Oli's questions

I have a three week old baby. Occasionally she refuses to sleep. Some people tell me this is the way life is, some people tell me I need to buy things to fix it. This is becoming an alarmingly common pattern in this parenting game.

Anyway one of these things "I need to buy" is a white noise generator. White noise defined as:

a random signal is considered "white noise" if it is observed to have a flat spectrum over the range of frequencies that is relevant to the context. For an audio signal, for example, the relevant range is the band of audible sound frequencies, between 20 to 20,000 Hz.

There are several things I can buy. Apps for Android, dedicated boxes that I'm sure just play a tiny clip of pre-generated noise, all the way to mega-expensive true-random white noise generators.

I want to generate my own white noise sample

I know I could download one with youtube-dl from one of the many videos out there but copyright aside, frequency compression is horrible online I want full-white-frequency goodness. If such a thing actually exists. Plus I'm a glutton for punishment and I believe that if something can be done via the command line, that's the way we should be doing it. That's how I aim to raise this one anyway.

So we have things like /dev/urandom and paplay. Is there a sensible way to take random data and channel it into the audible range of white noise and out of my speakers? Answers that write to file are okay too. The important thing is a steady range-confined sample. No squawks.

Note: answers that generate the brown note will not be appreciated ☹

A new super-cheap version of the Raspberry Pi was recently announced. I'd like to stuff these all over my house doing cool nonsense.

My question is, will I be able to use Ubuntu on them?

My scanner has broken! I do have a good camera though so I've taken a few photos of the documents I want to scan... However they look like photos of paper, not scanned documents:

• Images aren't flat
• Lighting isn't even (shadows as the page warps, etc)
• Text obviously isn't processed into copy-pasteable PDF text.

They simply aren't suitable for professional use, but they're close.

I'm looking for some thing (or method) that can do any or all of the above so I can go from a number of JPG files to a single [optionally] annotated PDF of the whole thing, that's in the right format (A4 typically).

Any suggestions (short of going out and buying a new scanner)?

I'm just talking about the standard KDE desktop. After a while (many days) of running the task bar stops working properly. This is due to some sort of undiagnosed bug but that's really not my boggle at the moment. It's fixed as soon as I log out and in again.

I have to close everything and ongoing processes like virtual machines have to shut down. It's a big pain. It typically means I put up with a bit of flickering for many days.

Is there a way to just reload the desktop without bombing all the running applications?

I have just noticed that Wine (and a number of other packages) have shifted their versioning scheme to something like:

1:1.6.2-0ubuntu3

I understand everything after the 1:... But what does the 1: refer to?

It doesn't seem to mirror the major version. Looking at a list of pending upgrades, there are versions like: 2:4.1.3... and there are plenty of packages without the #: prefix.

What's going on?

In the STAT column of ps there are a load of letters that don't really make much sense. What do they mean?

Here's an example of ps aux | head:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.0  27176  2960 ?        Ss   Sep20   0:02 /sbin/init
root         2  0.0  0.0      0     0 ?        S    Sep20   0:00 [kthreadd]
root         3  0.0  0.0      0     0 ?        S    Sep20  13:05 [ksoftirqd/0]
root         5  0.0  0.0      0     0 ?        S<   Sep20   0:00 [kworker/0:0H]
root         7  0.0  0.0      0     0 ?        S<   Sep20   0:00 [kworker/u:0H]
root         8  0.0  0.0      0     0 ?        S    Sep20   2:16 [migration/0]
root         9  0.0  0.0      0     0 ?        S    Sep20   0:00 [rcu_bh]
root        10  0.0  0.0      0     0 ?        S    Sep20  20:08 [rcu_sched]
root        11  0.0  0.0      0     0 ?        S    Sep20   0:07 [watchdog/0]
root        12  0.0  0.0      0     0 ?        S    Sep20   0:05 [watchdog/1]
root        13  0.0  0.0      0     0 ?        S    Sep20   2:21 [ksoftirqd/1]
root        14  0.0  0.0      0     0 ?        S    Sep20   1:00 [migration/1]

Since upgrading my user's crontab has been wiped out. This is not the first time this has happened this year and it's a pain restoring it each time.

I'd like to be able to back up the crontab for my user but for that I need to know where it's stored.

Every so often I'll bash out a bash script and it strikes me there are a few ways of setting a variable:

key=value
env key=value
export key=value

When you're inside a script or a single command (for instance, I'll often chain a variable with a Wine launcher to set the right Wine prefix) these seem to be completely interchangeable but surely that can't be the case.

What's the difference between these three methods and can you give me an example of when I would specifically want to use each one?

_{Definitely related to What is the difference between `VAR=...` and `export VAR=...`? but I want to know how env fits into this too, and some examples showing the benefits of each would be nice too :)}

Yes, I'm sorting out my music. I've got everything arranged beautifully in the following mantra: /Artist/Album/Track - Artist - Title.ext and if one exists, the cover sits in /Artist/Album/cover.(jpg|png).

I want to scan through all the second-level directories and find the ones that don't have a cover. By second level, I mean I don't care if /Britney Spears/ doesn't have a cover.jpg, but I would care if /Britney Spears/In The Zone/ didn't have one.

Don't worry about the cover-downloading (that's a fun project for me tomorrow) I only care about the glorious bash-fuiness about an inverse-ish find example.

A few facts: I use Wine. Wine ships its own version of Notepad. For some files, this copy of Notepad has somehow become associated. There is no possibility of me ever actually wanting to open anything in Notepad.

I figure I could try and find out what Notepad is associated with and re-associate that with my editor of choice but that seems deeply tedious. Is there any global way to stop Notepad existing as a method for opening files?

I'm sure this must be fairly simple but can't find it here.

How does one go from having a blank SD card to having an SD card that boots a Raspi?

I want to give a client access to my server, but I want to limit those users to their home directories. I will bind-mount in any files I want them to be able to see.

I've created a user called bob and added him to a new group called sftponly. They have a home directory at /home/bob. I've changed their shell to /bin/false to stop SSH logins. Here is their /etc/passwd line:

bob:x:1001:1002::/home/bob:/bin/false

I've also changed the /etc/ssh/sshd_config to include the following:

Match Group sftponly
        ChrootDirectory /home/%u
        ForceCommand internal-sftp
        AllowTcpForwarding no

When I try to log in as them, here's what I see

$ sftp bob@server
bob@server's password: 
Write failed: Broken pipe
Couldn't read packet: Connection reset by peer

If I comment out the ChrootDirectory line I can SFTP in but then they have free rein over the server. I have found that ChrootDirectory /home works, but it still gives them access to any home directory. I have explicitly tried ChrootDirectory /home/bob but that doesn't work either.

What am I doing wrong? How can I limit bob to /home/bob/?

----EDIT-----

Okay so I just had a look at /var/log/auth.log and saw this:

May  9 14:45:48 nj sshd[5074]: pam_unix(sshd:session): session opened for user bob by (uid=0)
May  9 14:45:48 nj sshd[5091]: fatal: bad ownership or modes for chroot directory component "/home/bob/"
May  9 14:45:48 nj sshd[5074]: pam_unix(sshd:session): session closed for user bob

I'm not entirely sure what's going on there, but it suggests something is wrong with the user directory. Here is the ls -h /home output:

drwxr-xr-x 26 oli      oli      4096 2012-01-19 17:19 oli
drwxr-xr-x  3 bob      bob      4096 2012-05-09 14:11 bob

I started using Sublime Text 2 a week or so ago and I loved it so much I've spent $60 on it and now want to use it for everything.

Gedit currently has ownership of most of the text file associations. I'd essentially like to replace any association to gedit with sublime-text-2.

Any tips available on bulk association changing? Desktop-neutral methods are preferred.

I've got problem with Handbrake/ffmpeg. After ~5 minutes transcoding, the computer locks up. I'm fairly sure it's a kernel panic because caps-lock starts flashing.

There are a few logical questions about what to do and some about specific bugs but I'm really after one thing: what happened right before everything died?!

I've checked /var/log/kern.log and all I see around the time is me sticking in a DVD and then a few minutes later, the system booting up. No errors, no panic notice.

Is there any way to force panics to be logged? I'm fairly sure I can reproduce this (it's happened 100% of the times I've tried recently) so while I'd rather this "just worked", I'm happy enough to reboot a few times if it means I can find the cause of the panic.

I've been building a website for a guy who uses Mac OS X and occasionally he sends me screenshots of bugs. They come out looking like this:

This is fairly typical of Mac screenshots. You get the window decorations, the shadow from the window and a white or transparent background (not the desktop wallpaper -- I've checked).

Compare this to an Ubuntu window-shot (Alt+Print screen):

It's impossible to keep a straight face and say the Ubuntu one anywhere near as elegant.

My question is: Is there an application that can do this in Ubuntu?

Edit: Follow up: Is there an application that can do this in one move? Shutter is pretty good but running the plugin for every screenshot is pretty tiresome as it doesn't seem to remember my preference (I want south-shadow and that requires selecting south, then clicking refresh, then save) and it's more clicks than I'd like.

Is there a simple way of telling shutter I want south-shadow for all screenshots (except entire desktop and area-selection)?

I need to show somebody a website running on my local machine tomorrow. Normally I'd accomplish this by port forwarding on my local router but thanks to failing hardware and its replacement being awful, my current router doesn't let me do port forwarding.

So stuck with this delay and not wanting to push the whole thing onto a proper server, I had a crazy idea: Can I just forward my port to an external server over SSH?

I've done port tunnelling before but I usually do it the right way around:

• I connect to a remote box and ask that port 12345 shows up on my local machine at port 12345.
• I start something on P12345 on the remote machine
• I can access it via localhost:12345

What I want to do:

• Connect to a remote PC and ask that that its local P12345 fetch things from my local P12345 (over the tunnel)
• I start something on my local computer on P12345
• Other people can access remote:12345 and see my localhost:12345

Just created a new virtual Ubuntu server and I'm in the process of hardening it for production use. I currently have a root account. I want to do the following:

• Create a new user (let's call them jim for the rest of this). I want them to have a /home/ directory.
• Give jim SSH access.
• Allow jim to su to root but not perform sudo operations.
• Turn off root SSH access.
• Move SSHd off to a non-standard port to help stop brute-attacks.

My problem lies with the first two items. I've already found useradd but for some reason, I can't log in as a user created with it over SSH. Do I need to beat SSHd to allow this?

I want to download a file from an active SSH session. In many cases I probably could just use SFTP, scp, rsync et al but there are times where I have elevated permissions on the remote server in a way I cannot use these methods.

If you're struggling to understand what I mean, imagine that you wanted to download something from /root/ or /var/log/auth.log. Root login is disabled (because we're not idiots). How do you get that file? Copy it out somewhere less protected and then move it? This is clunky. There are also scenarios where the remote path is complex or temporary, or isn't even a path because I want the output of a remote command stored locally. Store remotely, then copy? Clunk!

There are several more clunky ways to achieve versions of these but in an ideal world, I would have something akin to local write access from the remote server, using the existing SSH session as a conduit. Something like (this is just an artist's impression):

$oli@remote: cp /root/cheesecake /local/

And it just appears in my local cwd. And bidirectional access wouldn't be a bad thing.

It's been eight long years since I asked this question and we've seen a real range of clunk, but it remains a problem that I still struggle with occasionally.

I've refactored the question into something a lot more idealistic. I fully understand that there may not currently be a perfect answer. All past and future efforts towards my ideal are appreciated.

As part of my job as a web developer, I spend an amount of time doing UI prototypes to show the client. It's a pain in the behind but sometimes it has to be done.

I've seen Shuttleworth (and the design team) pump out images like this:

That's made by something called Balsamiq Mockups... Something that balances on top of Adobe Air (yack!) and costs $79.

I've tried it but it kept falling over. I think it had something to do with Air not the app itself. My point is if I'm paying out for something, I want it to be native.

Whenever Ubuntu boots up, a dialogue pops up asking me to unlock my default keyring.

Is there some way this can unlock automatically through PAM or some other magical way?