mirror of https://github.com/pikvm/pikvm.git
51 lines
2.1 KiB
Markdown
51 lines
2.1 KiB
Markdown
# Persistent storage
|
|
|
|
!!! note
|
|
This feature is available on images newer than 2022.06.20
|
|
|
|
Sometimes advanced use of PiKVM requires storing some data on disk like API keys, config files, or something like that.
|
|
For example, you want to have a script that will update SSL certificates once a week.
|
|
However, the root file system is in a read-only state and does not involve remounting automatically by user scripts.
|
|
|
|
To solve this problem, new versions of PiKVM have a small 256MiB storage partition that can be used to store that data.
|
|
A special `kvmd-pst` daemon makes sure that this partition is mounted in read-only all the time, and remounts it to RW
|
|
only when some user script requires it. This also solves the problems of simultaneous access, so the RW mode will be
|
|
keeped as long as at least one client is working with the storage.
|
|
|
|
|
|
## Usage
|
|
|
|
Below is an example of a script `/root/test.sh` that wants to save a certain file in PST:
|
|
|
|
```bash
|
|
#!/bin/bash
|
|
echo `date` + $@ > $KVMD_PST_DATA/foo
|
|
cat $KVMD_PST_DATA/foo
|
|
```
|
|
|
|
To run it use:
|
|
```
|
|
# kvmd-pstrun -- /root/test.sh --some --script --args
|
|
-- INFO -- Opening PST session ...
|
|
-- INFO -- PST write is allowed: /var/lib/kvmd/pst/data
|
|
-- INFO -- Running the process ...
|
|
Mon Jun 20 04:23:14 MSK 2022 + --some --script --args
|
|
-- INFO -- Process finished: returncode=0
|
|
```
|
|
|
|
So, what's going on here:
|
|
|
|
1. `kvmd-pstrun` connects to the `kvmd-pst` daemon, which manages the mounting of the storage.
|
|
|
|
2. If everything is fine, the daemon will remount the storage to RW mode and report the data root to `kvmd-pstrun`.
|
|
|
|
3. `kvmd-pstrun` runs the script and pass the data root path using the environment variable `KVMD_PST_DATA` (`/var/lib/kvmd/pst/data`).
|
|
|
|
4. If the `kvmd-pst` daemon stops or any other daemon error occurs, the script will be killed.
|
|
|
|
5. After the script is finished, the daemon will remount the storage to RO mode.
|
|
|
|
To be able to write to the storage, the user must be a member of `kvmd-pst` group, or have to be `root`.
|
|
|
|
The return code will be equal to the script code if it was run, or 1 if a remount error occurred.
|