linux Archives - Page 10 of 15

To list all VM on a KVM server, run

virsh list

Example

root@s3-m12:~# virsh list
 Id    Name                           State
----------------------------------------------------
 6     foo                            running

root@s3-m12:~#

To view all Virtual machines including stopped VM’s, use –all option.

root@mail:~# virsh list --all
 Id   Name       State
---------------------------
 1    iredmail   running
 -    win10      shut off

root@mail:~#

To see all network

root@server1:~# virsh net-list --all
 Name      State    Autostart   Persistent
--------------------------------------------
 Bridge0   active   yes         yes

root@server1:~#

See virsh

August 31, 2019

Install KVM

KVM Networking

Working with KVM

KVM Errors

libvirt qemu unexpectedly closed the monitor Failed to create chardev

August 31, 2019

virsh

virsh command is used to manage KVM vps. It is part of libvirt package.

http://libvirt.org

To list KVM virtual machines, run

virsh list

Start a VM

virsh start VM_ID

To shutdown a VM, run

virsh shutdown VM_ID

To delete a VM, run

virsh shutdown VM_ID

Connect to a Remote Server

virsh --connect qemu+ssh://[email protected]/system

You need SSH Key based authentication setup.

List All VM

boby@fwhlin:~ $ virsh list --all
 Id    Name                           State
----------------------------------------------------
 -     vm1                            shut off

boby@fwhlin:~ $

List All Running VM

[root@server70 ~]# virsh list
 Id    Name                           State
----------------------------------------------------
 1     vm10                           running
 3     vm12                           running
 5     vm15                           running
 7     vm17                           running
 12    vm16                           running

[root@server70 ~]#

Get Info About a VM

virsh dominfo VM_NAME

example

[root@server70 ~]# virsh dominfo vm18
Id:             10
Name:           vm18
UUID:           b6c3a3d8-d96a-c3fa-1fad-04aff28e476a
OS Type:        hvm
State:          running
CPU(s):         2
CPU time:       422.9s
Max memory:     524288 KiB
Used memory:    524288 KiB
Persistent:     yes
Autostart:      disable
Managed save:   no
Security model: none
Security DOI:   0

[root@server70 ~]#

Change the Memory of a VM

virsh dumpxml vm18 > vm18.xml
virsh shutdown vm18

vi vm18.xml

Find

<memory unit='KiB'>524288</memor<memory unit='KiB'>524288</memory>
<currentMemory unit='KiB'>524288</currentMemory>

To change Memory to 1 GB, Replace it with

<memory unit='KiB'>1048576</memory>
<currentMemory unit='KiB'>1048576</currentMemory>

Load configuration

virsh define vm18.xml

Example

[root@server70 ~]# virsh define vm18.xml
Domain vm18 defined from vm18.xml

[root@server70 ~]#

Start VM

virsh start vm18

[root@server70 ~]# virsh start vm18
Domain vm18 started

[root@server70 ~]#

See kvm

August 31, 2019

LXD container snapshot and restore

lxc allow you to take snapshot, restore snapshot of a container.

Here we create a snapshot, then delete the /etc folder from the container. Now the container is useless. Restore the container from snapshot to get it work again.

root@UNUSED:~# lxc snapshot my-vm-2 my-vm-2-snap1
root@UNUSED:~# lxc exec my-vm-2 -- rm -rf /etc
root@UNUSED:~# lxc exec my-vm-2 -- bash
I have no name!@my-vm-2:~# ls -l / | grep etc
I have no name!@my-vm-2:~# exit
root@UNUSED:~# lxc restore my-vm-2 my-vm-2-snap1
root@UNUSED:~# lxc exec my-vm-2 -- bash
root@my-vm-2:~# ls -l / | grep etc
drwxr-xr-x  89 root   root    4096 Aug 27 07:06 etc
root@my-vm-2:~# exit
root@UNUSED:~#

August 31, 2019

Install LXD on Ubuntu

To create LXD containers, run

lxc launch ubuntu:22.04 VM-NAME-HERE
lxc launch ubuntu:24.04 VM-NAME-HERE
lxc launch images:almalinux/8 VM-NAME-HERE
lxc launch images:almalinux/9 VM-NAME-HERE
lxc launch images:amazonlinux/2023 VM-NAME-HERE
lxc launch images:archlinux VM-NAME-HERE
lxc launch images:centos/9-Stream VM-NAME-HERE
lxc launch images:debian/11 VM-NAME-HERE
lxc launch images:debian/12 VM-NAME-HERE
lxc launch images:fedora/39 VM-NAME-HERE
lxc launch images:fedora/40 VM-NAME-HERE
lxc launch images:oracle/8 VM-NAME-HERE
lxc launch images:oracle/9 VM-NAME-HERE

LXD is a tool to manage LXC (Linux Containers). lxd allow you to create and manage lightweight Linux containers, it is like docker, but more like an actual virtual machine. LXD is more user-friendly than using LXC directly, has more features like clustering of servers.

On Ubuntu/Debian, run

apt install -y lxd lxd-client

Before you start using lxd, run

lxd init --auto --storage-backend=dir

Or

lxd init

Just press enter for all questions. Defaults should work. lxd is a demon, only used one time during “lxd init”. After this, you will be using lxc command for everything.

Example

root@b24:~# lxd init
Would you like to use LXD clustering? (yes/no) [default=no]: 
Do you want to configure a new storage pool? (yes/no) [default=yes]: 
Name of the new storage pool [default=default]: 
Name of the storage backend to use (dir, lvm, ceph, btrfs) [default=btrfs]: 
Create a new BTRFS pool? (yes/no) [default=yes]: 
Would you like to use an existing empty block device (e.g. a disk or partition)? (yes/no) [default=no]: 
Size in GB of the new loop device (1GB minimum) [default=30GB]: 
Would you like to connect to a MAAS server? (yes/no) [default=no]: 
Would you like to create a new local network bridge? (yes/no) [default=yes]: 
What should the new bridge be called? [default=lxdbr0]: 
What IPv4 address should be used? (CIDR subnet notation, “auto” or “none”) [default=auto]: 
What IPv6 address should be used? (CIDR subnet notation, “auto” or “none”) [default=auto]: none
Would you like the LXD server to be available over the network? (yes/no) [default=no]: 
Would you like stale cached images to be updated automatically? (yes/no) [default=yes] 
Would you like a YAML "lxd init" preseed to be printed? (yes/no) [default=no]: 
root@b24:~#

When it ask for IPv6, I selected “none”, everything else is the default.

To create a container, run

lxc launch ubuntu:22.04 vm-1

Create CentOS container

lxc launch images:centos/7 vm-2

Create Debian 10 container

lxc launch images:debian/10 vm-3

To list all containers, run

lxc ls

To stop a VM, run

lxc stop VM-NAME

To start VM,

lxc start VM-NAME

To see information about a container

lxc info VM-NAME

Folders

/var/snap/lxd/

To see storage, run

lxc storage ls

All containers share the following disk image.

/var/snap/lxd/common/lxd/disks/default.img

August 30, 2019

blkid

To list UUID for all your storage devices, run ”’blkid -c /dev/null”’

blkid - locate/print block device attributes

Example

boby@bizhat ~ $ sudo blkid -c /dev/null
[sudo] password for boby: 
/dev/sda1: UUID="c17be3a7-dd65-448a-8930-b9d0369c6575" TYPE="ext4" 
/dev/sda2: UUID="c72e257f-b210-4f81-b1de-e5130d61454e" TYPE="ext4" 
/dev/sda3: UUID="ab289ee4-fa14-4da0-af60-a9c4360327b2" TYPE="swap" 
/dev/sda5: UUID="b1ebdc91-64a8-46b0-a9ee-8e71c659bba0" TYPE="ext4" 
/dev/sda8: LABEL="Drive J" UUID="01CE4B5BC914BE10" TYPE="ntfs" 
/dev/sdb1: UUID="67fd4ee7-1123-433c-aab4-ed877051976d" TYPE="ext4" 
/dev/sdb5: UUID="28f4e904-ecfa-4a9f-b632-60c58c826cfc" TYPE="swap" 
/dev/sdb6: UUID="19ca47a8-d894-44ff-a7af-77fa16635e98" TYPE="ext4" 
/dev/sdc1: LABEL="Drive E" UUID="709409F99409C298" TYPE="ntfs" 
/dev/sdc2: LABEL="Drive C" UUID="BC108B2C108AECA8" TYPE="ntfs" 
/dev/sdc5: LABEL="Drive D" UUID="2ED4A94DD4A917DB" TYPE="ntfs" 
/dev/sdc6: LABEL="New Volume" UUID="FEA6945FA69419EB" TYPE="ntfs" 
/dev/sdc7: LABEL="Drive G" UUID="A4A08A44A08A1CC4" TYPE="ntfs" 
/dev/sr1: LABEL="Idea Net Setter" TYPE="iso9660" 
boby@bizhat ~ $

To mount /dev/sda5, i added following to /etc/fstab

UUID=b1ebdc91-64a8-46b0-a9ee-8e71c659bba0 /home/boby/store ext4  defaults  0 2

It is same as

/dev/sda5 /home/boby/store ext4  defaults  0 2

Linux Commands > hdd

August 27, 2019

atop

The program atop is an interactive monitor to view the load on a Linux system.

To install on Ubuntu/Debian

apt-get install atop

On CentOS/RHEL

yum install atop

On CentOS, you will need epel repo enabled.

View Historical Data

One of the powerful features of atop is its ability to record and store detailed snapshots of system performance, allowing you to go back and review exactly how resources were used at any given time. This is invaluable for diagnosing past performance issues, investigating system load patterns, and understanding resource usage over time. With atop’s logging capabilities, you can access historical data quickly and analyze it interactively, just as if you were viewing real-time activity.

Atop stores its log files by default in the /var/log/atop/ directory, with filenames that include the date (formatted as atop_YYYYMMDD), making it easy to locate and access historical performance data for specific days.

To view past data with atop, use the replay mode by running the following command:

atop -r

This will open today’s log file in replay mode. If you need older logs, you can specify the log file with -r option.

atop -r /var/log/atop/atop_YYYYMMDD

Replace YYYYMMDD with the desired date to load the log file for that day.

Once in replay mode, you can navigate through the data using keyboard shortcuts t and T to jump forward or backward in 10-minute intervals, and b or e to jump to the beginning or end of the log. This lets you explore historical resource usage interactively, just as you would with real-time data.

Back to Linux Commands

August 27, 2019

Using apt-get to manage software

apt-get used to manage packages in Debian/Ubuntu server.

Install A Package

apt-get install PKG_NAME

Uninstall a software (keep configuration file)

apt-get remove PKG_NAME

Uninstall a software and its configuration files

apt-get --purge remove PKG_NAME

To upgrade a software

apt-get upgrade PKG_NAME

Update Package Info

apt-get update

Remove Unwanted Programs

apt-get autoremove

Back to apt

August 27, 2019

PHP script to monitor exim mail queue

When you run exim mail server, it is good to keep an eye on number of emails in mail queue. here is a PHP script that will check number of emails in queue, if it exceed pre-set number, it will email you.

Create file

mkdir /usr/serverok/
vi /usr/serverok/mail_q_monitor.php

Add following content.

 $alertOn) {
    $hostname = exec('/bin/hostname');
    $subject = 'Mail queue alert on ' . $hostname;
    $mail_text = 'Mail queue on server ' . $hostname . ' have ' . $num_mails . ' mails';
    mail($adminEmail, $subject, $mail_text);
}

In this case, if mails in queue exceeded 100, you get email.

$alertOn = 100;

You can change 100 to whatever number you need.

$adminEmail = "[email protected]";

Replace [email protected] with your email address.

Set script to run every 10 minutes using cronjob

*/10 * * * * /usr/local/bin/php /usr/serverok/mail_q_monitor.php >/dev/null 2>&1

August 26, 2019

Tag: linux

Load Testing

bandwidth

virsh list

virsh nodeinfo

Linux KVM Virtualization

Install KVM

KVM Networking

Working with KVM

KVM Errors

virsh

Connect to a Remote Server

List All VM

List All Running VM

Get Info About a VM

Change the Memory of a VM

LXD container snapshot and restore

Install LXD on Ubuntu

blkid

atop

View Historical Data

Using apt-get to manage software

PHP script to monitor exim mail queue