Shallow Thoughts : : linux

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

Fri, 05 Feb 2016

Updating Debian under a chroot

Debian's Unstable ("Sid") distribution has been terrible lately. They're switching to a version of X that doesn't require root, and apparently the X transition has broken all sorts of things in ways that are hard to fix and there's no ETA for when things might get any better.

And, being Debian, there's no real bug system so you can't just CC yourself on the bug to see when new fixes might be available to try. You just have to wait, try every few days and see if the system

That's hard when the system doesn't work at all. Last week, I was booting into a shell but X wouldn't run, so at least I could pull updates. This week, X starts but the keyboard and mouse don't work at all, making it hard to run an upgrade. has been fixed.

Fortunately, I have an install of Debian stable ("Jessie") on this system as well. When I partition a large disk I always reserve several root partitions so I can try out other Linux distros, and when running the more experimental versions, like Sid, sometimes that's a life saver. So I've been running Jessie while I wait for Sid to get fixed. The only trick is: how can I upgrade my Sid partition while running Jessie, since Sid isn't usable at all?

I have an entry in /etc/fstab that lets me mount my Sid partition easily:

/dev/sda6 /sid ext4 defaults,user,noauto,exec 0 0
So I can type mount /sid as myself, without even needing to be root.

But Debian's apt upgrade tools assume everything will be on /, not on /sid. So I'll need to use chroot /sid (as root) to change the root of the filesystem to /sid. That only affects the shell where I type that command; the rest of my system will still be happily running Jessie.

Mount the special filesystems

That mostly works, but not quite, because I get a lot of errors like permission denied: /dev/null.

/dev/null is a device: you can write to it and the bytes disappear, as if into a black hole except without Hawking radiation. Since /dev is implemented by the kernel and udev, in the chroot it's just an empty directory. And if a program opens /dev/null in the chroot, it might create a regular file there and actually write to it. You wouldn't want that: it eats up disk space and can slow things down a lot.

The way to fix that is before you chroot: mount --bind /dev /sid/dev which will make /sid/dev a mirror of the real /dev. It has to be done before the chroot because inside the chroot, you no longer have access to the running system's /dev.

But there is a different syntax you can use after chrooting:

mount -t proc proc proc/
mount --rbind /sys sys/
mount --rbind /dev dev/

It's a good idea to do this for /proc and /sys as well, and Debian recommends adding /dev/pts (which must be done after you've mounted /dev), even though most of these probably won't come into play during your upgrade.

Mount /boot

Finally, on my multi-boot system, I have one shared /boot partition with kernels for Jessie, Sid and any other distros I have installed on this system. (That's somewhat hard to do using grub2 but easy on Debian though you may need to turn off auto-update and Debian is making it harder to use extlinux now.) Anyway, if you have a separate /boot partition, you'll want it mounted in the chroot, in case the update needs to add a new kernel. Since you presumably already have the same /boot mounted on the running system, use mount --bind for that as well.

So here's the final set of commands to run, as root:

mount /sid
mount --bind /proc /sid/proc
mount --bind /sys /sid/sys
mount --bind /dev /sid/dev
mount --bind /dev/pts /sid/dev/pts
mount --bind /boot /sid/boot
chroot /sid

And then you can proceed with your apt-get update, apt-get dist-upgrade etc. When you're finished, you can unmount everything with one command:

umount --recursive /sid

Some helpful background reading:

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[ 11:43 Feb 05, 2016    More linux/install | permalink to this entry | comments ]

Sun, 31 Jan 2016

Setting mouse speed in X

My mouse died recently: the middle button started bouncing, so a middle button click would show up as two clicks instead of one. What a piece of junk -- I only bought that Logitech some ten years ago! (Seriously, I'm pretty amazed how long it lasted, considering it wasn't anything fancy.)

I replaced it with another Logitech, which turned out to be quite difficult to find. Turns out most stores only sell cordless mice these days. Why would I want something that depends on batteries to use every day at my desktop?

But I finally found another basic corded Logitech mouse (at Office Depot). Brought it home and it worked fine, except that the speed was way too fast, much faster than my old mouse. So I needed to find out how to change mouse speed.

X11 has traditionally made it easy to change mouse acceleration, but that wasn't what I wanted. I like my mouse to be fairly linear, not slow to start then suddenly zippy. There's no X11 property for mouse speed; it turns out that to set mouse speed, you need to call it Deceleration.

But first, you need to get the ID for your mouse.

$ xinput list| grep -i mouse
⎜   ↳ Logitech USB Optical Mouse                id=11   [slave  pointer  (2)]

Armed with the ID of 11, we can find the current speed (deceleration) and its ID:

$ xinput list-props 11 | grep Deceleration
        Device Accel Constant Deceleration (259):       3.500000
        Device Accel Adaptive Deceleration (260):       1.000000

Constant deceleration is what I want to set, so I'll use that ID of 259 and set the new deceleration to 2:

$ xinput set-prop 11 259 2

That's fine for doing it once. But what if you want it to happen automatically when you start X? Those constants might all stay the same, but what if they don't?

So let's build a shell pipeline that should work even if the constants aren't.

First, let's get the mouse ID out of xinput list. We want to pull out the digits immediately following "id=", and nothing else.

$ xinput list | grep Mouse | sed 's/.*id=\([0-9]*\).*/\1/'

Save that in a variable (because we'll need to use it more than once) and feed it in to list-props to get the deceleration ID. Then use sed again, in the same way, to pull out just the thing in parentheses following "Deceleration":

$ mouseid=$(xinput list | grep Mouse | sed 's/.*id=\([0-9]*\).*/\1/')
$ xinput list-props $mouseid | grep 'Constant Deceleration'
        Device Accel Constant Deceleration (262):       2.000000
$ xinput list-props $mouseid | grep 'Constant Deceleration' | sed 's/.* Deceleration (\([0-9]*\)).*/\1/'

Whew! Now we have a way of getting both the mouse ID and the ID for the "Constant Deceleration" parameter, and we can pass them in to set-prop with our desired value (I'm using 2) tacked onto the end:

$ xinput set-prop $mouseid $(xinput list-props $mouseid | grep 'Constant Deceleration' | sed 's/.* Deceleration (\([0-9]*\)).*/\1/') 2

Add those two lines (setting the mouseid, then the final xinput line) wherever your window manager will run them when you start X. For me, using Openbox, they go in .config/openbox/autostart. And now my mouse will automatically be the speed I want it to be.

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[ 13:42 Jan 31, 2016    More linux | permalink to this entry | comments ]

Sun, 27 Dec 2015

Extlinux on Debian Jessie

Debian "Sid" (unstable) stopped working on my Thinkpad X201 as of the last upgrade -- it's dropping mouse and keyboard events. With any luck that'll get straightened out soon -- I hear I'm not the only one having USB problems with recent Sid updates. But meanwhile, fortunately, I keep a couple of spare root partitions so I can try out different Linux distros. So I decided to switch to the current Debian stable version, "Jessie".

The mouse and keyboard worked fine there. Except it turned out I had never fully upgraded that partition to the "Jessie"; it was still on "Wheezy". So, with much trepidation, I attempted an apt-get update; apt-get dist-upgrade

After an interminable wait for everything to download, though, I was faced with a blue screen asking this:

No bootloader integration code anymore.
The extlinux package does not ship bootloader integration anymore.
If you are upgrading to this version of EXTLINUX your system will not boot any longer if EXTLINUX was the only configured bootloader.
Please install GRUB.

No -- it's not okay! I have good reasons for not using grub2 -- besides which, extlinux on exact machine has been working fine for years under Debian Sid. If it worked on Wheezy and works on Sid, why wouldn't it work on the version in between, Jessie?

And what does it mean not to ship "bootloader integration", anyway? That term is completely unclear, and googling was no help. There have been various Debian bugs filed but of course, no explanation from the developers for exactly what does and doesn't work.

My best guess is that what Debian means by "bootloader integration" is that there's a script that looks at /boot/extlinux/extlinux.conf, figures out which stanza corresponds to the current system, figures out whether there's a new kernel being installed that's different from the one in extlinux.conf, and updates the appropriate kernel and initrd lines to point to the new kernel.

If so, that's something I can do myself easily enough. But what if there's more to it? What would actually happen if I upgraded the extlinux package?

Of course, there's zero documentation on this. I found plenty of questions from people who had hit this warning, but most were from newbies who had no idea what extlinux was or why their systems were using it, and they were advised to install grub. I only found one hit from someone who was intentionally using extlinux. That person aborted the install, held back the package so the potentially nonbooting new version of extlinux wouldn't be installed, then updated extlinux.conf by hand, and apparently that worked fine.

It sounded like a reasonable bet. So here's what I did (as root, of course):

It worked fine. I booted into jessie with the kernel I had specified. And hooray -- my keyboard and mouse work, so I can continue to use my system until Sid becomes usable again.

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[ 17:28 Dec 27, 2015    More linux/install | permalink to this entry | comments ]

Sat, 12 Dec 2015

Emacs rich-text mode: coloring and styling plain text

I use emacs a lot for taking notes, during meetings, while watching lectures in a MOOC, or while researching something.

But one place where emacs falls short is highlighting. For instance, if I paste a section of something I'm researching, then I want to add a comment about it, to differentiate the pasted part from my added comments, I have to resort to horrible hacks like "*********** My comment:". It's like the stuff Outlook users put in emails because they can't figure out how to quote.

What I really want is a simple rich-text mode, where I can highlight sections of text by changing color or making it italic, bold, underlined.

Enter enriched-mode. Start it with M-x enriched-mode and then you can apply some styles with commands like M-o i for italic, M-o b for bold, etc. These styles may or may not be visible depending on the font you're using; for instance, my font is already bold and emacs isn't smart enough to make it bolder, the way some programs are. So if one style doesn't work, try another one.

Enriched mode will save these styles when you save the file, with a markup syntax like <italic>This text is in italic.</italic> When you load the file, you'll just see the styles, not the markup.


But they're all pretty subtle. I still wanted colors, and none of the documentation tells you much about how to set them.

I found a few pages saying that you can change the color of text in an emacs buffer using the Edit menu, but I hide emacs's menus since I generally have no use for them: emacs can do everything from the keyboard, one of the things I like most about it, so why waste space on a menu I never use? I do that like this:

(tool-bar-mode 0)
(menu-bar-mode 0)

It turns out that although the right mouse button just extends the selection, Control-middleclick gives a context menu. Whew! Finally a way to change colors! But it's not at all easy to use: Control-middleclick, mouse over Foreground Color, slide right to Other..., click, and the menu goes away and now there's a prompt in the minibuffer where you can type in a color name.

Colors are saved in the file with a syntax like: <x-color><param>red</param>This text is in red.</x-color>

All that clicking is a lot of steps, and requires taking my hands off the keyboard. How do I change colors in an easier, keyboard driven way? I drew a complete blank with my web searches. A somewhat irritable person on #emacs eventually hinted that I should be using overlays, and I eventually figured out how to set overlay colors ((overlay-put (make-overlay ...)) turned out to be the way to do that) but it was a complete red herring: enriched-mode doesn't pay any attention to overlay colors. I don't know what overlays are useful for, but it's not that.

But in emacs, you can find out what's bound to a key with describe-key. Maybe that works for mouse clicks too? I ran describe-key, held down Control, clicked the middle button -- the context menu came up -- then navigated to Foreground Color and Other... and discovered that it's calling (facemenu-set-foreground COLOR &optional START END).

Binding to keys

Finally, a function I can bind to a key! COLOR is just a string, like "red". The documentation implies that START and END are optional, and that the function will apply to the selected region if there is one. But in practice, if you don't specify START and END, nothing happens, so you have to specify them. (region-beginning) and (region-end) work if you have a selected region.

Similarly, I learned that Face->italic from that same menu calls (facemenu-set-italic), and likewise for bold, underline etc. They work on the selected region.

But what if there's no region defined? I decided it might be nice to be able to set styles for the current line, without selecting it first. I can use (line-beginning-position) and (line-end-position) for START and END. So I wrote a wrapper function. For that, I didn't want to use specific functions like (facemenu-set-italic); I wanted to be able pass a property like "italic" to my wrapper function.

I found a way to do that: (put-text-property START END 'italic). But that wasn't quite enough, because put-text-property replaces all properties; you can't make something both italic and bold. To add a property without removing existing ones, use (add-text-properties START END (list 'face 'italic)).

So here's the final code that I put in my .emacs. I was out of excuses to procrastinate, and my enriched-mode bindings worked fine for taking notes on the project which had led to all this procrastination.

;; Text colors/styles. You can use this in conjunction with enriched-mode.

;; rich-style will affect the style of either the selected region,
;; or the current line if no region is selected.
;; style may be an atom indicating a rich-style face,
;; e.g. 'italic or 'bold, using
;;   (put-text-property START END PROPERTY VALUE &optional OBJECT)
;; or a color string, e.g. "red", using
;;   (facemenu-set-foreground COLOR &optional START END)
;; or nil, in which case style will be removed.
(defun rich-style (style)
  (let* ((start (if (use-region-p)
                    (region-beginning) (line-beginning-position)))
         (end   (if (use-region-p)
                    (region-end)  (line-end-position))))
     ((null style)      (set-text-properties start end nil))
     ((stringp style)   (facemenu-set-foreground style start end))
     (t                 (add-text-properties start end (list 'face style)))

(defun enriched-mode-keys ()
  (define-key enriched-mode-map "\C-ci"
    (lambda () (interactive)    (rich-style 'italic)))
  (define-key enriched-mode-map "\C-cB"
    (lambda () (interactive)    (rich-style 'bold)))
  (define-key enriched-mode-map "\C-cu"
    (lambda () (interactive)    (rich-style 'underline)))
  (define-key enriched-mode-map "\C-cr"
    (lambda () (interactive)    (rich-style "red")))
  ;; Repeat for any other colors you want from rgb.txt

  (define-key enriched-mode-map (kbd "C-c ")
    (lambda () (interactive)    (rich-style nil)))
(add-hook 'enriched-mode-hook 'enriched-mode-keys)

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[ 14:48 Dec 12, 2015    More linux/editors | permalink to this entry | comments ]

Fri, 04 Dec 2015

Distclean part 2: some useful zsh tricks

I wrote recently about a zsh shell function to run make distclean on a source tree even if something in autoconf is messed up. In order to save any arguments you've previously passed to configure or, my function parsed the arguments from a file called config.log.

But it might be a bit more reliable to use config.status -- I'm guessing this is the file that make uses when it finds it needs to re-run However, the syntax in that file is more complicated, and parsing it taught me some useful zsh tricks.

I can see the relevant line from config.status like this:

$ grep '^ac_cs_config' config.status
ac_cs_config="'--prefix=/usr/local/gimp-git' '--enable-foo' '--disable-bar'"

--enable-foo --disable-bar are options I added purely for testing. I wanted to make sure my shell function would work with multiple arguments.

Ultimately, I want my shell function to call --prefix=/usr/local/gimp-git --enable-foo --disable-bar The goal is to end up with $args being a zsh array containing those three arguments. So I'll need to edit out those quotes and split the line into an array.

Sed tricks

The first thing to do is to get rid of that initial ac_cs_config= in the line from config.status. That's easy with sed:

$ grep '^ac_cs_config' config.status | sed -e 's/ac_cs_config=//'
"'--prefix=/usr/local/gimp-git' '--enable-foo' '--disable-bar'"

But since we're using sed anyway, there's no need to use grep to get the line: we can do it all with sed. First try:

sed -n '/^ac_cs_config/s/ac_cs_config=//p' config.status

Search for the line that starts with ac_cs_config (^ matches the beginning of a line); then replace ac_cs_config= with nothing, and p print the resulting line. -n tells sed not to print anything except when told to with a p.

But it turns out that if you give a sed substitution a blank pattern, it uses the last pattern it was given. So a more compact version, using the search pattern ^ac_cs_config, is:

sed -n '/^ac_cs_config=/s///p' config.status

But there's also another way of doing it:

sed '/^ac_cs_config=/!d;s///' config.status

! after a search pattern matches every line that doesn't match the pattern. d deletes those lines. Then for lines that weren't deleted (the one line that does match), do the substitution. Since there's no -n, sed will print all lines that weren't deleted.

I find that version more difficult to read. But I'm including it because it's useful to know how to chain several commands in sed, and how to use ! to search for lines that don't match a pattern.

You can also use sed to eliminate the double quotes:

sed '/^ac_cs_config=/!d;s///;s/"//g' config.status
'--prefix=/usr/local/gimp-git' '--enable-foo' '--disable-bar'
But it turns out that zsh has a better way of doing that.

Zsh parameter substitution

I'm still relatively new to zsh, but I got some great advice on #zsh. The first suggestion:

sed -n '/^ac_cs_config=/s///p' config.status | IFS= read -r; args=( ${(Q)${(z)${(Q)REPLY}}} ); print -rl - $args

I'll be using final print -rl - $args for all these examples: it prints an array variable with one member per line. For the actual distclean function, of course, I'll be passing the variable to, not printing it out.

First, let's look at the heart of that expression: the args=( ${(Q)${(z)${(Q)REPLY}}}.

The heart of this is the expression ${(Q)${(z)${(Q)x}}} The zsh parameter substitution syntax is a bit arcane, but each of the parenthesized letters does some operation on the variable that follows.

The first (Q) strips off a level of quoting. So:

$ x='"Hello world"'; print $x; print ${(Q)x}
"Hello world"
Hello world

(z) splits an expression and stores it in an array. But to see that, we have to use print -l, so array members will be printed on separate lines.

$ x="a b c"; print -l $x; print "....."; print -l ${(z)x}
a b c

Zsh is smart about quotes, so if you have quoted expressions it will group them correctly when assigning array members:

x="'a a' 'b b' 'c c'"; print -l $x; print "....."; print -l ${(z)x} 'a a' 'b b' 'c c' ..... 'a a' 'b b' 'c c'

So let's break down the larger expression: this is best read from right to left, inner expressions to outer.

${(Q) ${(z) ${(Q) x }}}
   |     |     |   \
   |     |     |    The original expression, 
   |     |     |   "'--prefix=/usr/local/gimp-git' '--enable-foo' '--disable-bar'"
   |     |     \
   |     |      Strip off the double quotes:
   |     |      '--prefix=/usr/local/gimp-git' '--enable-foo' '--disable-bar'
   |     \
   |      Split into an array of three items
    Strip the single quotes from each array member,
    ( --prefix=/usr/local/gimp-git --enable-foo --disable-bar )

For more on zsh parameter substitutions, see the Zsh Guide, Chapter 5: Substitutions.

Passing the sed results to the parameter substitution

There's still a little left to wonder about in our expression, sed -n '/^ac_cs_config=/s///p' config.status | IFS= read -r; args=( ${(Q)${(z)${(Q)REPLY}}} ); print -rl - $args

The IFS= read -r seems to be a common idiom in zsh scripting. It takes standard input and assigns it to the variable $REPLY. IFS is the input field separator: you can split variables into words by spaces, newlines, semicolons or any other character you want. IFS= sets it to nothing. But because the input expression -- "'--prefix=/usr/local/gimp-git' '--enable-foo' '--disable-bar'" -- has quotes around it, IFS is ignored anyway.

So you can do the same thing with this simpler expression, to assign the quoted expression to the variable $x. I'll declare it a local variable: that makes no difference when testing it in the shell, but if I call it in a function, I won't have variables like $x and $args cluttering up my shell afterward.

local x=$(sed -n '/^ac_cs_config=/s///p' config.status); local args=( ${(Q)${(z)${(Q)x}}} ); print -rl - $args

That works in the version of zsh I'm running here, 5.1.1. But I've been warned that it's safer to quote the result of $(). Without quotes, if you ever run the function in an older zsh, $x might end up being set only to the first word of the expression. Second, it's a good idea to put "local" in front of the variable; that way, $x won't end up being set once you've returned from the function. So now we have:

local x="$(sed -n '/^ac_cs_config=/s///p' config.status)"; local args=( ${(Q)${(z)${(Q)x}}} ); print -rl - $args

You don't even need to use a local variable. For added brevity (making the function even more difficult to read! -- but we're way past the point of easy readability), you could say:

args=( ${(Q)${(z)${(Q)"$(sed -n '/^ac_cs_config=/s///p' config.status)"}}} ); print -rl - $args
or even
print -rl - ${(Q)${(z)${(Q)"$(sed -n '/^ac_cs_config=/s///p' config.status)"}}}
... but that final version, since it doesn't assign to a variable at all, isn't useful for the function I'm writing.

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[ 13:25 Dec 04, 2015    More linux/cmdline | permalink to this entry | comments ]

Fri, 30 Oct 2015

HDMI presentation setup on Linux, Part II: problems and tips

In Part I of HDMI Presentation Setup on Linux, I covered the basics of getting video and audio working over HDMI. Now I want to cover some finer-grained details: some problems I had, and ways to make it easier to enable HDMI when you need it.

Testing follies, delays, and screen blinking/flashing woes

While I was initially trying to get this working, I was using my own short sound clip (one of the alerts I use for IRC) and it wasn't working. Then I tried the test I showed in part I, $ aplay -D plughw:0,3 /usr/share/sounds/alsa/Front_Center.wav and that worked fine. Tried my sound clip again -- nothing. I noticed that my clip was mono and 8-bit while the ALSA sample was stereo and 16-bit, and I wasted a lot of time in web searches on why HDMI would play one and not the other.

Eventually I figured out that the reason my short clip wasn't playing was that there's a delay when switching on HDMI sound, and the first second two two of any audio may be skipped. I found lots of complaints about people missing the first few seconds of sound over HDMI, so this problem is quite common, and I haven't found a solution.

So if you're giving a talk where you need to play short clips -- for instance, a talk on bird calls -- be aware of this. I'm probably going to make a clip of a few seconds of silence, so I can play silence before every short clip to make sure I'm fully switched over to HDMI before the clip starts: aplay -D plughw:0,3 silence.wav osprey.wav

Another problem, probably related, when first starting an audio file: the screen blinks brieftly off then on again, then blinks again a little while after the clip ends. ("Flicker" turns out to be a better term to use when web searching, though I just see a single blink, not continued flickering). It's possible this is something about my home TV, and I will have to try it with another monitor somewhere to see if it's universal. It sounds like kernel bug 51421: Enabling HDMI sound makes HDMI video flicker, but that bug was marked resolved in 2012 and I'm seeing this in 2015 on Debian Jessie.

Making HDMI the sound default

What a pain, to have to remember to add -D plughw:0,3 every time you play a sound. And what do you do for other programs that don't have that argument?

Fortunately, you can make HDMI your default sound output. Create a file in your home directory called .asoundrc with this in it (you may be able to edit this down -- I didn't try) and then all audio will go to HDMI:

pcm.dmixer {
  type dmix
  ipc_key 1024
  ipc_key_add_uid false
  ipc_perm 0660
  slave {
    pcm "hw:0,3"
    rate 48000
    channels 2
    period_time 0
    period_size 1024
    buffer_time 0
    buffer_size 4096
pcm. !default {
  type plug
  slave.pcm "dmixer"

Great! But what about after you disconnect? Audio will still be going to HDMI ... in other words, nowhere. So rename that file:

$ mv .asoundrc asoundrc-hdmi
Then when you connect to HDMI, you can copy it back:
$ cp asoundrc-hdmi .asoundrc 

What a pain, you say again! This should happen automatically!

That's possible, but tricky: you have to set up udev rules and scripts. See this Arch Linux discussion on HDMI audio output switching automatically for the gory details. I haven't bothered, since this is something I'll do only rarely, when I want to give one of those multimedia presentations I sometimes contemplate but never actually give. So for me, it's not worth fighting with udev when, by the time I actually need HDMI audio, the udev syntax probably will have changed again.

Aliases to make switching easy

But when I finally do break down and design a multimedia presentation, I'm not going to be wanting to do all this fiddling in the presentation room right before the talk. I want to set up aliases to make it easy.

There are two things that need to be done in that case: make HDMI output the default, and make sure it's unmuted.

Muting can be done automatically with amixer. First run amixer with no arguments to find out the channel name (it gives a lot of output, but look through the "Simple mixer control" lines, or speed that up with amixer | grep control.

Once you know the channel name (IEC958 on my laptop), you can run: amixer sset IEC958 unmute The rest of the alias is just shell hackery to create a file called .asoundrc with the right stuff in it, and saving .asoundrc before overwriting it. My alias in .zshrc is set up so that I can say hdmisound on or hdmisound off (with no arguments, it assumes on), and it looks like this:

# Send all audio output to HDMI.
# Usage: hdmisound [on|off], default is on.
hdmisound() {
    if [[ $1 == 'off' ]]; then
        if [[ -f ~/.asoundrc ]]; then
            mv ~/.asoundrc ~/.asoundrc.hdmi
        amixer sset IEC958 mmute
        if [[ -f ~/.asoundrc ]]; then
            mv ~/.asoundrc ~/.asoundrc.nohdmi
        cat >> ~/.asoundrc <<EOF
pcm.dmixer {
  type dmix
  ipc_key 1024
  ipc_key_add_uid false
  ipc_perm 0660
  slave {
    pcm "hw:0,3"
    rate 48000
    channels 2
    period_time 0
    period_size 1024
    buffer_time 0
    buffer_size 4096
pcm. !default {
  type plug
  slave.pcm "dmixer"
        amixer sset IEC958 unmute

Of course, I could put all that .asoundrc content into a file and just copy/rename it each time. But then I have another file I need to make sure is in place on every laptop; I decided I'd rather make the alias self-contained in my .zshrc.

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[ 11:57 Oct 30, 2015    More linux/laptop | permalink to this entry | comments ]

Tue, 27 Oct 2015

HDMI presentation setup on Linux, video and audio: Part I

For about a decade now I've been happily connecting to projectors to give talks. xrandr --output VGA1 --mode 1024x768 switches on the laptop's external VGA port, and xrandr --auto turns it off again after I'm disconnected. No fuss.

But increasingly, local venues are eschewing video projectors and instead using big-screen TVs, some of which offer only an HDMI port, no VGA. I thought I'd better figure out how to present a talk over HDMI now, so I'll be ready when I need to know.

Fortunately, my newest laptop does have an HDMI port. But in case it ever goes on the fritz and I have to use an older laptop, I discovered you can buy VGA to HDMI adaptors rather cheaply (about $10) on ebay. I bought one of those, tested it on my TV at home and it at least worked there. Be careful when shopping: you want to make sure you're getting something that takes VGA in and outputs HDMI, rather than the reverse. Ebay descriptions aren't always 100% clear on that, but if you check the gender of the connector in the photo and make sure it's right to plug into the socket on your laptop, you should be all right.

Once you're plugged in (whether via an adaptor, or native HDMI built into your laptop), connecting is easy, just like connecting with VGA:

xrandr --output HDMI1 --mode 1024x768

Of course, you can modify the resolution as you see fit. I plan to continue to design my presentations for a 1024x768 resolution for the forseeable future. Since my laptop is 1366x1024, I can use the remaining 342-pixel-wide swath for my speaker notes and leave them invisible to the audience.

But for GIMP presentations, I'll probably want to use the full width of my laptop screen. --mode 1366x768 didn't work -- that resolution wasn't available -- but running xrandr with no arguments got me a list of available resolutions, which included 1360x768. That worked fine and is what I'll use for GIMP talks and other live demos where I want more screen space.

Sound over HDMI

My Toastmasters club had a tech session where a few of us tried out the new monitor in our meeting room to make sure we could use it. One person was playing a video with sound. I've never used sound in a talk, but I've always wanted to find an excuse to try it. Alas, it didn't "just work" -- xrandr's video settings have nothing to do with ALSA's audio settings. So I had to wait until I got home so I could do web searches and piece together the answer.

First, run aplay -l , which should show something like this:

$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: Intel [HDA Intel], device 0: STAC92xx Analog [STAC92xx Analog]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 0: Intel [HDA Intel], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Find the device number for the HDMI device, which I've highlighted here: in this case, it's 3 (which seems to be common on Intel chipsets).

Now you can run a test:

$ aplay -D plughw:0,3 /usr/share/sounds/alsa/Front_Center.wav
Playing WAVE '/usr/share/sounds/alsa/Front_Center.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Mono
If you don't hear anything, don't worry: the HDMI channel is probably muted if you've never used it before. Run either alsamixer or alsamixergui.

[alsamixergui with HDMI muted] [alsamixer] Now find the channel representing your HDMI connection. (HDMI must be plugged in for this to work.) In alsamixer, it's called S/PDIF; in alsamixergui, it's called IEC958. If you look up either of those terms, Wikipedia S/PDIF will tell you that S/PDIF is the Sony/Philips Digital Interconnect Format, a data protocol and a set of physical specifications. Those physical specifications appear to have nothing to do with video, and use connectors that are nothing like HDMI. So it doesn't make much sense. Just remember that if you see IEC958 or S/PDIF in ALSA, that's probably your HDMI channel.

In the alsamixergui screenshot, IEC958 is muted: you can tell because the little speaker icon at the top of the column is bright white. If it were unmuted, the speaker icon would be grey like most of the others. Yes, this seems backward. It's Linux audio: get used to obscure user interfaces.

In the alsamixer screenshot, the mutes are at the bottom of each column, and MM indicates a channel is muted (like the Beep channel in the screenshot). S/PDIF is not muted here, though it appears to be at zero volume. (The 00 doesn't tell you it's at zero volume; 00 means it's not muted. What did I say about Linux audio?) ALSA apparently doesn't let you adjust the volume of HDMI output: presumably they expect that your HDMI monitor will have its own volume control. If your S/PDIF is muted, you can use your right-arrow key to arrow over to the S/PDIF channel, then type m to toggle muting. You can exit alsamixer with Ctrl-C (Q and Ctrl-Q don't work).

Now try that aplay -D command again and see if it works. With any luck, it will (loudly).

A couple of other tests you might want to try:
speaker-test -t sine -f 440 -c 2 -s 1 -D hw:0,3
plays a sine wave. speaker-test -c 2 -r 48000 -D hw:0,3
runs a general speaker test sequence.

In Part II of Linux HDMI Presentations, I'll cover some problems I had, and how to write an alias to make it easy to turn HDMI audio on and off.

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[ 14:36 Oct 27, 2015    More linux/laptop | permalink to this entry | comments ]

Thu, 15 Oct 2015

Viewer for email attachments in Office formats

I seem to have fallen into a nest of Mac users whose idea of email is a text part, an HTML part, plus two or three or seven attachments (no exaggeration!) in an unholy combination of .DOC, .DOCX, .PPT and other Microsoft Office formats, plus .PDF.

Converting to text in mutt

As a mutt user who generally reads all email as plaintext, normally my reaction to a mess like that would be "Thanks, but no thanks". But this is an organization that does a lot of good work despite their file format habits, and I want to help.

In mutt, HTML mail attachments are easy. This pair of entries in ~/.mailcap takes care of them:

text/html; firefox 'file://%s'; nametemplate=%s.html
text/html; lynx -dump %s; nametemplate=%s.html; copiousoutput
Then in .muttrc, I have
auto_view text/html
alternative_order text/plain text

If a message has a text/plain part, mutt shows that. If it has text/html but no text/plain, it looks for the "copiousoutput" mailcap entry, runs the HTML part through lynx (or I could use links or w3m) and displays that automatically. If, reading the message in lynx, it looks to me like the message has complex formatting that really needs a browser, I can go to mutt's attachments screen and display the attachment in firefox using the other mailcap entry.

Word attachments are not quite so easy, especially when there are a lot of them. The straightforward way is to save each one to a file, then run LibreOffice on each file, but that's slow and tedious and leaves a lot of temporary files behind. For simple documents, converting to plaintext is usually good enough to get the gist of the attachments. These .mailcap entries can do that:

application/msword; catdoc %s; copiousoutput
application/vnd.openxmlformats-officedocument.wordprocessingml.document; docx2txt %s -; copiousoutput
Alternatives to catdoc include wvText and antiword.

But none of them work so well when you're cross-referencing five different attachments, or for documents where color and formatting make a difference, like mail from someone who doesn't know how to get their mailer to include quoted text, and instead distinguishes their comments from the text they're replying to by making their new comments green (ugh!) For those, you really do need a graphical window.

I decided what I really wanted (aside from people not sending me these crazy emails in the first place!) was to view all the attachments as tabs in a new window. And the obvious way to do that is to convert them to formats Firefox can read.

Converting to HTML

I'd used wvHtml to convert .doc files to HTML, and it does a decent job and is fairly fast, but it can't handle .docx. (People who send Office formats seem to distribute their files fairly evenly between DOC and DOCX. You'd think they'd use the same format for everything they wrote, but apparently not.) It turns out LibreOffice has a command-line conversion program, unoconv, that can handle any format LibreOffice can handle. It's a lot slower than wvHtml but it does a pretty good job, and it can handle .ppt (PowerPoint) files too.

For PDF files, I tried using pdftohtml, but it doesn't always do so well, and it's hard to get it to produce a single HTML file rather than a directory of separate page files. And about three quarters of PDF files sent through email turn out to be PDF in name only: they're actually collections of images of single pages, wrapped together as a PDF file. (Mostly, when I see a PDF like that I just skip it and try to get the information elsewhere. But I wanted my program at least to be able to show what's in the document, and let the user choose whether to skip it.) In the end, I decided to open a firefox tab and let Firefox's built-in PDF reader show the file, though popping up separate mupdf windows is also an option.

I wanted to show the HTML part of the email, too. Sometimes there's formatting there (like the aforementioned people whose idea of quoting messages is to type their replies in a different color), but there can also be embedded images. Extracting the images and showing them in a browser window is a bit tricky, but it's a problem I'd already solved a couple of years ago: Viewing HTML mail messages from Mutt (or other command-line mailers).

Showing it all in a new Firefox window

So that accounted for all the formats I needed to handle. The final trick was the firefox window. Since some of these conversions, especially unoconv, are quite slow, I wanted to pop up a window right away with a "converting, please wait..." message. Initially, I used a javascript: URL, running the command:

firefox -new-window "javascript:document.writeln('<br><h1>Translating documents, please wait ...</h1>');"

I didn't want to rely on Javascript, though. A data: URL, which I hadn't used before, can do the same thing without javascript:

firefox -new-window "data:text/html,<br><br><h1>Translating documents, please wait ...</h1>"

But I wanted the first attachment to replace the contents of that same window as soon as it was ready, and then subsequent attachments open a new tab in that window. But it turned out that firefox is inconsistent about what -new-window and -new-tab do; there's no guarantee that -new-tab will show up in the same window you recently popped up with -new-window, and running just firefox URL might open in either the new window or the old, in a new tab or not, or might not open at all. And things got even more complicated after I decided that I should use -private-window to open these attachments in private browsing mode.

In the end, the only way firefox would behave in a repeatable, predictable way was to use -private-window for everything. The first call pops up the private window, and each new call opens a new tab in the private window. If you want two separate windows for two different mail messages, you're out of luck: you can't have two different private windows. I decided I could live with that; if it eventually starts to bother me, I can always give up on Firefox and write a little python-webkit wrapper to do what I need.

Using a file redirect instead

But that still left me with no way to replace the contents of the "Please wait..." window with useful content. Someone on #firefox came up with a clever idea: write the content to a page with a meta redirect.

So initially, I create a file pleasewait.html that includes the header:

<meta http-equiv="refresh" content="2;URL=pleasewait.html">
(other HTML, charset information, etc. as needed). The meta refresh means Firefox will reload the file every two seconds. When the first converted file is ready, I just change the header to redirect to URL=first_converted_file.html. Meanwhile, I can be opening the other documents in additional tabs.

Finally, I added the command to my .muttrc. When I'm viewing a message either in the index or pager screens, F10 will call the script and decode all the attachments.

macro index <F10> "<pipe-message>~/bin/viewmailattachments\n" "View all attachments in browser"
macro pager <F10> "<pipe-message>~/bin/viewmailattachments\n" "View all attachments in browser"

Whew! It was trickier than I thought it would be. But I find I'm using it quite a bit, and it takes a lot of the pain out of those attachment-full emails.

The script is available at: viewmailattachments on GitHub.

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[ 15:18 Oct 15, 2015    More linux | permalink to this entry | comments ]