Link: ZFS Storage Overhead
ZFS Storage Overhead ( via )is not quite about what you might think. It's not about, say, theoverhead added by ZFS's RAIDZ storage ( where there are surprises ); instead it's about some interestinglow level issues of where space disappears to even in very simplepools. The bit about metaslabs was especially interesting to me.It goes well with Matthew Ahrens' classic ZFS RAIDZ stripe width,or: How I Learned to Stop Worrying and Love RAIDZ ,which is endlessly linked and
SELinux's problem of keeping up with general Linux development
Fedora 26 was released on Tuesday, so today I did my usual thingof doing a stock install of it in a virtual machine as a test, tosee how it looks and so on. Predictable things ensued with SELinux . In theresulting Twitter conversation, I came to a realization :
It seems possible that the rate of change in what programslegitimately do is higher than the rate at which SELinux policies canbe fixed.
Most people who talk about SELinux policy problems, myself included,usually implicitly treat developing SELinux
Some people feel that all permanent SMTP failures are actually temporary
It all started with a routine delivery attempt to my sinkhole SMTPserver that I use as aspamtrap:
remote 165.227.10.85:36462 at 2017-07-03 13:30:28220 This server does not deliver email.EHLO mail.travelshopnews7.com[...]MAIL FROM:250 Okay, I'll
Recursive DNS servers send the whole original query to authoritative servers
As a long term sysadmin, I usually feel that I have a solid technicalgrasp of DNS (apart from DNSSEC, which I ignore on principle ). Then every so often, I get to findout that I'm wrong. Today is one of those days.
Before today, if you had asked me how a recursive DNS server did alookup from authoritative servers, I would have told you what isbasically the standard story. If you're looking up the A record forfred.blogs.example
Understanding the .io TLD's DNS configuration vulnerability
First there was Matthew Bryant's The .io Error - Taking Controlof All .io Domains With a Targeted Registration ,about a configuration error that allegedly allowed you to take overcontrol of some .io nameservers, and then there was a response toit, Matt Pounsett's The .io Error: A Problem With Bad Optics, ButLittle Substance ,which argued that this was much ado about nothing much. While Iagree that the consequences are less severe than Bryant thought, Ithink that Pounsett's
The BSD r* commands and the history of privileged TCP ports
Once upon a time, UCB was adding TCP/IPto (BSD) Unix. They had multiple Unix machines, and one obvious thingto want when you have networking and multiple Unix machines is a wayto log in and transfer files from one machine to another. Fortunatelyfor the UCB BSD developers, TCP/IP already had well-specified programs(and protocols) to do this, namely telnet and FTP. So all they had todo was implement telnet and FTP clients and servers and they were done,
Ubuntu's 'Daily Build' images aren't for us
In response to my wish for easily updating the packages on UbuntuISO images , Aneurin Price brought up jigdo . In researching what Jigdois, I wound up running into a tantalizing mention of Ubuntu dailybuilds (perhaps from here ). This sentme off to Internet searches and eventually I wound up on Ubuntu'spage for the Ubuntu Server 16.04.2 LTS (Xenial Xerus) Daily Build .This looked like exactly what we wanted, already pre-built for us(which is perfectly fine
Why we're not currently interested in PXE-based Linux installs
In theory, burning Ubuntu install DVDs (or writing USB sticks) andthen booting servers from them in order to do installs is anold-fashioned and unnecessary thing. One perfectly functional modernway is to PXE-boot your basic installer image, go through whateverquestions your Ubuntu install process needs to ask, and then likelyhave the installer get more or less everything over the networkfrom regular Ubuntu package repositories (or perhaps a local mirror).Assuming that it works, you might as well enable the Ubuntu update
I wish you could easily update the packages on Ubuntu ISO images
Our system for installing Ubuntu machines starts from a somewhat customized Ubuntu ISO image (generally burnedonto a DVD, although I want to experiment with making it work on aUSB stick) and proceeds through some post-install customizationscripts. One of the things that these scripts do is apply all ofthe accumulated Ubuntu updates to the system.In the beginning, when an Ubuntu LTS release is fresh and brightand new, this update process doesn't need to do much and goes quitefast. As time goes by
Programming Bourne shell scripts is tricky, with dim corners
There have been a bunch of good comments on my entry about myviews on Shellcheck , so I want to sayjust a bit too much to fit in a comment of my own. I'll mostlybe talking about this script, where I thought the unquoted '
$1'was harmless:#!/bin/shecho Error: $1Leah Neukirchen immediately pointedout something I had completely forgotten, which is that unquotedBourne shell variable expansion also does globbing . The followingtwo lines give you the same
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