Remote tunefs -n enable

Peter Jeremy peterjeremy at
Wed Feb 22 23:03:00 PST 2006

On Wed, 2006-Feb-22 10:03:44 +0000, Miguel Lopes Santos Ramos wrote:
>> From: MC <rossiya at>
>> Consequently he hasn't set softupdates on the main '/' partition
>It wasn't his fault. It is the default install option.
>You see, root is mainly a read file system. Typical writes are a kernel
>install (not too important to optimize) and updating configuration files
>(it shouldn't be so often).

The real reason is that there is a "bug" in softupdates which means
that space freed up by deleting a file is not available for allocation
for about 30 seconds.  (Fixing this is non-trivial).  The root file-
system is traditionally relatively small and a substantial portion of
it is re-written during installworld and installkernel, leading to a
non-trivial likelihood that you could get a false "filesystem full"

>Furthermore, if one can avoid any risky operation on /, all the better.
>I think that's why the option for / is using synchronous writes without

Actually, / uses traditional Unix semantics - synchronous metadata updates
(inodes and directories) and asynchronous data updating.

>I think the filesystem must be unmounted to enable softupdates.

One approach would be to stick a script into /etc/rc.d that executes
early (before root is made R/W) to run "tunefs -n enable ..." and then
delete the script after rebooting.

Peter Jeremy

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