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In the sidebar to yesterday's entry I (originally) made a Unix command line mistake by unthinkingly leaving out an ordinary, innocent looking space (it's corrected in the current version of the entry after it was noted by Emilio in a comment). This innocent looking mistake and its consequences are an illustration of...

Suppose that you need to scan your filesystems and pass some files with specific names, ownerships, or whatever, except that you want to exclude scanning under /tmp and /var/tmp (as illustrative examples). Perhaps also you're feeding the file names to a shell script, especially in a pipeline, which means that you'd ...

Recently I ran across (and eventually reported) an issue on pre-beta Ubuntu 24.04 where a grub package update would fail for systems with software RAID root disks and BIOS MBR booting. The specific error was that grub-install could not install the new version of GRUB's boot-time code on '/dev/md0', the (nominal) dev...

Bash has an interesting and broadly useful feature called 'programmable completion' (this has sort of come up before). Programmable completion makes it possible for Bash to auto-complete things like command line options for the current program for you. Unfortunately one flaw in Bash's programmable completion is that...

Often, programs have build time configuration settings for features they include, paths they use, and so on. Some of the time, people suggest that the way to handle these is not through systems like 'configure' scripts (whether produced by Autoconf or some other means) but instead by having people edit their setting...

I've been buying digital music from one of the reasonably good online sources of it (the one that recently got acquired, again, making people nervous about its longer term future). In addition to the DRM-free lossless downloads of your purchases, this place lets you stream albums through your web browser, which in m...

Recently I wrote about the problem of using basic Prometheus to monitor DNS query results, which comes about primarily because the Blackbox exporter requires a configuration stanza (a module) for every DNS query you want to make and doesn't expose any labels for what the query type and name are. In a comment, Mike K...

In the beginning, Unix only had processes and processes had process IDs (PIDs), and life was simple. Then people added (kernel-supported) threads, so processes could be multi-threaded. When you add threads, you need to give them some user-visible identifier. There are many options for what this identifier is and how...

If you run a recent enough version of iotop on a typical Linux system, it may nag at you to the effect of: CONFIG_TASK_DELAY_ACCT and kernel.task_delayacct sysctl not enabled in kernel, cannot determine SWAPIN and IO % You might wonder whether you should turn on this sysctl, how much you care, and why it was default...

Pretty much every modern system defaults to having data you write to filesystems be buffered by the operating system and only written out asynchronously or when you specially request for it to be flushed to disk, which gives you general questions about how much write buffering you want. Now suppose, not hypothetical...

In the long ago past, Linux gained some support for block IO priorities, with some limitations that I noticed the first time I looked into this. These days the Linux kernel has support for more IO scheduling and limitations, for example in cgroups v2 and its IO controller. However ionice is still there and now I wan...

Over on the Fediverse, I had a realization: This is my face when I realize that on a big multi-core machine, I want to do 'sed ... | sed ... | sed ...' instead of the nominally more efficient 'sed -e ... -e ... -e ...' because sed is single-threaded and if I have several costly patterns, multiple seds will paralleli...

Every window system has windows, as an entity. Usually we think of these as being used for, well, windows and window like things; application windows, those extremely annoying pop-up modal dialogs that are always interrupting you at the wrong time, even perhaps things like pop-up menus. In its original state, X has ...

One of the bits of technology news that I saw recently was that AWS was changing how long it ran servers, from five years to six years. Obviously one large motivation for this is that it will save Amazon a nice chunk of money. However, I suspect that one enabling factor for this is that old servers are more similar ...

Today I learned about the M-X command (well, key binding) (via), which "[queries the] user for a command relevant to the current mode, and then execute it". In other words it's like M-x but it restricts what commands it offers to relevant ones. What is 'relevant' here? To quote the docstring: [...] This includes com...

A while back I wrote about how doing work that scales requires being able to scale your work, which in the open source world requires time, energy, and the willingness to engage in the public sphere of open source regardless of the other people there and your reception. Not everyone has this sort of time and energy,...

It's general wisdom in the sysadmin community that if you expose a SSH port to the Internet, people will show up to poke at it, and by 'people' I mean 'attackers that are probably mostly automated'. For several years, the pattern to this that I've noticed was an apparent combination of two activities. There was a co...

The ZFS Intent Log (ZIL) is effectively ZFS's version of a filesystem journal, writing out hopefully brief records of filesystem activity to make them durable on disk before their full version is committed to the ZFS pool. What the ZIL is doing and how it's performing can be important for the latency (and thus respo...

A traditional irritation with building (or specifying) desktop computers is the issue of ECC RAM, which for a long time was either not supported at all or was being used by Intel for market segmentation. First generation AMD Ryzens sort of supported ECC RAM with the right motherboard, but there are many meanings of ...

One of the somewhat odd things about my old fashioned X Window System environment is that when I 'iconify' or 'minimize' a window, it (mostly) winds up as an actual icon on my root window (what in some environments would be called the desktop), in contrast to the alternate approach where the minimized window is repr...

Today we had a significant machine room air conditioning failure in our main machine room, one that certainly couldn't be fixed on the spot ('glycol all over the roof' is not a phrase you really want to hear about your AC's chiller). To keep the machine room's temperature down, we had to power off as many machines a...

One of the things that we have had for a long time is a serial console server, which is to say a server that collects and logs serial console output from all of our regular servers (this is primarily Linux kernel messages, as we've moved away from making the serial port the 'real' kernel console). To date we've done...

Once upon a time, you could readily get basic graphics cards, generally passively cooled and certainly single-width even if they had to have a fan in order to get you dual output support; this is, for example, more or less what I had in my 2011 era machines. These days these cards are mostly extinct, so when I put t...

When I wrote about how CGI programs aren't particularly slow these days, one of the reactions I saw was to suggest that one might as well use a FastCGI system to run your 'CGI' as a persistent daemon, saving you the overhead of starting a CGI program on every request. One of the practical answers is that FastCGI doe...