Modifying virtual machine images

What to do when you have a virtual machine image and for a example you need to some files contents like ssh config or so? Modified images can be uploaded to glance – repeating same step after running several VMs of the same type can be easily avoided in this way.

There are few tools that can be used for that purpose and are extremely powerful (most importantly, these are usually run in place :

Example – install wireshark & nmap in an RHEL minimal install image (we assume there is Internet access from a machine running virt-customize command) – below is basically running locally a VM, modifying it and saving the changes to the image.

Example – modify ssh server config. Following edits a file in a filesystems and saves the changes to the image.

Guestfish gives access to the filesystem – it is more powerful the virt-edit in a sense that it allows browsing through the filesystems rather than modifying a file that you know a path for. You can also create new files and add contents to them. Example sequence of step to perform is as follows:

1) OPTIONAL: export LIBGUESTFS_BACKEND=direct

2) guestfish -a <qcow2/img>

3) run

4) list-filesystems

5) mount <root_filesystem> /

6) modify files

7) umount /

8) exit

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