Re: How to determine if a file is a mount point?

Under Unix-like systems, sometimes checking the device field returned by lstat() will work. For instance, here's the wanted() routine generated by find2perl / -xdev:

use File::Find;

File::Find::find({wanted => \&wanted}, '/');
exit;

sub wanted {
    my ($dev,$ino,$mode,$nlink,$uid,$gid);

    (($dev,$ino,$mode,$nlink,$uid,$gid) = lstat($_)) &&
    !($File::Find::prune |= ($dev != $File::Find::topdev))
    && print("$name\n");
}
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$File::Find::topdev is simply the device associated with the root directory /:

($File::Find::topdev) = lstat("/");
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Re^2: How to determine if a file is a mount point? by gw1500se (Beadle) on Jun 29, 2008 at 08:59 UTC
Thanks. That seems to help with one exception so far. Using that method, it makes /dev look like a mounted file system which it is not. Is there some special meaning to $dev for certain directories like /dev?	[reply]
Re^3: How to determine if a file is a mount point? by pc88mxer (Vicar) on Jun 29, 2008 at 15:02 UTC
Actually, `/dev` is a mounted file system -- see what the `mount` command reports. It is not a remote file system like `NFS`, but then Linux doesn't differentiate "remote" file systems from other kinds of file systems (like `/proc` or EXT2 or NTFS or FTPFS). The value of the `device` field identifies the handler (file system driver) that the OS uses to implement the file system object. If you only interested in `NFS` files, you could find out what its `device` id is and just check for that particular value.	[reply] [d/l] [select]
Re^3: How to determine if a file is a mount point? by grep (Monsignor) on Jun 29, 2008 at 15:04 UTC
/dev and /proc are both mounted file systems. They are just special, because they are not disk based. Look at the output of mount. It should list both /dev and /proc. grep `One dead unjugged rabbit fish later...`	[reply]
Re^4: How to determine if a file is a mount point? by gw1500se (Beadle) on Jun 30, 2008 at 22:18 UTC
Thanks for the reply. The mount output shows /proc but not /dev. In additional it seems each ext3 mounted filesystem has a different $dev value (which to me makes sense since each is on a separate partition). The ext3 filesystems seems to have a $dev value of >760 while the specials like /dev have a value of <50. It is reliable to use that to determine which is which?	[reply]