How to Configure Time Server (NTP Server) on Centos 7?


VM/ Physical – It is recommended to have the time server as a physical server, but VMs should be okay depending on your setup and requirement. My virtual lab environment is VMware based so here’s the guide for a VM. Once the CentOS Minimal is installed on the VM make sure to install open-vm-tools.

If you are not conformable with Vi Editor please use install nano for editing.

Installing the time server:

  1. First we need to install NTPd . to do this open command line :

  2. Then open NTP main configuration file for editing:
    If you are planning on hosting your time servers externally like time01.yourdomain.com, time02.yourdomain.com with ports 123 open on the firewall. Each of the time server will be talking to 0.us.pool.ntp.org, 0.us.pool.ntp.org, 0.us.pool.ntp.org, 0.us.pool.ntp.org. Later on you can probably add your time servers to the NTP.org by joining the pool. For my example, I am not using the centos default pool, but i am using the U.S. zone. For internal servers/workstations you can point it to the local ip/dns name for the local time servers.

  3. Then start and enable ntp server:

  4. You need to allow ntp service on firewall(NTP service uses UDP port 123). So run next command:

  5. Verify you ntp service with next command:

Your output should be similar to:

How to restart management agents on ESX or ESXi host

If you are not unable to connect ESXi server to vCenter, or when you cannot connect to ESXi server from VI client it may be necessary to restart the management agents on ESX or ESXi host.

To restart the management agents on ESXi 6.x

This applies to ESX4/5.x/6.x

For the restart of the management agents (mgmt-vmware and vmware-vpxa) do the following:

Log in to SSH or Local console as root.
Run these commands:

Or also (alternative way)
To reset the management network on a specific VMkernel interface, by default vmk0, run the command:

Note: Using a semicolon (;) between the two commands ensures the VMkernel interface is disabled and then re-enabled in succession. If the management interface is not running on vmk0, change the above command according to the VMkernel interface used.

to restart all management agents on the host, run the command:

To restart the Management agents on ESXi Server – via the console:

1.) Connect to the console of your ESX Server and press F2
2.) Login as root and when using the Up/Down arrows navigate to Restart Management Agents.
3.) Press Enter and press F11 to restart the services.
4.) When the service has been restarted, press Enter. Then you can press Esc to logout of the system.

Screen should be similar to:

To restart the management agents on ESXi 4.x and 5.x:

From Local Console or SSH:
  1. Log in to SSH or Local console as root.
  2. Run this command:
You can also check:  Service mgmt-vmware restart may not restart hostd (1005566).

To restart the management agents on ESX Server 3.x, ESX 4.x:

  1. Login to your ESX Server as root from SSH session or directly from the console.
  2. Type service mgmt-vmware restart and press Enter
    Make sure that automatic Startup/Shutdown of virtual machines is disabled before running this command otherwise you might reboot the virtual machines. See more at 103312
  3. Type service vmware-vpxa restart and press Enter.
  4. Type logout and press Enter to disconnect from the ESX Server.

Successful output :

This may also server as a solution for the error “Unable to access file since it is locked. An error occurred while consolidating disks: One or more disks are busy.”

Configure SNMP on an ESXi Host or multiple Hosts

Recently I needed to configure all of our 40 or so ESXi hosts to forward SNMP traps to our corporate monitoring solution. This meant enabling and configuring SNMP on each of the hosts. Naturally, I wrote a script for this as 40 hosts is way too many to do manually.

This article shows you how configure SNMP on an ESXi host manually, via PowerCLI and via host profiles.

Option 1: Manually via Command Line

This is the most boring approach and should really only be used if you only have a few ESXi hosts to do, or if you really like doing things manually 🙂

  1. Start the SSH service on the ESXi host (Configuration >> Software >> Security Profile >> Services)
  2. SSH into host (using putty or something similar)
  3. Run the following to configure SNMP settings, enable SNMP in the firewall and start the SNMP agent:
    Note 1: Replace <COMMUNITY_STRING> with the community string for your monitoring solution.

    Note 2: Replace <TARGET_STRING> with the target string that maps to your environment, in the format of [email protected]/community_string.

    Option 2: Manually via PowerCLI

    Option number 2 is to use PowerCLI to configure SNMP on an ESXi host. The following script is how to do this on a single host. To configure SNMP on an whole bunch of ESXi hosts, see option 3 below.

    Note: Prior to being able to use the script above, ensure you configure the following variable values:

    • <ESXI_HOST> – The FQDN or the IP address of the ESXi host you want to enable SNMP on.
    • <COMMUNITY> – This is the community string you require for your environment (same as in option 1 above).
    • <TARGET> – This is the FQDN or IP address of the target you want to send the SNMP traps to. Note: THIS IS NOT A TARGET STRING as in option 1. In this instance you ONLY need the FQDN or IP address. The @port and the community_string will be added automatically by the Set-VMHostSnmp cmdlet.
    • <PORT> – The port you require SNMP traps to be sent on.

Option 3: Automatically via PowerCLI

If you have to configure SNMP for more than just a handful of ESXi hosts, then it is worth automating the entire process through a PowerCLI script. The logic around enabling SNMP on the ESXi host is the same as in option 2 above, with some additional logic around this to enumerate and complete the process on all ESXi Hosts.

Here is a script that will connect to a vCenter Server, get a list of all ESXi Hosts and then configure SNMP on each ESXi host:

Note: Similar to option 2 above, you will need to configure the following variables first:

  • <COMMUNITY> – This is the community string you require for your environment (same as in option 1 above).
  • <TARGET> – This is the FQDN or IP address of the target you want to send the SNMP traps to.
    Note: THIS IS NOT A TARGET STRING as in option 1. In this instance you ONLY need the FQDN or IP address. The @port and the community_string will be added automatically by the Set-VMHostSnmp cmdlet.
  • <PORT> – The port you require SNMP traps to be sent on.

Option 4: Automatically via Host Profiles

Finally, if you are lucky enough to be running Enterprise Plus licensing, then you will have the ability to use Host Profiles. This allows you to configure SNMP within the host profile and then just apply that profile to all of your ESXi hosts.

Follow these steps to add the SNMP configuration into an existing Host Profile:

  1. From the VI Client, navigate to Management >> Host Profiles
  2. Select the profile you want to add the SNMP settings and click Edit Profile
  3. Expand the SNMP Agent Configuration policy and select SNMP Agent Configuration
  4. In the Configuration Details pane, complete the followng:
    • Enable or Disable agent: Ticked
    • IP/UDP Port: The port you require SNMP traps to be sent on
    • SNMP Community String: The community string for your environment
    • Notification Receiver: The target string that maps to your environment, in the format of [email protected]/community_string
  5. Click OK to save changes
  6. For each ESXi host attach and apply the profile (Note: An ESXi host needs to be in maintenance mode to be able to apply the host profile)

And that concludes how to configure SNMP on a ESXi host.


VMware: Intermittent Error: Unexpected character ‘’ (code 65279 / 0xfeff) in prolog; expected ‘<' at [row,col {unknown-source}]: [1,1] pop up in Windows vSphere client ?

Recently, I got the error below when using the vSphere client.



I have only tested this solution on:



Repair your installation of Microsoft Visual J#® 2.0 Redistributable Package – Second Edition (x64)


The error went away after repair.

In trying to google the error some user have reported that uninstall the patch KB3147458 worked for them. I didn’t have the patch.

Hope this helps.

ESXi 6.0 not detecting BROCADE HBA adapter


  1. Make sure HBA is connected on the PCI slot and visible under esx hardware list:
  2. Check if VMKernel can detect any storage via Fibre Channel
    (output will be blank line if HBA driver is missing but HBA appears to be in PCI card determined from step 1)
  3. Search and download the relevant ESXi drivers for HBAthe recommended driver (bfa) version for 82B in ESXi 5.1 is
    You can download it from the following URL.
  4. Download the driver and install it using following instructions:

New Installation

For new installs, you should perform the following steps:

  1. Copy the VIB to the ESX server.  Technically, you can place the file anywhere that is accessible to the ESX console shell, but for these instructions, we’ll assume the location is in ‘/tmp’. Here’s an example of using the Linux ‘scp’ utility to copy the file from a local system to an ESX server located at
  2. Issue the following command (full path to the VIB must be specified):

In the example above, this would be:

Note: Depending on the certificate used to sign the VIB, you may need to change the host acceptance level.  To do this, use the following command:

Also, depending on the type of VIB being installed, you may have to put ESX into maintenance mode.  This can be done through the VI Client, or by adding the ‘–maintenance-mode’ option to the above esxcli command.

Upgrade Installation

The upgrade process is similar to a new install, except the command that should be issued is the following:

Reboot host.

Now you should have the HBA should the datastores.

Remove licensing from ESXi host

WARNING: This is for education/informational testing/development purposes only, and should not be used on a production server.

WARNING: This trick will only work with an ESX(i) stand alone server.  It will not work if the ESX(i) server is connected to a vCenter Server, as the vCenter Server knows better than to let you do this.  (you can always remove and readd the ESX(i) server to vCenter.)

To reset your ESX 4.x, ESXi 4.x and ESXi 5.x 60 day evaluation license:

  1. Login to the TSM through SSH or Shell
  2. Remove the following two files:
  3. Reboot server

If your ESX server is connected to a vCenter server, please remove the ESX server first.  Once the steps above are completed, you can add it back to the vCenter server.

Command to remove the license and reboot the ESX host:

After reboot, logging on the ESXi server, you should be greeted with this message.


For ESXi 5.1 and ESXi 5.5, you may need to continually remove the license files as the server reboots for this to work.  The following should do this quite nicely:

An alternative would be restarting the services, it should work just as well as rebooting the server:

For vCenter
1) Create a DSN to your local SQL Express instance that holds your vCenter DB.
2) Uninstall virtual center
3) Re-install virtual center and point to your DSN making sure not to overwrite.

With this method, I have been able to refresh my 4.1 and 5.0 hosts.  Have not confirmed if this works for 5.1.

How to Install VMware Tools on RHEL 7/CentOS 7

VMware Tools is one of important components for virtual machine (VM) in order get excellent performance. It is a group of utilities that help to enhances the overall performance of the virtual machine’s guest operating system (OS) and improves management of the VM. Without the VMware Tools, guest OS performance will lacks some of the important functionality. Below steps shows how to install the VMware Tools on RHEL 7, CentOS 7 and Oracle Linux 7.

How to Install VMware Tools ?

Option 1 (Recommended by VMware) – VMware support of open-vm-tools

open-vm-tools is an open source implementation of VMware Tools from third parties and contains utilities that enhances virtualization management, administration and functions of the virtual machine in VMware environments. The ultimate goal is to enable the operating system vendors and/or communities and virtual appliance vendors to bundle VMware Tools into their product releases.

Option 2 :

1. Install prerequisites :

2. Attach the vmware tools sofware from vSphere client.

3. Mount the vmware tools package into /mnt :

4. Copy vmware tool packagae into /tmp :
5. Go to /tmp directory and extract the vmware tools package :
6. Go to extracted folder, vmware-tools-distrib :
7. Run vmware-install.pl to start installation :
8. Once successfully installed, make sure you umount (not unmount- missing the n) back the /mnt :