Wandering Thoughts archives


Link: Readable colour text combinations

Color Test Results is a summary of the results of surveying a bunch of Internet users about what colour text on what background they found the easiest to read. The summary quote:

As you can see, the most readable color combination is black text on white background; overall, there is a stronger preference for any combination containing black.

Not coincidentally, most of my text is black on white (or black on slightly off-white). I was interested to see that white on black actually rates fairly highly, because for me bright colours on black (like white, jwz's green, etc) rapidly give me eye-searing, headache inducing afterimages.

(The survey is pretty old, but human perception is unlikely to have changed that much in ten years or so.)

(From Bill de hÓra.)

links/TextColours written at 15:08:20; Add Comment

Peeking under mount points with NFS

Normally, one of NFS's irritating features is that when you mount a filesystem from a server, you don't automatically get access to any sub-filesystems mounted on that filesystem; you have to know about them and mount them yourself.

(Yes, yes, some NFS servers offer features to do this for you; such features have their own problems.)

But there's an old sysadmin trick that turns this into a feature. If you NFS mount a filesystem, such as /, you can see inside directories covered up by active mount points. If you're evil, you can write things there too. Because this is just NFS, you can do it while the system is up in regular multiuser mode without having to perturb it.

The usual situations I've wound up needing this are:

  • something accidentally scribbles into a 'filesystem' that isn't mounted at the time, and it needs to be cleaned up. This usually happens either during early boot or during system maintenance when I make a mistake and don't notice it until later.
  • I need to plant strategic files into the root filesystem to fake having a filesystem mounted; for example, I might need a /var/tmp that still exists before /var is mounted, or need a few device nodes to be in /dev before the dynamic /dev filesystem gets mounted.

(The other not to be discounted peculiar sysadmin use for NFS mounts is that it bypasses all of the usual rootkit infrastructure used to hide files from user-level programs. Most of those modify either user level shared libraries or system call entry points, both of which kernel NFS servers bypass.)

sysadmin/PeekingUnderMountsWithNFS written at 00:33:13; Add Comment

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