Martijn Dekker <mart...@inlv.org> wrote, on 21 Oct 2017:
>
> Op 19-10-17 om 15:06 schreef Martijn Dekker:
> > Op 18-10-17 om 16:11 schreef Geoff Clare:
> >> After the filesystem name there are four numeric fields with a trailing '%'
> >> on the fourth. Treating this as the terminator for the filesystem name
> >> ought to be good enough in practice. It would only not work in the
> >> extremely unlikely event that a filesystem name has within it four numeric
> >> fields with a trailing '%' on the fourth, or if two different filesystem
> >> names are the same when trailing blanks are removed.
> >>
> >> I tried it with the following command and it seems to work:
> >>
> >> df -P file1 file2 |
> >> sed '1d;s/\([[:blank:]]\{1,\}[[:digit:]]\{1,\}\)\{4\}%[[:blank:]].*//'
> >
> > That's very clever, and does seem to be fairly bullet-proof. Thanks!
>
> Hmm... on Linux, there can be several tmpfs mounts and they all have the
> same file system name in the first column. Example:
>
> tmpfs 33039212 0 33039212 0% /dev/shm
> tmpfs 33039212 3277180 29762032 10% /run
> tmpfs 5120 0 5120 0% /run/lock
> tmpfs 33039212 0 33039212 0% /sys/fs/cgroup
>
> Looks like we also need the mount point to uniquely identify a file
> system. A little tweak to the sed incantation accomplishes that:
>
> df -P /dev/shm /run |
> sed '1d;
> s/\([[:blank:]]\{1,\}[[:digit:]]\{1,\}\)\{4\}%[[:blank:]]\{1,\}/,/'
>
> gives
>
> tmpfs,/dev/shm
> tmpfs,/run
>
> But then, wouldn't it be sufficient simply to use the mount point only?
> Can two file systems ever be on the same mount point?
Linux allows two mounts to the same mount point. (I tested it with
"mount --bind ..."; not sure if it would work with a "real" mount.)
However, the files in the first mount are inaccessible until the
second is unmounted, so passing that mount point (or anything below
it) to "df -P" only shows the second mount.
So I think just comparing the mount points is indeed sufficient.
--
Geoff Clare <g.cl...@opengroup.org>
The Open Group, Apex Plaza, Forbury Road, Reading, RG1 1AX, England
