[systemd-devel] What's mounting this partition?

[Lennart Poettering]

On Sat, 26.09.15 00:47, Paul D. DeRocco (pderocco at ix.netcom.com) wrote:

> I have a Yocto-built x86 system, running off a USB flash drive that has
> two partitions on it. /dev/sda1 is a small FAT file system that I use for
> persistent data storage, and isn't bootable. /dev/sda2 is the root file
> system, which boots via Syslinux. I use a mount unit to mount /dev/sda1 on
> /media/chroma. However, it finds that /dev/sda1 is already mounted on
> /media/sda1. It goes ahead and mounts it anyway, with a warning, but my
> mount options (noatime,tz=UTC) are ignored.
> 
> I tried putting the /media/chroma mount in fstab. Now it fails entirely,
> perhaps because systemd-fstab-generator won't create a mount unit for
> something that's already mounted somewhere else.
> 
> But what I can't figure out is what the heck is mounting /dev/sda1 on
> /media/sda1 in the first place. None of the generators in
> /lib/systemd/system-generators seem to be to blame, according to their
> docs. How do I make it not do that, so that I can mount it with my own
> options, either in fstab or with an explicit mount unit? The version of
> the system I did a couple of years ago, with an earlier Yocto, an earlier
> systemd, and an earlier kernel, didn't have this behavior.
> 
> And while we're at it, is there a way to control what mount options it
> uses for the root? I'd like to use noatime, so that it doesn't abuse my
> flash drive needlessly.

None of systemd's components will mount anything to /media, unless
explicitly configured for that via /etc/fstab or so. 

/media is traditionally the place to mount removable media, but it's a
pretty bad place for that, since it is vulnerable to DoS attacks by
different users. As such, even if we had a logic to handle removable
media (which we don't), we'd certainly not mount it there...

I think some distros (Ubuntu? Debian?) patch udisks to mount removable
media to /media, because they ignore the DoS vulnerability that is
using a shared namespace for such mounts. Maybe you have udisks
installed from one of those distros?

Either way, systemd is not responsible.

Lennart

-- 
Lennart Poettering, Red Hat