David Rio Deiros
117 lines
2.8 KiB
Markdown
117 lines
2.8 KiB
Markdown
---
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title: "Access permanent data"
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menuTitle: "Access permanent data"
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weight: 70
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---
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## Create the filesystem
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gokrazy provides a handy way to create the permanent data filesystem on the fourth partition of your gokrazy installation.
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The [gokrazy/mkfs](https://github.com/gokrazy/mkfs) program will create the filesystem.
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To actually access the permanent data partition from your own program, gokrazy will mount the partition under `/perm` directory during the startup.
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You can add the `gokrazy/mkfs` program to your gokrazy instance:
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```bash
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gok add github.com/gokrazy/mkfs
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```
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…or, if you want to run it only once without otherwise including it in your
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installation, you can use `gok run`:
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```bash
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git clone https://github.com/gokrazy/mkfs
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cd mkfs
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gok -i bakery run
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```
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## Permanent data in action
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The Go program demonstrates the functionality of the permanent data mount:
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```go
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package main
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import (
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"encoding/json"
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"errors"
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"fmt"
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"io/fs"
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"io/ioutil"
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"os"
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)
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const config = "/perm/my-example/config.json"
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type Config struct {
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FilesToCreate int `json:"files_to_create"`
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}
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func main() {
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_, err := os.Stat(config)
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if err != nil {
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fsErr := &fs.ErrNotExist
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if !errors.As(err, fsErr) {
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panic(err)
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}
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content, err := json.Marshal(&Config{FilesToCreate: 4})
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if err != nil {
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panic(err)
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}
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if err = ioutil.WriteFile(config, content, 0600); err != nil {
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panic(err)
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}
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}
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content, err := ioutil.ReadFile(config)
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if err != nil {
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panic(err)
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}
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var c Config
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if err := json.Unmarshal(content, &c); err != nil {
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panic(err)
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}
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for i := 0; i < c.FilesToCreate; i++ {
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if err := ioutil.WriteFile(fmt.Sprintf("/perm/my-example/%d.txt", i), []byte("gokrazy rocks"), 0600); err != nil {
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panic(err)
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}
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}
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}
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```
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## Manual inspection/modification
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You can inspect and modify the data on the permanent data filesystem manually.
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This can be handy if you need e.g. to pass a configuration file for your application.
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To access the filesystem put the SD card into your PC/notebook. Your OS will likely mount the filesystem automatically.
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Copy the file to the permanent data filesystem.
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```bash
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mkdir /path/to-mounted/filesystem/my-example
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sudo cp config.json /path/to-mounted/filesystem/my-example
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```
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If you want to access files on the permanent data filesystem you may need the [sudo](https://en.wikipedia.org/wiki/Sudo) capability.
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## Notes about macOS
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In macOS, to identify what device file maps to the mini sd card use:
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```bash
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$ diskutil list
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```
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If you want to create an ext4 filesystem from macOS, use the ext2/3/4 [utilities](https://e2fsprogs.sourceforge.net/).
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The easiest way to install them is via [homebrew](https://formulae.brew.sh/formula/e2fsprogs#default).
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With the utilities installed you can run (replace X and Y based on the <code>diskutil list</code> output):
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```bash
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$ sudo `brew --prefix e2fsprogs`/sbin/mkfs.ext4 /dev/diskXsY
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```
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