now your Pi should be ready to boot with USB networking enabled. Plug in a USB cable (if it's a model A or B) or a micro USB cable (if it's a Zero), plug the other end into your computer, then power up the Pi.

Setting up a Linux machine for USB networking

The final step is to configure your local computer's USB ethernet to use

On Linux, find the name of the USB ethernet interface. This will only show up after you've booted the Pi with the ethernet cable plugged in to both machines.

ip a
The USB interface will probably start eith en and will probably be the last interface shown.

On my Debian machine, the USB network showed up as enp0s26u1u1. So I can configure it thusly (as root, of course):

ip a add dev enp0s26u1u1
ip link set dev enp0s26u1u1 up
(You can also use the older ifconfig rather than ip: sudo ifconfig enp0s26u1u1 up)

You should now be able to ssh into your Raspberry Pi using the address, and you can make an appropriate entry in /etc/hosts, if you wish.

For a less hands-on solution, if you're using Mac or Windows, try Adafruit's USB gadget tutorial. It's possible that might also work for Linux machines running Avahi. If you're using Windows, you might prefer CircuitBasics' ethernet gadget tutorial.

Happy networking!

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[ 14:53 Feb 02, 2018    More linux | permalink to this entry | comments ]

Thu, 25 Jan 2018

Tricks for Installing a Laser Printer on Linux in CUPS

(Wherein I rant about how bad CUPS has become.)

I had to set up two new printers recently. CUPS hasn't gotten any better since the last time I bought a printer, maybe five years ago; in fact, it's gotten quite a bit worse. I'm amazed at how difficult it was to add these fairly standard laser printers, both of which I'd researched beforehand to make sure they worked with Linux.

It took me about three hours for the first printer. The second one, a few weeks later, "only" took about 45 minutes ... at which point I realized I'd better write everything down so it'll be faster if I need to do it again, or if I get the silly notion that I might want to print from another computer, like my laptop.

I used the CUPS web interface; I didn't try any of the command-line tools.

Figure out the connection type

In the CUPS web interface, after you log in and click on Administration, whether you click on Find New Printers or Add Printer, you're faced with a bunch of identical options with no clue how to choose between them. For example, Find New Printers with a Dell E310dw connected shows:

Available Printers
  • [Add This Printer] Virtual Braille BRF Printer (CUPS-BRF)
  • [Add This Printer] Dell Printer E310dw (Dell Printer E310dw)
  • [Add This Printer] Dell Printer E310dw (Dell Printer E310dw)
  • [Add This Printer] Dell Printer E310dw (Dell Printer E310dw (driverless))

What is a normal human supposed to do with this? What's the difference between the three E210dw entries and which one am I supposed to choose? (Skipping ahead: None of them.) And why is it finding a virtual Braille BRF Printer?

The only way to find out the difference is to choose one, click on Next and look carefully at the URL. For the three E310dw options above, that gives:

Again skipping ahead: none of those are actually right. Go ahead, try all three of them and see. You'll get error messages about empty PPD files. But while you're trying them, write down, for each one, the URL listed as Connection (something like the dnssd:, lpd: or ipp: URLs listed above); and note, in the driver list after you click on your manufacturer, how many entries there are for your printer model, and where they show up in the list. You'll need that information later.

Download some drivers

Muttering about the idiocy of all this -- why ship empty drivers that won't install? Why not just omit drivers if they're not available? Why use the exact same name for three different printer entries and four different driver entries? -- the next step is to download and install the manufacturer's drivers. If you're on anything but Redhat, you'll probably either need to download an RPM and unpack it, or else google for the hidden .deb files that exist on both Dell's and Brother's websites that their sites won't actually find for you.

It might seem like you could just grab the PPD from inside those RPM files and put it wherever CUPS is finding empty ones, but I never got that to work. Much as I dislike installing proprietary .deb files, for both printers that was the only method I found that worked. Both Dell and Brother have two different packages to install. Why two and what's the difference? I don't know.

Once you've installed the printer driver packages, you can go back to the CUPS Add Printer screen. Which hasn't gotten any clearer than before. But for both the Brother and the Dell, ipp: is the only printer protocol that worked. So try each entry until you find the one that starts with ipp:.

Set up an IP address and the correct URL

But wait, you're not done. Because CUPS gives you a URL like ipp://DELL316BAA.local:631/ipp/print, and whatever that .local thing is, it doesn't work. You'll be able to install the printer, but when you try to print to it it fails with "unable to locate printer".

(.local apparently has something to do with assuming you're running a daemon that does "Bonjour", the latest name for the Apple service discovery protocol that was originally called Rendezvous, then renamed to Zeroconf, then to Bonjour. On Linux it's called Avahi, but even with an Avahi daemon this .local thing didn't work for me. At least it made me realize that I had the useless Avahi daemon running, so now I can remove it.).

So go back to Add Printer and click on Internet Printing Protocol (ipp) under Other network printers and click Continue. That takes you to a screen that suggests that you want URLs like:





None of these is actually right. What these printers want -- at least, what both the Brother and the Dell wanted -- was ipp://printerhostname:631/ipp/print

printerhostname? Oh, did I forget to mention static IP? I definitely recommend that you make a static IP for your printer, or at least add it to your router's DHCP list so it always gets the same address. Then you can make an entry in /etc/hosts for printerhostname. I guess that .local thing was supposed to compensate for an address that changes all the time, which might be a nifty idea if it worked, but since it doesn't, make a static IP and use it in your ipp: URL.

Choose a driver

Now, finally! you can move on to choosing a driver. After you pick the manufacturer, you'll be presented with a list that probably includes at least three entries for your printer model. Here's where it helps if you paid attention to how the list looked before you installed the manufacturer's drivers: if there's a new entry for your printer that wasn't there before, that's the non-empty one you want. If there are two or more new entries for your printer that weren't there before, as there were for the Dell ... shrug, all you can do is pick one and hope.

Of course, once you manage to get through configuration to "Printer successfully added", you should immediately run Maintenance->Print Test Page. You may have to power cycle the printer first since it has probably gone to sleep while you were fighting with CUPS.

All this took me maybe three hours the first time, but it only took me about 45 minutes the second time. Hopefully now that I've written this, it'll be much faster next time. At least if I don't succumb to the siren song of thinking a fairly standard laser printer ought to have a driver that's already in CUPS, like they did a decade ago, instead of always needing a download from the manufacturer.

If laser printers are this hard I don't even want to think about what it's like to install a photo printer on Linux these days.

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[ 16:19 Jan 25, 2018    More linux | permalink to this entry | comments ]

Sun, 17 Sep 2017

Screen Brightness on an Asus 1015e (and other Intel-based laptops)

When I upgraded my Asus laptop to Stretch, one of the things that stopped working was the screen brightness keys (Fn-F5 and Fn-F6). In Debian Jessie they had always just automagically worked without my needing to do anything, so I'd never actually learned how to set brightness on this laptop. The fix, like so many things, is easy once you know where to look.

It turned out the relevant files are in /sys/class/backlight/intel_backlight. cat /sys/class/backlight/intel_backlight/brightness tells you the current brightness; write a number to /sys/class/backlight/intel_backlight/brightness to change it.

That at least got me going (ow my eyes, full brightness is migraine-inducing in low light) but of course I wanted it back on the handy function keys.

I wrote a script named "dimmer", with a symlink to "brighter", that goes like this:


curbright=$(cat /sys/class/backlight/intel_backlight/brightness)
echo dollar zero $0
if [[ $(basename $0) == 'brighter' ]]; then
  newbright=$((curbright + 200))
  newbright=$((curbright - 200))
echo from $curbright to $newbright

sudo sh -c "echo $newbright > /sys/class/backlight/intel_backlight/brightness"

That let me type "dimmer" or "brighter" to the shell to change the brightness, with no need to remember that /sys/class/whatsit path. I got the names of the two function keys by running xev and typing Fn and F5, then Fn and F6. Then I edited my Openbox ~/.config/openbox/rc.xml, and added:

<keybind key="XF86MonBrightnessDown">
  <action name="Execute">
<keybind key="XF86MonBrightnessUp">
  <action name="Execute">

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[ 19:57 Sep 17, 2017    More linux/laptop | permalink to this entry | comments ]

Sun, 30 Jul 2017

Remapping the Caps Lock key on Raspbian

I've remapped my CapsLock key to be another Ctrl key since time immemorial. (Actually, since the ridiculous IBM PC layout replaced the older keyboards that had Ctrl there already, to the left of the A.)

On normal current Debian distros, that's fairly easy: you can edit /etc/default/keyboard to have XKBOPTIONS="ctrl:nocaps.

You might think that would work in Raspbian, since it also has /etc/default/keyboard and raspi-config writes keyboard options to it if you set any (though of course CapsLock isn't among the choices it offers you). But it doesn't work in the PIXEL desktop: there, that key still acts as a Caps Lock.

Apparently lxde (under PIXEL's hood) overrides the keyboard options in /etc/default/keyboard without actually giving you a UI to set them. But you can add your own override by editing ~/.config/lxkeymap.cfg. Make the option line look something like this:

option = ctrl:nocaps

Then when you restart PIXEL, you should have a Control key where CapsLock used to be.

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[ 10:30 Jul 30, 2017    More linux | permalink to this entry | comments ]

Sat, 24 Jun 2017

Mutt: Fixing Erroneous Charsets, part 632

Someone forwarded me a message from the Albuquerque Journal. It was all about "New Mexico\222s schools".

Sigh. I thought I'd gotten all my Mutt charset problems fixed long ago. My system locale is set to en_US.UTF-8, and accented characters in Spanish and in people's names usually show up correctly. But I do see this every now and then.

When I see it, I usually assume it's a case of incorrect encoding: whoever sent it perhaps pasted characters from a Windows Word document or something, and their mailer didn't properly re-encode them into the charset they were using to send the message.

In this case, the message had User-Agent: SquirrelMail/1.4.13. I suspect it came from a "Share this" link on the newspaper's website.

I used vim to look at the source of the message, and it had

Content-Type: text/plain; charset=iso-8859-1
For the bad characters, in vim I saw things like
New Mexico<92>s schools

I checked an old web page I'd bookmarked years ago that had a table of the iso-8859-1 characters, and sure enough, hex 0x92 was an apostrophe. What was wrong?

I got some help on the #mutt IRC channel, and, to make a long story short, that web table I was using was wrong. ISO-8859-1 doesn't include any characters in the range 8x-9x, as you can see on the Wikipedia ISO/IEC 8859-1.

What was happening was that the page was really cp1252: that's where those extra characters, like hex 92/octal 222 for an apostrophe, or hex 96/octal 226 for a dash (nitpick: that's an en dash, but it was used in a context that called for an em dash; if someone is going to use something other than the plain old ASCII dash - you'd think they'd at least use the right one. Sheesh!)

Anyway, the fix for this is to tell mutt when it sees iso-8859-1, use cp1252 instead:

charset-hook iso-8859-1 cp1252

Voilà! Now I could read the article about New Mexico's schools.

A happy find related to this: it turns out there's a better way of looking up ISO-8859 tables, and I can ditch that bookmark to the old, erroneous page. I've known about man ascii forever, but someone I'd never thought to try other charsets. Turns out man iso_8859-1 and man iso_8859-15 have built-in tables too. Nice!

(Sadly, man utf-8 doesn't give a table. Of course, that would be a long man page, if it did!)

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[ 11:06 Jun 24, 2017    More linux | permalink to this entry | comments ]

Fri, 09 Jun 2017

Emacs: Typing dashes in html mode (update for Emacs 24)

Back in 2006, I wrote an article on making a modified copy of sgml-mode.el to make it possible to use double-dashed clauses -- like this -- in HTML without messing up auto-fill mode.

That worked, but the problem is that if you use your own copy of sgml-mode.el, you miss out on any other improvements to HTML and SGML mode. There have been some good ones, like smarter rewrap of paragraphs. I had previously tried lots of ways of customizing sgml-mode without actually replacing it, but never found a way.

Now, in emacs 24.5.1, I've found a easier way that seems to work. The annoying mis-indentation comes from the function sgml-comment-indent-new-line, which sets variables comment-start, comment-start-skip and comment-end and then calls comment-indent-new-line.

All I had to do was redefine sgml-comment-indent-new-line to call comment-indent-new-line without first defining the comment characters:

(defun sgml-comment-indent-new-line (&optional soft)
  (comment-indent-new-line soft))

Finding emacs source

I wondered if it might be better to call whatever underlying indent-new-line function comment-indent-new-line calls, or maybe just to call (newline-and-indent). But how to find the code of comment-indent-new-line?

Happily, describe-function (on C-h f, or if like me you use C-h for backspace, try F-1 h) tells you exactly what file defines a function, and it even gives you a link to click on to view the source. Wonderful!

It turned out just calling (newline-and-indent) wasn't enough, because sgml-comment-indent-new-line typically calls comment-indent-new-line when you've typed a space on the end of a line, and that space gets wrapped and then messes up indentation. But you can fix that by copying just a couple of lines from the source of comment-indent-new-line:

(defun sgml-comment-indent-new-line (&optional soft)
  (save-excursion (forward-char -1) (delete-horizontal-space))

That's a little longer than the other definition, but it's cleaner since comment-indent-new-line is doing all sorts of extra work you don't need if you're not handling comments. I'm not sure that both of the delete-horizontal-space lines are needed: the documentation for delete-horizontal-space says it deletes both forward and backward. But I have to assume they had a good reason for having both: maybe the (forward-char -1) is to guard against spurious spaces already having been inserted in the next line. I'm keeping it, to be safe.

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[ 11:16 Jun 09, 2017    More linux/editors | permalink to this entry | comments ]

Mon, 05 Jun 2017

HTML Email from Mutt

I know, I know. We use mailers like mutt because we don't believe in HTML mail and prefer plaintext. Me, too.

But every now and then a situation comes up where it would be useful to send something with emphasis. Or maybe you need to highlight changes in something. For whatever reason, every now and then I wish I had a way to send HTML mail.

I struggled with that way back, never did find a way, and ended up writing a Python script, to send an HTML page, including images, as email.

Sending HTML Email

But just recently I found a neat mutt hack. It turns out it's quite easy to send HTML mail.

First, edit the HTML source in your usual mutt message editor (or compose the HTML some other way, and insert the file). Note: if there's any quoted text, you'll have to put a <pre> around it, or otherwise turn it into something that will display nicely in HTML.

Write the file and exit the editor. Then, in the Compose menu, type Ctrl-T to edit the attachment type. Change the type from text/plain to text/html.

That's it! Send it, and it will arrive looking like a regular HTML email, just as if you'd used one of them newfangled gooey mail clients. (No inline images, though.)

Viewing HTML Email

Finding out how easy that was made me wonder why the other direction isn't easier. Of course, I have my mailcap set up so that mutt uses lynx automatically to view HTML email:

text/html; lynx -dump %s; nametemplate=%s.html; copiousoutput

Lynx handles things like paragraph breaks and does in okay job of showing links; but it completely drops all emphasis, like bold, italic, headers, and colors. My terminal can display all those styles just fine. I've also tried links, elinks, and w3m, but none of them seem to be able to handle any text styling. Some of them will do bold if you run them interactively, but none of them do italic or colors, and none of them will do bold with -dump, even if you tell them what terminal type you want to use. Why is that so hard?

I never did find a solution, but it's worth noting some useful sites I found along the way. Like tips for testing bold, italics etc. in a terminal:, and for testing whether the terminal supports italics, which gave me these useful shell functions:

echo -e "\e[1mbold\e[0m"
echo -e "\e[3mitalic\e[0m"
echo -e "\e[4munderline\e[0m"
echo -e "\e[9mstrikethrough\e[0m"
echo -e "\e[31mHello World\e[0m"
echo -e "\x1B[31mHello World\e[0m"

ansi()          { echo -e "\e[${1}m${*:2}\e[0m"; }
bold()          { ansi 1 "$@"; }
italic()        { ansi 3 "$@"; }
underline()     { ansi 4 "$@"; }
strikethrough() { ansi 9 "$@"; }
red()           { ansi 31 "$@"; }

And in testing, I found that a lot of fonts didn't offer italics. One that does is Terminus, so if your normal font doesn't, you can run a terminal with Terminus: xterm -fn '-*-terminus-bold-*-*-*-20-*-*-*-*-*-*-*'

Not that it matters since none of the text-mode browsers offer italic anyway. But maybe you'll find some other use for italic in a terminal.

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[ 18:28 Jun 05, 2017    More linux | permalink to this entry | comments ]