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Topics - kek

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Lets talk about FANs, especially Noctua fans, many may not be aware of that there are different fans for different configurations and deployments aside form case fans and cpu fans, at the base level any fan is better than no fan at all, unless you are custom building a fan less appliance.

Knowing what fan to use in the different cases makes all the differens in stability of the system as it get the correct amount of cooling, noise reduction as you use the right fan you need less of them and by that you also reduce noise production

The main difference between the fan models are that some are designed for Air Flow and others for Static Pressure

Air Flow fans are commonly used where there is little to no obstacles to push the air around it in a specific direction these fans usually have larger space between the blades and run at lower RPM

Static Pressure fans on the other hand is uses to push as much air through tight spaces such as radiators and cooling tower heatsinks and in some tower cases as intake fans as they have obstetrical like drive cages inches away from the intake vents

Now you should ask your self which Noctua fan is right for my setup?

Here is an overview of the different 120mm models form Noctua

NF-S12A: The NF-S12A has been optimized for “low impedance” applications that don’t require high static pressure and thus combines moderate pressure with outstanding airflow and superb quietness of operation. Choose the NF-S12A for case ventilation, applications with little or no obstruction to airflow as well as all other applications where minimum noise emission has first priority.

NF-P12: The NF-P12 has been designed with more pressure demanding “high impedance” applications in mind. It provides an even balance of high static pressure, high airflow and excellent quietness, which has made it a standard choice for low noise CPU cooling, cases with tight fan grills and other low noise cooling applications with mid- to high airflow resistance.

NF-F12: The NF-F12’s unique Focused Flow™ system produces extremely high static pressure and focuses the airflow in order to achieve even better results on air cooling heatsinks and water cooling radiators. With a top speed of 1500rpm, it also offers more performance headroom for less noise-sensitive applications. Choose the NF-F12 if you’re looking for the best possible performance on heatsinks and radiators.

This information is based on:

Linux and BSD / [How-To] - Enable Serial Com Port in CentOS 7
« on: November 29, 2017, 11:19:37 PM »
[How-To] - Enable Serial Com Port in CentOS 7

In this post I want to share how you enable the serial console to work at boot and have the server send the login screen both to the regular monitor and to the serial com connection in CentOS 7. If you need to know more about what it is or why you should use a serial connection for your servers see my other post: What is a Serial Console, and why would we use it?, but in short is goes something like this:

you connect to your headless server using SSH or WebGUI over IP \ DNS but you messed up some configurations and you are no longer able to access your server over the network, and now you have to find a keyboard and monitor to access it and restore it. and that in it self can be a hassle and if you had serial connection enabled on a rs-232 com port you would only need to connect a console cable to it and do the troubleshooting needed, not to say most of the networking gear like routers and switches you see in business and enterprise environment need to be configured over console connection before they are deployed and you can use SSH or WebGUI over IP \ DNS.

Before I begin the configurations I will make two assumptions:
1. You have a clean and fresh install of CentOS 7 using LVM partitioning.
2. That your server have a working RS-232 Console Port installed and are recognized by the kernel and the drivers are installed.

To make the serial console available at boot we need to adjust the boot loader of the system to send the output to both the console port and the monitor, and to do this you need to login to the system whit a user that has sudo or root access.[/size]

Hardware Information:
Now that you are logged in to your system you want to first check that your Serial Comport is installed, to do this type the command: sudo dmesg | grep tty

Output should look like this example:
Code: [Select]

   [kek@centos7 ~]# sudo dmesg | grep tty
    [    0.000000] console [tty1] enabled
    [    0.000000] console [ttyS0] enabled
    [    1.891572] 00:05: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

In this example I have one input \ output (I\O) console hardware port in the server and that is ttyS0 whit the full path of /dev/ttyS0, note this down as we need it later in the configuration

Now we need to check what LVM labels where given to the system if you used the easy installer option, in most cases it uses the hostname as labels, but since it can break the system if we do not get this part correct we better check as we do not want to do any unnessecary work or troubleshooting, to check LVM labels of your partitions run the command: sudo lvscan

Output should look similar to this:
Code: [Select]

   [kek@centos7 ~]# sudo lvscan
    ACTIVE      '/dev/cl_centos7/swap' [  2.00 GiB] inherit
    ACTIVE      '/dev/cl_centos7/root'  [<17.00 GiB] inherit

What we need to note from this command is the cl_centos7/root and cl_centos7/swap labeles as we need this later to get the device mapper string to point to the correct hard drive partitions for booting.

System Configuration:
Now that we have all the needed hardware information we are ready to configure the serial console and the boot loader, to do this you need to edit the following configuration file: /etc/sysconfig/grub to do this use your favourite text editor like vim or nano (not installed by default), command is: sudo vi /etc/sysconfig/grub

The file should look similar to this before editing:
Code: [Select]

GRUB_CMDLINE_LINUX=" crashkernel=auto rhgb quiet"

You would need to make some changes to this file, as you can see it contains no information about the serial connection or the terminal settings to use, in my setup I use the following configuration:

Code: [Select]

GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_TERMINAL="console serial"
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"
GRUB_CMDLINE_LINUX="crashkernel=auto rhgb quiet"
GRUB_CMDLINE_LINUX_DEFAULT="console=tty1 console=ttyS0,115200"

The settings in here should be self explainatory and should be generic egnouh to cover 90% of all serial adapters, but the general descripton of them are:
GRUB_TERMINAL is set to both Console and Serial enabling it for both on screen monitor and serial output.
GRUB_SERIAL_COMMAND sets the value of what speed it should run and how it should communicate whit the remote device these settings needs to match at both sides to make a connection.
GRUB_CMDLINE_LINUX specifies where the swap and root partition is stored for the LVM so the system can boot, this is why we looked up the disk information.
GRUB_CMDLINE_LINUX_DEFAULT tells the boot loader to where it should send the information where tty1 is the monitor and ttyS0 is the Serial port.

At this point you are nearly done, just a few commands left to run as the majority of the configuration is the get the grub config correct, now we just need to enable our Serial connection using the command:
 stty -F /dev/ttyS0 ispeed 115200

You may get an error saying it could not run all of the settings, but do not worry about that for now, next up would be to generate a new bootloader file for grub whit the settings we just saved in
/etc/sysconfig/grub we do that by running the following command: grub2-mkconfig -o /boot/grub2/grub.cfg

Now you are ready to connect the serial console cable and connect from your workstation or laptop using something like screen or putty depending on OS you are using, the console will at this point connect to a black screen as it has not active console running at the moment, and if you are at a blank window whit no errors then you can run the command: sudo /sbin/reboot on your CentOS 7 server and you should see the grub and boot process both on the monitor and the serial terminal window.


Hardware / What is a Serial Console, and why would we use it?
« on: November 29, 2017, 05:22:29 PM »
What is a Serial Console, and why would we use it?

In this post I would like to take the time to tell you a little about Serial Consoles and COM ports, and why we still uses it

What is Serial Console?
The serial console is a connection over the RS-232 or serial port connection that allows a person access to a computer or network device console. Typically, a console is accessed over an SSH connection. However, with software, hardware, or other access problems, it may only be possible to access the machine or device (e.g. routers and switches) over a serial connection. Older computers and headless computer (computers or devices without monitors) also use the serial console as the main way to access the console.

The system console, computer console, root console, operator's console, or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the kernel, from the init system and from the system logger. It is a physical device consisting of a keyboard and a screen, and traditionally is a text terminal, but may also be a graphical terminal. System consoles are generalized to computer terminals, which are abstracted respectively by virtual consoles and terminal emulators. Today communication with system consoles is generally done abstractly, via the standard streams (stdin, stdout, and stderr), but there may be system-specific interfaces, for example those used by the system kernel.

The console is the text output device for system administration messages. These messages come from the kernel, from the init system and from the system logger. On modern small computers the console is usually the computer's attached monitor and keyboard. On many older computers the console is an RS-232 link to a terminal such as a DEC VT100. This terminal is in a locked room and is continually observed by the minicomputer's operators. Large systems from Sun, Hewlett-Packard and IBM still use serial consoles. It is usually possible to login from the console. A login session from the console is treated by many parts of the operating system as being more trustworthy than a login session from other sources. Logging in as the root super-user from the console is the Command Line of Last Resort when faced with a misbehaving system.

Why should we use a serial console?
For the average user a serial console has no advantage over a console offered by a directly attached keyboard and screen. Serial consoles are much slower, taking up to a second to fill a 80 column by 24 line screen. Serial consoles generally only support non-proportional ASCII text, with limited support for languages other than English. A new terminal can be more expensive than an old PC.

There are some scenarios where serial consoles are useful. These are:

 - Systems administration of remote computers
 - High density racks of computers
 - Recording console messages
 - Embedded software development

Systems administration of remote computers
Linux is a good operating system for deployment at unstaffed sites. Linux is also good for hosting critical network infrastructure such as DNS and DHCP services. These services are generally installed at every site of an organisation including sites which may be too small or too remote to have information technology staff. System administration of these remote computers is usually done using SSH, but there are times when access to the console is the only way to diagnose and correct software failures. Major upgrades to the installed distribution may also require console access. In these cases the serial console is attached to a modem. Access to the console is gained from a remote computer by dialing into the modem. This allows the console to be reached from any telephone socket.

High density racks of computers
Clusters of personal computers can outperform mainframe computers and form competitive supercomputers for some applications. See the Cluster-HOWTO for more information on clustering. These clusters are typically assembled into 19 inch telecommunications equipment racks and the system unit of each computer is typically one rack unit (or 1.75 inches) tall. It is not desirable to put a keyboard and monitor on each computer, as a small cathode ray tube monitor would consume the space used by sixteen rack units. A first glance it seems that a monitor and keyboard switch is the best solution. However the VGA signal to the monitor is small, so even with the switch the monitor cannot be placed very far away from the rack of computers. It is desirable to allow the consoles to be monitored in the operators' room of the computer center, rather than in the very expensive space of the machine room. Although monitor switches with remote control and fiber optical extensions are available, this solution can be expensive. A standard RS-232 cable can be 15 meters in length. Longer distances are easily possible. The cabling is cheap. Terminal servers can be used to allow one terminal to access up to 90 serial consoles.

Recording console messages
This is useful in two very different cases.

Kernel programmers are often faced with a kernel error message that is displayed a split second before the computer reboots. A serial console can be used to record that message. Another Linux machine can be used as the serial terminal. Some secure installations require all security events to be unalterably logged. One way to meet this requirement is to print all console messages. Connecting the serial console to a serial printer can achieve this.

Embedded software development
Linux is increasingly being used as an operating system for embedded applications. These computers do not have keyboards or screens. A serial port is a cheap way to allow software developers to directly access the embedded computer. This is invaluable for debugging. Most chip sets designed for embedded computers have a serial port precisely for this purpose. The shipping product need not present the RS-232 port on an external connector. Alternatively the RS-232 port is often used for downloading software updates.

News from the Admin team / Deleted accounts during maintinace
« on: November 29, 2017, 04:21:34 PM »
Hello folks, there as been a few inactive accounts on this forum that was never registered online and as activated accounts, these was today (2017-11-29) deleted from the system if some of these where real and active accounts, please contact one of our admin or moderators staff and we will be looking at restoring your profile back


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