What's up with stat on Mac OS X/Darwin? Or filesystems without names...

Posted by Charles Stewart on Super User See other posts from Super User or by Charles Stewart
Published on 2010-02-02T10:40:54Z Indexed on 2010/04/01 4:53 UTC
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In response to a question I asked on SO, Give the mount point of a path, one respondant suggested using stat to get the device name associated with the volume of a given path. This works nicely on Linux, but gives crazy results on Mac OS X 10.4. For my system, df and mount give:

cas cas$ df
Filesystem              512-blocks     Used     Avail Capacity  Mounted on
/dev/disk0s3              58342896 49924456   7906440    86%    /
devfs                          194      194         0   100%    /dev
fdesc                            2        2         0   100%    /dev
<volfs>                       1024     1024         0   100%    /.vol
automount -nsl [166]             0        0         0   100%    /Network
automount -fstab [170]           0        0         0   100%    /automount/Servers
automount -static [170]          0        0         0   100%    /automount/static
/dev/disk2s1             163577856 23225520 140352336    14%    /Volumes/Snapshot
/dev/disk2s2             409404102  5745938 383187960     1%    /Volumes/Sparse
cas cas$ mount
/dev/disk0s3 on / (local, journaled)
devfs on /dev (local)
fdesc on /dev (union)
<volfs> on /.vol
automount -nsl [166] on /Network (automounted)
automount -fstab [170] on /automount/Servers (automounted)
automount -static [170] on /automount/static (automounted)
/dev/disk2s1 on /Volumes/Snapshot (local, nodev, nosuid, journaled)
/dev/disk2s2 on /Volumes/Sparse (asynchronous, local, nodev, nosuid)

Trying to get the devices from the mount points, though:

cas cas$ df | grep -e/ 
            | awk '{print $NF}' 
            |  while read line; do echo $line $(stat -f"%Sdr" $line); done
/ disk0s3r
/dev ???r
/dev ???r
/.vol ???r
/Network ???r
/automount/Servers ???r
/automount/static ???r
/Volumes/Snapshot disk2s1r
/Volumes/Sparse disk2s2r

Here, I'm feeding each of the mount points scraped from df to stat, outputting the results of the "%Sdr" format string, which is supposed to be the device name: Cf. stat(1) man page:

The special output specifier S may be used to indicate that the
output, if applicable, should be in string format.  May be used
in combination with:
             dr      Display actual device name.

What's going on? Is it a bug in stat, or some Darwin VFS weirdness?

Postscript Per Andrew McGregor, try passing "%Sd" to stat for more weirdness. It lists some apparently arbitrary subset of files from CWD...

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