:date: 2022-03-05 07:39 :tags:
I was doing some quick operations on a couple of images in
I ran this simple ImageMagick command to
quickly see exactly what their dimensions were.
$ identify /tmp/*jpg
Simple, right? I was pretty surprised to get this output.
/tmp/image1.jpg JPEG 520x473 520x473+0+0 8-bit sRGB 28564B 0.000u 0:00.000 /tmp/image2.jpg JPEG 446x307 446x307+0+0 8-bit sRGB 43772B 0.000u 0:00.000 identify-im6.q16: unable to open image `/tmp/systemd-private-dc07b3ba0d8d4a5bb3f871d462a4c015-systemd-logind.service-9rFjpg': Permission denied @ error/blob.c/OpenBlob/2924.
What's going on there? Well, it seems that this is a flaw in Systemd, the double edged sword of Damocles which tries to make Linux less Linuxy (unfortunately).
In its internal housekeeping, Systemd has created a temporary file in
a public temporary file location that ends in a random string. And
in this case, luck runs out and today's file's random string is
9rFjpg, which of course ends in
jpg, just like the well known
photography file format.
Although Systemd is both irritating and useful, I don't mean to single
it out. This is really a problem with the unix
mktemp command which
uses the C
mkstemp() function from
stdlib.h. So this is a pretty
You could argue that I should have done what DOS people were trained to
do and specify my shell glob as
*.jpg. But why? If we're going to
have extensions be a thing at all (and trigger all kinds of automatic
responses), surely we should respect them and not write random strings
to the end of filenames. (Especially if we're delimiting parts of the
filename with dashes instead of periods!) That's certainly my opinion
and I'm posting this to encourage others — and my future self — to
consider this a mistake and not make it. But given this problem, when
doing serious scripting it probably does make sense to be defensive
when specifying files by extension and insist on the period too if
possible. That may not actually solve all problems of this type but it
should cure most issues with default