shrinking kernel reserve space

Avi Greenbury lists at
Thu Mar 15 14:46:52 UTC 2012

CJ Tres wrote:

> I've got a 3 TB drive dedicated to backup a data partition and
> therefore I don't need the 5% reserved for the kernel.
> I found a command several days ago to shrink that space to a certain 
> percentage but cannot remember what it was and evidently can't figure 
> what the appropriate search term is to find it again.
> Anyone?

It's not merely for privileged processes - it's also the free space used
to defragment the data on the filesystem, for example.

What you're after is tune2fs, specifically its -m switch:

    -m reserved-blocks-percentage
          Set the percentage of the filesystem which may only be
          allocated by privileged processes.   Reserving some
          number of filesystem blocks for use by privileged  pro-
          cesses  is  done  to  avoid filesystem fragmentation, and
          to allow system daemons, such as syslogd(8), to continue
          to function correctly after non-privileged pro- cesses
          are prevented from writing to the filesystem.  Normally,
          the default percentage of reserved blocks is 5%.


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