Package: tech-ctte
Severity: normal
X-Debbugs-Cc: 761424@bugs.debian.org
As reported in #761424, the "sizes" output by df(1) are not actual
sizes, due to the "units" used. The "units" used are merely unit
prefixes. Moreover, df uses the same pseudo-units with different
meanings. The output can therefore be misleading if one attempts to
interpret it. 2 different calls seem to give different measurements
for the same filesystems:
chealer@debian:~$
LANG=C df -h
Filesystem Size Used
Avail Use% Mounted on
rootfs 1.8T
317G 1.4T 19% /
udev 10M
0 10M 0% /dev
tmpfs 252M
5.4M 247M 3% /run
/dev/disk/by-uuid/a00f8767-e954-4b81-8035-c6bb414671cb 1.8T
317G 1.4T 19% /
tmpfs 5.0M
4.0K 5.0M 1% /run/lock
tmpfs 961M
0 961M 0% /run/shm
/dev/sdb2 2.2G
122M 2.0G 6% /tmp
chealer@debian:~$ LANG=C df -H
Filesystem Size Used
Avail Use% Mounted on
rootfs 2.0T
340G 1.6T 19% /
udev 11M
0 11M 0% /dev
tmpfs 264M
5.7M 259M 3% /run
/dev/disk/by-uuid/a00f8767-e954-4b81-8035-c6bb414671cb 2.0T
340G 1.6T 19% /
tmpfs 5.3M
4.1k 5.3M 1% /run/lock
tmpfs 1.1G
0 1.1G 0% /run/shm
/dev/sdb2 2.4G
128M 2.2G 6% /tmp
chealer@debian:~$
In the first example call, JEDEC prefixes are used, while SI
prefixes are used in the second.
Michael Stone denies, excusing the behavior with space scarcity,
documentation, and what he considers as little impact:
I'm not going to deviate from upstream. [...] The
space is more important (in my opinion) than the need for a constant
reminder of the unit. The documentation is there for people to read the
first time, after that it's just not that important. (Even for the
numbers above the difference isn't really significant--the relative
sizes are the consistent, and what are the odds that you need exactly 12
gigasomethings? If you did need exactly that much space, you're probably
better off looking at kbytes or bytes anyway.)
The space scarcity and impact arguments do not hold, and
unfortunately, even the documentation does not define the
pseudo-sizes currently output.
--
Filipus Klutiero
http://www.philippecloutier.com
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