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doc/ephemeral: Describe how to detect the environment #101

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18 changes: 18 additions & 0 deletions docs/src/ephemeral-run.md
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Expand Up @@ -22,6 +22,24 @@ bcvk ephemeral run-ssh quay.io/fedora/fedora-bootc:42
bcvk ephemeral run --memory 4096 --cpus 4 --name myvm quay.io/fedora/fedora-bootc:42
```

## Detecting an ephemeral environment

Conceptually now with `bcvk ephemeral`, there's *four* different ways to run
a bootc container:

- `podman|docker run <image> bash` - directly run a shell (or other process) the container without systemd. Uses the host kernel, not kernel in the container.
- `podman|docker run <image>` - by default runs systemd. See also <https://docs.fedoraproject.org/en-US/bootc/provisioning-container/>. Uses the host kernel, not kernel in the container.
- `bootc install` - Run directly on metal or a virtualized environment. Uses the kernel in the container.
- `bcvk ephemeral` - Run as a virtual machine, but *not* a true "bootc install". Uses the kernel in the container.

Some systemd units may need adaption to work in all of these modes. For example, if you have a systemd generator
which synthesizes mount units for expected partitions, it can use `ConditionVirtualization=!container` to skip
those in the first two cases (ensuring it still runs after a `bootc install`), but that won't be skipped in `bcvk ephemeral`
even though there won't be any block devices (by default).

At the current time there is not a dedicated way to detect `bcvk ephemeral`, but `ConditionKernelCommandLine=!rootfstype=virtiofs`
should work reliably in the future.
Comment on lines +27 to +41
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@gemini-code-assist gemini-code-assist Bot Oct 29, 2025

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medium

This new section is very helpful! I have a few suggestions to improve grammar, spelling, and clarity:

  • On line 27, "there's" should be "there are" since it refers to multiple items.
  • On line 35, "adaption" should be "adaptation".
  • The final sentence on lines 40-41 is a bit tentative ("should work reliably in the future"). If this is the recommended method now, we could phrase it more confidently and explain its purpose.

Here's a suggested revision for the whole section that incorporates these points:

Suggested change
Conceptually now with `bcvk ephemeral`, there's *four* different ways to run
a bootc container:
- `podman|docker run <image> bash` - directly run a shell (or other process) the container without systemd. Uses the host kernel, not kernel in the container.
- `podman|docker run <image>` - by default runs systemd. See also <https://docs.fedoraproject.org/en-US/bootc/provisioning-container/>. Uses the host kernel, not kernel in the container.
- `bootc install` - Run directly on metal or a virtualized environment. Uses the kernel in the container.
- `bcvk ephemeral` - Run as a virtual machine, but *not* a true "bootc install". Uses the kernel in the container.
Some systemd units may need adaption to work in all of these modes. For example, if you have a systemd generator
which synthesizes mount units for expected partitions, it can use `ConditionVirtualization=!container` to skip
those in the first two cases (ensuring it still runs after a `bootc install`), but that won't be skipped in `bcvk ephemeral`
even though there won't be any block devices (by default).
At the current time there is not a dedicated way to detect `bcvk ephemeral`, but `ConditionKernelCommandLine=!rootfstype=virtiofs`
should work reliably in the future.
Conceptually now with `bcvk ephemeral`, there are *four* different ways to run
a bootc container:
- `podman|docker run <image> bash` - directly run a shell (or other process) the container without systemd. Uses the host kernel, not kernel in the container.
- `podman|docker run <image>` - by default runs systemd. See also <https://docs.fedoraproject.org/en-US/bootc/provisioning-container/>. Uses the host kernel, not kernel in the container.
- `bootc install` - Run directly on metal or a virtualized environment. Uses the kernel in the container.
- `bcvk ephemeral` - Run as a virtual machine, but *not* a true "bootc install". Uses the kernel in the container.
Some systemd units may need adaptation to work in all of these modes. For example, if you have a systemd generator
which synthesizes mount units for expected partitions, it can use `ConditionVirtualization=!container` to skip
those in the first two cases (ensuring it still runs after a `bootc install`), but that won't be skipped in `bcvk ephemeral`
even though there won't be any block devices (by default).
At the current time there is not a dedicated way to detect `bcvk ephemeral`, but `ConditionKernelCommandLine=!rootfstype=virtiofs`
should work reliably.


## Use Cases

- Quick testing of bootc images
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4 changes: 4 additions & 0 deletions docs/src/man/bcvk-ephemeral-run-ssh.md
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Expand Up @@ -81,6 +81,10 @@ Run ephemeral VM and SSH into it

Add metadata to the container in key=value form

**-e**, **--env**=*ENV*

Set environment variables in the container (key=value)

**--bind**=*HOST_PATH[:NAME]*

Bind mount host directory (RW) at /run/virtiofs-mnt-<name>
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4 changes: 4 additions & 0 deletions docs/src/man/bcvk-ephemeral-run.md
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Expand Up @@ -107,6 +107,10 @@ This design allows bcvk to provide VM-like isolation and boot behavior while lev

Add metadata to the container in key=value form

**-e**, **--env**=*ENV*

Set environment variables in the container (key=value)

**--bind**=*HOST_PATH[:NAME]*

Bind mount host directory (RW) at /run/virtiofs-mnt-<name>
Expand Down