If working:

dev.eviport.com points to svn checkout folder
localhost points to your usual local dev

hosts file:
127.0.0.1       localhost
127.0.0.1   dev.project.com

apache conf:
Comment out other document root lines and paste the following at the bottom of the file:

NameVirtualHost *:80
NameVirtualHost 127.0.0.1:80

<VirtualHost 127.0.0.1>
ServerName dev.project.com
DocumentRoot “D:/dev/project/trunk/”
<Directory “D:/dev/project/trunk/”>
allow from all
order allow,deny
AllowOverride All
</Directory>
DirectoryIndex index.html index.php
</VirtualHost>

<VirtualHost 127.0.0.1>
ServerName localhost
DocumentRoot “D:/dev/”
</VirtualHost>

Incoming search terms:

• wamp (12)
• wamp server logo (2)

yum install gcc make libXext-devel libSM-devel libICE-devel zlib-devel libXfixes-devel libXdamage-devel libvorbis-devel libtheora-devel

Because CentOS does not official an RPM for recordmydesktop, we will have to install it from source. We will download a tar of the source code, untar the source, and remove the tar file:

wget http://downloads.sourceforge.net/project/recordmydesktop/recordmydesktop/0.3.8.1/recordmydesktop-0.3.8.1.tar.gz
tar xf recordmydesktop-0.3.8.1.tar.gz
rm -rf recordmydesktop-0.3.8.1.tar.gz

Now, let’s go into the folder and install Recordmydesktop.

cd recordmydesktop-0.3.8.1
./configure
make
make install

If you did not set a custom prefix, running /usr/bin/recordmydesktop should begin recording your desktop! Use the following command (just as with most commands) to view the options available:

recordmydesktop –help

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• recordmydesktop centos 6 (1)
• record my desktop linux (1)

If you have any 3rd party propriatory graphics card drivers installed it is recommended you remove them prior to the upgrade process to avoid any problems during the update, you can reinstalled them after the upgrade has completed.

Always take a backup before carrying out an operating system upgrade!

How To Upgrade to 12.04 Desktop using the GUI

This is by far the easiest way to upgrade you simple wait until the official release date of 12.04 (which is currently the 26th of April 1012) and upgrade when prompted. If this does not happen it’s probably as the servers are getting hammered by users updating you can either wait or follow the instructions below on how to carry out the network upgrade.

How to Upgrade from 11.10 to 12.o4 for Desktops using Update Manager

If Ubuntu fails to prompt you to upgrade to 12.04 Desktop you can run the update manager process manually, note these instructions are for 11.10 to 12.04 only.

• Run the Update Manager application from the Unity Dash
• In Update Manager, click on “Settings” and enter your password to start the Software Sources application
• Select the sub menu Updates from the Software Sources application
• Check the “Release upgrade – Show new distribution releases” drop down to make sure “Normal releases” is selected, and change it if otherwise
• Close the Software Sources application and return to Update Manager
• In Update Manager, click the Check button to check for new updates.
• If there are any updates to install, use the Install Updates button to install them, and press Check again after that is complete
• A message will appear informing you of the availability of the new release
• Click Upgrade
• Follow the on-screen instructions

Upgrade from 10.04 to 12.o4 for Desktops using Update Manager

The following instructions are for 10.04 to 12.04 Desktop upgrades, this uses a network installation using update manager, please only use these instructions for 10.04 to 12.04 desktops.

• Open the Update Manager application from the System → Administration menu
• In Update Manager, click the “Settings…”, and enter your password to start the Software Sources application
• Select the sub menu Updates from the Software Sources application
• Check the “Release upgrade – Show new distribution releases” drop down to make sure “Long term support releases only” is selected, and change it if otherwise
• Close the Software Sources application and return to Update Manager
• In Update Manager, click the Check button to check for new updates
• If there are any updates to install, use the Install Updates button to install them, and press Check again after that is complete
• A message will appear informing you of the availability of the new release
• Click Upgrade
• Follow the on-screen instructions

Ubuntu Server upgrade to 12.04 using the command line

This is my preferred method of upgrading to 12.04 as it can be ran over SSH or on any version of Ubuntu Server.

To start off with make sure update-manager-core is installed and fully up to date:

sudo apt-get install update-manager-core

Edit the file /etc/update-manager/release-upgrades and add set:

Prompt=normal

Start the upgrade process:

sudo do-release-upgrade

Hope you will find it helpful!

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Check network properties.

To show network properties type in ifconfig command.
1. Open terminal and type in ifconfig command and hit enter key.

[fedora@localhost ~]$ ifconfig

em1 Link encap:Ethernet HWaddr 00:13:21:65:C7:2D
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
Interrupt:17

em2 Link encap:Ethernet HWaddr 00:13:21:65:C7:2C
inet addr:60.49.199.75 Bcast:60.49.199.79 Mask:255.255.255.248
inet6 addr: fe80::213:21ff:fe65:c72c/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:14743744 errors:0 dropped:3610 overruns:0 frame:0
TX packets:691939 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1863873005 (1.7 GiB) TX bytes:84722609 (80.7 MiB)
Interrupt:18

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:429 errors:0 dropped:0 overruns:0 frame:0
TX packets:429 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:36564 (35.7 KiB) TX bytes:36564 (35.7 KiB)

virbr0 Link encap:Ethernet HWaddr 52:54:00:B7:EB:4F
inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)

[fedora@localhost ~]$

Open NetworkManager configuration tools.

Then to start the network configuration process, open NetworkManager configuration tools by type in nm-connection-editor on the terminal.

2. Then type in nm-connection-editor and hit enter key, this open the interface of NetworkManager configuration tools…

3. Choose network device that you need to configure and the click edit button… on the example, we choose system em1 network device to edit as an example… then go to IPv4 Settings tab and choose Manual by clicking the Method drop down menu

4. Then… Click on Add button and start adding IP Address. then proceed to put your network DNS server address…

5. Then click on Save button to apply the changes. to activate network interface or to enable disable network interface go to NetworkManager applet (nm-applet) as show on the screenshot below.

Please note :- that this network configuration example tested on Linux Fedora 16 machine… the output may vary base on your machine use, operating system and command version.

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When we Surf the Internet Many Visitors See That Some Website has Auto-Detect System For Viewport Size,Screen Resolution and Mouse Position of User System.

This System is Created By Using JavaScript.So Here Is The Code For Creating this Auto-Detect System in JavaScript.

To Use This Code Just Copy and Paste It.

<script type="text/javascript">
function getViewportWidth()
{
if (window.innerWidth)
{
return window.innerWidth;
}
else if (document.body && document.body.offsetWidth)
{
return document.body.offsetWidth;
}
else
{
return 0;
}
}
function getViewportHeight()
{
if (window.innerHeight)
{
return window.innerHeight;
}
else if (document.body && document.body.offsetHeight)
{
return document.body.offsetHeight;<br />
}
else
{
return 0;
}
}
var tellMeTheSizes=function()
{
document.getElementById("viewportwidth").innerHTML = getViewportWidth() + "px";
document.getElementById("viewportheight").innerHTML = getViewportHeight() + "px";
document.getElementById("resolutionheight").innerHTML = screen.height + "px";
document.getElementById("resolutionwidth").innerHTML = screen.width + "px";
}
window.onload=function()
{
tellMeTheSizes();
}
window.onresize=function()
{
tellMeTheSizes();
}
window.onmousemove=function(event)
{
ev = event || window.event;
document.getElementById("mousetop").innerHTML = ev.pageY + "px";
document.getElementById("mouseleft").innerHTML = ev.pageX + "px";
}
</script>

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Delete Windows Partition:

1. List the windows partition that you want to delete using fdisk -l [target device] command. The example below show that the Windows partition that we want to delete is on the /dev/sdb hard disk device and on the partition number 1 ( show as sdb1 )

[root@fedora ~]# fdisk -l /dev/sdb

Disk /dev/sdb: 40.0 GB, 40007761920 bytes
64 heads, 32 sectors/track, 38154 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
Disk identifier: 0x00b4c6f2

Device Boot Start End Blocks Id System

/dev/sdb1 1 38154 39069680 c W95 FAT32 (LBA)

[root@fedora ~]#

2. Execute the fdisk command as show on the example below.

[root@fedora ~]# fdisk /dev/sdb

The number of cylinders for this disk is set to 38154.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:

1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs

(e.g., DOS FDISK, OS/2 FDISK)

3. Then type in ‘m’ key and hit Enter key to display the help menu for fdisk command. Command (m for help): m

Command action

a toggle a bootable flag
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition
l list known partition types
m print this menu
n add a new partition
o create a new empty DOS partition table
p print the partition table
q quit without saving changes
s create a new empty Sun disklabel
t change a partition’s system id
u change display/entry units
v verify the partition table
w write table to disk and exit
x extra functionality (experts only)

4. Type in ‘d’ key and hit Enter key to delete a partition, select the partition that you want to delete.
Command (m for help): d

Selected partition 1

5. Verify again by type in ‘p’ command, to list all partition table inside the hard disk.
Command (m for help): p

Disk /dev/sdb: 40.0 GB, 40007761920 bytes
64 heads, 32 sectors/track, 38154 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
Disk identifier: 0x00b4c6f2
Device Boot Start End Blocks Id System

6. Save the changes that you made by type in the ‘w’ key then hit Enter key
Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

[root@fedora ~]#

Check deleted partition on hard disk

To verify: After exit the fdisk command… check Windows deleted partition again using fdisk command as show on example below.

[root@fedora ~]# fdisk -l /dev/sdb

Disk /dev/sdb: 40.0 GB, 40007761920 bytes
64 heads, 32 sectors/track, 38154 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
Disk identifier: 0x00b4c6f2

Device Boot Start End Blocks Id System

[root@fedora ~]#

Hope the example will be helpful!

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DEVICE=”eth0″
HWADDR=”xx:xx:xx:xx:xx:xx”
NM_CONTROLLED=”yes”
ONBOOT=”no”

Follow this steps to set static ip and set it auto start once rebooted in CentOS 6.2 :

1. Configure eth0:

[root@centos6 ~]# vi /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=”eth0″
HWADDR=”00:0C:29:67:51:B1″
NM_CONTROLLED=”yes”
ONBOOT=”yes”
IPADDR=192.168.1.44
BOOTPRO=static
NETMASK=255.255.255.0

2. Configure Default gateway:

[root@centos6 ~]# vi /etc/sysconfig/network

NETWORKING=yes
HOSTNAME=centos6.2
GATEWAY=192.168.1.1

3. Restart Network interface:

[root@centos6 ~]# /etc/init.d/network restart

or

[root@centos6 ~]# Service network restart

4. Configure DNS server:

[root@centos6 ~]# vi /etc/resolv.conf

nameserver 8.8.8.8
nameserver 192.168.1.1

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Previously installing Webmin on your Ubuntu server required a few workarounds thanks to its reliance on deprecated perl libraries, but nowadays you can actually do a full install via the standard APT mechanism.

First, edit your sources file to add the Webmin repository:

sudo nano /etc/apt/sources.list

Add the following two lines at the end of the file:

deb http://download.webmin.com/download/repository sarge contrib
deb http://webmin.mirror.somersettechsolutions.co.uk/repository sarge contrib

Next, add the necessary key to ensure smooth access:

cd ~
wget http://www.webmin.com/jcameron-key.asc
sudo apt-key add jcameron-key.asc

Now that we’re all set up, time to do the actual download and install:

sudo apt-get update
apt-get install webmin
apt-get -f install

Done. You should now be able to login to Webmin at the URL http://localhost:10000/. Or if accessing it remotely, replace localhost with your system’s IP address. You can login in with any user account that has sudo powers.

Related Link
http://www.webmin.com/index.html

Reference

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Question:

My main concern is having packet sniffers and what not getting access to the data.

The only ways I see at the moment is to have VPN running on the network or use IPSec policy’s to do this. Is there any other way to do that?

Answer:
IPSEC is the network layer encryption designed specifically to cover this case (among others).

If you do not want to mess with it because of the complexity and cannot use HTTPS throughout for some reason, you might consider relying on your network equipment’s isolation features. WPA2-enterprise encrypts client-to-AP traffic and is not susceptible to man-in-the-middle attacks due to a secret shared among all users as WPA-PSK would be. Managed switches allow either for locking down the MAC forwarding database or using authenticated connections (802.1x) with a MAC address lockdown so MAC spoofing attacks allowing authenticated users to sniff on other user’s data would be mitigated. This would not protect your users from a direct tap on layer 1 though (e.g. a hub or a wiretap device installed somewhere between the switch port and the user’s laptop Ethernet jack).

Answered by syneticon-dj

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tar.gz files are commonly used on Linux operating systems for source packages and for grouping large amounts of small files, tar.gz is by far the most common compressed archive software used on Linux, if you are from a Windows background you will be familiar with .zip this is a similar propitiatory equivalent.

How to untar tar.gz archive

tar -xvzf archive.tar.gz

You should be left with your extracted files in a directory or in the directory where you extracted your tar.gz file.

I will explain the Linux untar options I used above:

x = Extract
v = Verbose (it shows you what files are extracted from the archive on the console)
z = Filter through gzip – allows us to extract gzip compression using the Linux tar command.
f = File, this tells the command we which to use a file

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This should include requests to the root domain as well as any (wildcard) subdomain.

I also don’t want any unnecessary if statements, as per the nginx pitfalls document.

Here’s what I have so far but it only seems to work for the root domain, not subdoamins.

server {
listen 80 default_server;
server_name www.*;
rewrite “^www\.(.*)” $scheme://$1 permanent;
}

Solution:
My understanding of your question is the following:
Redirect all requests reaching any subdomain of an arbitrary root domain to the root domain – in a reasonably general manner. For example:

www.example1.com -> example1.com
abcd.example2.com -> example2.com
*.exampleN.com -> exampleN.com

Let’s start with the easy case first – a known root domain, with any subdomain:

server{
server_name *.example.com;
rewrite ^ $scheme://example.com permanent;
}server{
listen 80 default_server;
server_name example.com;
#your main config
}

This is fairly well optimized – no if statements, no unnecessary captures in the rewrite – and wildcard server_names are hashed for performance. The first server block matches any subdomain and will issue a redirect to the second server block which only matches the root domain. (Note, although it is easy to match both conditions in one server block (server_name .example.com – no * needed) the two server blocks are needed to prevent a redirect loop).

The more generalized case requires some way of identifying the domain, since it is ‘unknown’. We therefore need to parse the server_name – and can do so with a regex capture.

server{
server_name ~^(.+\.)(?.+\..+)$;
rewrite ^ $scheme://$domain permanent;
}server{
listen 80 default_server;
server_name _;
#your main config
}

Here we have a (required) subdomain – (.+\.) means any character (.) repeated one or more times (+) followed by an actual ‘.’ (escaped with the backslash) – this capture will be assigned to $1 if we need it.

The next section is very similar – we are using Perl 5.1/PCRE7 notation for a ‘named capture’ – ?assigns the capture to $domain. Our domain can be anything (.) one or more characters in length (+), followed by an actual ‘.’ and then another set of any characters (the TLD). This regex will not work for TLDs which contain a ‘.’ – e.g. ‘co.uk’ – if you will be using those, it is probably best to specify the valid TLDs in your regex. For example:

server_name ^(.+\.)(?.+\.(co\.uk|net|org|com))$

We use the same rewrite as above, just replacing the static root domain with the captured domain.

Since a common case with the ‘unknown’ domain scenario will see you passing the same files to all the domains, you probably don’t need to capture the domain name in the default_server block (it is more efficient to avoid the regex when possible).

It is important to note that regex matches have the lowest priority – exact names, and wildcard entries take precendence over regexes. Additionally, unlike exact names and wildcard entries – regexes are not hashed. Finally, when using regexes with captures, even if only one server block is defined, the expression must be evaluated for every request to obtain the captures.

As a result of the above, if you do have to do something specific with a particular domain name, simply define a new server block for it and that will take precedence over the default_server block defined above.

If you know the domain names, even if they are numerous, you will get better performance if you can include the static name instead of using a regex. That said, there are some cases (e.g. allowing users to point their (unknown) domain at your IP as part of a service) where you may not know the domain and where the regex approach is necessary.

(Of course, this needs a matching wildcard DNS entry for the requests to ever reach the server.)

Reference

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Dim the Lights

In most of the devices, including cellphones, the display is the biggest culprit when it comes to reduced battery life. A brightly lit laptop won’t really help you get through a whole workday. The best solution to this problem is to dim the screen as much as possible. If, in certain cases like movie-watching or reading you need a bright display, you can turn the brightness up for that period and them dim the screen back when you’re finished.

Kill the Slowpokes

It’s not just the display that hurts the battery, it’s also those CPU-hogging programs that make you reach out for the charger sooner than expected. That said, it’s not always easy for a user to spot that the CPU is under a load. It takes a real slowdown or freezing to realize that the program has become a mess and needs to be killed.

Don’t worry yet, as you can always keep an eye on your CPU or RAM by using any of the following methods:

1. Take a look at the system monitor if you feel the slightest of difference in performance. From there, you can kill any misbehaving task.

2. Ubuntu users can install the System Load Indicator from a ppa, which, once installed, will let you take a look at the performance right from the indicator menu. To install, go to the terminal (Ctrl+Alt+T) and paste/type in the following commands.

sudo add-apt-repository ppa:indicator-multiload/stable-daily

sudo apt-get update && sudo apt-get install indicator-multiload

Power Management

The computer’s power management scheme is one of the most important factors that decide the fate of your battery. In the power management settings window, always make sure you choose a balanced plan that helps you get through a whole workday without looking for an adapter. Another great way to take advantage of this setting is by making sure that the laptop goes into suspend mode as soon as the lid is closed. Though, it might not be a suitable setting for folks who are a tad impatient, it still is one of the most effective ways of saving battery life. To access the power management settings in Ubuntu, open the Dash (Super/Windows key) and type in the word “Power” without quotes.

Hibernate over Suspend

If, instead of shutting down your laptop, you put it on suspend mode, always make sure you’re connected to a charger. If not, then put the computer in hibernate mode and go for a nice nap. That way, neither would you lose any precious battery life nor would you lose your current work.

Keep It Cool

Most of the battery loss also occurs due to overheating laptops. The overheating issue is something that affects a lot of laptops. To remedy that problem, simply use a laptop cooling pad, a simple accessory that saves your computer from overheating. It’s also a good idea to keep an eye on the temperature; to do that, simply install the system monitor indicator that comes with various temperature sensors.

sudo add-apt-repository ppa:alexeftimie/ppa

sudo apt-get update && sudo apt-get install indicator-sysmonitor

Or, if all you want is a simple hardware sensor, then try out the following indicator applet:

sudo add-apt-repository ppa:alexmurray/indicator-sensors

sudo apt-get install indicator-sensors

Update Update Update

Finally, always remember to update your computer. The Linux kernel is continuously improving, and so are the distributions. In Ubuntu 12.04 for example, users will get to see an improved support for battery life. So, make sure you don’t ignore your computer when it badgers you to give it a big update.

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I’m using Debian on daily basis, and everybody that had even little of experience with Debian should already be aware about the existence of the handy:
/etc/modules file.
On Debian to enable a certain kernel module to load up on Linux boot, all necessery is to just place the kernel module name in /etc/modules.

For example loading the tun tunneling kernel module I issue the command:

debian:~# echo tun >> /etc/modules


I wondered if CentOS, also supports /etc/modules as it was necessery now to add this tun module to load up on CentOS’s boot.
After a bit of research I’ve figured out CentOS does not have support for adding modules names in /etc/modules , anyhow after consulting CentOS documentation on  http://www.centos.org , I found CentOS and RHEL use /etc/rc.modules instead of Debian’s /etc/modules to load up any custom kernel modules not loaded by default during system boot.

Therefore instructing the RHEL Linux to load up my desired tun module in kernel on next boot was as easy as executing:

[root@centos ~]# echo 'modprobe tun' >> /etc/rc.modules
[root@centos ~]# chmod +x /etc/rc.modules


Now on next boot CentOS will load up the tun module in kernel. Achiving the same module load up is also possible through /etc/rc.local , but it’s not recommended way as /etc/rc.local would load up the kernel module after all of the rest init boot scripts complete and therefore will load up the module slightly later, at the final boot stage.

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• centos /etc/modules (2)
• automatic rdp on centos6 2 (2)
• ubuntu 11 10 tun module (2)
• load kernel modules centos (2)
• rhel 6 2 tun support (2)

I’m aware of the existence of Hardware Watchdog devices, which are capable to detect if a server is hanged and auto-restart it, however the servers I administrate does not have Hardware support for Watchdog timer.

Thankfully there is a free software project called Watchdog which is easily configured and mitigates the terrible downtimes caused every now and then by a server crash and respective delays by tech support in Data Centers.

I’ve recently blogged on the topic of Debian Linux auto-restart in case of kernel panic , however now i had to configure watchdog on some dozen of CentOS Linux servers.

It appeared installation & configuration of Watchdog on CentOS is a piece of cake and comes to simply following few easy steps, which I’ll explain quickly in this post:

1. Install with yum watchdog to CentOS

[root@centos:/etc/init.d ]# yum install watchdog
…

2. Add to configuration a log file to log watchdog activities and location of the watchdog device

The quickest way to add this two is to use echo to append it in /etc/watchdog.conf:

[root@centos:/etc/init.d ]# echo ‘file = /var/log/messages’ >> /etc/watchdog.conf
echo ‘watchdog-device = /dev/watchdog’ >> /etc/watchdog.conf

3. Load the softdog kernel module to initialize the software watchdog via /dev/watchdog

[root@centos:/etc/init.d ]# /sbin/modprobe softdog

Initialization of softdog should be indicated by a line in dmesg kernel log like the one above:

[root@centos:/etc/init.d ]# dmesg |grep -i watchdog
Software Watchdog Timer: 0.07 initialized. soft_noboot=0 soft_margin=60 sec (nowayout= 0)

4. Include the softdog kernel module to load on CentOS boot up

This is necessary, because otherwise after reboot the softdog would not be auto initialized and without it being initialized, the watchdog daemon service could not function as it does automatically auto reboots the server if the /dev/watchdog disappears.

It’s better that the softdog module is not loaded via /etc/rc.local but the default CentOS methodology to load module from /etc/rc.module is used:

[root@centos:/etc/init.d ]# echo modprobe softdog >> /etc/rc.modules
[root@centos:/etc/init.d ]# chmod +x /etc/rc.modules

5. Start the watchdog daemon service

The successful initialization of Softdog in step 4, should have provided the system with /dev/watchdog, before proceeding with starting up the watchdog daemon it’s wise to first check if /dev/watchdog is existent on the system. Here is how:

[root@centos:/etc/init.d ]# ls -al /dev/watchdogcrw——- 1 root root 10, 130 Aug 10 14:03 /dev/watchdog

Being sure, that /dev/watchdog is there, I’ll start the watchdog service.

[root@centos:/etc/init.d ]# service watchdog restart
…

Very important note to make here is that you should never ever configure watchdog service to run on boot time with chkconfig. In other words the status from chkconfig for watchdog boot on all levels should be off like so:

[root@centos:/etc/init.d ]# chkconfig –list |grep -i watchdog
watchdog 0:off 1:off 2:off 3:off 4:off 5:off 6:off

Enabling the watchdog from the chkconfig will cause watchdog to automatically restart the system as it will probably start the watchdog daemon before the softdog module is initialized. As watchdog will be unable to read the /dev/watchdog it will though the system has hanged even though the system might be in a boot process. Therefore it will end up in an endless loops of reboots which can only be fixed in a linux single user mode!!! Once again BEWARE, never ever activate watchdog via chkconfig!

Next step to be absolutely sure that watchdog device is running it can be checked with normal ps command:

[root@centos:/etc/init.d ]# ps aux|grep -i watchdog
root@hosting1-fr [~]# ps axu|grep -i watch|grep -v greproot 18692 0.0 0.0 1816 1812 ? SNLs 14:03 0:00 /usr/sbin/watchdog
root 25225 0.0 0.0 0 0 ? ZN 17:25 0:00 [watchdog]

You have probably noticed the defunct state of watchdog, consider that as absolutely normal, above output indicates that now watchdog is properly running on the host and waiting to auto reboot in case of sudden /dev/watchdog disappearance.

As a last step before, after being sure its initialized properly, it’s necessery to add watchdog to run on boot time via /etc/rc.local post init script, like so:

[root@centos:/etc/init.d ]# echo ‘echo /sbin/service watchdog start’ >> /etc/rc.local

Now enjoy, watchdog is up and running and will automatically restart the CentOS host.

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On a VMware ESXi 5.0 host, how can I check if fiber storage adapters are properly connected to the fiber switch/SAN, i.e. if the fiber link is up?

Solution:

This information is shown nowhere in the vSphere Client, and there is no command-line tool to check it, either.

The only way to verify if a fiber link is up is to access the ESXi shell and go to /proc/scsi/your_hba_driver (in my case, /proc/scsi/qla2xxx); there is a (virtual) file there for each fiber port, and the contents of these files include one of the following:

For an active link:

Host adapter:Loop State = <READY>, flags = 0xaa68
Link speed = <8 Gbps>

For an inactive link:

Host adapter:Loop State = <DEAD>, flags = 0x1a268
Link speed = <Unknown>

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If you are a system administrator, you have probably wondered at least once how to configure your Linux server to automatically reboot itself if it crashes, is going through a mass CPU overload, e.g. the server load average “hits the sky”.

I just learned from a nice article found here that there is a kernel variable which when enabled takes care to automatically restart a crashed server with the terrible Kernel Panic message we all know.

The variable I’m taking about is kernel.panic for instance kernel.panic = 20 would instruct your GNU Linux kernel to automatically reboot if it experiences a kernel panic system crash within a time limit of 20 seconds.

To start using the auto-reboot linux capabilities on a kernel panic occurance just set the variable to /etc/sysctl.conf

debian-server:~# echo 'kernel.panic = 20' >> /etc/sysctl.conf

Now we will also have to enable the variable to start being use on the system, so execute:

debian-server:~# sysctl -p

There you go automatic system reboots on kernel panics is now on.
Now to further assure yourself the linux server you’re responsible of will automatically restart itself on a emergency situation like a system overload I suggest you check Watchdog

You might consider checking out this auto reboot tutorial which explains in simple words how watchdog is installed and configured.
On Debian installing and maintaining watchdog is really simple and comes to installing and enabling the watchdog system service, right afteryou made two changes in it’s configuration file /etc/watchdog.conf

To do so execute:

debian-server:~# apt-get install watchdog
debian-server:~# echo "file = /var/log/messages" >> /etc/watchdog.conf
debian-server:~# echo "watchdog-device = /dev/watchdog" >> /etc/watchdog.conf


Well that should be it, you might also need to load some kernel module to monitor your watchdog.
On my system the kernel modules related to watchdog are located in:

/lib/modules/2.6.26-2-amd64/kernel/drivers/watchdog/
If not then you should certainly try the software watchdog linux kernel module called softdog , to do so issue:

debian-server:~# /sbin/modprobe softdog


It’s best if you load the module while the softdog daemon is disabled.
If you consider auto loadig the softdog software watchdog kernel driver you should exec:

debian-server:~# echo 'softdog' >> /etc/modules


Finally a start of the watchdog is necessery:


debian-server:~# /etc/init.d/watchdog start
Stopping watchdog keepalive daemon....
Starting watchdog daemon....


That should be all your automatic system reboots should be now on!

Reference

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This function parses a URL and returns an associative array containing any of the various components of the URL that are present. It is important to note that parse_url does not validate the given URL, it simply breaks it up into parts. Partial URLs are also accepted, and whilst parse_url tries its best to parse them correctly, it may return -1 if the URL provided is too malformed.

So what exactly does it break an URL up into then?

Well, given an URL like below, parse_url would return the following:

$url = ‘http://username:password@hostname/path?arg=value#anchor’;

print_r(parse_url($url));

echo parse_url($url, PHP_URL_PATH);

The output:

Array
(
[scheme] => http
[host] => hostname
[user] => username
[pass] => password
[path] => /path
[query] => arg=value
[fragment] => anchor
)

/path

So pretty useful if you want say just the host or query value from a given URL then!

Another thing to note is that it is not designed to work with relative URLs, meaning that you do need to provide it with fully qualified URLs in order to get something usable back.

Still, a pretty nifty little function to keep in mind when writing parsing scripts…

Reference

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• url contains ?arg= (1)

I have few servers, which have automatically enabled IPv6 protocols (IPv6 gets automatically enabled on Debian), as well as on most latest Linux distribituions nowdays.

Disabling IPv6 network protocol on Linux if not used has 2 reasons:

1. Security (It’s well known security practice to disable anything not used on a server)
   Besides that IPv6 has been known for few criticil security vulnerabilities, which has historically affected the Linux kernel.
2. Performance (Sometimes disabling IPv6 could have positive impact on IPv4 especially on heavy traffic network servers).
   I’ve red people claiming disabling IPv6 improves the DNS performance, however since this is not rumors and did not check it personally I cannot positively confirm this.

Disabling IPv6 on all GNU / Linuces can be achieved by changing the kernel sysctl settings net.ipv6.conf.all.disable_ipv6 by default net.ipv6.conf.all.disable_ipv6 equals 1 which means IPv6 is enabled, hence to disable IPv6 I issued:

server:~# sysctl net.ipv6.conf.all.disable_ipv6=0


To set it permanently on system boot I put the setting also in /etc/sysctl.conf :

server:~# echo 'net.ipv6.conf.all.disable = 1 >> /etc/sysctl.conf

The aforedescribed methods should be working on most Linux kernels version > 2.6.27 in that number it should work 100% on recent versions of Fedora, CentOS, Debian and Ubuntu.

To disable IPv6 protocol on Debian Lenny its necessery to blackist the ipv6 module in /etc/modprobe.d/blacklist by issuing:

echo 'blacklist ipv6' >> /etc/modprobe.d/blacklist

On Fedora / CentOS there is a another universal “Redhat” way disable IPv6.

On them disabling IPv6 is done by editting /etc/sysconfig/network and adding:

NETWORKING_IPV6=no
IPV6INIT=no

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• disable ipv6 redhat 6 2 (12)
• disable ipv6 centos 6 (11)
• disable ipv6 in centos 6 2 (10)
• disable ipv6 on centos 6 2 (8)

Thus I was curious if Debian guys were smart enough to implement a proxy cache cleaning option as an option to be passed on to squid’s init script.

Honestly I was quite suprised squid clear cache option is not there;

squid-cache:~# /etc/init.d/squid3
Usage: /etc/init.d/squid3 {start|stop|reload|force-reload|restart}
squid-cache:/#


As it was not embedded into init script I still hoped, there might be some Debian way to do the proxy cache clearing, so I spend some 10 minutes checking online as well as checked in squid3‘s manual just to find there is no specific command or Debian accepted way to clean squid’s cache.

Since I couldn’t find any Debian specific, way I did it the old fashioned way (deleted directory/file structures in /var/spool/squid3/* and used squid’s -z option, to recreate the swap directories.

Here is how:

squid-cache:~# /etc/init.d/squid3 stop;
squid-cache:~# rm -Rf /var/spool/squid3/*;
squid-cache:~# squid3 -z; /etc/init.d/squid3 start


Finally I was quite amazed to realize, there was not even a crontab script to periodically clear and re-create proxy cache.

My previous experience with maintaning an office Squid proxy cache has prooved, that periodic cache clean ups are very helpful, especially to resolve issues with cached unreslovable DNS entries in the server.
Clearing up squid cache every week or something, guarantees that failure to resolve certain hosts at certain times would not stay unresolvable like forever

In that manner of thougths, I decided to put the following crontab which will twice a month clear up proxy’s cache, to possibly solve some failed squid DNS issues.

squid-cache:~# crontab -u root -l > file;
echo '00 04 12,26 * * /etc/init.d/squid3 stop; rm -Rf /var/spool/squid3/*; squid3 -z; /etc/init.d/squid3 start >/dev/null 2>&1'
>> file; crontab file


By the way, implementing the squid clear cache in Debian and Ubuntu ‘s init scripts and putting a periodic proxy clear up cron, seems like a feature worthy to be proposed to the distro developers and hopefully be embbed in some of the upcoming distro releases

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#!/bin/sh
user="$1";
realm="$2";
pass="$3";
if [ -z "$1" -o -z "$2" -o -z "$3" ] ; then
echo "Usage: $0 user password 'realm'";
exit 1
fi
ha1=$(echo -n "$user:$realm:$pass"|md5sum |cut -f1 -d' ')
echo "$user:$realm:$ha1"

You can alternatively download the squid_generate_pass.sh script here

The script accepts three arguments;

proxy-server:~# ./squid_generate_pass.sh
Usage: ./squid_generate_pass.sh user password 'realm'

Thus to generate a new user and password and insert it immediately into let’s say a squid configured user/pass file in /etc/squid3/users execute command:

proxy-server:~# ./squid_generate_pass.sh admin_user MySecretPassword 'Squid_Configured_Realm'
>> /etc/squid3/users

Where Squid_Configured_Realm depends on the realm name configured in squid.conf, for example if squid.conf includes some auth configuration similar to:

auth_param digest program /usr/lib/squid3/digest_pw_auth -c /etc/squid3/users
auth_param digest children 2
auth_param digest realm My_Proxy_Realm
acl localusers proxy_auth REQUIRED

The realm script argument should be My_Proxy_realm . If squid_generate_pass does completes without errors, it should add a line to /etc/squid3/users file similar to:

proxy-server:~# cat /etc/squid3/users
admin_user:My_Proxy_realm:3bbcb35e505c52a0024ef2e3ab1910b0

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