wafers
Named file system wafer stack trees
Why
I use this to compose bootable root filesystems for linux containers. I don't want all of Docker and machinectl clone is really only useful with btrfs (overlayfs feels like a better fit to me at the moment).
How
overlayfs and a bit of bash.
Usage
$ wafers stack name [parent]
$ wafers unstack stack1 [stack2] [..]
Commands
stack
Create a new stack based on the wafer name.
-
name
The uppermost of a stack of wafers you want to create at${STACKS}/name. The ancestry of this wafer is recursively traced automatically to produce the full stack. -
[parent]
If the wafernamedoes not yet exist, it can be created automatically as long as aparentis specified to base it on.
unstack
Assume each positional argument corresponds to a wafer stack in $STACKS, and unstack each one.
Environment variables
WAFERS
Set this to override default value of /var/lib/wafers.
STACKS
Set this to override default value of /var/lib/machines.
Example
# create and cd to $WAFERS (/var/lib/wafers by default)
$ mkdir -p /var/lib/wafers
$ cd /var/lib/wafers
# create a directory tree to represent a base wafer
$ mkdir -p archbase/data
# get some bootable rootfs in there
$ pacstrap -cdi archbase/data base --ignore linux --ignore linux-firmware
# create a new wafer on top of another wafer and recursively mount
# the resulting stack into $STACKS (/var/lib/machines by default)
$ wafers stack archbase2 archbase
2 wafers stacked at /var/lib/machines/archbase2
# have a look at the raw wafer
$ tree archbase2/data
archbase2/data
0 directories, 0 files
# and have a look at the mounted stack
$ ls /var/lib/machines/archbase2
bin boot dev etc home lib lib64 mnt opt proc root run sbin srv sys tmp usr var
# boot into the stack with your fav container tool, make a change, get back out
$ systemd-nspawn -bD /var/lib/machines/archbase2
Spawning container archbase2 on /var/lib/machines/archbase2.
Press ^] three times within 1s to kill container.
systemd 237 running in system mode. (+PAM -AUDIT -SELINUX -IMA -APPARMOR +SMACK -SYSVINIT +UTMP ..snip
Detected virtualization systemd-nspawn.
Detected architecture x86-64.
Welcome to Arch Linux!
[ OK ] Started Dispatch Password Requests to Console Directory Watch.
[ OK ] Reached target Remote File Systems.
..snip
[ OK ] Reached target Multi-User System.
[ OK ] Reached target Graphical Interface.
Arch Linux 4.15.3-300.fc27.x86_64 (console)
archbase2 login: root
Last login: Fri Feb 23 03:14:32 on pts/0
[root@archbase2 ~]$ useradd -s/bin/bash -m jesse
[root@archbase2 ~]$
Container archbase2 terminated by signal KILL.
# have another look at the raw wafer to see where useradd made changes to the stack
$ tree archbase2/data
archbase2/data
├── etc
│ ├── group
│ ├── group-
│ ├── gshadow
│ ├── gshadow-
│ ├── machine-id
│ ├── passwd
│ ├── passwd-
│ ├── resolv.conf
│ ├── shadow
│ └── shadow-
├── home
│ └── jesse
├── root
└── var
└── log
├── btmp
├── faillog
├── journal
│ └── 7ee3294689ca4a9394ad8a34cc44d1d8
│ ├── system@000565dde63c6d7b-87320e8b62aabc30.journal~
│ └── system.journal
├── lastlog
├── tallylog
└── wtmp
# unstack
wafers unstack archbase2
# restack (note parent wafer is only required the first time)
wafers stack archbase2
# you can also stack wafers that have no parent(s)
wafers stack archbase
# use with machinectl
machinectl start archbase
machinectl shell archbaseLicense
MIT
