The propagation flag is changed by
man 7 mount_namespaces:
systemd(1) automatically remounts all mount points as MS_SHARED on system startup. Thus, on most modern systems, the default propagation type is in
/* Mark the root directory as shared in regards to mount propagation. The kernel defaults to "private", but we
* think it makes more sense to have a default of "shared" so that nspawn and the container tools work out of
* the box. If specific setups need other settings they can reset the propagation mode to private if
* needed. Note that we set this only when we are invoked directly by the kernel. If we are invoked by a
* container manager we assume the container manager knows what it is doing (for example, because it set up
* some directories with different propagation modes). */
if (detect_container() <= 0)
if (mount(NULL, "/", NULL, MS_REC|MS_SHARED, NULL) < 0)
The implications depend on your particular use cases. I think that most programs will continue to work. However, your change will be overwritten on reboot.
You can read more in the comment from Lennart Poettering in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=739593
Here is a part of it:
b) If you patch systemd to go back to MS_PRIVATE for the root dir, you
disable propagation to containers, and nobody can opt-in to it anymore
for their specific namespace.
Advantage: you don't have to patch those few programs which
currently assume the root dir is MS_PRIVATE and don't disassociate
Disadvantage: the apps are still broken for those who switch to
MS_SHARED for /. You hence only cover the usecases where people do
not dissassocitate. You break the usecase where people want the
propagation to tkae place.