Aug 22, 2017

CoreOS: structure of the ISO image

After some first steps with CoreOS ("First step to micorservices: CoreOS on virtualbox") my problem is, how to customize CoreOS. After each reboot all changes are gone (tmpfs / squashfs).

There are some tutorials which recommend the usage of etcd, but even this has to be configured into the CoreOS linux...

The first idea: what about customizing the ISO image...

mount -o loop coreos_production_iso_image.iso /media/iso
Inside this:
$ ls
coreos  isolinux  syslinux
du -sh *
276M    coreos
1,9M    isolinux
2,5K    syslinux
and inside the coreos directory:
ls -l coreos
insgesamt 282349
-r--r--r-- 1 root root 253738975 Jul  6 03:47 cpio.gz
-r--r--r-- 1 root root  35385632 Jul  6 03:47 vmlinuz
$ gunzip cpio.gz
$ cat cpio | cpio -idmv
The directory etc is empty. And usr.sqashfs can be mounted:
mount usr.squashfs /media/sqashfs
and here we go:
du -sh *
221M    bin
34M    boot
512    lib
240M    lib64
18M    libexec
2,5K    local
0    lost+found
512    postinst
29M    sbin
69M    share
512    tmp
I think modifying these files is not really helpful. Although there is no home directory to install my authorized_keys file.

CoreOS itself states:
But i hope there is another way without ignition to modify the coreos. Stay tuned ;-)

Other posts around this topic: Core OS

  • Installing CoreOS on Virtualbox
  • Core OS - a minimal linux? A quick overview: diskspace, mounts, commands, kernel, ...
  • How to login via ssh (default password?!)
  • structure of the ISO image
  • Customizing a CoreOS image/iso: Ignition
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