Why did you set MountFlags=slave in systemd-udevd.service.in

[lennart@xxxxxxxxxxxxxx (Lennart Poettering)]

On Do, 01.03.18 14:44, Hongzhi, Song (hongzhi.song at windriver.com) wrote:

> Thank you very much. It dose work.
> 
> Would you tell me that how the '--no-block' works,

"systemd-mount" talks to systemd (i.e. PID 1) to issue mount/automount
operations. By default it will do so synchronously, thus blocking
until the mount is established. If you specify "--no-block" then you
turn off this synchronous behaviour, and instead request asynchronous
behaviour, where the rule will just request the operation to be
executed, but won't wait for it to finish. When you invoke
"systemd-mount" from a udev rule then using "--no-block" is a
necessity to avoid a deadlock. That's because PID 1 won't operate on a
device to mount before udev reported it to be fully availabled and
probed. Now, if synchronously wait for that from inside the udev rule
you hence delay precisely that probing forever.

> I doesn't deeply understand the interpretation in
> 
> https://www.freedesktop.org/software/systemd/man/systemd-mount.html#SYSTEMD_MOUNT_OPTIONS=
> 
> 
> And why systemd-mount can solve the problem brought by MountFlag=slave.

systemd-mount request the mount operation to be executed by PID 1, and
hence outside of the mount context of udev.

Lennart

-- 
Lennart Poettering, Red Hat