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Difference between bytes and bits

Submitted by sandip on Sat, 07/26/2008 - 13:34

Bits are 1s or 0s representing the state of a switch, in binary form.

A byte is a binary word, consisting of 8 bits.

8 bits equals one Byte.

1024 bytes equals one KiloByte (KB)

1024 KiloBytes equals one MegaByte (MB)

1024 MegaBytes equals one GigaByte (GB)

Sometimes people use 1000 instead of 1024, so numbers sometimes get screwy.

A bit is always represented by a small "b", a Byte is always represented by a large "B".

It is common practice to use bits in reference to interface speeds and bytes in reference to memory and storage capacities.

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Importing existing SSL key and certificate for tomcat

Submitted by sandip on Fri, 07/25/2008 - 16:50
  1. Convert key and cert to a single pkcs12 format.

    openssl pkcs12 -export -inkey <pathto>/key.txt -in <pathto>/cert.txt -out cert.pkcs12

  2. Remove existing tomcat aliased PrivateKeyEntry from cacerts.

    keytool -delete -alias tomcat -keystore <pathto>/cacerts

  3. Use java-1.6 keytools to import PKCS12 keystoretype into existing cacerts keystore file.

    keytool -importkeystore -destkeystore cacerts -srckeystore cert.pkcs12 -srcstoretype PKCS12

  4. Note the alias of the newly imported PrivateKeyEntry, which would normally be 1.

    keytool -list -keystore <pathto>/cacerts | grep PrivateKeyEntry

  5. Change the alias to tomcat.

    keytool -changealias -alias 1 -destalias tomcat -keystore <pathto>/cacerts

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Simple captcha for oscommerce contact form

Submitted by sandip on Thu, 07/24/2008 - 21:52

Embed the captcha image by calling a php script in "contact_us.php":

<input type="text" name="verify" />
<img src="/image.php" width="60" height="20" alt="Please enter the values from this image" />

Edit contact_us.php file and exactly after the below line:

  if (isset($HTTP_GET_VARS['action']) && ($HTTP_GET_VARS['action'] == 'send')) {

place the verification code:

        // Captcha check
        $t = trim($HTTP_POST_VARS['verify']);
        if ($t == "") {
                $captcha_error = "Enter the verification code!";
                $error = true;
                $messageStack->add('contact', $captcha_error);
        } else if (trim($_SESSION["thecode"]) == "") {
                $captcha_error = "No verification code generated!";
                $error = true;
                $messageStack->add('contact', $captcha_error);
        } else if ($_SESSION["thecode"] != strtoupper($t)) {
                $captcha_error = "Invalid verification code!";
                $error = true;
                $messageStack->add('contact', $captcha_error);
        }
        else
        { // End Captcha Check

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Support for 32 bit development libraries on 64 bit CentOS

Submitted by sandip on Fri, 07/18/2008 - 09:45

To support C/C++ 32 bit development libraries on CentOS-5.2 x86_64 arch the below devel packages are required:

yum install glibc-devel.i386 libstdc++-devel.i386

Below is example output of multilib support for gcc:

$ gcc -print-multi-lib; gcc -print-multi-os-directory; gcc -print-multi-os-directory -m32
.;
32;@m32
../lib64
../lib

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Create users in OpenVZ Containers

Submitted by sandip on Fri, 07/11/2008 - 00:35

Helper script to create users on all OpenVZ VEs simultaneously:

#!/bin/bash
# create_ve_users.sh
# Usage: ./create_ve_users.sh <username> <password> <uid> <group1,group2>

USERNAME=$1
PASSWORD=$2
USERID=$3
GROUP=$4
EXPECTED_ARGS=4

OUT_FILE=.create_users_$$

if [ $# -ne $EXPECTED_ARGS ]
then
  echo "Usage: `basename $0` <username> <password> <uid> <group1,group2>"
  exit 65
fi

VE_LIST=$(/usr/sbin/vzlist -H -o veid)

for VE in ${VE_LIST}
do
        vzctl exec $VE \
                "echo useradd -u $USERID -G $GROUP -p \''`openssl passwd -1 $PASSWORD`'\' $USERNAME > /tmp/${OUT_FILE} ; \
                sh /tmp/${OUT_FILE} ; \
                rm -f /tmp/${OUT_FILE}"
done

exit 0

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Update OpenVZ containers

Submitted by sandip on Wed, 07/09/2008 - 16:51

If you manage several OpenVZ containers, here is a simple bash script to keep the OpenVZ containers upto date.

#!/bin/bash
# vzyum_updates.sh
# updates VEs

VE_LIST=$(/usr/sbin/vzlist -H -o veid | grep -v Warning)

for VE in ${VE_LIST}
do
  /usr/bin/vzyum $VE update
done

exit 0

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OpenVZ CentOS template cache creation with vzpkgcache

Submitted by sandip on Mon, 07/07/2008 - 23:44

Following the instruction over at OpenVZ Wiki, I've had no problems with the installation and creation of templates prior to CentOS-5.2 on x86_64 systems. However, with the latest set of updates to CentOS-5.2, the vzpkgcache seems to have been broken as sysklogd is no longer being installed by default. Below is how I got it to work:

Note: edit /vz/template/centos/5/x86_64/config/minimal.list and append .x86_64 to all except for the addons packages. Then run:

# vzpkgcache -f centos-5-x86_64-minimal

which gives the below error at the end:

sed: can't read /etc/init.d/syslog: No such file or directory
ERROR: Script install-post failed

The solution was to edit "/vz/template/centos/5/x86_64/config/install-post" and set syslog and syslog.conf sed replacements with exit status of "0".

# Disable klogd
$VZCTL exec2 $VEID \
        "sed -i -e 's/daemon\\ klogd/passed\\ klogd\\ skipped/' \
                -e 's/killproc\\ klogd/passed\\ klogd\\ skipped/' \
                        /etc/init.d/syslog; exit 0"
...
# Disable fsync() in syslog
$VZCTL exec2 $VEID \
        "sed -i -e 's@\\\([[:space:]]\\\)\\\(/var/log/\\\)@\\\1-\\\2@' \
                /etc/syslog.conf; exit 0"

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Reducing logical volume

Submitted by sandip on Thu, 07/03/2008 - 09:56

I've had to reduce the logical volume that was alloted for mysql data from 8GB to 4GB, which was a breeze with e2fsadm available for lvm1 on RHEL-3 .

Stop the running serivces using the volume:

# service httpd stop
# service mysqld stop

e2fsadm will reduce the filesystem and then the logical volume.

# umount /mnt/lv-mysql
# e2fsadm -L -4G /dev/hdb2-vg00/lv-mysql
# mount /mnt/lv-mysql

Check with df, which should now show the new volume size:

$ df -h /mnt/lv-mysql
Filesystem              Size  Used Avail Use% Mounted on
/dev/hdb2-vg00/lv-mysql 4.0G  531M  3.3G  14% /mnt/lv-mysql

Start the running serivces using the volume:

# service httpd start
# service mysqld start

Note: e2fsadm is not available in lvm2 and will need to reduce in two steps:

1. Reduce the filesystem residing on the logical volume.
2. Reduce the logical volume.

# resize2fs /dev/vg0/lv0 4G
# lvreduce -L -4G /dev/vg0/lv0

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ffmpeg with mp3 encoder support on Ubuntu Dapper

Submitted by sandip on Wed, 07/02/2008 - 00:26

The default install of ffmpeg on Ubuntu Dapper does not come with support for encoding mp3. I had to get the source and re-compile with mp3 support using lame as the encoder.

Make sure you have multiverse and universe enabled.

$ sudo apt-get build-dep ffmpeg
$ sudo apt-get install liblame-dev libfaad2-dev libfaac-dev libxvidcore4-dev liba52-0.7.4 liba52-0.7.4-dev libx264-dev
$ apt-get source ffmpeg
$ cd ffmpeg-*/
$ ./configure --enable-gpl --enable-pp --enable-pthreads \
        --enable-libogg --enable-a52 --enable-dts \
        --enable-dc1394 --enable-libgsm --disable-debug --enable-mp3lame \
        --enable-faad --enable-faac --enable-xvid --enable-x264
$ make
$ sudo make install

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Password Less SSH LOGIN

Submitted by manoj on Thu, 06/26/2008 - 19:55

The main idea behind having a Password Less SSH LOGIN is to be more secure over the internet.
The idea comes from encryption. A set of Public and Private Keys are generated.
The public key stays on the serve rand the private key stays with the user. Only they private key can talk to the public key.

The user needs to upload the public key to the server on
~/.ssh folder and name the file as authorized_keys2

To get the keys working make sure the folder permissons are set correct.

chmod 700 ~/.ssh
chmod 644 ~/.ssh/authrozied_keys2

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