[SOLVED] How does `ls -lh` round file size?

Issue

I'm comparing the rounded file size value displayed by ls -lh to the raw size in bytes (as displayed by ls -l, say). I'm having a hard time figuring out what algorithm it uses to do the conversion from bytes.

My assumption is that it interprets the units K,M,G as either

• (a) 10^3, 10^6, 10^9, or
• (b) 1024, 1024^2, 1024^3.

On the one hand, I have one file that ls -l reports as 2052 bytes, and ls -lh rounds to 2.1K:

$ ls -l usercount.c 
-rw-r--r-- 1 squirrel lsf 2052 May 13 15:41 usercount.c
$ ls -lh usercount.c 
-rw-r--r-- 1 squirrel lsf 2.1K May 13 15:41 usercount.c

This would seem to support hypothesis (a), because 2052/1000=2.052 which rounds up to 2.1K but 2052/1024=2.0039 which clearly would display as 2.0K when rounded to one decimal place.

On the other hand, I have another file that ls -l reports as being 7223 bytes, which ls -lh displays as 7.1K:

$ ls -l traverse.readdir_r.c
-rw-r--r-- 1 squirrel lsf 7223 Jul 21  2014 traverse.readdir_r.c
$ ls -lh traverse.readdir_r.c
-rw-r--r-- 1 squirrel lsf 7.1K Jul 21  2014 traverse.readdir_r.c

This confusingly supports hypthesis (b), because 7223/1000=7.223 which should round down to 7.2K, but 7223/1024=7.0537 which rounds up to the displayed 7.1K

This leads me to conclude that my assumption is wrong and that it does neither (a) nor (b) exclusively. What algorithm does ls use to do this rounding?

Solution

GNU ls will by default round up in 1024-based units.

It does not round to nearest, as you've taken for granted.

Here's the formatting flag from gnulib human.h:

/* Round to plus infinity (default).  */
human_ceiling = 0,

This is consistent with everything you're seeing:

• 2052 is 2.0039 KiB which rounds up to 2.1
• 7223 is 7.0537 KiB which rounds up to 7.1

Answered By - that other guy

Answer Checked By - David Goodson (WPSolving Volunteer)