Understand data center tiers: tier 1 to tier 4

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Understand and learn about data center tier. The article explains the data center standardization matrix: tier 1 to tier 4 along with its eligibility criteria.

Most of our readers are system administrators and surely come across term call data center tiers in their sysadmin life. This article will walk you through what is data center tiers? Different types of data center tiers, what is tier 1, tier 2, tier 3, and tier 4 data center? Which tier data center have maximum availability? etc.

All these might be interview questions for system architects at the beginner level. As a sysadmin its always good to know data center tiers so that you are well verse with your company infrastructure and can decide if that can really deliver on SLAs defined in your environment.

Without further delay, lets start with our topic.

What is data center tier?

Datacenter tier is the standardization matrix that defines overall performance, availability, fault tolerance capability, operating environment of a data center. It defines how the data center is fault-tolerant, how it can sustain to failures of various components, power, connectivity links, etc. It defines availability being offered for hosted servers.

Basically data center tier helps customers to determine which tier is best suitable for their application depending on the SLA requirement and data critical index they have. Mission-critical services should be hosted under a higher tier data center whereas less critical data should be hosted in lower-tier data centers. Obviously cost is another factor here too. As you go on high with tier, cost increases for hosting.

Different data center tiers

There are 4 data center tier standards defined by Uptime Institute. They are as below :

Tier 1: Non-redundant capacity and single power, connectivity distribution
Tier 2: Tier 1 feature + redundant capacity
Tier 3: Tier 2 features + Multiple independent power, connectivity distribution + onsite energy production system
Tier 4: Tier 3 features + All components are fault-tolerant, continuous cooling equipment.

A detailed list of requirements to be fulfilled by the data center to be eligible for specific tier is available here.

Data center tier deciding factors :

Datacenter to be eligible for certain tier it should complete certain criteria (as we saw above). There are many factors that affect/help in achieving those criteria. These factors are as below –

Datacenter design, location
Mechanical infrastructure design
Technology infrastructure design
Electric power distribution
Cables distribution
Network and internet connectivity distribution
Fire protection
Security in terms of soft security and physical security controls like biometric etc
Energy production, use, efficiency
Waste management
Environmental control and effects
Cooling management
Capacity management

Accepted downtime and availability tier wise

Tier 1: 99.671% uptime, 28.8 hours downtime per year
Tier 2: 99.749% uptime, 22 hours downtime per year
Tier 3: 99.982% uptime, 1.6 hours downtime per year
Tier 4: 99.995% uptime, 26.3 minutes downtime per year

That’s all I have to share with you about data center tier standards. Feel free to point out mistakes, suggestions, feedback in the comments section below.

KernelTalks turned one!

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Kerneltalks blog turned one today. This article crafts a year blog journey in info-graphics! Keep visiting us. Thank you!

Yay! Happy Birthday KernelTalks!

Yup. The blog turned one today. It was slow but exponential growth for KernelTalks. Let me walk you through this one year journey with the info-graphic format below :

Kerneltalks one year journey Infographics

Thanks for stopping by! Subscribe us. Follow us. Contact us. Keep visiting us!

Have a happy shell!

device eth0 does not seem to be present, delaying initialization error on Linux VM

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Step by step procedure to resolve “device eth0 does not seem to be present, delaying initialization.” error on Linux VM.

If you are working on VMware infrastructure when your Linux VM is hosted on it, you must have come across below error while bringing up Ethernet in Linux :

Bringing up interface eth0: Device eth0 does not seem to be present, delaying initialization.

root@kerneltalks # service network restart
Shutting down interface eth0:                              [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:  Device eth0 does not seem to be present, delaying initialization.
                                                           [FAILED]

In this article, we are going to resolve this error. First, let’s see the background of this error. This method works well on Red Hat, CentOS, Oracle Linux, etc.

This error comes up normally in VM which is cloned from other Linux VM or from the template. The root cause of this error is MAC address of eth0 which is same as the source (source VM or template) in its configuration file ifcfg-eth0. While as during boot NIC gets unique MAC address and it does not match with one in ifcfg-eth0.

So here are steps to resolve this error.

Step 1.

Remove file /etc/udev/ rules.d/70-persistent-net.rules and reboot the server.

root@kerneltalks # rm /etc/udev/rules.d/70-persistent-net.rules
root@kerneltalks # reboot

This ensures new fresh files to be generated at the next boot and get unique MAC assigned.

Step 2.

After reboot, confirm above file is generated again. It will look like :

root@kerneltalks # cat /etc/udev/rules.d/70-persistent-net.rules
# This file was automatically generated by the /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.

# PCI device 0x15ad:0x07b0 (vmxnet3)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:50:56:99:3f:25", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

Observe that new MAC is generated for eth1 (NAME="eth1"). Note down the MAC address from the file.

Step 3.

Now you have two choices :

Use eth1 as device name under ifcfg-eth0 config file.
Edit /etc/udev/ rules.d/70-persistent-net.rules with eth name as eth0

If you are choosing the first option then along with name change you need to change MAC.

root@kerneltalks # cat ifcfg-eth0
DEVICE=eth1
HWADDR=00:50:56:99:3f:25
TYPE=Ethernet
---- output truncated ----

If you are choosing the second option. Edit your ifcfg-eth0 located under /etc/sysconfig/network-scripts with new MAC address from above file. Also, since you made changes to /etc/udev/ rules.d/70-persistent-net.rules you have to again reboot the server. Rebooting the server here is important.

root@kerneltalks # cat ifcfg-eth0
DEVICE=eth0
HWADDR=00:50:56:99:3f:25
TYPE=Ethernet
---- output truncated ----

I would suggest going with the second choice since you will maintain naming conventions on your system. The first choice may create confusion to fellow sysadmins if you have more than one NIC on your server.

Step 4.

If you have used choice 1 i.e. using device name as eth1 under config file ifcfg-eth0 then you just need to restart network service and you should be all set.

root@kerneltalks # service network restart
Shutting down interface eth0:                              [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:                                [  OK  ]

If you have opted the second choice then reboot already taken care of things and your ethernet along with IP should be post-boot.

How to download files from EC2 to local machine using winSCP

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Learn how to transfer files between desktop and EC2 using WinSCP. Using key-based authentication, winSCP can be connected to EC2 to download/upload files from/to the server.

While working on the EC2 server hosted on AWS, one of the basic requirements you come across is to transfer data between your desktop/laptop and EC2 instance. Since EC2 uses key-based authentication, for beginners it’s hard to understand how to transfer data from desktop to EC2 cloud.

Normally, programs like WinSCP are used to transfer data between the Linux server and the windows machine. In this article we will walk you through how to add key-based authentication in WinSCP. Later how to download files from EC2 to the local machine.

Other EC2 related posts which might interest you :

Step 1: Know your DNS name

Make sure your EC2 instance is spun up. You have the Public DNS name of your EC2 instance. You can see it under instance description in your AWS EC2 console.

Take our AWS CSA exam quiz! Check your knowledge.

Refer screenshot below :

Step 2 : Set private key for authentication

Open WinSCP tool. Click on Advanced to open settings of tool.

Under settings, click on Authentication under SSH in the left panel. This will open up authentication settings on the right panel.

Under, Authentication parameters tick ‘Allow agent forwarding‘ and browse your private key file in it. This private key file is key the same file you use to authenticate to EC2 when connecting via PuTTY

Click OK and close settings.

Step 3 : Connect

Copy public DNS of your EC2 instance, username as ec2-user for RedHat (different Linux distro has diff default logins in AWS. List of all is here) and hit connect. It will pop up to accept the key if you are connecting for the first time via WinSCP. Accept it and you will be connected to the EC2 server!

I have created small GIF which shows whole above process. Have a look .

Now you can download or upload files from EC2 to local like you normally do!

How to reset iptables to the default settings

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Learn how to reset iptables to default settings. The default setting of iptable is to accept all for all types of connections.

In our last post, we saw iptables basics, where we learned about how iptables works, what are the policies, and how to configure iptables policies.

While working on iptables, if you get confused about policies and you need to start afresh then you need to reset iptables to default settings. By default, I mean to set accept all policy and flush any existing configured rules from settings.

In this article, we will walk through a set of commands to reset iptables to default settings. This can also be treated as how to reset firewall in Linux like ubuntu, centos, Redhat, Debian, etc. It’s a pretty simple 2 steps process.

Step 1 : Set accept all policy to all connections

Using the below set of commands you will set accept rule for all types of connections.

root@kerneltalks # iptables -P INPUT ACCEPT
root@kerneltalks # iptables -P OUTPUT ACCEPT
root@kerneltalks # iptables -P FORWARD ACCEPT

This will confirm, iptables gonna accept all requests for all types of connections.

Step 2 : Delete all existing rules.

Using below set of commands, delete your currently configured rules from iptables.

root@kerneltalks # iptables -F INPUT
root@kerneltalks # iptables -F OUTPUT
root@kerneltalks # iptables -F FORWARD

Or you can do it in single command –

root@kerneltalks # iptables -F

That’s it! Your iptables are reset to default settings i.e. accept all! Now, neatly and carefully design your policies and configure them.

How to setup domain name in Linux server

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Learn how to setup domain names in RedHat, Ubuntu, CentOS, Fedora like Linux servers. Also, see how to verify domain name in Linux and FQDN setup in Linux

Many companies have an internal domain for their IT infrastructure. This needs its servers to be configured with a domain name. This will ensure all servers will have FQDN (Fully Qualified Domain Name). For example, server12 is hostname and server12.kerneltalks.com is its FQDN. In such setup, many tools, monitoring requires servers to be identified by FQDN only.

For such a scenario you have to configure the domain name for your Linux server. We will walk you through steps that need to be taken to the setup domain name on your Linux server.

First of all, check if your server is having domain name already set up or not using below command :

root@server12 # dnsdomainname
kerneltalks.com

If you get output like above then your server is configured with the domain name. If your output is blank then you have to the setup domain name for your server.

Without further delay lets jump into steps to configure domain name.

Step 1.

How to setup FQDN in Linux?

First thing to be done is add FQDN to your hostname in /etc/hosts file.

root@server12 # cat /etc/hosts
10.10.2.32    server12.kerneltalks.com server12

To confirm your FQDN, run below command :

root@server12 # hostname -f
server12.kerneltalks.com

Output should be hostname.domain name

Step 2.

Configure domain name in Red Hat RHEL, Fedora and CentOS

Add below line in /etc/sysconfig/network

DOMAINNAME=<domainname>

Add below parameter in /etc/sysctl.conf

kernel.domainname = <domainname>

Configure domain name in Ubuntu

Edit your hostname (not FQDN) in /etc/hostname file. and restart hostname service. If you see below error :

# service hostname restart
Failed to restart hostname.service: Unit hostname.service is masked.

you can set hostname using :

# hostnamectl set-hostname server12

Once done, confirm normal hostname (using hostname) and FQDN (using hostname -f)

Step 3.

Add domain in /etc/resolv.conf. This file used for setting nameservers as well.

root@server12 # cat /etc/resolv.conf
search kerneltalks.com

This addition makes sure that you can resolves hostnames within your domain.

Step 4.

Confirm that changes are working perfectly. Question is how to check the domain name of the Linux server?

Below are the commands to check hostname, FQDN, and domain name of your server.

root@server12 # hostname
server12

root@server12 # hostname -f
server12.kerneltalks.com

root@server12 #dnsdomainname
kerneltalks.com

hostname command shows your server’s hostname. hostname -f shows your FQDN. dnsdomainname command shows your domain name of the server!

How to configure nameserver in Linux

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Beginners guide on how to configure nameserver in Red Hat, CentOs, Fedora, Debian, Ubuntu or Suse Linux to resolve DNS queries.

Nameserver is the DNS server to which your machine query for name resolutions. This is pretty much important on servers facing the Internet or having an active internet connection or if your system is part of an organization where the internal domain name system is implemented for IT Infra. In this article, we will walk you through how to set up nameserver in your Linux machine

What is nameserver?

Its server which response to the queries normally domain name resolution. It’s like a phone directory, where you query name and you get phone number. Nameserver receives hostname or domain name in the query and responds back with IP address.

How to setup nameserver in Red Hat?

You need to open file /etc/resolv.conf in a text editor like vi or nano and add your name server IP in the below format.

nameserver X.X.X.X

For example :

root@kerneltalks # cat /etc/reolv.conf
nameserver 10.10.2.56

You can use the same above same method to configure nameserver in CentOS, Debian, Fedora.

How to setup nameserver in Ubuntu?

Addition to /etc/resolv.conf file, in ubuntu, you can edit file /etc/network/interfaces with the same above said information. The format remains the same.

root@kerneltalks # cat /etc/network/interfaces
nameserver 10.10.2.56

How to configure nameserver in Suse Linux?

If you have access to Suse desktop environment i.e. GUI then you can go to YaST network settings. Navigate to ‘Hostname/DNS‘. Like below :

Here you will be able to add name servers and click Ok to save.

Alternatively, /etc/resolv.conf is way out from command line.

How to install VMware Tools on Linux guest machine

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Learn to install VMware tools in Linux VMs like RedHat, Suse, Debian, Ubuntu, CentOS, etc. The article includes screenshots, commands, and a complete installation log.

Even the cloud market is bursting nowadays, many corporations still prefer to have in-house Infra virtualization using technologies like VMware. A wide variety of Operating systems can be hosted on virtual machines created under it.

Linux servers like Red Hat, Ubuntu, Suse, Fedora are hosted on VMware infra. After fresh installation you will see warning under VMware console that VMware Tools are not installed on your guest machine. Like below :

VMware Tools is not installed on this virtual machine!

It is not mandatory to install these tools but recommended having them on the guest machine so that host and guest can communicate properly. As a result, your VMware console has more power, visibility over your guest machine.

In this article, we will walk through steps on how to install VMWare tools on Linux guest OS like Red Hat, Ubuntu, Kali, Suse, Debian, etc.

Step 1.

First make sure you have one empty CD-ROM drive attached with the guest machine. Click on the “Install VMware Tools” link in the warning shown above. That will be under the ‘Summary‘ tab of your virtual machine in the VMware console. This will pop up a message confirming to mount VMware tools cdrom on your guest OS.

Click ‘Mount‘ on the pop-up and it will mount VMware tools disc on your guest Linux machine. If you have VMware tools ISO, you can mount ISO as well.

Step 2.

Login to guest Linux machine and you will notice disc is automatically mounted on /media/VMware Tools. Verify it using df command.

root@kerneltalks # df -h
Filesystem                 Size  Used Avail Use% Mounted on
/dev/sr0                    71M   71M     0 100% /media/VMware Tools

If it’s not mounted automatically, you can mount it manually with below set of commands –

root@kerneltalks # mkdir /mnt/cdrom
root@kerneltalks # mount /dev/cdrom /mnt/cdrom
root@kerneltalks # df -h
Filesystem                 Size  Used Avail Use% Mounted on
/dev/sr0                    71M   71M     0 100% /mnt/cdrom

Once mounted confirm the content of discs are visible to you.

root@kerneltalks # cd "/media/VMware Tools"
root@kerneltalks # ll
total 71888
-r--r--r-- 1 root root 72162730 Feb 17  2016 VMwareTools-10.0.6-3560309.tar.gz
-r-xr-xr-x 1 root root     2012 Feb 17  2016 manifest.txt
-r-xr-xr-x 1 root root     1850 Feb 17  2016 run_upgrader.sh
-r-xr-xr-x 1 root root   687524 Feb 17  2016 vmware-tools-upgrader-32
-r-xr-xr-x 1 root root   757944 Feb 17  2016 vmware-tools-upgrader-64

It is important to copy files from disc to local directory. Since if you try to directly run things from the disc you may encounter permission related errors because the disc is mounted as read-only.

Step 3.

Copy installers in the local directory. Goto disc and copy tar file in it to local directory e.g. /tmp/vmware

root@kerneltalks # mkdir /tmp/vmware
root@kerneltalks # cp VMwareTools-10.0.6-3560309.tar.gz /tmp/vmware

Now, untar and unzip this file. You will see newly created directory named vmware-tools-distrib

root@kerneltalks # cd /tmp/vmware
root@kerneltalks # tar -zxpf VMwareTools-10.0.6-3560309.tar.gz
root@kerneltalks # ll
total 140944
-r--r--r-- 1 root root 72162730 Sep 23 09:46 VMwareTools-10.0.6-3560309.tar.gz
drwxr-xr-x 1 root root      162 Feb 17  2016 vmware-tools-distrib

Navigate to vmware-tools-distrib where the actual installer script is located. Its a Perl script vmware-install.pl so make sure you have Perl installed on your server.

root@kerneltalks  # cd vmware-tools-distrib
root@kerneltalks  # ll
total 488
-rw-r--r-- 1 root root 282475 Feb 17  2016 FILES
-rw-r--r-- 1 root root   2538 Feb 17  2016 INSTALL
drwxr-xr-x 1 root root    114 Feb 17  2016 bin
drwxr-xr-x 1 root root     18 Feb 17  2016 caf
drwxr-xr-x 1 root root     74 Feb 17  2016 doc
drwxr-xr-x 1 root root    598 Feb 17  2016 etc
drwxr-xr-x 1 root root    114 Feb 17  2016 installer
drwxr-xr-x 1 root root    158 Feb 17  2016 lib
drwxr-xr-x 1 root root     14 Feb 17  2016 vgauth
-rwxr-xr-x 1 root root    243 Feb 17  2016 vmware-install.pl
-rwxr-xr-x 1 root root 205571 Feb 17  2016 vmware-install.real.pl

Step 4.

Install VMware tools. The final step is to run the Perl script and install tools. It will ask you a couple of questions regarding directory structures, you can customize or just accept defaults.

All the below installation logs are minimized for the better reading experience. To view them, click on them to expand code.

root@kerneltalks # ./vmware-install.pl
Creating a new VMware Tools installer database using the tar4 format.

Installing VMware Tools.

In which directory do you want to install the binary files?
[/usr/bin]

What is the directory that contains the init directories (rc0.d/ to rc6.d/)?
[/etc/init.d]

What is the directory that contains the init scripts?
[/etc/init.d]

In which directory do you want to install the daemon files?
[/usr/sbin]

In which directory do you want to install the library files?
[/usr/lib/vmware-tools]

The path "/usr/lib/vmware-tools" does not exist currently. This program is
going to create it, including needed parent directories. Is this what you want?
[yes]

In which directory do you want to install the common agent library files?
[/usr/lib]

In which directory do you want to install the common agent transient files?
[/var/lib]

In which directory do you want to install the documentation files?
[/usr/share/doc/vmware-tools]

The path "/usr/share/doc/vmware-tools" does not exist currently. This program
is going to create it, including needed parent directories. Is this what you
want? [yes]

The installation of VMware Tools 10.0.6 build-3560309 for Linux completed
successfully. You can decide to remove this software from your system at any
time by invoking the following command: "/usr/bin/vmware-uninstall-tools.pl".

Before running VMware Tools for the first time, you need to configure it by
invoking the following command: "/usr/bin/vmware-config-tools.pl". Do you want
this program to invoke the command for you now? [yes]

Once it receives all the answers, installation begins –

Initializing...


Making sure services for VMware Tools are stopped.

Stopping VMware Tools services in the virtual machine:
   Guest operating system daemon:                                      done
   VMware User Agent (vmware-user):                                    done
   Unmounting HGFS shares:                                             done
   Guest filesystem driver:                                            done


Found a compatible pre-built module for vmci.  Installing it...


Found a compatible pre-built module for vsock.  Installing it...


The module vmxnet3 has already been installed on this system by another
installer or package and will not be modified by this installer.

The module pvscsi has already been installed on this system by another
installer or package and will not be modified by this installer.

The module vmmemctl has already been installed on this system by another
installer or package and will not be modified by this installer.

During installation it will ask you if you want to enable specific features or not. Submit your choices accordingly.

The VMware Host-Guest Filesystem allows for shared folders between the host OS
and the guest OS in a Fusion or Workstation virtual environment.  Do you wish
to enable this feature? [no]

Found a compatible pre-built module for vmxnet.  Installing it...


The vmblock enables dragging or copying files between host and guest in a
Fusion or Workstation virtual environment.  Do you wish to enable this feature?
[no]

VMware automatic kernel modules enables automatic building and installation of
VMware kernel modules at boot that are not already present. This feature can
be enabled/disabled by re-running vmware-config-tools.pl.

Would you like to enable VMware automatic kernel modules?
[no]


Disabling timer-based audio scheduling in pulseaudio.

Do you want to enable Guest Authentication (vgauth)? Enabling vgauth is needed
if you want to enable Common Agent (caf). [yes]

Do you want to enable Common Agent (caf)? [yes]

Finally it will detect and confirms GUI related parameters and builds boot image.

Detected X server version 1.6.5


Unable to detect guest resolution.


Please choose one of the following display sizes that X will start with:

[1]< 640x480
[2]  800x600
[3]  1024x768
[4]  1280x800
Please enter a number between 1 and 4:

[1] 2


X is running fine with the new config file.

Creating a new initrd boot image for the kernel.

Kernel image:   /boot/vmlinuz-3.0.101-63-default
Initrd image:   /boot/initrd-3.0.101-63-default
Root device:    UUID=6b24d38e-094f-471b-8215-aaf85a47fe8e (/dev/dm-2) (mounted on / as btrfs)
Resume device:  /dev/swapvg/swaplv
modprobe: Module crct10dif not found.
WARNING: no dependencies for kernel module 'crct10dif' found.
Kernel Modules: hwmon thermal_sys thermal processor fan scsi_mod libata libahci ahci scsi_transport_spi mptbase mptscsih mptspi ata_piix ata_generic vmxnet3 

vmw_pvscsi vmxnet dm-mod dm-log dm-region-hash dm-mirror dm-snapshot scsi_dh scsi_dh_alua scsi_dh_emc scsi_dh_hp_sw scsi_dh_rdac libcrc32c zlib_deflate btrfs 

usb-common usbcore ohci-hcd uhci-hcd ehci-hcd xhci-hcd hid usbhid linear crc-t10dif sd_mod crc32c
Features:       acpi dm block usb lvm2 btrfs resume.userspace resume.kernel
Bootsplash:     SLES (800x600)
51984 blocks
>>> Network: auto
>>> Calling mkinitrd -k /boot/vmlinuz-3.0.101-63-default -i /tmp/mkdumprd.XwBasPAr7V -f 'kdump network' -B  -s ''
Regenerating kdump initrd ...

Kernel image:   /boot/vmlinuz-3.0.101-63-default
Initrd image:   /tmp/mkdumprd.XwBasPAr7V
Root device:    UUID=6b24d38e-094f-471b-8215-aaf85a47fe8e (/dev/dm-2) (mounted on / as btrfs)
Resume device:  /dev/swapvg/swaplv
Dump device:    UUID=cbc439cd-3514-442e-bb42-b80f7823bdc1 (/dev/dm-3)
Boot device:    /dev/disk/by-uuid/9278503b-3bed-45b0-968a-6de4c9264d94 (/dev/sda1)
modprobe: Module crct10dif not found.
WARNING: no dependencies for kernel module 'crct10dif' found.
Kernel Modules: hwmon thermal_sys thermal processor fan scsi_mod libata libahci ahci scsi_transport_spi mptbase mptscsih mptspi ata_piix ata_generic vmxnet3 

vmw_pvscsi vmxnet dm-mod dm-log dm-region-hash dm-mirror dm-snapshot scsi_dh scsi_dh_alua scsi_dh_emc scsi_dh_hp_sw scsi_dh_rdac libcrc32c zlib_deflate btrfs 

usb-common usbcore ohci-hcd uhci-hcd ehci-hcd xhci-hcd hid usbhid af_packet linear nls_utf8 mbcache jbd ext3 crc-t10dif sd_mod crc32c
Features:       acpi dm block usb network lvm2 btrfs resume.userspace resume.kernel kdump
64862 blocks
Generating the key and certificate files.
Successfully generated the key and certificate files.
   Checking acpi hot plug                                              done
Starting VMware Tools services in the virtual machine:
   Switching to guest configuration:                                   done
   VM communication interface:                                         done
   VM communication interface socket family:                           done
   Guest operating system daemon:                                      done
   VGAuthService:                                                      done
   Common Agent:                                                       done
The configuration of VMware Tools 10.0.6 build-3560309 for Linux for this
running kernel completed successfully.

In the end, it presents you with the command to be used for VMware tools, greets and un-mount VMware tools disc (if it was mounted automatically in beginning)

You must restart your X session before any mouse or graphics changes take
effect.

You can now run VMware Tools by invoking "/usr/bin/vmware-toolbox-cmd" from the
command line.

To enable advanced X features (e.g., guest resolution fit, drag and drop, and
file and text copy/paste), you will need to do one (or more) of the following:
1. Manually start /usr/bin/vmware-user
2. Log out and log back into your desktop session; and,
3. Restart your X session.

Enjoy,

--the VMware team

Found VMware Tools CDROM mounted at /media/VMware Tools. Ejecting device
/dev/sr0 ...

VMware tools silent install on Linux VM

If you do not want to customize any of the answers asked during installation and want to go with all default values then you can use below command for starting non-interactive installation :

root@kerneltalks # ./vmware-install.pl -d default

This will install VMware tools in silent mode. No human interaction required and all default settings will be used for installation.

That’s it! You have successfully installed VMware tools on your Linux guest machine in VMware. You can now see IP details of guests in the VMware console. Also VMware tools status will be shown as ‘Installed and running‘.

4 ways to check the size of physical memory (RAM) in Linux

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An article explaining how to check physical memory (RAM) in the Linux server. 4 different commands to get memory information from the Linux server.

In this article we will see basic commands to check physical memory on a server in Linux. Many beginners struggle with knowing their system well in context to resources like CPU, Memory, disks, etc. So I decided to write this small article pinpointing commands to check RAM on the Linux server. These commands will work in different flavors of Linux like Red Hat, CentOS, Suse, Ubuntu, Fedora, Debian, etc.

Without much delay lets dive into commands –

1. Using free command

The first command is free. This is the simplest command to check your physical memory. This command is mainly used for checking RAM and SWAP on the system. Using different switch you can change the byte-format of output. Like -b for bytes, -k for kilobytes, -m for megabytes and -g for gigabytes.

Check row with Mem: and number against it. That’s the physical RAM of your server.

root@kerneltalks # free -b
             total       used       free     shared    buffers     cached
Mem:    135208493056 1247084544 133961408512          0  175325184  191807488
-/+ buffers/cache:  879951872 134328541184
Swap:   17174347776          0 17174347776

root@kerneltalks # free -k
             total       used       free     shared    buffers     cached
Mem:     132039544    1218368  130821176          0     171216     187316
-/+ buffers/cache:     859836  131179708
Swap:     16771824          0   16771824

root@kerneltalks # free -m
             total       used       free     shared    buffers     cached
Mem:        128944       1189     127754          0        167        182
-/+ buffers/cache:        839     128105
Swap:        16378          0      16378

root@kerneltalks # free -g
             total       used       free     shared    buffers     cached
Mem:           125          1        124          0          0          0
-/+ buffers/cache:          0        125
Swap:           15          0         15

In the above output you can see the system is installed with 125GB of physical RAM (observe highlighted rows). By using a different switch -b, -k, -m and -g output changed numbers according to selected byte-format.

2. Using /proc/meminfo file

Another way is to read memory info from the proc filesystem. /proc/meminfo is the file you should read to get detailed information about memory. The very first line or line starts with MemTotal is your total physical memory on the server.

root@kerneltalks # cat /proc/meminfo |grep MemTotal
MemTotal:       132039544 kB

As you can see from output, memory is displayed in kilobytes.

3. Using top command

The famous top command also lists physical memory information in a very clear way. In the upper section of the top command output lies the CPU, Memory, and SWAP information.

root@kerneltalks # top
top - 16:03:41 up 89 days,  3:43,  1 user,  load average: 0.00, 0.01, 0.05
Tasks: 141 total,   1 running, 140 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  132039544k total,  1218336k used, 130821208k free,   171224k buffers
Swap: 16771824k total,        0k used, 16771824k free,   187420k cached

I clipped the above section of the top command output in the above example. Check second last line saying Mem: (highlighted row). This shows physical memory in kilobytes. You can see the total, used, and free portions of it. Total is your actual RAM installed on the server.

4. Using vmstat

Another way is to use vmstat (virtual memory stats) command with -s switch. This will list memory in detail with the first-line being total memory on the server.

# vmstat -s
    132039544  total memory
      1218692  used memory
       181732  active memory
----output trimmed----

Memory is displayed in kilobytes by default. The very first line shows you total memory on the server.

14 find command examples for Linux

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Learn to find command with these 14 examples. Find command examples handpicked to help you in your day-to-day operations.

One of the most important, used and helpful command in Linux terminal is ‘find’ command. It will search files depending on your search criteria and bring the list for you! It saves you from going to many directories and wasting time looking out your required files.

In this article we will see a list of different find commands to search files. Normally find command syntax is –

# find <path_to_search> -switch <search_criteria>

Where, path_to_search is a directory location where you want to search and search_criteria is a condition that should be matched to search files. Note here that find command will search all sub-directories of given path_to_search recursively.

Let’s see 14 find command examples that are very helpful for you in your day to day operations on Linux servers like RedHat, Ubuntu, CentOS, Debian, etc.

Find file using name

Using –name switch you can specify the name of files to search in a particular location.

root@kerneltalks # find /tmp -name "*.gz"

You can use wild cards as well while specifying your search criteria. In the above example, we searched /tmp directory for all gun-zipped files.

Find only files

To search specific file type -type switch needs to be defined in find command.

root@kerneltalks # find /tmp -type f -name "*log"

For searching only files, we defined -type as f in the above example. The above command will search /tmp for files whose name ends with a log.

Find only directories

For searching only directories define -type as d.

root@kerneltalks # find /tmp -type d -name "box*"

In the above example, find command will search /tmp for only directories whose name starts with a box.

Find files which are modified in last 7 days

Searching files that are modified in the last X days is helpful for log management. When you don’t have utilities like logrotate configured then you will have to search and house keep files with this command.

root@kerneltalks # find /tmp -mtime 7

-mtime is a switch which takes a number of days as an argument. mtime stands for modification time.

You can combine the same switch two times to get a range of days for your search. For example to search files which are modified between last 10 to 20 days you can use :

root@kerneltalks # find /tmp -mtime -20 -mtime +10

Find files accessed in last 7 days

Another variant of the above search is to find files that are accessed in the last X days. So that decisions can be made for those files who are not accessed for a long period of time and can be zipped/trimmed to save disk space.

root@kerneltalks # find /tmp -atime 7

-atime switch to be used and number of days to be supplied as argument.

You can combine the same switch two times to get a range of days for your search. For example to search files which are accessed between last 10 to 20 days you can use :

root@kerneltalks # find /tmp -atime -20 -atime +10

Find files with particular size

Some times housekeeping is done based on file size too. To search file based on its size you can use -size and supply human-readable size formats like 10M, 2G, etc.

root@kerneltalks # find /tmp -size 5M

Above command will search file with 5MB size.

Find files having size greater than

But, exact size search mostly doesn’t yield expected. It’s always good if you search with a file size range. To find files with size greater than X –

root@kerneltalks # find /tmp -size +10M

This command will search /tmp for files whose size is greater than 10MB.

Find files having size lesser than

Same way files can be searched with size less than specified value like –

root@kerneltalks # find /tmp -size -20M

Using above two option we can even define range of size to search file from.

root@kerneltalks # find /tmp -size +10M -size -20M

This command will search files whose size is greater than 10MB and less than 20MB!

Find hidden files

As you know in Linux/Unix, hidden files name starts with .

So we can search for hidden files using -name switch explained earlier with the wild card as below –

root@kerneltalks # find /tmp  -type f -name .*

We specified wild card asterisk with . means search all files whose name starts with .

Find files with particular permission

Searching files with particular permission is one of the tasks while auditing. This will help you to trace down files that might be having un-necessary extra permissions and can pose a security threat to the system.

-perm (permission) the switch can be used with findcommand followed by permissions.

root@kerneltalks # find / -type f -perm 0777

In above command we are searching all files with 777 permission.

Find world readable files

With the above example, we can search world-readable files i.e. everyone has only read access on that file (444 or -r--r--r-- permission)

root@kerneltalks # find / -type f -perm 444
OR
root@kerneltalks # find / -type f -perm /u=r -perm /g=r -perm /o=r

You can see numeric as well as u-g-o (user, group, others) format can be used with this switch.

Find files owner by particular user

If you are suspecting some user is spamming files on the server, you can directly search files with his ownership using -user switch.

root@kerneltalks # find / -type f -user shrikant

This command will search whole root directory for files which are owned by user ‘shrikant’

Find files owned by particular group

Similarly, files owned by a specific group can be searched using find command with -group switch

root@kerneltalks # find / -type f -group dba

In above example we are searching for files owned by group named ‘dba’

Find empty files or directories

Empty files and directories cleanup is crucial when you are hitting your inode limits. Sometimes deleting sources of soft links, left link files empty on server occupying inode. In such a case we can search them with -empty switch to find command.

root@kerneltalks # find / -type f -empty
root@kerneltalks # find / -type d -empty

Defining file type as file or directory will search respective empty entities.