[Bug 208071] AutoFS seems to disturb NFS server

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Sat Mar 19 02:06:40 UTC 2016


Rick Macklem <rmacklem at FreeBSD.org> changed:

           What    |Removed                     |Added
                 CC|                            |rmacklem at FreeBSD.org

--- Comment #5 from Rick Macklem <rmacklem at FreeBSD.org> ---
Every time you mount(8) any file system on the NFS server, mountd reloads
the /etc/exports. This has two effects:
1 - Unless you are running mountd with the "-S" option, the file systems
    will become unexported for a short period of time during the reload.
2 - If the new file system is mounted on top of the exported file system,
    mountd will try to export that new file system.
    --> NFS mounts can never be exported, so if the new file system is
        an NFS client mount, the export will no longer work. (This has
        been the case since 1985 and is in part the case because you
        can't safely put a file handle inside a file handle.)

To fix #1, add "-S" to mountd_flags.
#2 just won't work and needs to be avoided. You can look at
/var/log/messages for entries related to export problems generated
by mountd.

I don't know amd-utils or autofs, but it may be that one of them uses
mount(8) and the other does not. FreeBSD's mount(8) always sends a
SIGHUP to mountd, which makes it reload /etc/exports.

Basically #1 and #2 only occurs because mountd reloads /etc/exports
and that happens when mountd receives a SIGHUP. It may be that amd-utils
doesn't send a SIGHUP to mountd?)


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