Shallow Thoughts : : Dec

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

Mon, 22 Dec 2014

Passwordless ssh with a key: the part most tutorials skip

I'm working on my Raspberry Pi crittercam again. I got a battery, so it can be a standalone box -- it was such a hassle to set it up with two power cords dangling from it at all times -- and set it up to run automatically at boot time.

But there was one aspect of the camera that wasn't automated: if close enough to the house to see the wi-fi router, I want it to mount a filesystem from our server and store its image files there. That makes it a lot easier to check on its progress, and also saves wear on the Pi's SD card.

Only one problem: I was using sshfs to mount the disk remotely, and ssh always prompts me for a password.

Now, there are a gazillion tutorials on how to set up an ssh key. Just do a web search for ssh key or passwordless ssh key. They vary a bit in their details, but they're all the same in the important aspects. They're all the same in one other detail: none of them work for me. I generate a new key (various types) with no pass phrase, I copy it to the server's authorized keys file (several different ways, two possible filenames), I try to ssh -- and I'm prompted for a password.

After much flailing I finally found out what was missing. In addition to those two steps, you need to modify your .ssh/config file to tell it which key to use. This is especially critical if you have multiple keys on the client machine, or if you've named the file anything but the default id_dsa or id_rsa.

So here are the real steps for making an ssh key. Assume the server, the machine to which you want to ssh, is named "myserver". But these steps are all run on the client machine, the one from which you want to run ssh.

ssh-keygen -t rsa -C "Comment"
When it prompts you for a filename, give it a full pathname, e.g. ~/.ssh/id_rsa_myserver. Type in a pass phrase, or hit return twice if you want to be able to ssh without a password.

Update May 2016: this now fails with Saving key ~/.ssh/id_rsa_myserver failed: No such file or directory
(duh, of course the file doesn't exist, I'm asking you to create it).
To get around this, specify the file on the command line:

ssh-keygen -t rsa -C "Comment" -f ~/.ssh/id_rsa_myserver
Update, April 2018: Do use RSA: DSA keys have now been deprecated. If you make a DSA rather than an RSA key, ssh will just ignore it and prompt you for a login password. No helpful error message or anything explaining why it's ignored.

Now copy your key to the remote machine:

ssh-copy-id -i .ssh/id_rsa_myserver user@myserver
You can omit the user@ if you're using the same username on both machines. You'll have to type in your password on myserver.

Then edit ~/.ssh/config, and add an entry like this:

Host myserver
  User my_username
  IdentityFile ~/.ssh/id_rsa_myserver
The User line is optional, and refers to your username on myserver if it's different from the one on the client. For instance, on the Raspberry Pi, everything has to run as root because most of the hardware and camera libraries can't work any other way. But I want it using my user ID on the server side, not root.

Eliminating strict host key checking

Of course, you can use this to go the other way too, and ssh to your Pi without needing to type a password every time. If you do that, and if you have several Pis, Beaglebones, plug computers or other little Linux gizmos which sometimes share the same IP address, you may run into the annoying whine ssh is prone to:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
The only way to get around this once it happens is by editing ~/.ssh/known_hosts, finding the line corresponding to the pi, and removing it (or just removing the whole file).

You're supposed to be able to turn off this check with StrictHostKeyChecking no, but it doesn't work. Fortunately, there's a trick I discovered several years ago and discussed in Three SSH tips. Here's how the Pi entry ends up looking in my desktop's ~/.ssh/config:

Host pipi
  HostName pi
  User pi
  StrictHostKeyChecking no
  UserKnownHostsFile /dev/null
  IdentityFile ~/.ssh/id_pi

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[ 16:25 Dec 22, 2014    More linux | permalink to this entry | comments ]

Thu, 18 Dec 2014

Firefox deprecates flash. How to get it back (on Debian).

Recently Firefox started refusing to run flash, including youtube videos (about the only flash I run). A bar would appear at the top of the page saying "This plug-in is vulnerable and should be upgraded". Apparently Adobe had another security bug. There's an "Update now" button in the Firefox bar, but it's a chimera: Firefox has never known how to install plug-ins for Linux (there are longstanding bugs filed on why it claims to be able to but can't), and it certainly doesn't know how to update a Debian package.

I use a Firefox downloaded from Mozilla.org, but flash from Debian's flashplugin-nonfree package. So I figured updating Debian -- apt-get update; apt-get dist-upgrade -- would fix it. Nope. I still got the same message.

A little googling found several pages recommending update-flashplugin-nonfree --install; I tried that but it didn't help either. It seemed to download a tarball, but as far as I could tell it never unpacked or installed the tarball it downloaded.

What finally did the trick was

apt-get install --reinstall flashplugin-nonfree
That downloaded a new tarball, AND unpacked and installed it. After restarting Firefox, I was able to view the video I'd been trying to watch.

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[ 15:21 Dec 18, 2014    More linux | permalink to this entry | comments ]

Wed, 10 Dec 2014

Not exponential after all

We're saved! From the embarrassing slogan "Live exponentially", that is.

Last night the Los Alamos city council voted to bow to public opinion and reconsider the contract to spend $50,000 on a logo and brand strategy based around the slogan "Live Exponentially." Though nearly all the councilors (besides Pete Sheehey) said they still liked the slogan, and made it clear that the slogan isn't for residents but for people in distant states who might consider visiting as tourists, they now felt that basing a campaign around a theme nearly of the residents revile was not the best idea.

There were quite a few public comments (mine included); everyone was civil and sensible and stuck well under the recommended 3-minute time limit.

Instead, the plan is to go ahead with the contract, but ask the ad agency (Atlas Services) to choose two of the alternate straplines from the initial list of eight that North Star Research had originally provided.

Wait -- eight options? How come none of the previous press or the previous meeting mentioned that there were options? Even in the 364 page Agenda Packets PDF provided for this meeting, there was no hint of that report or of any alternate strap lines.

But when they displayed the list of eight on the board, it became a little clearer why they didn't want to make the report public: they were embarrassed to have paid for work of this quality. Check out the list:

I mean, really. Great Beyond? Are we're all dead? High Intelligence in the High Desert? That'll certainly help with people who think this might be a bunch of snobbish intellectuals.

It was also revealed that at no point during the plan was there ever any sort of focus group study or other tests to see how anyone reacted to any of these slogans.

Anyway, after a complex series of motions and amendments and counter-motions and amendments and amendments to the amendments, they finally decided to ask Atlas to take the above list, minus "Live Exponentially"; add the slogan currently displayed on the rocks as you drive into town, "Where Discoveries are Made" (which came out of a community contest years ago and is very popular among residents); and ask Atlas to choose two from the list to make logos, plus one logo that has no slogan at all attached to it.

If we're lucky, Atlas will pick Discoveries as one of the slogans, or maybe even come up with something decent of their own.

The chicken ordinance discussion went well, too. They amended the ordinance to allow ten chickens (instead of six) and to try to allow people in duplexes and quads to keep chickens if there's enough space between the chickens and their neighbors. One commenter asked for the "non-commercial' clause to be struck because his kids sell eggs from a stand, like lemonade, which sounded like a very reasonable request (nobody's going to run a large commercial egg ranch with ten chickens); but it turned out there's a state law requiring permits and inspections to sell eggs.

So, folks can have chickens, and we won't have to live exponentially. I'm sure everyone's breathing a little more easily now.

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[ 16:27 Dec 10, 2014    More politics | permalink to this entry | comments ]

Sun, 07 Dec 2014

My Letter to the Editor: Make Your Voice Heard On 'Live Exponentially'

More on the Los Alamos "Live Exponentially" slogan saga: There's been a flurry of letters, all opposed to the proposed slogan, in the Los Alamos Daily Post these last few weeks.

And now the issue is back on the council agenda; apparently they're willing to reconsider the October vote to spend another $50,000 on the slogan.

But considering that only two people showed up to that October meeting, I wrote a letter to the Post urging people to speak before the council: Letter to the Editor: Attend Tuesday's Council Meeting To Make Your Voice Heard On 'Live Exponentially'.

I'll be there. I've never actually spoken at a council meeting before, but hey, confidence in public speaking situations is what Toastmasters is all about, right?

(Even though it means I'll have to miss an interesting sounding talk on bats that conflicts with the council meeting. Darn it!)

A few followup details that I had no easy way to put into the Post letter:

The page with the links to Council meeting agendas and packets is here: Los Alamos County Calendar.

There, you can get the short Agenda for Tuesday's meeting, or the full 364 page Agenda Packets PDF.

[Breathtaking raised to the power of you] The branding section covers pages 93 - 287. But the graphics the council apparently found so compelling, which swayed several of them from initially not liking the slogan to deciding to spend a quarter million dollars on it, are in the final presentation from the marketing company, starting on page p. 221 of the PDF.

In particular, a series of images like this one, with the snappy slogan:

Breathtaking raised to the power of you
LIVE EXPONENTIALLY

That's right: the advertising graphics that were so compelling they swayed most of the council are even dumber than the slogan by itself. Love the superscript on the you that makes it into an exponent. Get it ... exponentially? Oh, now it all makes sense!

There's also a sadly funny "Written Concept" section just before the graphics (pages 242- in the PDF) where they bend over backward to work in scientific-sounding words, in bold each time.

But there you go. Hopefully some of those Post letter writers will come to the meeting and let the council know what they think.

The council will also be discussing the much debated proposed chicken ordinance; that discussion runs from page 57 to 92 of the PDF. It's a non-issue for Dave and me since we're in a rural zone that already allows chickens, but I hope they vote to allow them everywhere.

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[ 18:05 Dec 07, 2014    More politics | permalink to this entry | comments ]

Tue, 02 Dec 2014

Ripping a whole CD on Linux

I recently discovered that my ancient stereo turntable didn't survive our move. So all those LPs I brought along, intending to rip to mp3 when I had more time, will never see bits.

So I need to buy new versions of some of that old music. In particular, I'd lately been wanting to listen to my old Flanders and Swann albums. Flanders and Swann were a terrific comedy music duo (think Tom Lehrer only less scientifically oriented) from the 1960s.

So I ordered a CD of The Complete Flanders & Swann, which contains all three of the albums I inherited from my parents. Woohoo! I ran a little script I have that rips a whole CD to a directory of separate MP3 songs, and I was all set.

Until I listened to it. It turns out that when the LP album was turned into a CD, they put the track breaks in the wrong place. These albums are recordings of live performances. Each song has a spoken intro, giving a little context for the song that follows. On the CD, each track starts with a song, and ends with the spoken intro for the next song. That's no problem if you always listen to whole albums in order. But I like to play individual tracks, or listen to music on random play. So this wasn't going to work at all.

I tried using audacity to copy the intro from the end of one track and paste it onto the beginning of another. That worked, but it was tedious and fiddly. A little research showed me a much better way.

First: Rip the whole CD

First I needed to rip the whole CD as one gigantic track. My script had been running cdparanoia tracknumber filename.wav. But it took some study of the cdparanoia manual before I finally found the way to rip a whole CD to one track: you can specify a range of tracks, starting at 0 and omitting the end track.

cdparanoia 0- outfile.wav

Use Audacity to split and save the tracks

Now what's the best way to split a recording into separate tracks? Fortunately the Audacity manual has a nice page on that very subject: Splitting a recording into separate tracks.

Mostly, the issue is setting labels -- with Tracks->Add Label at Selection or Tracks->Add Label at Playback Position. Use Ctrl-1 to zoom as much as you need to see where the short pauses are. Then listen to the audio, pausing or clicking and setting labels appropriately.

It's a bit fiddly. For instance, if you pause your listening to set a label, you might want to save the audacity project so you don't lose the label positions you've set so far. But you can't save unless you Stop the playback; and that loses the current playback position which you may not yet have set a label for. Even if you have set a label for it, you'll need to click to set the selection to the label you just made if you want to continue playing from where you left off. It all seems a little silly and unintuitive ... but after a few tries you'll find a routine that works for you.

When all your labels are set, then File->Export Multiple.... You will have to go through a bunch of dialogs involving metadata for each track; just hit return, since audacity ignores any metadata you type in and won't actually write it to the MP3 file. I have no idea why it always prompts for metadata then doesn't use it, but you can use a program like id3tool later to add proper metadata to the tracks.

So, no, the tools aren't perfect. On the other hand, I now have a nice set of Flanders and Swann tracks, and can listen to Misalliance, Ill Wind and The GNU Song complete with their proper introductions.

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[ 13:35 Dec 02, 2014    More linux | permalink to this entry | comments ]