07-03-2012
Why is read-ahead a problem since above is only a 512bytes read, all it takes is normally positioning the drive head .. Then if the cache is the reason, it should affect the file as well, but I am getting the same result for all reps?
More importantly, my experiment is really about time/vs blocksize, and I am trying to make it more accurate :
- Shall I only use regular files?
- position the disk head somewhere else after each test?
- is it possible to flush all caches programmatically ?
Sorry for all those questions ..
![Big Grin Smilie](https://www.unix.com/images/smilies/biggrin.gif)
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head(1) User Commands head(1)
NAME
head - display first few lines of files
SYNOPSIS
head [-number | -n number] [filename...]
DESCRIPTION
The head utility copies the first number of lines of each filename to the standard output. If no filename is given, head copies lines from
the standard input. The default value of number is 10 lines.
When more than one file is specified, the start of each file will look like:
==> filename <==
Thus, a common way to display a set of short files, identifying each one, is:
example% head -9999 filename1 filename2 ...
OPTIONS
The following options are supported:
-n number The first number lines of each input file will be copied to standard output. The number option-argument must be a positive
decimal integer.
-number The number argument is a positive decimal integer with the same effect as the -n number option.
If no options are specified, head will act as if -n 10had been specified.
OPERANDS
The following operand is supported:
file A path name of an input file. If no file operands are specified, the standard input will be used.
USAGE
See largefile(5) for the description of the behavior of head when encountering files greater than or equal to 2 Gbyte ( 2**31 bytes).
EXAMPLES
Example 1: Writing the first ten lines of all files
To write the first ten lines of all files (except those with a leading period) in the directory:
example% head *
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of head: LANG, LC_ALL, LC_CTYPE, LC_MES-
SAGES, and NLSPATH.
EXIT STATUS
The following exit values are returned:
0 Successful completion.
>0 An error occurred.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
|CSI |enabled |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
SEE ALSO
cat(1), more(1), pg(1), tail(1), attributes(5), environ(5), largefile(5), standards(5)
SunOS 5.10 1 Feb 1995 head(1)