home-impermanence/README.md

# home-impermanence

OpenBSD and Linux compatible implementation of the [impermanence project from the NixOS community](https://nixos.wiki/wiki/Impermanence)

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`:

``` yaml
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.