Operating Systems

Syntax To display the HTTP Headers using just tcpdump the following syntax can be used : root@webserver1 ~]#  tcpdump -vvvs 1024 -l -A host  www.fir3net.com Example [root@webserver1 ~]# tcpdump -vvvs 1024 -l -A host www.fir3net.com tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 1024 bytes 19:51:57.742793 IP (tos 0x0, ttl 64, id 39410, offset … Read more

To install mplayer onto your Centos / RHEL distro you will need to : 1. Download and install the rpmforge repository. rpm -ivh  2. Add the following text to a new file : /etc/yum.repos.d/fc6.repo. cat > /etc/yum.repos.d/fc6.repo[PASTE THE FOLLOWING] [fc6-base] name=Fedora Core 6 mirrorlist=http://mirrors.fedoraproject.org/mirrorlist?repo=core-6&arch=$basearch enabled=1 gpgcheck=0 [CTRL-C]  3. Install mplayer using yum. yum install mplayer

Curl is a tool to transfer data from or to a server, using one of the supported protocols (HTTP, HTTPS, FTP, FTPS, TFTP, DICT,  TELNET, LDAP or FILE) and is designed to work without user interaction. Below shows some useful examples: Total Retrieval Time [root@webserver1 ~]# curl -s -w “%{time_total}\n” -o /dev/null www.bbc.com 0.196 Host … Read more

The other day I was faced with the problem of determining the networking bandwidth of a Linux system via just the shell. After some googling and some head scratching I eventually came up with the following command. echo “scale=2; `curl  –progress-bar -w “%{speed_download}” http://speedtest.wdc01.softlayer.com/downloads/test10.zip -o test.zip` / 131072″ | bc | xargs -I {} echo … Read more

Below details the basic steps required to compile Apache 2.2 upon a CentOS based distro. Update System yum install gcc Download Source cd /var/tmp/wget Unzip / Untar gunzip httpd-2.2.19.tar.gzmkdir httpdcd httpdtar -xvf ../httpd-2.2.19.tarcd httpd-2.2.19/ Compile ./configuremake Install make install Confirm Install [root@localhost httpd-2.2.19]# /usr/local/apache2/bin/apachectl -vServer version: Apache/2.2.19 (Unix)Server built: Jul 10 2011 17:59:10

ISSUE When configuring the timezone within Centos the correct timezone is not propagated and the output of the command date does not represent the timezone previously configured. SOLUTION This can be caused by corrupted timezone files. To resolve the issue remove the soft-link, reinstall tzdata and then recreate the soft-link to the necessary timezone. [root@server … Read more

To extract or open RAR files within Linux the unrar binary is used. Below provides the installation and basic operational syntax for the unrar program. 1. Installation 1.1 REDHAT yum install unrar 1.2 UBUNTU apt-get install unrar 2. Basic Syntax To extract a RAR file the following syntax is used: unrar e contents.rar 3. Example … Read more

When Installing Ubuntu from a Live CD via the graphical installer ubiquity you may receive the following error :               The username you entered is invalid. Note that usernames               must start with a lower-case letter, which can be followed               by any combination of numbers and more lower-case letters. Solution This error can occur … Read more

This is caused by additional carriage returns within your script. In Windows the end of a line is denoted by CRLF (Carriage-Return, Line-Feed). In Unix-like systems, the end of a line is donated by a single LF. This means when you try to run your script, every line has an extra carriage return which in turn causes … Read more

Conditional execution is a term used to describe the execution of processes or commands based on specfic conditions. This can also be thought of as conditional logic.  Like with most scripting or programming languages conditional logic is built upon the use of return codes. A return code (exit status)  is returned upon process completion to … Read more

Below is a small method for running Java daemons within Linux. The syntax is as follows: nohup is used so that it doesn’t get killed when user logs off </dev/null is used so that it doesn’t require a command-promt of it’s own & is used so that the Java daemon runs as a background process. … Read more

The following syntax will scan a range of IP addresses. At the point of a ARP response being received it will show a reply message (shown in below example). Note : In this example it will scan IPs between 10.1.1.1-255. if [ -x  /sbin/arping ] ; then for i in {1..255} ; do echo arping … Read more

The following command will place a clock within the top right corner of your shell. while sleep 1;do tput sc;tput cup 0 $(($(tput cols)-25));date;tput rc;done &

INTRODUCTION This article aims to explain the various steps required in configuring Wireless connectivity within Backtrack 4 r2. It is also worth mentioning that as Backtrack is based upon Ubuntu/Debian you may find steps and solutions within this article useful when faced with other Ubuntu/Debian based wireless issues. MY SETUP Backtrack installation consists of a … Read more

When running the command iptables -vL you may find that : the output displays slowly. the output (appears) to have hung. You can further see what IPtables is doing via running iptables -vL. From this you will most likely see iptables trying to run a reverse DNS lookup (and failing). Solution Due to IPtables trying to … Read more