Here we have a virtual machine image (test1.img) that contains an MBR-style partition with an ext2 filesystem on the first partition, and we create a file /hello on that filesystem. For more explanation see this posting. Very experimental code is in this git repository. Note that we aren’t building or running any of this as root.
$ guestfish
Welcome to guestfish, the libguestfs filesystem interactive shell for
editing virtual machine filesystems.
Type: 'help' for help with commands
'quit' to quit the shell
><fs> help
Command Description
help display a list of commands or help on a command
quit quit guestfish
add add a guest image to be examined or modified
cdrom add a CD-ROM image to be examined
launch launch the subprocess
mount mount a guest disk at a position in the filesystem
sync sync disks, writes are flushed through to the disk image
touch update file timestamps or create a new file
Use -h <cmd> / help <cmd> to show detailed help for a command.
><fs> add test1.img
><fs> launch
><fs> mount /dev/sda1 /
><fs> touch /hello
><fs> sync
><fs> exit
Richard WM Jones 