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Posted by drgraefy on Tue 21 Oct 2008 at 18:44
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The emergency shell in the debian initramfs is a wonderful thing. I recently had to use it when I encountered some disk mounting problems when migrating system disks to a new machine. The problem I ran into was that the rootfs was on LVM on a raid array that was not properly detected during boot. I was able to use mdadm to get the raid going, but then I had to get LVM going so that I could mount the root file system and get the rest of the boot going.

However, at first glance, it appeared that the only LVM utility in the initramfs is /sbin/vgimport. This one utility was not sufficient for me to get LVM going. I remembered, though, that lvm on a full system is in fact just a single utility linked by various names:
servo:~ 0$ readlink -f $(which vgimport)
/sbin/lvm
servo:~ 0$ 
It turns out that this is also true on the initramfs: the full lvm binary is available on the initramfs, it's just called 'vgimport'. To get around this, I just linked /sbin/vgimport to /sbin/lvm, and was then able to get full lvm capability with the "lvm < subcommand>" syntax.

 

Posted by drgraefy on Tue 4 Mar 2008 at 04:53
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So I'm trying to figure out how to prepopulate the prompt for the bash read function with text that could be edited and then passed to the readline output. For some reason I'm having an exceptionally hard time figuring out how to do this. It's either not possible, or I'm just having no luck. For example

The read help says that "One line is read from the standard input", but that doesn't actually seem to be the case:

servo:/tmp/cdtemp.VI3235 0$ foo=
servo:/tmp/cdtemp.VI3235 0$ read -e -p : foo
:asdf
servo:/tmp/cdtemp.VI3235 0$ echo $foo
asdf
servo:/tmp/cdtemp.VI3235 0$ foo=
servo:/tmp/cdtemp.VI3235 0$ echo -n asdf | read -e -p : foo
servo:/tmp/cdtemp.VI3235 1$ echo $foo

servo:/tmp/cdtemp.VI3235 0$ echo asdf >bar
servo:/tmp/cdtemp.VI3235 0$ read -e -p : foo < bar
servo:/tmp/cdtemp.VI3235 0$ echo $foo
asdf
servo:/tmp/cdtemp.VI3235 0$

This appears to indicate that read can accept input from a file, but not from a pipe. Why would that be?

Does anyone know how to prepopulate a read or readline prompt? Maybe it's not possible with read, but with some other function? It must be possible if I were to code it in C or something, cause plenty programs that do stuff like this (take the emacs mini-buffer, for instance).

 

Posted by drgraefy on Thu 8 Nov 2007 at 16:01
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For the better part of the last year, I have been struggling with a frustrating svn problem. My group's svn is served through apache2+ssl. Seemingly totally inconsitently, svn checkouts/updates would hang indefinitely, a "C-c" the only way to escape. Certain files would seem to be especially problematic, but again not consistently. Most times, but not always, hangs would be accompanied by the following message in /var/log/apache/error.log:

[Thu Feb 22 12:46:37 2007] [error] [client 1.2.3.4] Provider encountered an error while streaming a REPORT response.  [500, #0]
[Thu Feb 22 12:46:37 2007] [error] [client 1.2.3.4] A failure occurred while driving the update report editor  [500, #104]
[Thu Feb 22 12:46:37 2007] [error] [client 1.2.3.4] Error writing base64 data: Connection reset by peer  [500, #104]

I have been trying for months to figure out what the problem is, but to no avail. Numerous google searches turned up people with similar issues, but never with any indication of what the problem might actually be, or how to get around it. Finally, after much struggle, we had a breakthrough yesterday.

Our network is on a private NAT'd lan. We finally noticed that the hangs were only occuring on machines located on our internal lan, and not for machines on the wan. This was a curious and important revelation. Internally the fqdn of our web site (foo.bar for the sake of argument), which resides on a server in our private lan, maps to our external IP address (1.2.3.4), just as it does externally, which in turn corresponds to the wan port of our crappy D-Link router/gateway. External ports 80 and 443 at 1.2.3.4 are then mapped to the web server (10.0.0.5).

What does this mean? Well, it means that internally, requests for foo.bar are first routed to the wan port of the router, which then sends them back to the web server. Apparently this was causing our crappy little router to choke, and drop connections. To confirm this, we changed the internal DNS to point foo.bar to the web server 10.0.0.5 directly. Once this was done, no more svn checkout/update hangs.

It's funny this never seemed to manifest itself elsewhere, but we don't do much heavy data transfer internally from the web server over ssl, except via svn. Basically the router couldn't turn around ssl packets fast enough. Ultimately, the problem is that we are running our network on a private, NAT'd lan. We shouldn't have to do this, and it's always a pain in the ass for one reason or another. As a wise man once quoted to me: 'NAT is not the answer. "NAT?" is the question, and the answer is "NOT!"'.

 

Posted by drgraefy on Tue 30 Oct 2007 at 14:32
I was having trouble using svn+ssh when the username differed on the local and remote hosts. For instance, if the user on the local machine is 'ape' and the user on the local machine is 'chimp', the following would fail:
ape@local:0:~$ svn co --username chimp svn+ssh://remote/path/to/repo
After a little bit of research, I found a relevant debian bug report filed against subversion. In it the reporter mentions something that works for him, that I confirmed does the trick: the username goes in the url:
ape@local:0:~$ svn co svn+ssh://chimp@remote/path/to/repo
Clearly this is still a bug with the svn client for not passing the username argument properly, but at least there's an easy way to get around it.

 

Posted by drgraefy on Fri 19 Oct 2007 at 04:15
Tags: none.

I have a server running munin-node. Almost 200 times a day (probably about 2/3 of the instances of munin-node running) I get a message such as the following in the kern.log:

Oct 18 23:00:06 chez kernel: munin-update[22368] general protection rip:2aacef9b51bd rsp:7fffbbe6f5b0 error:0

I have been able to find essentially no information to explain why this is happening, or even what the error means. Is anyone familiar with anything like this? Any help would be hugely appreciated.

 

Posted by drgraefy on Sun 28 Jan 2007 at 18:29
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In configuring a new LDAP server, I recently stumbled upon on an incredibly useful tool: ldapvi (available in both sarge (v1.1) and etch (v1.6)). I can't say enough about how useful this tool is. If you need to make a couple of small changes to your database, it's perfect. You can either open up the entire database, or any filtered search result, in the text editor of your choosing at the command line. You can then view the changes before they're committed. Very highly recommended for any LDAP administrator.

 

Posted by drgraefy on Sun 28 Jan 2007 at 17:50
So on a fresh install with the new d-i the other day, in the partitioner, I used the "configure entire disk using lvm" option. I was very impressed. It did basically exactly what I would have done myself, ie. broke the disk into 2 primary partitions, one small one for /boot, and the rest for a physical volume for the main volume group. It then created smartly sized logical volumes for all the major filesystems (/, /usr, /var, /home, /tmp, and scratch). Sure saved me some time.

Sometimes I make a separate partition for scratch, but I'm still undecided it's worth the trouble or not. I also usually put /tmp on a tempfs, which I think makes a lot more sense.

 

Posted by drgraefy on Sun 26 Nov 2006 at 23:37
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i know this is totally insane, but i'm completely and utterly convinced that xgammon cheats. i don't have any proof, yet. but i will. eventually...