home-impermanence

OpenBSD and Linux compatible implementation of the impermanence project from the NixOS community

Such a tool permits to have your $HOME mounted with a memory filesystem and populate it from an explicit list of files and directories hooked from a persistent storage directory (like a place in your /home partition), the point is to have a clean and reproducible environment every time you log in with only the content you selected. No more extra files when you start a program only once.

Installation

Run make install as root, this will copy the program file in /usr/local/bin/impermanence and the service file in /etc/rc.d/impermanence.

On OpenBSD, You need some packages as dependencies:

• p5-File-HomeDir
• p5-List-MoreUtils
• p5-YAML

On Alpine Linux, you need the following packages: apk add perl-file-homedir perl-list-moreutils perl-yaml.

Configuration

The configuration is done in two parts, system wide to configure the impermanence service that will mount the memory filesystem and populate it.

System wide

OpenBSD

Using rcctl: rcctl set impermanence flags -d /home/persist/ -u my-user and rcctl enable impermanence.

Alpine Linux

Lazy way is to enable the service local with rc-update add local, and create two files /etc/local.d/99-impermanence.start and /etc/local.d/99-impermanence.stop with the following content:

#!/bin/sh
/usr/local/bin/impermanence -d /home/persist -u my-user start

and

#!/bin/sh
/usr/local/bin/impermanence -d /home/persist -u my-user stop

User configuration

The user configuration will be done in /home/persist/my-user/impermanence.yml if you chose -d /home/persist for the service and -u my-user.

The configuration file describes the size of the memory filesystem, the list of files and the list of directories that should be added to the filesystem as symbolic links from the persistent directory.

There are currently five keys:

• size: which is a parameter to mount_mfs -s to give the ramdisk size
• files: which is a list of files relative to $HOME to symlink into the persist home
• directores: which is a list of directories relative to $HOME to symlink into the persist home
• skeleton: which is a list of directories relative to $HOME to recreate on every mount
• chezmoi: indicate to use chezmoi apply for populating config files

Minimalistic example of /home/persist/my-user/impermanence.yml:

size: 200m
files:
  - .bashrc
  - .gitconfig
  - .profile
  - .tmux.conf
  - .xsession
directories:
  - .config
  - .local/share
  - .mozilla
  - .ssh
  - src
skeleton:
  - tmp
  - prg
  - Downloads
chezmoi: true

home-impermanence rc service

restart

The restart parameter to the service will unmount the device and recreate it, allowing a fresh restart.

It is a bad idea to use while the user is connected.

start

Creates and populates the home filesystem.

stop

Umount the home filesystem.

It is a bad idea to use while the user is connected.

status

Tells if the mount is currently done.

Tips

I configured something in a GUI program, how do I know what changed on disk?

If you want to add a file to the persistent area after a change, you may want to know exactly what changed on disk to add the file or directory to your configuration file.

Using find it's easy to scan all the files from the ramdisk (excluding the symbolic links) and order them by date of change.

This can be done with find -x ~/ -type f -exec ls -altr {} +, the last files are the most recently modified.

Beware file loss

When using this way of life, you need to remember all changes that don't belong in the persistent areas will be lost. For example, this will happen for all new files or directories at the root of your $HOME.

Impermanence requires the user to be aware of what files must stay over time, this is the point of impermanence after all.

I want to make a new file/directory persistent

If you are using your system and want to keep a newly created file or directory, move it to your persistent area at the correct place and create a symbolic link, this will allow a drop-in replacement without rebooting.

Then, update your configuration file to add the new entry.

How does a good configuration file look

There are no good or bad configuration file content (except if it's invalid obviously). The whole point of impermanence is to hand-pick every directories and files you want to run your session, by admitting all others files will be thrown away at reboot.

While you can list .config and .local which is a very large include, you could rather list only a subset of those, which will make a long list and require a few guess&fix sessions to get the things right.

The less directories are at the top level, the more you will pinpoint the exact configuration you want to keep over time.

Restarting impermanence

If you are actively tweaking your configuration file, you may have issues when impermanence is unmounting the ramdisk device even with your graphical session stopped, a process may still be running and using the partition. You would have to find the running PID by looking at processes and their owner and kill it.

As a side effect, you shouldn't be able to stop impermanence while you are using your session because the system will prevent the ramdisk to be umounted.