Category:

Linux

xm destroy – restore vanished vms

by mn.sobieh July 29, 2020

this article addresses a common issue that happens when you use xm destroy command. Hence it will show how to solve this issue and restore vanished VMs.

What is XM?

xm command is a program that allows you to manage Xen virtualization guest virtual machines. In other words, This program can list, create, pause, and shutdown VMs. in addition, it controls the machine’s virtual block devices. though it’s very powerful, it does not handle error checking or configuration file errors very well and mistakes can lead to system instability or errors in virtual machines. Therefore, in future you should use virsh or virt-manager commands instead.

I was taking a course one of the tasks is to crash the server which runs the services. I applied the command to crash the VM

Linux XM command explained.

To take any action on XEN based virtual machines using xe command. generally, you need to add a parameter and define your target virtual machine.

xm <options>  <Target>

XM options

`xm list`	List active virtual machines
`xm create [-c] vmName/ID`	Start a virtual machine. If the -c option is used, the start up process will attach to the guest’s console.
`xm consolevmName/ID`	Open a virtual machine’s console
`xm destroy vmName /ID`	Force a virtual machine to power off.
`xm reboot vmName /ID`	Reboot a virtual machine, runs through the normal system shut down and start up process.
`xm shutdown vmName /ID`	Shut down a virtual machine, runs a normal system shut down procedure.
`xm pause`	Pause virtual machine
`xm unpause`	Resume virtual machine
`xm start vmName`	Start powered off virtual machines

problem xm destroy hide VMs, how to solve it ? .

It happens, that when you execute xm start command, it returns an error that there is no machine with that name, apparently, xm destroy hide the VM as if it’s deleted. moreover, When you list the available machines using xm –list. the machine does not show in the list.

The solution is to find where the config files of that VM. then, create a new virtual machine or rather I registered it again by executing

cd /location/of/vmFiles
xm create <virtName.conf>

the result of this command creates a new instance of the virtual machine using its existing configuration files and registers it again. and by that, you will be able to restore that vanished vm

Install ansible on oracle featured Image

Install Ansible on Oracle Linux

by mn.sobieh July 27, 2020

The Oracle Linux operating system is engineered to deliver leading performance, scalability, reliability, and security for the enterprise environment, covering SaaS and PaaS workloads as well as traditional enterprise applications. This article shows you the steps to install ansible on Oracle Linux in a simple way.

Ansible is an open-source software provisioning, configuration management, and application-deployment tool. It runs on Unix-like systems and can configure both Linux as well as Windows.

Why Install ansible?

Ansible allows you to simply claim control of your environment. hence, increase your productivity by automating your IT infrastructure, Application Deployment, and Configuration Management.

simple model-driven configuration management.
allows multi-node deployment, and remote task execution system.
It works over SSH and
Ansible is agentless, which means, it does not require additional software or daemons to manage remote nodes.

Steps to install Ansible on Oracle Linux

In recent releases of Oracle Linux, it comes with the Public yum repository file. though. In the following steps, we will enable it.

First, open the public yum repository file.

vi /etc/yum.repos.d/public-yum-ol7.repo

Then, navigate to the ol7_developer_EPL section to enable it. Just change the value of enabled=0 to 1 then save and exit.

Check if ansible in the repository by executing

[root@s59 ~]#yum list ansible
Loaded plugins: langpacks, ulninfo
Available Packages
ansible.noarch             2.7.9-1.el7                   ol7_developer

install ansible from by executing using YUM package manager

# yum install ansible -y

Now, you have Ansible installed. Next, you configure the servers you will control. therefore, read these articles to have a full-fledged Ansibled controlled environment.

Configure Ansible inventory to manage windows OS

Linux Operating Systems

vi text editor basics – P1

by mn.sobieh July 23, 2020

If you deal with recent versions of Linux you might use an enhanced version of improved vi text editor vim. it has a lot of improvement. however, This article focus on the original vi that is found in UNIX machines. So, we will discuss how to use the Linux vi text editor. in addition, explain vi mechanism. if you already know how it works, then you might want to read its man pages.

vi a powerful text editor.

once you know vi, you can edit files really quickly, as it is extremely economical with the keystrokes. Due to its different modes for inserting and issuing commands, it is much faster than most non-mode based editors. also, It is a very small editor. nevertheless, it can do almost anything, as long as you know how to get it to do what you want

The 3 Modes of VI

The first thing most users learn about the VI editor is that it has three modes command, insert, and execute.

1 – Command Mode

allows the entry of commands to manipulate text. for example, copy, delete, past, cut …etc.. These commands are usually one or two characters long and can be entered with few keystrokes.

2 – Edit Mode (vi Insert mode).

puts anything typed on the keyboard into the current file. in other words, act like a normal text editor and insert text …etc

3 – vi Execute Mode

Commands Used to do multiple operations. for example, save files, quite the editor, search file content, or open a file … etc.

Switch vi modes

into insert mode

VI starts out in command mode. There are several ways to switch vi mode to insert mode and add texts.

The most commonly used command to get into insert mode is by pressing on the letter a or letter i. These two commands are described below.

Get back to command mode

Most commands are one character long, including those which use control characters. Once you are in insert mode, you get out of it and return to command mode by pressing the escape key. If your terminal does not have an escape key, ^[ should work ( control + [ ). basically, You can hit escape twice in a row and VI would definitely return to command mode.

Hitting escape while you are already in command mode doesn’t take the editor out of command mode. It may beep to tell you that you are already in that mode.

Save and Exist vi, here an example,

– to switch to vi execute mode, firstly, you must be in command mode. then, press or type Colon “:“. after that, add the letter related to command to be executed. for example

to save the changes, type :w then press enter.

to quite without saving type :q! then press enter.

So, If I want to save my changes and close the editor. I will follow these steps

Press escape twice to make sure that I am in command mode.
Type colon : and wq .so the final look is “:wq”.

Conclusion, vi Linux editor is a powerful tool. hence, as an administrator, you should know vi editor basics.

Linux Operating Systems

vmhgfs-fuse mount error [solved]

by mn.sobieh July 19, 2020

vmhgfs-fuse is part of open-vm-tools. open-vm-tools comes with major Linux distributions. this article shows you how to use it and fix vmhgfs-fuse mount errors. like:

Error -107 cannot open connection

You can find more information about the difference between vmware-tools and open-vm-tools. Also, for in-depth information read VMware documentation.

Install open-vm-tools

for RPM-based Linx like RHEL, centOS, Oracle, and fedora. execute the following command:

yum install -y open-vm-tools or  dnf  install -y open-vm-tools

for Debian, ubuntu.

apt-get install -y open-vm-tools

Mount vmhgfs-fuse file system

Temporary mount.

To access to the host’s shared folders from your guest operation system by using the open-vm-tools. You need to mount a vmhgfs-fuse block device.

Just execute the following command.

mount -t fuse.vmhgfs-fuse .host:/ /mnt/hgfs -o allow_other

This command allows temporary access to the host’s shared folder, however, you’ll need to execute it every time you restart your virtual machine.

Persistent mount.

We will make OS mount vmhgfs-fuse shard-folders on its startup, Thus, Edit /etc/fstab file with your favorite editor, then append the following entry to the end of the file.

.host:/     /mnt/hgfs     fuse.vmhgfs-fuse      allow_other      0 0

or execute the following command.

echo ".host:/     /mnt/hgfs     fuse.vmhgfs-fuse     allow_other     0 0 " >> /etc/fstab

if you want to read more about fstab mount options, I mentioned a few while explaining how to mount ntfs partitions in linux

Let’s get rid of

To unmount the host’s shared-folders. follow these steps to avoid any future errors in your virtual machine.

first, umount the shared folder

umount /mnt/hgfs

then, comment the line in /etc/fstab which vmhgfs-fuse word. by adding a # in the line beginning.

Finally, remove the shared from the virtual machine’s settings page. this process will fix vmhgfs-fuse mount error in any new cloned virtual machine.

Fix vmhgfs-fuse mount error.

mount errors happen usually when you clone a machine you previously configured the vmhgfs-fuse in it, or the machine has that entry into /etc/fstab, you’ll get an error and the system might not start. because the operating system tries to mount non-accessible resources ( host’s shared folders).

Solution :

If you faced this issue just do the following

Initially, power off your virtual machine.
after that, enable the shared-folder feature from the virtual machine’s setting. then add any drive/folder from your host.
Finally, start your virtual machine.

This will fix your issue with vmhgfs-fuse shared-folder and your machine will work without any complaints.

As to summarize, In this article we’ve found out how to how to install open-vm-tools, and mount vmhgfs-fuse file system. Also, how to remove the shared-folder, and solve vmhgfs-fuse mount error in Linux startup.

vmware-tools vs open-vm tools Featured Image

Linux Operating Systems

Compare vmware-tools vs open-vm-tools.

by mn.sobieh July 18, 2020

Any virtual machine hosted by VMware hypervisors needs a software called vmware-tools. It’s a suite of utilities that enhances its performance and improves the management of the virtual machine. VMware provides two packages vmware-tools and open-vm-tools. both provide the same features with a slight difference. for example:

open-vm-tools comes with Linux distributions, in contrast, VMware comes with the hypervisor.
vmware-tools requires a restart of the guest operating system. even more, It does not auto-updates.

In ESXi/vCenter :

If you use an open-vm-tools, you will find VMware tools status has value Guest Managed on VM’s Summary tab. This status means that vCenter Server to manage VMware Tools and you cannot use vSphere Update Manager to upgrade VMware Tools.

folders from myHost to the famous /mnt/hgfs directory. Though It is easy to do.

We used open-vm-tools and did troubleshooting related to vmhgfs-fuse mount errors.

Linux Operating Systems

Enable EPEL repo for CentOS

by mn.sobieh July 17, 2020

EPEL (Extra Packages for Enterprise Linux) is an open-source and free community-based repository. We will explain what it is, then show how to enable EPEL repository for CentOS Linux. starting from earlier available version (currently CentOS 4)

What is EPEL ?

Though, It is a complementary repository, It provides Enterprise-grade packages. The best thing is, EPEL Packages will not conflict with any packages come from distribution channels. Also, packages are suitable for RHEL-based distributions such as Fedora, CentOS, Oracle Linux, and Scientific Linux.

It is not often operating systems gets an upgrade in production environments, So, we will mention older release, like Versions 4, 5, and 6.

For information about it and communicate with the team maintaining it, you can visit them from here.

There are many situations when we needed it, for example, to mount and access NTFS partition from Linux.

Install EPEL in CentOS older releases

CentOS 4

To Install EPEL on your CentOS, Just run the following command.

su -c 'rpm -Uvh https://download.fedoraproject.org/pub/epel/epel-release-latest-4.noarch.rpm'

CentOS 5

To Install EPEL on your CentOS, Just run the following command.

su -c 'rpm -Uvh https://download.fedoraproject.org/pub/epel/epel-release-latest-5.noarch.rpm'

CentOS 6

For release v 6, you have the option to use RPM or YUM command. Therefore, use one of the following commands.

su -c ‘rpm -Uvh https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm’

Or, you can use yum.

yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm

Install EPEL in CentOS 7 and 8

EPEL for CentOS 7

CentOS 7 has an EPEL package stored in the Extra repository. nevertheless, this package causes a few troubles. therefore, I recommend installing the latest packages by following the instructions below. Firstly, EPEL packages might require packages from option repository. Enable Optional, Extra, and HA repositories.

subscription-manager repos --enable "rhel-*-optional-rpms" --enable "rhel-*-extras-rpms"  --enable "rhel-ha-for-rhel-*-server-rpms"

Then, You can install it by executing the following command.

su -c 'rpm -Uvh https://download.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm'

or, from The Extra repository

yum install epel-release

Enable EPEL for CentOS 8

Enable Powetools repository before you start using EPEL because some packages have dependencies from it:

dnf config-manager --set-enabled PowerTools 
yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm

To summarize, EPEL repository is a major contribution and has important packages. Installation is easy, nevertheless, it holds a lot fo useful packages. Therefore, I strongly recommend to have it in your operating system.

Linux Operating Systems

mount NTFS partition on Linux in simple steps.

by mn.sobieh July 15, 2020

NTFS, NT File System, or New Technology File System is a file system that Microsoft invented. In other words, it is the default file system Windows NT family, that is to say, till Windows 2008 R2. Later Windows releases have ReFS beside it. This article will explain, by example, how to mount ntfs partition on Linux.

Why Linux can’t mount NTFS partitions?

Linux is free software work under GPL (GNU Public license). GPL grants permission to reuse or modify the source code to make derivative works, however, if you distribute your software, it requires you to license your derivative work under GPL too. that is to say, you have to make your code available to your users and allow them to further modify and redistribute it. Therefore, Linux can’t include any proprietary software, like graphic drivers or audio codecs.

To allow Linux to read and write files in NTFS partitions, It needs a driver ( ntfs-3g ) to recognize it. Fortunately, most Linux distributions include and use NTFS-3G by default. Next, we will explain the steps in three :

install the drivers.
mount NTFS partition.
Permanent mount NTFS.

Give it what it needs!

To Install ntfs-3g drivers. You need to enable a repository EPEL ( Extra Packages for Enterprise Linux ). If you don’t have it, then follow the instructions in these articles :

Install EPEL on CentOS.
Enable EPEL for Oracle Linux.

Next, Install driver packages by executing your Operating system counterpart command.

Enable ntfs-3g on CentOS 7 and OEL 7 .

yum -y install ntfs-3g ntfsprogs 
yum clean up

Enable ntfs-3g on CentOS 8 and OEL 8.

dnf -y install ntfs-3g ntfsprogs

Enable ntfs-3g on Ubuntu or Debian.

By executing the following command, you will give you OS the capability to mount NTFS partitions.

apt-get install ntfs-3g

Install ntfs-3g from source code.

For maximum stability use The ntfs-3g package which comes with your distributions. On the other hand, if it’s too old, you might want to compile the latest version from the source. If so, then follow these instructions.

make sure you have installed the basic development tools (gcc compiler, libc-dev libraries)

Download ntfs-3g latest version, then extract it, next, navigate into NTFS-3g directory.

wget https://tuxera.com/opensource/ntfs-3g_ntfsprogs-2017.3.23.tgz 
tar -xvf ntfs-3g_ntfsprogs-2017.3.23.tgz 
cd ntfs-3g_ntfsprogs-2017.3.23

Proceed with the compilation process. Initially, verify the compilation requirement.

./configure

Then, Compile the files

make

Finally, install the driver, thus distribute binary files into OS directories.

make install

if you aren’t root

sudo make install

Mount your NTFS partition.

If there was no error during installation then you can mount the NTFS volume in a read-write mode for everybody as follows. Just replace /dev/sda1, and /mnt/ntfs_partition with your relevant paths.

mount -t ntfs-3g /dev/sda1 /mnt/ntfs_partition

Linux permanent mount for NTFS partitions.

The configuration file /etc/fstab contains the information for automating partition mounting. Basically, fstab provides The OS with a list of internal devices, CD/DVD devices, and network shares (samba/NFS/sshfs) to mount in its startup.

You can set mount options in fstab which are similar to mount command. Hence, you must the proper options to mount your partition.

The syntax of a fstab entry as follows:

[Device] [Mount Point] [File System Type] [Options] [Dump] [Pass]

The following examples of how to add NTFS partition to your fstab

Example 1: mount NTFS partition meanwhile, ownership user and group and access permissions for files and directories to 655

/dev/sda1     /mnt/ntfs_partition     ntfs     rw,auto,user,fmask=133,dmask=022,uid=1001,gid=1001     0     0

Example 2: mount we added file system encoding. Keep in mind that you will need to set access permission in a later step.

/dev/sda2   /mnt/ntfs_partition ntfs-3g    permissions,locale=en_US.utf8    0   2
sudo chown your_user:your_user /mnt/ntfs_partition

Example 3: Simple mount for partition without any additional options

/dev/sda2 /mnt/ntfs_partition ntfs-3g defaults 0 0

in brief, In recent years, If you follow these steps, you will access your NTFS partition. unless your Windows OS was not cleanly shutdown.

Solving NFS error mount system call failed

Linux Operating Systems

fix mount.nfs: mount system call failed

by mn.sobieh July 5, 2020

NFS allows you to share local disk over your local network. NFS originally supported by Linux, however, in recent releases of Windows supports it. Sometimes, you might face the error message mount.nfs: mount system call failed or check lease failed on NFSv4 server when you mount shared directory from NFS server. hence, failing to mount your directory.

Investigating the issue

During investigating any issue you cloud obtain knowledge about many things more than getting a direct solution from someone. hence, I suggest continuing reading.

Check connectivity to the server.

The first thing is to confirm that you don’t have any connectivity issues to the server. because sometimes network guys do unintentionally.

you can check nfs status by executing rpcinfo command.

[root@MFVMDML-UNOCONV01 var]# rpcinfo -p 172.16.10.26
program vers proto port service
100000 2 tcp 111 portmapper
100000 2 udp 111 portmapper
100024 1 udp 58355 status
100024 1 tcp 34069 status
100003 2 tcp 2049 nfs 
100227 2 tcp 2049 nfs_acl  
100021 1 tcp 55381 nlockmgr
100005 1 udp 56628 mountd
100005 1 tcp 58276 mountd

The above results reported by the server saying I’m OK, however, it’s a misleading report. therefore, further investigation is required.

Check client OS logs.

Further scrutiny is required, hence, we will dive into OS logs and check kernel ring buffer messages.

Our objective to search for our famous error message “mount.nfs: mount system call failed” or error related to NFS. So, execute dmesg command as shown below.

[root@MFVMDML-UNOCONV01 ~]#dmesg
[1981456.923442] nfs: server 172.16.10.26 not responding, timed out
[1981456.923533] nfs: server 172.16.10.26 not responding, still trying
[1981637.403831] nfs: server 172.16.10.26 not responding, timed out
[2118031.199289] NFS: state manager: check lease failed on NFSv4 server 172.16.10.26 with error 13
[2118036.225762] NFS: state manager: check lease failed on NFSv4 server 172.16.10.26 with error 13

Similar results might show that the NFS server is not responding. So that leads to focus our efforts on the server

dmesg is used to examine or control the kernel ring buffer.

Solving the problem

All NFS servers maintain a table of local directories that are accessible to NFS clients. Yet, restarting NFS services solve nothing. therefore, We need to force NFS to re-check its shares table and update it with the current configurations. luckily NFS tools come with one called exportfs.

This tool maintains table of exported NFS file systems as described in man pages.

login into NFS server with superuser privileges. then, execute exportfs command with parameter -a to rebuild all exports tables.

root@mfvmmdls01:/var/www# exportfs -a

Linux Operating Systems

Linux network device control using ethtool

by mn.sobieh July 4, 2020

In Linux systems. You can control ethernet speed using many tools. In this article, we will explain the tool ” ethtool “. This tool displays the Ethernet device settings and changes them.

ethtool can be used to query and change ethernet hardware settings such as speed, auto-negotiation, and checksum offload on Ethernet devices.

Install ethtool package

ethtool is pre-packages by most Linux distributions. So, to install this package

Debian / Ubuntu.

sudo apt update

sudo apt install ethtool -y

Redhat / OEL

yum install ethtool -y

ethtool syntax

The command syntax is as following

ethtool devname [settings]

Common options

-S –statistics

Queries the specified network device for NIC- and driver-specific statistics.

-s –change

Allows changing some or all settings of the specified network device. All following options only apply if -s was specified.

-4

speed NSet speed in Mb/s.

ethtool with just the device name as an argument will show you the supported device speeds.

duplex half|fullSets full or half duplex mode.

port tp|aui|bnc|mii Selects device port.

autoneg on|offSpecifies whether autonegotiation should be enabled. Autonegotiation is enabled by default, but some network devices may have trouble with it, so you can disable it if really necessary.

advertise NSets the speed and duplex advertised by autonegotiation. The argument is a hexadecimal value using one or a combination of the following values:

phyad N PHY address.

xcvr internal|externalSelects transceiver type. Currently only internal and external can be specified, in the future further types might be added.

wol p|u|m|b|a|g|s|d…Sets Wake-on-LAN options. Not all devices support this. The argument to this option is a string of characters specifying which options to enable.

Example

# ethtool eth0 -s speed 100 duplex full autoneg off

In conclusion, The ethtool is a utility that allows you to manage network device hardware

Ansible Linux Operating Systems Windows

Configure ansible inventory to manage Windows

by mn.sobieh June 26, 2020

As an adventurer, It is time to see how to manages windows using ansible, hence this article is part of a series focus on how to configure ansible for windows automation.

I use Ansible documentation as my reference.

Configure Ansible to connect to Windows servers

Firstly, we will enable Linux network authentication protocol, to allow remote authentication. then, add sever. Finally, we will test our configuration.

You should know that the following instruction will not succeed unless you already configured your Windows to permit remote commands to execute.

Step one: Install few packages

Log into your ansible server. then, install packages for Kerberos, Python package manager.

In this article, I explain using Ubuntu. therefore, If you have ansible on CentOS or Other RPM-based OS check the other article Configure Ansible for Windows Authentication.

At first, Install the following packages

apt-get install -y gcc python3-pip python3-dev libkrb5-dev krb5-user

Secondly, update Python package manager.

pip install --upgrade pip

Finally, install python packages essential for Ansible.

pip install pywinrm Kerberos

Step two: add your server to ansible Inventory

Ansible inventory file is /etc/ansible/hosts, however, you can have multiple inventory files, So, in our adventure, we will create an inventory file to manage windows using ansible.

Ansible Inventory file has the following properties:

It will have a group, So, it makes it easier to manage a group of servers that have the same role.
a variables group, then we will add four variables.
You can add a server by IP, or DNS-name under the group name.

the variables will set how ansible connects to windows server, for example, It will define the credentials and how to validate the SSL certificate used.

In the following example, it shows a simple inventory file for a group of windows 2008 servers. Also, it tells ansible that group is not Linux, locally managed, provides username and password.

[winsrv]
s06
[winsrv:vars]
ansible_connection=winrm
ansible_winrm_server_cert_validation=ignore
ansible_user=Administrator
ansible_password=p@ssw0rd

I usually use servers name instead of IP. I usually add a comment with name and functionality, If I used the IP.

Step three : Test Ansible configuration

I prefer to use multiple inline commands to verify our work, For instance , i use win_ping and win_shell modules.

ansible winsrv -m win_ping

the output should be like this

Other modules, for example both win_command or win_shell allow executing window commands. like command whoami to identify who is executing the command

$ ansible winsrv -m win_shell -a "whoami"
$ ansible winsrv -m win_command -a "whoami"

If results like that

In conclusion, it is easy to configure your server to be managed by Ansible. That is to say, If your servers are domain authenticated, It will be easier. Just flow instructions shown in Kerberos setting for ansible article.

Newer Posts

Older Posts

Linux

What is XM?

Linux XM command explained.

XM options

problem xm destroy hide VMs, how to solve it ? .

Why Install ansible?

Steps to install Ansible on Oracle Linux

vi a powerful text editor.

The 3 Modes of VI

1 – Command Mode

2 – Edit Mode (vi Insert mode).

3 – vi Execute Mode

Switch vi modes

into insert mode

Get back to command mode

Save and Exist vi, here an example,

Install open-vm-tools

Mount vmhgfs-fuse file system

Temporary mount.

Persistent mount.

Let’s get rid of

Fix vmhgfs-fuse mount error.

Solution :

What is EPEL ?

Install EPEL in CentOS older releases

CentOS 4

CentOS 5

CentOS 6

Install EPEL in CentOS 7 and 8

EPEL for CentOS 7

Enable EPEL for CentOS 8

Why Linux can’t mount NTFS partitions?

Give it what it needs!

Enable ntfs-3g on CentOS 7 and OEL 7 .

Enable ntfs-3g on CentOS 8 and OEL 8.

Enable ntfs-3g on Ubuntu or Debian.

Install ntfs-3g from source code.

Mount your NTFS partition.

Linux permanent mount for NTFS partitions.

Investigating the issue

Check connectivity to the server.

Check client OS logs.

Solving the problem

Install ethtool package

ethtool syntax

Common options

Example

Related Topics

Configure Ansible to connect to Windows servers

Step one: Install few packages

Step two: add your server to ansible Inventory

Step three : Test Ansible configuration