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

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

[Filip Schauer]

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@proxmox.com>
---
 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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