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(fileutils.info)Block size

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Block size
==========

   Some GNU programs (at least `df', `du', and `ls') display file sizes
in "blocks".  You can adjust the block size to make file sizes easier
to read.  The block size used for display is independent of any
filesystem block size.

   Normally, disk usage sizes are rounded up, disk free space sizes are
rounded down, and other sizes are rounded to the nearest value with ties
rounding to an even value.

   The default block size is chosen by examining the following
environment variables in turn; the first one that is set determines the
block size.

`DF_BLOCK_SIZE'
     This specifies the default block size for the `df' command.
     Similarly, `DU_BLOCK_SIZE' specifies the default for `du' and
     `LS_BLOCK_SIZE' for `ls'.

`BLOCK_SIZE'
     This specifies the default block size for all three commands, if
     the above command-specific environment variables are not set.

`POSIXLY_CORRECT'
     If neither the `COMMAND_BLOCK_SIZE' nor the `BLOCK_SIZE' variables
     are set, but this variable is set, the block size defaults to 512.

   If none of the above environment variables are set, the block size
currently defaults to 1024 bytes, but this number may change in the
future.

   A block size specification can be a positive integer specifying the
number of bytes per block, or it can be `human-readable' or `si' to
select a human-readable format.

   With human-readable formats, output sizes are followed by a size
letter such as `M' for megabytes.  `BLOCK_SIZE=human-readable' uses
powers of 1024; `M' stands for 1,048,576 bytes.  `BLOCK_SIZE=si' is
similar, but uses powers of 1000; `M' stands for 1,000,000 bytes.  (SI,
the International System of Units, defines these power-of-1000
prefixes.)

   An integer block size can be followed by a size letter to specify a
multiple of that size.  When this notation is used, the size letters
normally stand for powers of 1024, and can be followed by an optional
`B' for "byte"; but if followed by `D' (for "decimal byte"), they stand
for powers of 1000.  For example, `BLOCK_SIZE=4MB' is equivalent to
`BLOCK_SIZE=4194304', and `BLOCK_SIZE=4MD' is equivalent to
`BLOCK_SIZE=4000000'.

   The following size letters are defined.  Large sizes like `1Y' may
be rejected by your computer due to limitations of its arithmetic.

`k'
     kilo: 2^10 = 1024 for `human-readable', or 10^3 = 1000 for `si'.

`M'
     Mega: 2^20 = 1,048,576 or 10^6 = 1,000,000.

`G'
     Giga: 2^30 = 1,073,741,824 or 10^9 = 1,000,000,000.

`T'
     Tera: 2^40 = 1,099,511,627,776 or 10^12 = 1,000,000,000,000.

`P'
     Peta: 2^50 = 1,125,899,906,842,624 or 10^15 =
     1,000,000,000,000,000.

`E'
     Exa: 2^60 = 1,152,921,504,606,846,976 or 10^18 =
     1,000,000,000,000,000,000.

`Z'
     Zetta: 2^70 = 1,180,591,620,717,411,303,424 or 10^21 =
     1,000,000,000,000,000,000,000.

`Y'
     Yotta: 2^80 = 1,208,925,819,614,629,174,706,176 or 10^24 =
     1,000,000,000,000,000,000,000,000.

   Block size defaults can be overridden by an explicit
`--block-size=SIZE' option.  The `-k' or `--kilobytes' option is
equivalent to `--block-size=1k', which is the default unless the
`POSIXLY_CORRECT' environment variable is set.  The `-h' or
`--human-readable' option is equivalent to
`--block-size=human-readable'.  The `--si' option is equivalent to
`--block-size=si'.