Tag: edit

How to delete a specific line from a text file in command line on Linux?

sed -i '4d' ./file

Here, -i means edit the file in-place. d is the command to “delete the pattern space; immediately start next cycle”. 4 means the 4th line.

Remove the last line:

sed '$d' filename.txt

Remove all empty lines:

sed '/^$/d' ./file

or

sed '/./!d' ./file

Remove lines from 7 to 9:

sed '7,9d' ./file

Remove the line matching by a regular expression REGULAR:

sed '/REGULAR/d' ./file

For a simple example, remove the lines containing “oops”:

sed '/oops/d' ./file

How to Add Memory, vCPU, Hard Disk to Linux KVM Virtual Machine

n this example, let us increase the memory of myRHELVM1’s VM from 2GB to 4GB.

First, shutdown the VM using virsh shutdown as shown below:

# virsh shutdown myRHELVM1
Domain myRHELVM1 is being shutdown

Next, edit the VM using virsh edit:

# virsh edit myRHELVM1

Look for the below line and change the value for memory to the following. In my example, earlier it was 2097152:

<memory unit='KiB'>4194304</memory>

Please note that the above value is in KB. After making the change, save and exit:

# virsh edit myRHELVM1
Domain myRHELVM1 XML configuration edited.

Restart the VM with the updated configuration file. Now you will see the max memory increased from 2G to 4G.

You can now dynamically modify the VM memory upto the 4G max limit.

Create the Domain XML file using virsh create

# virsh create /etc/libvirt/qemu/myRHELVM1.xml
Domain myRHELVM1 created from /etc/libvirt/qemu/myRHELVM1.xml

View the available Memory for this domain. As you see below, even though the maximum available memory is 4GB, this domain only has 2GB (Used memory).

# virsh dominfo myRHELVM1 | grep memory
Max memory:     4194304 KiB
Used memory:    2097152 KiB

Set the memory for this domain to 4GB using virsh setmem as shown below:

# virsh setmem myRHELVM1 4194304

Now, the following indicates that we’ve allocated 4GB (Used memory) to this domain.

# virsh dominfo myRHELVM1 | grep memory
Max memory:     4194304 KiB
Used memory:    4194304 KiB

2. Add VCPU to VM

To increase the virtual CPU that is allocated to the VM, do virsh edit, and change the vcpu parameter as explained below.

In this example, let us increase the memory of myRHELVM1’s VM from 2GB to 4GB.

First, shutdown the VM using virsh shutdown as shown below:

# virsh shutdown myRHELVM1
Domain myRHELVM1 is being shutdown

Next, edit the VM using virsh edit:

# virsh edit myRHELVM1

Look for the below line and change the value for vcpu to the following. In my example, earlier it was 2.

<vcpu placement='static'>4</vcpu>

Create the Domain XML file using virsh create

# virsh create /etc/libvirt/qemu/myRHELVM1.xml
Domain myRHELVM1 created from /etc/libvirt/qemu/myRHELVM1.xml

View the virtual CPUs allocated to this domain as shown below. This indicates that we’ve increased the vCPU from 2 to 4.

# virsh dominfo myRHELVM1 | grep -i cpu
CPU(s):         4
CPU time:       21.0s

3. Add Disk to VM

In this example, we have only two virtual disks (vda1 and vda2) on this VM.

# fdisk -l | grep vd
Disk /dev/vda: 10.7 GB, 10737418240 bytes
/dev/vda1   *           3        1018      512000   83  Linux
/dev/vda2            1018       20806     9972736   8e  Linux LVM

There are two steps involved in creating and attaching a new storage device to Linux KVM guest VM:

  • First, create a virtual disk image
  • Attach the virtual disk image to the VM

Let us create one more virtual disk and attach it to our VM. For this, we first need to create a disk image file using qemu-img create command as shown below.

In the following example, we are creating a virtual disk image with 7GB of size. The disk images are typically located under /var/lib/libvirt/images/ directory.

# cd /var/lib/libvirt/images/

# qemu-img create -f raw myRHELVM1-disk2.img 7G
Formatting 'myRHELVM1-disk2.img', fmt=raw size=7516192768

To attach the newly created disk image, use the virsh attach-disk command as shown below:

# virsh attach-disk myRHELVM1 --source /var/lib/libvirt/images/myRHELVM1-disk2.img --target vdb --persistent
Disk attached successfully

The above virsh attach-disk command has the following parameters:

  • myRHELVM1 The name of the VM
  • –source The full path of the source disk image. This is the one that we created using qemu-image command above. i.e: myRHELVM1-disk2.img
  • –target This is the device mount point. In this example, we want to attach the given disk image as /dev/vdb. Please note that we don’t really need to specify /dev. It is enough if you just specify vdb.
  • –persistent indicates that the disk that attached to the VM will be persistent.

As you see below, the new /dev/vdb is now available on the VM.

# fdisk -l | grep vd
Disk /dev/vda: 10.7 GB, 10737418240 bytes
/dev/vda1   *           3        1018      512000   83  Linux
/dev/vda2            1018       20806     9972736   8e  Linux LVM
Disk /dev/vdb: 7516 MB, 7516192768 bytes

Now, you can partition the /dev/vdb device, and create multiple partitions /dev/vdb1, /dev/vdb2, etc, and mount it to the VM. Use fdisk to create the partitions as we explained earlier.

Similarly to detach a disk from the guest VM, you can use the below command. But be careful to specify the correct vd* otherwise you may end-up removing wrong device.

# virsh detach-disk myRHELVM1 vdb
Disk detached successfully

4. Save Virtual Machine Configuration

If you make lot of changes to your VM, it is recommended that you save the configurations.

Use the virsh dumpxml file to take a backup and save the configuration information of your VM as shown below.

# virsh dumpxml myRHELVM1 > myrhelvm1.xml

# ls myrhelvm1.xml
myrhelvm1.xml

Once you have the configuration file in the XML format, you can always recreate your guest VM from this XML file, using virsh create command as shown below:

virsh create myrhelvm1.xml

5. Delete KVM Virtual Machine

If you’ve created multiple VMs for testing purpose, and like to delete them, you should do the following three steps:

  • Shutdown the VM
  • Destroy the VM (and undefine it)
  • Remove the Disk Image File

In this example, let us delete myRHELVM2 VM. First, shutdown this VM:

# virsh shutdown myRHELVM2
Domain myRHELVM2 is being shutdown

Next, destory this VM as shown below:

# virsh destroy myRHELVM2
Domain myRHELVM2 destroyed

Apart from destroying it, you should also undefine the VM as shown below:

# virsh undefine myRHELVM2
Domain myRHELVM2 has been undefined

Finally, remove any disk image file that you’ve created for this VM from the /var/lib/libvirt/images directory:
Now you can remove the disk img file under /var/lib/libvirt/images

rm /var/lib/libvirt/images/myRHELVM2-disk1.img
rm /var/lib/libvirt/images/myRHELVM2-disk2.img

Modify a virtual machine image with guestfish

Guestfish is a shell and command-line tool for examining and modifying virtual machine filesystems. It uses libguestfs and exposes all of the functionality of the guestfs API.

Sometimes you must modify a virtual machine image to remove any traces of the MAC address that was assigned to the virtual network interface card when the image was first created. This is because the MAC address is different when the virtual machine images boots. This example shows how to use the guestfish to remove references to the old MAC address by deleting the/etc/udev/rules.d/70-persistent-net.rules file and removing the HWADDR line from the /etc/sysconfig/network-scripts/ifcfg-eth0 file.

Assume that you have a CentOS qcow2 image called centos63_desktop.img. Mount the image in read-write mode as root, as follows:

# guestfish --rw -a centos.img

Welcome to guestfish, the libguestfs filesystem interactive shell for
editing virtual machine filesystems.

Type: 'help' for help on commands
'man' to read the manual
'quit' to quit the shell

><fs>

This starts a guestfish session.

Notethe guestfish prompt looks like a fish: ><fs>.

We must first use the run command at the guestfish prompt before we can do anything else. This will launch a virtual machine, which will be used to perform all of the file manipulations.

><fs> run
  1. We can now view the file systems in the image using the list-filesystems command: 
    ><fs> list-filesystems
/dev/vda1: ext4
/dev/vg_centosbase/lv_root: ext4
/dev/vg_centosbase/lv_swap: swap
  2. We need to mount the logical volume that contains the root partition: 
    ><fs> mount /dev/vg_centosbase/lv_root /
  3. Next, we want to delete a file. We can use the rm guestfish command, which works the same way it does in a traditional shell. 
    ><fs> rm /etc/udev/rules.d/70-persistent-net.rules
  4. We want to edit the ifcfg-eth0 file to remove the HWADDR line. The edit command will copy the file to the host, invoke your editor, and then copy the file back. 
    ><fs> edit /etc/sysconfig/network-scripts/ifcfg-eth0
  5. If you want to modify this image to load the 8021q kernel at boot time, you must create an executable script in the/etc/sysconfig/modules/ directory. You can use the touch guestfish command to create an empty file, the edit command to edit it, and the chmod command to make it executable. 
    ><fs> touch /etc/sysconfig/modules/8021q.modules
><fs> edit /etc/sysconfig/modules/8021q.modules
  6. We add the following line to the file and save it: 
    modprobe 8021q
  7. Then we set to executable: 
    ><fs> chmod 0755 /etc/sysconfig/modules/8021q.modules
  8. We are done, so we can exit using the exit command: 
    ><fs> exit

Example 2: Add passwordless sudo to a user:

guestfish --rw -a centos.img
><fs> run
><fs> list-filesystems
/dev/sda1: ext4
><fs> mount /dev/sda1 /
><fs> touch /etc/sudoers.d/user1-sudo
><fs> vi /etc/sudoers.d/useer1-sudo
><fs> quit

This will add the sudoers file and enable passwordless sudo for user1

How to access kubernetes dashboard from outside cluster

Edit kubernetes-dashboard service.

$ kubectl -n kube-system edit service kubernetes-dashboard

You should see yaml representation of the service. Change type: ClusterIP to type: NodePort and save file. If it’s already changed go to next step.

# Please edit the object below. Lines beginning with a '#' will be ignored,
# and an empty file will abort the edit. If an error occurs while saving this file will be
# reopened with the relevant failures.
#
apiVersion: v1
...
  name: kubernetes-dashboard
  namespace: kube-system
  resourceVersion: "343478"
  selfLink: /api/v1/namespaces/kube-system/services/kubernetes-dashboard-head
  uid: 8e48f478-993d-11e7-87e0-901b0e532516
spec:
  clusterIP: 10.100.124.90
  externalTrafficPolicy: Cluster
  ports:
  - port: 443
    protocol: TCP
    targetPort: 8443
  selector:
    k8s-app: kubernetes-dashboard
  sessionAffinity: None
  type: ClusterIP
status:
  loadBalancer: {}

Next we need to check port on which Dashboard was exposed.

$ kubectl -n kube-system get service kubernetes-dashboard
NAME                   CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
kubernetes-dashboard   10.100.124.90   <nodes>       443:31707/TCP   21h

Dashboard has been exposed on port 31707 (HTTPS). Now you can access it from your browser at:
]https://master-ip:31707]

master-ip can be found by executing kubectl cluster-info. Usually it is either 127.0.0.1 or IP of your machine, assuming that your cluster is running directly on the machine, on which these commands are executed.

In case you are trying to expose Dashboard using NodePort on a multi-node cluster, then you have to find out IP of the node on which Dashboard is running to access it. Instead of accessinghttps://master-ip:nodePort

you should access https://node-ip:nodePort.

If the dashboard is still not accessible execute the below:

sudo iptables -P FORWARD ACCEPT