How to reset a KVM clone virtual Machines with virt-sysprep on Linux

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I know how to clone a KVM VM. Once cloned I would like to reset cloned VM. How do I reset, unconfigure or customize a virtual machine so clones can be made? How can I reset a KVM clone virtual Machines with virt-sysprep command on a Linux server based hypervisor?

Introduction: You need to use the virt-sysprep command to reset a virtual machine. You can remove ssh-keys, hostname, network mac configuration, user accounts and more. You can enable or disable specific features. This page shows how to use the virt-clone and virt-sysprep commands together to clone a KVM VM on a Linux based server.

Syntax to reset a KVM clone virtual Machines with virt-sysprep command

The syntax is:
virt-sysprep -d kvmDomain
virt-sysprep -d kvmDomainHere options

A list of sysprep operations to perform on a KVM VM to reset it

abrt-data Remove the crash data generated by ABRT
backup-files Remove editor backup files from the guest
bash-history Remove the bash history in the guest
blkid-tab Remove blkid tab in the guest
ca-certificates Remove CA certificates in the guest
crash-data Remove the crash data generated by kexec-tools
cron-spool Remove user at-jobs and cron-jobs
customize Customize the guest
dhcp-client-state Remove DHCP client leases
dhcp-server-state Remove DHCP server leases
dovecot-data Remove Dovecot (mail server) data
firewall-rules Remove the firewall rules
flag-reconfiguration Flag the system for reconfiguration
fs-uuids Change filesystem UUIDs
kerberos-data Remove Kerberos data in the guest
logfiles Remove many log files from the guest
lvm-uuids Change LVM2 PV and VG UUIDs
machine-id Remove the local machine ID
mail-spool Remove email from the local mail spool directory
net-hostname Remove HOSTNAME and DHCP_HOSTNAME in network interface configuration
net-hwaddr Remove HWADDR (hard-coded MAC address) configuration
pacct-log Remove the process accounting log files
package-manager-cache Remove package manager cache
pam-data Remove the PAM data in the guest
passwd-backups Remove /etc/passwd- and similar backup files
puppet-data-log Remove the data and log files of puppet
rh-subscription-manager Remove the RH subscription manager files
rhn-systemid Remove the RHN system ID
rpm-db Remove host-specific RPM database files
samba-db-log Remove the database and log files of Samba
script Run arbitrary scripts against the guest
smolt-uuid Remove the Smolt hardware UUID
ssh-hostkeys Remove the SSH host keys in the guest
ssh-userdir Remove “.ssh” directories in the guest
sssd-db-log Remove the database and log files of sssd
tmp-files Remove temporary files
udev-persistent-net Remove udev persistent net rules
user-account Remove the user accounts in the guest
utmp Remove the utmp file
yum-uuid Remove the yum UUID

You can choose which sysprep operations to perform. Give a comma-separated list of operations, for example:
virt-sysprep -d {vmDomainHere} --enable ssh-hostkeys,udev-persistent-net

Step 1. Clone your VM and spawn new instances in KVM

First use the virsh list command to get a list of all running VM domains/guest:
virsh list
Sample outputs:

 1     openbsd62                      running
 2     freebsd11-nixcraft             running
 3     fedora28-nixcraft              running
 4     rhel7                          running
 5     centos7-nixcraft               running
 6     sles12sp3                      running
 16    bionic                         running

First suspend the KVM, run:
virsh suspend bionic
Domain bionic suspended

To clone vm named ‘bionic’ as testvm using the virt-clone command, run:
virt-clone --original bionic --name testvm --auto-clone
virt-clone linux command demo
You can specify disk file instead of --auto-clone option:
# virt-clone --original bionicVM --name testVM02 --file /var/lib/libvirt/images/testvm02-disk01.qcow2
You may resume bionic VM, run:
virsh resume bionic
Domain bionic resumed

Step 2. Use virt-sysprep command

Simply run as follows to reset everything:
virt-sysprep -d testvm
reset a KVM clone virtual Machines with virt-sysprep command
You can setup the hostname of the guest and force to keep the user account named vivek in the guest:
virt-sysprep -d testvm --hostname testvm --enable user-account --keep-user-accounts vivek
You can create a new Linux user account called tom and force password change on first login as follows:
virt-sysprep -d testvm --firstboot-command 'useradd -s /bin/bash -m -G sudo tom; chage -d 0 tom'
You can set root user account password too:
virt-sysprep -d testvm --root-password password:MySuperSecureRootPasswordHere
Or combine all of them:
virt-sysprep -d testvm --hostname testvm --keep-user-accounts vivek --root-password password:MySuperSecureRootPasswordHere

How to skip certain guest VM reset features

You can enable specific operations with --enable. For example, enable all options except resetting fs-uuids ( Change filesystem UUIDs), lvm-uuids ( Change LVM2 PV and VG UUIDs), and ssh-userdir ( Remove “.ssh” directories in the guest):

w=$(virt-sysprep --list-operations | egrep -v 'fs-uuids|lvm-uuids|ssh-userdir' | awk '{ printf "%s,", $1}' | sed 's/,$//')
echo "$w"

Now run it as follows:
virt-sysprep -d testvm --hostname testvm --keep-user-accounts vivek --enable $w
Another example:
virt-sysprep -d testvm --hostname testvm --keep-user-accounts vivek --enable $w --firstboot-command 'dpkg-reconfigure openssh-server'

virt-sysprep command list options

  -a, --add <file>                    Add disk image file
  --append-line <FILE:LINE>           Append line(s) to the file
  -c, --connect <uri>                 Set libvirt URI
  --chmod <PERMISSIONS:FILE>          Change the permissions of a file
  --color, --colors, --colour, --colours
                                      Use ANSI colour sequences even if not tty
  --commands-from-file <FILENAME>     Read customize commands from file
  --copy <SOURCE:DEST>                Copy files in disk image
  --copy-in <LOCALPATH:REMOTEDIR>     Copy local files or directories into image
  -d, --domain <domain>               Set libvirt guest name
  --delete <PATH>                     Delete a file or directory
  -n, --dryrun, --dry-run             Perform a dry run
  --echo-keys                         Don't turn off echo for passphrases
  --edit <FILE:EXPR>                  Edit file using Perl expression
  --enable <operations>               Enable specific operations
  --firstboot <SCRIPT>                Run script at first guest boot
  --firstboot-command <'CMD+ARGS'>    Run command at first guest boot
  --firstboot-install <PKG,PKG..>     Add package(s) to install at first boot
  --format <format>                   Set format (default: auto)
  --help                              Display brief help
  --hostname <HOSTNAME>               Set the hostname
  --install <PKG,PKG..>               Add package(s) to install
  --keep-user-accounts <users>        Users to keep
  --keys-from-stdin                   Read passphrases from stdin
  --link <TARGET:LINK[:LINK..]>       Create symbolic links
  --list-operations                   List supported operations
  --mkdir <DIR>                       Create a directory
  --mount-options <opts>              Set mount options (eg /:noatime;/var:rw,noatime)
  --move <SOURCE:DEST>                Move files in disk image
  --network                           Enable appliance network
  --no-logfile                        Scrub build log file
  --no-network                        Disable appliance network (default)
  --no-selinux-relabel                Compatibility option, does nothing
  --operation, --operations <operations>
                                      Enable/disable specific operations
  --password <USER:SELECTOR>          Set user password
  --password-crypto <md5|sha256|sha512>
                                      Set password crypto
  -q, --quiet                         Don't print progress messages
  --remove-user-accounts <users>      Users to remove
  --root-password <SELECTOR>          Set root password
  --run <SCRIPT>                      Run script in disk image
  --run-command <'CMD+ARGS'>          Run command in disk image
  --script <script>                   Script or program to run on guest
  --scriptdir <dir>                   Mount point on host
  --scrub <FILE>                      Scrub a file
  --selinux-relabel                   Relabel files with correct SELinux labels
  --sm-attach <SELECTOR>              Attach to a subscription-manager pool
  --sm-credentials <SELECTOR>         Credentials for subscription-manager
  --sm-register                       Register using subscription-manager
  --sm-remove                         Remove all the subscriptions
  --sm-unregister                     Unregister using subscription-manager
  --ssh-inject <USER[:SELECTOR]>      Inject a public key into the guest
  --timezone <TIMEZONE>               Set the default timezone
  --touch <FILE>                      Run touch on a file
  --truncate <FILE>                   Truncate a file to zero size
  --truncate-recursive <PATH>         Recursively truncate all files in directory
  --uninstall <PKG,PKG..>             Uninstall package(s)
  --update                            Update packages
  --upload <FILE:DEST>                Upload local file to destination
  -V, --version                       Display version and exit
  -v, --verbose                       Enable libguestfs debugging messages
  --write <FILE:CONTENT>              Write file
  -x                                  Enable tracing of libguestfs calls

Step 3. Start the VM

virsh start testvm
Domain testvm started

Verify it with the following virsh command:
virsh list

Step 4. Login to the VM

Find/get the DHCP IP address of testvm using the following command along with the grep command:
virsh net-dhcp-leases default
virsh net-dhcp-leases default | grep testvm
virsh net-dhcp-leases default | grep testvm | awk '{ print $5}'

Sample outputs:

192.168.122.174/24

Use the ssh command:
ssh vivek@192.168.122.174

Conclusion

You just learned how to clone a KVM VM and reset the data. I strongly suggest that you read virt-sysprep help page here.

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

Notable Replies

  1. You need to pass the –enable user-account option as follows:

    virt-sysprep -n -d test10 --hostname test10  --enable user-account --keep-user-accounts username
    

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