2009-07-07
Posted in Computers, Personal, PlanetDebian, rant at 10:57 CEST (+0200) by sven
Oh well, I think RHELs support for multiple architectures installed at the same time (and thus the same support in CentOS) really needs some rethinking.
While the following might not be able to happen with the default installation media (I didn’t verify), it still can happen if you run your own mirrors and actually need both architectures listed in your yum repositories…
Anyway, what happened today is just one example of how the multi-arch support caused problems for me:
On a Xen Dom0, I needed to apply a kernel upgrade (from 2.6.18-92something to 2.6.18-128something) and as a result, a reboot. At this point you should memorize that the old kernel worked quite fine and all I did was a yum update followed by a reboot. A procedure I did on quite a number of Dom0 machines in the past weeks.
Well, the reboot this time didn’t work, the kernel halted after printing:
request_module: runaway loop modprobe binfmt-464c
Well, reboot again, select old kernel, systems boots fine….
What happened was that both the x86_64 and i686 versions of the old kernel was installed, so yum update updated both, probably first the x86_64 version, then the i686 version (but I didn’t check). Well, while for the old kernel, grub booted the x86_64 kernel with the x86_64 initrd, for the new kernel it tried to boot the i686 kernel with the x86_64 initrd. (verified by unpacking the initrd and the vmlinuz kernel image and running file on the binaries therein)
Now the big question is: How could the stupid yum/rpm/postinstall script system end up doing this? It is supposed to warn about conflicts if two packages ship different versions of the same file AFAICT, but there is no way the i686 and x86_64 versions of /boot/vmlinuz* could be identical. So there should have been a warning about this. And after that, how come the mkinitrd tool doesn’t even try to check wether the kernel architecture and that of the initrd binaries match? It happily packed 64bit binaries and 64bit kernel modules(sic!) when run against a 32bit kernel….
OK, enough of my frustration….
I really wished I had to maintain not RHEL/CentOS machines but Debian (based distro) machines here at work. Unfortunately, that won’t happen for various reasons…
While the bi-arch support in RHEL/CentOS is helpful in many ways, RPM and the way bi-arch works on these distros caused almost as much trouble to me already as it helped avoid.
See also Unifying config file syntaxes with nesting
See also Why is VoIP/SIP so hard?
See also init script generators
Permalink
2009-06-22
Posted in Computers, Personal, PlanetDebian at 08:45 CEST (+0200) by sven
I seem not to post anything but links lately, but anyway,
Eddy Petrișor has a post about transitioning from lilo to grub2 (considering usage of LVM).
Romain Beauxis writes about what he dislikes about git (or probably most distributes version control systems) when it comes to team-maintained packages, to which Martin F. Krafft responded with an interesting post that puts some aspects of distributed versioning into a more balanced perspective then Romain had. After all though, I agree that there are uses to DVCSs which make sense (like being able to commit while not having any sort of connection to the “central” repository). However, I still think that relatively small “projects” like maintaining Debian packages have more to gain from the central repository then from the ability to commit while not connected. That is, at least as long as upstream doesn’t use a DVCS already, in which case there are other benefits from using the same DVCS, like easily pulling in upstream changes.
David Welton posted about a small script that swaps virtual desktops (please note that you will need to enable javascript to actually see the script).
While not technologically new to me, this post by David Pashley about copying files with netcat was a nice summarization of how to do it (and why it is sometime preferable over scp or rsync, plain or over ssh). One of the comments refers to mbuffer, which might also prove useful if you need really high speeds (>200MByte/s) or want some more advanced buffering options. The pv tool (alias Pipe Viewer) might be of interest to meter the throughput.
Phil Hands writes about getting an USB stick to boot (certain) ISO images with the help of grub4dos.
See also Link collection 2009/03
See also Link collection 2009/05/18
See also Unifying config file syntaxes with nesting
Permalink
2009-05-18
Posted in Computers, Personal, PlanetDebian, Uncategorized at 14:06 CEST (+0200) by sven
That’s it for now, will update the post if I find more interesting links in the next few days.
See also Link collection 2009/03
See also Another link collection 2009-06-22
See also Dual boot and full encryption – Part 2
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2009-03-31
Posted in Computers, PlanetDebian, Random links at 14:22 CEST (+0200) by sven
Well, I normally despise of thinks like this link collection, but I thought I might add it anyway, since these are useful links for me and if I don’t post them here, I’m likely to forget where to find them in the near future:
- Sean Finney has a nice post about storing the list of parameters a (shell) script got in a way that it can be restored later. Quite handy if your script walks through the arguments parsing them (and consuming them while doing so) but you want to be able to display them in a helpful way if the parsing fails at some point.
- A while ago, Ingo Jürgensmann had a post that helps retrieving files from lost+found after a filesystem check, provided that you run his helper script on a regular basis. The same approach can also be used if you have a backup of all files, but lost the sorting work you did after the backup was done. This is possible because running the script can be done more often then you would normally do backups.
- He also has a small post about mtr oddities when IPv6 comes into play
- Adeodato Simó wrote about databases and when timestamps that store the timezone information really are more useful then timestamps that don’t.
- Adeodato also has a short post on using ssh as a socks proxy, which can be quite handy if you are behind a firewall.
Update: Fixed link to Ingo’s file retrieval from lost+found article. Thanks to Patrick Schoenfeld who pointed me at the wrong link.
Also thanks to the anonymous poster who found an alternative way to store and (in a way) restore commandline parameters. The solution doesn’t work in an as general way as that by Sean Finney et al., but it is much shorter and therefore interesting for where it can be used (when you control how commandline parameters are processed). See comments on this post for details.
See also Link collection 2009/05/18
See also Another link collection 2009-06-22
See also Dual boot and full encryption – Part 2
Permalink
2009-03-26
Posted in Computers, PlanetDebian at 16:07 CET (+0100) by sven
If you ever have the problem described below, you have to realize that Apache HTTPD is selecting the SSL certificate (and/or key) not based on you VirtualHost definition, but based on the ServerName in the current context. This means that you have two virtual hosts with the same ServerName, but on two different IPs, and are wondering why the wrong key (and/or certificate) is used, it might be because of this. Assume we have the following (simplified) configuration:
<VirtualHost a.b.c.d:443>
ServerName a.b.c.d
SSLCertificateFile /etc/ssl/certs/a.b.c.d_443.pem
SSLCertificateKeyFile /etc/ssl/certs/a.b.c.d_443-key.pem
</VirtualHost>
<VirtualHost a.b.c.d:444>
ServerName a.b.c.d
SSLCertificateFile /etc/ssl/certs/a.b.c.d_444.pem
SSLCertificateKeyFile /etc/ssl/certs/a.b.c.d_444-key.pem
</VirtualHost>
(note: This happened to me when wanting to open a SSL server for subversion on a host that also had Apache run as a reverse/application proxy for some specific application that managed its own CA)
Both VirtualHosts will use the very same certificate and key (as far as I was able to tell, but at least the same key), in my case that of the specific application (which was(is?), in its way, broken regarding SSL).
This might as well be a bug or a design decision (AKA feature), I don’t know. However the “workaround” that worked for us was to change one of the server names to something else (since it seems it is unused anyway, unless the apache decides to generate a self-refering URL, which it certainly won’t do for the reverse/application proxy part).
Update: Fixed formatting on configuration sample to make it clear this is not about namebased virtual hosts.
See also IP addresses
See also Unifying config file syntaxes with nesting
Permalink
2009-03-01
Posted in Computers, PlanetDebian at 18:49 CET (+0100) by sven
Oh well, I tried to search for it but failed miserably, so I’m blogging about it hoping the original author might read my post on planet.debian.org (where I read the original post):
A friend of mine might need exactly the sort of scripts someone posted here:
- Creating a list of file checksum+pathname/filename
- Reading files from lost+found and moving them to their original filename by identifying from the list in (1)
However, I can’t recall who posted about this, and don’t want to do the same work again. Please, Dear Lazyweb, help me 
See also Unifying config file syntaxes with nesting
See also User configuration
See also Link collection 2009/03
Permalink
2009-01-08
Posted in Computers, PlanetDebian at 17:20 CET (+0100) by sven
Sami Haahtinen wrote a nice post about usability. I do mostly agree with him, except for one little thing:
A few years back, I noticed that I often started as a kind of “Joe User” with new applications, and often even stayed that way, often wishing that the UI of that application was simpler or at least made it more obvious which options are important and which I could most likely keep at their defaults.
Yet I am a system administrator and programmer/developer, so most people would probably consider me as an advanced user by default (wether that is correct in any given context or not, for example I still don’t really grok GIMP).
Also I did have quite a lot of contact with users that have very little experience, knowledge and interest in computers and software and only use them to achive certain goals.
Anyway, I’m quite sure most readers of this blog are aware that Linus Torvalds once complained about the Gnome printing dialog being simplified way too much. And at that time, I had to agree (note that I didn’t check out Gnome again since those days, at least 2 years ago).
What I really wonder (especially since I realized this in some of my own applications) is why it is so hard for developers to add some additional checkbox or button that enables/disables advanced options. For example, let’s take an applications printing dialog. By default, it would only allow the selection of a printer, orientation (if sensible) and (if the selected printer supports more than one) the paper size. Now advanced options might include duplex printing (automatic or manual), printing mutliple pages on a single sheet of paper, printing in grey on color printers,…
These options might be of use to anyone, but would most likely confuse beginners. So what I did in most of my little application was to just show the basic options and add an “advanced options” button which provided access to additional functionality which was not normally needed.
As for the issue with firefox updates mentioned by Sami: I don’t think it is a problem that firefox asks what to do with extensions. For one, it only lists extensions which are installed but claim not to support the new version of firefox. Second, practically everyone I know of who uses any extension can be considered to be an advanced user. And third: The dialog is pretty straightforward about what it is asking and when I once hit it while a (”dumb user”) friend was sitting with me, he understood what it was about quite easily (I didn’t explain the dialog, just what extensions were).
So my idea of a good UI is:
As simple as possible for beginning users, but allow advanced users to get to the details (”Details” or “Advanced options” buttons/checkboxes/dialogs).
See also No related posts
Permalink
2008-11-29
Posted in Computers, PlanetDebian at 12:10 CET (+0100) by sven
In Silly translations, Gintautas Miliauskas wrote about some rather silly translations. This reminded me of a finding by a colleague a few days ago.
He had recently updated his Ubuntu installation to KDE4 (using a german locale). After this, he reassigned a hotkey (to CTRL-SPACE). However, KDE showed: STRG-Weltraum (ctrl-”outer space”) instead of STRG-Leertaste (ctrl-space key) 
UPDATE: Since Frederik (see comments) reminded me of the fact I already knew:
This silly translation is not the fault of the german KDE members, but a bug in the Ubuntu package, which is taking more or less random translations from Rosetta.
See also No related posts
Permalink
2008-01-04
Posted in Computers, PlanetDebian at 21:47 CET (+0100) by sven
Anthony Towns wrote about user configuration (i.e. ~/.foo) and the XDG spec/proposal versus his own (and according to him) simpler version. The main goal of all this is to get rid of all the ~/.foo directories and files in a users home directory. Apart from technically minor differences, I don’t see why AJs proposal would be simpler than the XDG approach. All it does is hardcoding the values which are adjustable in XDG via XDG_*_DIRS.
There is one notable difference though: AJ proposes fallback values which are compatible with existing application paths (i.e. HOME_ETC/XDG_CONFIG_HOME should default to ~/ – resulting in ~/.foo files/dirs). This is a good proposal in a way: If you patch an existing application to strictly follow the proposal made by AJ, it still finds its old configuration (and other files) if the new environment variables are not set. No need to move anything around. However, I think the XDG approach is better since it makes sure that compliant applications don’t clutter ~/ anymore. They do need some mechanism to move existing configurations and data around though if the XDG-compliant stuff isn’t already there, but an old style config exists.
All in all, I think it is worth following the XDG spec, even if it is slightly more complex than AJs proposal. For one, it already exists for a while and I think that some applications already started following that spec. It also makes slightly more sense to me to have the system fully configurable as to where the apps store data as opposed to the hardcoded fallback/default values AJ proposes (even if we would change AJs proposal to use “$HOME-cleaning” default values).
See also About Usability
See also Unifying config file syntaxes with nesting
See also Apache SSL oddity
Permalink
2007-10-17
Posted in Computers, Personal, PlanetDebian at 15:03 CEST (+0200) by sven
Since I never really found a nice overview of which CPU flags (see /proc/cpuinfo) mean what, so I gathered some information using the web, with the most notable sources being the BOINC FAQ entry on CPU Register Acronyms at [1] and the output of the nice little (though seemingly mostly unmaintained) cpuid utility. See my results at [2]. Any suggestions for enhancements and completions are highly welcome, just leave a comment to this post.
[1]: href=”http://boincfaq.mundayweb.com/index.php?language=1&view=176
[2]: http://blog.incase.de/index.php/cpu-feature-flags-and-their-meanings/
See also CPU feature flags and their meanings
See also Why is VoIP/SIP so hard?
See also live-cd-on-removable-disk
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