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free memory drop_caches

free memory drop_caches

Writing to this will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.

To free pagecache:

echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:

echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:

echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation, and dirty objects are not freeable, the user should run "sync" first in order to make sure all cached objects are freed.

This tunable was added in 2.6.16.

Recursive search using "grep"

Typically, the answer is to use find, xargs, and grep. That's
horribly slow for a full filesystem search, and it's painfully
difficult to properly construct a pipeline that will avoid
searching binaries if you don't want to, won't get stuck on named
pipes or blow up on funky filenames (beginning with -, or sometimes
spaces, punctuation etc). There are ways around all these things,
but they are all ugly.

BTW, something that almost never gets mentioned but that I will
frequently use under conditions where it is appropriate is a
simple

grep pattern * */* */*/* 2>/dev/null

Not useful much beyond that, and may not even be good at that
except for certain starting points, but it's faster than any find
xargs pipeline can ever be if the set is small enough.

The simplistic approach using find is

find /whereveryouwantostart -exec grep whatever {} dev/null \;

That's not necessarily very efficient. Using xargs can help

find . xargs grep whatever

But it also has bugs if the filenames could have "-" at their
beginning. Fixing that can be a little nasty.

You may not want to grep binary files:

find . -type f -printxargs filegrep -i textcut -fl -d: xargs grep whatever

That's pretty awful, but it's what you have to get into if you
have special cases. Special cases are what makes this question more
difficult. If you have a small number of files and subdirs to
search, the simple approach may work fine for you. If not, you have
to get more creative.

Bill Campbell offers this Perl script:

I have a perlscript I call ``textfiles'' that I use for many

things like this:

textfiles dirname [dirname... ] xargs ...

Essentially it runs ``gfind @ARGV -type f'', then uses perl's -T

option on each file to determine whether it's a text file.

My textfiles script also has options to add options to the gnu

find command like -xdev, -mindepth, and -maxdepth.

Hell, it's short so I'm attaching it for anybody who wants to use

it. It does assume that the gnu version of find is in your PATH

named gfind (I make a symlink to /usr/bin/find on Linux systems

so that it works there as well).

#!/usr/local/bin/perl

eval ' exec /usr/local/bin/perl -S $0 "$@" '

if $running_under_some_shell;

# $Header: /u/usr/cvs/lbin/textfiles,v 1.7 2000/06/22 18:29:08 bill Exp $

# $Date: 2000/06/22 18:29:08 $

# @(#) $Id: textfiles,v 1.7 2000/06/22 18:29:08 bill Exp $

#

# find text files

( $progname = $0 ) =~ s!.*/!!; # save this very early

$USAGE = "

# Find text files

#

# Usage: $progname [-v] [file [file...]]

#

# Options Argument Description

# -f Follow symlinks

# -M maxdepth maxdepth argument to gfind

# -m mindepth mindepth argument to gfind

# -x Don't cross device boundaries

# -v Verbose

#

";

sub usage {

die join("\n",@_) .

"\n$USAGE\n";

}

do "getopts.pl";

&usage("Invalid Option") unless do Getopts("fM:m:xvV");

$verbose = '-v' if $opt_v;

$suffix = $$ unless $opt_v;

$\ = "\n"; # use newlines as separators.

# use current directory if there aren't any arguments

push(@ARGV, '.') unless defined($ARGV[0]);

$args = join(" ", @ARGV);

$xdev = '-xdev' if $opt_x;

$opt_f = '-follow' if $opt_f;

$opt_m = "-mindepth $opt_m" if $opt_m;

$opt_M = "-maxdepth $opt_M" if $opt_M;

$cmd = "gfind @ARGV -type f $xdev $opt_f $opt_m $opt_M ";

print STDERR "cmd = >$cmd<" if $verbose;

open(INPUT, $cmd);

while(<INPUT>) {

chop($name = $_);

print STDERR "testing $name..." if $verbose;

print $name if -T $name;

}

Compare two directory in Linux

The cmptree script is as follows:

#!/bin/bash
#
# cmptree: compare directory trees recursively and report the differences.
# Author: Ives Aerts

function gettype () {
  if [ -L $1 ]; then
    echo "softlink"
  elif [ -f $1 ]; then
    echo "file"
  elif [ -d $1 ]; then
    echo "directory"
  else
    echo "unknown"
  fi
}

function exists () {
  if [ -e $1 -o -L $1 ]; then
    return 0;
  else
    echo "$1 does not exist."
    return 1;
  fi
}

function comparefile () {
  cmp -s $1 $2
  if [ $? -gt 0 ]; then
    echo "$1 different from $2"
#  else
#    echo "$1 same as $2"
  fi
  return
}

function comparedirectory () {
  local result=0
  for i in `(ls -A $1 && ls -A $2) | sort | uniq`; do
    compare $1/$i $2/$i || result=1
  done
  return $result
}

function comparesoftlink () {
  local dest1=`ls -l $1 | awk '{ print $11 }'`
  local dest2=`ls -l $2 | awk '{ print $11 }'`

  if [ $dest1 = $dest2 ]; then
    return 0
  else
    echo "different link targets $1 -> $dest1, $2 -> $dest2"
    return 1
  fi
}

# compare a file, directory, or softlink
function compare () {
  (exists $1 && exists $2) || return 1;

  local type1=$(gettype $1)
  local type2=$(gettype $2)

  if [ $type1 = $type2 ]; then
    case $type1 in
      file)
        comparefile $1 $2
        ;;
      directory)
        comparedirectory $1 $2
        ;;
      softlink)
        comparesoftlink $1 $2
        ;;
      *)
        echo "$1 of unknown type"
        false
        ;;
    esac
  else
    echo "type mismatch: $type1 ($1) and $type2 ($2)."
    false
  fi

  return
}

if [ 2 -ne $# ]; then
cat << EOU
Usage: $0 dir1 dir2
Compare directory trees:
  files are binary compared (cmp)
  directories are checked for identical content
  soft links are checked for identical targets
EOU
  exit 10
fi

compare $1 $2
exit $?

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