Ελληνικά δωρεάν WiFi HotSpots

Ένας συνδιασμός των προσπαθειών των vrypan και javapapo για καταγραφή δωρεάν WiFi σημείων ανά την Ελλάδα. ο χάρτης είναι ανοιχτός οπότε όποιος έχει όρεξη μπορεί να προσθέσει σημεία που δεν έχουν καταγραφεί.

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Report disk space usage

A quick shell script that reports which disks use more than a specified percentage of disk space. Can be used as a cronjob to mail the results.

############################################################################
# Copyright (C) 2009  Panagiotis Kritikakos <panoskrt@gmail.com>           #
#                                                                          #
#    This program is free software: you can redistribute it and/or modify  #
#    it under the terms of the GNU General Public License as published by  #
#    the Free Software Foundation, either version 3 of the License, or     #
#    (at your option) any later version.                                   #
#                                                                          #
#    This program is distributed in the hope that it will be useful,       #
#    but WITHOUT ANY WARRANTY; without even the implied warranty of        #
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         #
#    GNU General Public License for more details.                          #
#                                                                          #
#    You should have received a copy of the GNU General Public License     #
#    along with this program.  If not, see <http://www.gnu.org/licenses/>. #
############################################################################

#!/bin/bash
if [ $# -lt 1 ] || [ $# -gt 2 ]; then
  echo "Usage ./disk_usage <percentage>";
  echo " Example: ./disk_usage 50";
  exit;
fi
space=(`df -h | awk '{sub(/%/,"");print $5}' | grep -v / | grep -v Use | grep -v ^$`)
spaceLen=${#space[*]}

i=0
echo "The disks bellow use more than ${1}% of their space" > /tmp/diskSpace
echo "-----------------------------------------------------" >> /tmp/diskSpace
while [ $i -lt $spaceLen ]; do
   checkval=${space[$i]}
   if [ $checkval -gt $1 ] || [ $checkval -eq $1 ]; then
        df -h | grep $checkval | awk '{print $1 "\t" $5 "\t" $6}' >> /tmp/diskSpace
   fi
        let i++
done
/usr/bin/Mail -s "Disk space usage" foo@bar.com < /tmp/diskSpace
rm -f /tmp/diskSpace

Bridging a network interface

I’ve been trying out recently KVM. It supports NAT by default but you need to manually configure one of the physical interfaces of the system as bridge in order to enable you to bridge a virtual machine’s network.
At fist place I had to create a new interface configuration file for the bridge in /etc/sysconfig/network-scripts/ifcfg-br0

DEVICE=br0
TYPE=Bridge
BOOTPROTO=dhcp
ONBOOT=yes

Once having the bridge file configured, I had to adjust the eth0 configuration:

DEVICE=eth0
HWADDR=00:22:29:18:A8:73
ONBOOT=yes
BRIDGE=br0

If instead of DHCP you’re using a static IP, then copy and paste the network information of ifcfg-eth0 to ifcfg-br

Checking after a reboot:

$ /sbin/ifconfig br0; /sbin/ifconfig eth0
br0       Link encap:Ethernet  HWaddr 00:22:29:18:A8:73
          inet addr:192.168.1.11  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::222:12ff:fe08:d113/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:449219 errors:0 dropped:0 overruns:0 frame:0
          TX packets:253636 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:593165878 (565.6 MiB)  TX bytes:133241643 (127.0 MiB)

eth0      Link encap:Ethernet  HWaddr 00:22:29:18:A8:73
          inet6 addr: fe80::222:12ff:fe08:d113/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:448789 errors:0 dropped:0 overruns:0 frame:0
          TX packets:313443 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:600638671 (572.8 MiB)  TX bytes:138369880 (131.9 MiB)
          Interrupt:177

In some cases I faced routing issues, the following solved them:

route add -net 192.168.1.0 gw 192.168.1.254 netmask 255.255.255.0 dev br0

Timestamp issue with Amazon EC2

I was playing yesterday with Eucalyptus Public Cloud, which is an Open Source project, that gives free access to some of the resources of their cloud where you can get a taste of Amazon’s EC2 tools. Having configured the environment of my system, I tried to retrieve the list of the available zones on which I could deploy some of Eucalyptus’ virtual machines. However, the first few tries returned a timestamp problem:

$ ec2-describe-availability-zones
Server: An error was discovered processing the  header.
(WSSecurityEngine: Invalid timestamp The security semantics of message have expired)

So it looked like there was an issue between the timing of my system against that of the server. I decided to synchronise my system with an NTP server. There was indeed something more than five minutes difference between my system’s manual time and that of the NTP sever:
Manual time:

$ date
Tue 12 May 2009 18:52:22 BST

NTP sync:

$ date
Tue 12 May 2009 18:57:37 BST

One more try to fetch the list:

$ ec2-describe-availability-zones
AVAILABILITYZONE	epc	mayhem9.cs.ucsb.edu

It worked this time. As mentioned hereeach message sent by the client contains a time-stamp. The server refuses messages sent more than five minutes ago. This is to prevent replay attacks (where an attacker gets hold of a valid message and then sends it again later)“.

Wikiloc

I just came across Wikiloc, which “is a free web app that lets you discover and share outdoor trails on the web in an easy way”. Really interesting project with thousands of trails around the globe. Available through the browser with Google Maps and exists as a layer within Google Earth as well. Really important that users can contribute with their own routes.

Globus Toolkit post-installation notes

A few problems encountered after Globus Toolkit 4.2.1 installation and configuration:

While submitting a job:

globusrun-ws: Job failed: Error code: 201Script stderr:
sudo: sorry, you must have a tty to run sudo

The “requiretty” option must be removed from sudoers file.

globusrun-ws: Job failed: Error code: 200Sudo is misconfigured to run the
globus-job-manager-script.pl script for user $USER.

User “globus” needs to be in sudoers file.

While transferring data with GridFTP:

error: globus_ftp_client: the server responded with an error
530 530-Login incorrect. : globus_gss_assist: Gridmap lookup failure: Could not map /DN ENTRY/
530-
530 End.

GridFTP server needs to run as ‘root’: http://www.globus.org/mail_archive/discuss/2002/05/msg00337.html