[pve-devel] [PATCH container] lxc config: mount /dev/shm tmpfs for application containers

[Fabian Grünbichler]

On December 2, 2025 4:27 pm, Filip Schauer wrote:
> Mount a tmpfs at /dev/shm into containers without an init system which
> would normally set up a shared memory filesystem. This satisfies the OCI
> Runtime Spec [0], which specifies that the following should be made
> available in the container:
> /proc       proc
> /sys        sysfs
> /dev/pts    devpts
> /dev/shm    tmpfs
> 
> The reason the mount is added conditionally is to avoid interfering with
> init systems: systemd correctly detects an existing /dev/shm, but OpenRC
> mounts it even if already present, resulting in duplicate mounts.
> 
> [0] https://github.com/opencontainers/runtime-spec/blob/fd25dd34a06b/config-linux.md#default-filesystems
> 
> Signed-off-by: Filip Schauer <f.schauer at proxmox.com>

Reviewed-by: Fabian Grünbichler <f.gruenbichler at proxmox.com>

@Wolfang - could you also take a look to ensure I haven't missed any
implications?

> ---
>  src/PVE/LXC.pm | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/src/PVE/LXC.pm b/src/PVE/LXC.pm
> index de54a0d..e5ff3a1 100644
> --- a/src/PVE/LXC.pm
> +++ b/src/PVE/LXC.pm
> @@ -756,6 +756,11 @@ sub update_lxc_config {
>          $raw .= "lxc.mount.auto = sys:mixed\n";
>      }
>  
> +    if (defined($conf->{entrypoint}) && $conf->{entrypoint} ne '/sbin/init') {
> +        # Mount /dev/shm tmpfs into the container, if no init system runs to set it up.
> +        $raw .= "lxc.mount.entry = shm dev/shm tmpfs rw,nosuid,nodev,create=dir 0 0\n";
> +    }
> +
>      PVE::LXC::Config->foreach_passthrough_device(
>          $conf,
>          sub {
> -- 
> 2.47.3
> 
> 
> 
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