How often should prelink run ?

[T. Nifty Hat Mitchell]

On Wed, Jun 23, 2004 at 07:13:26PM +0200, Hannes Mayer wrote:
> 
> Hi all!
> 
> I know that prelink'ing is for gathering information about
> shared libraries and causes stuff to start faster.
> 
> What I have missed so far is how often it should run ?

It only really "needs" to run after a library has been installed new or
updated.

> Is it really necessary for a daily prelink via cron ?

No.  But it should be run (in my opinion).

> Prelink causes heavy disk activity and CPU utilization on my
> machine. I suppose it's sufficent to run it only if I have
> updated/installed stuff, right ?
> 
> Thanks for any insight!

Check /etc/sysconfig/prelink  and look for the line 

  PRELINK_FULL_TIME_INTERVAL=14

This implies that the time of day in the box stays sane.
Some might check for insane file time stamps.

  touch /tmp/now
  find / -newer /tmp/now -print | grep -v /proc | xargs ls -l 

And of course the line at the top of /etc/sysconfig/prelink is
interesting.

  PRELINKING=yes

You can turn prelinking off by changing yes to no as per the comments
or adjust the full system prelink time interval (RTFM).  Add notes in your
system notebook if you make changes.

The improvement in startup time and the value of randomizing memory
slot assignments are real so you should run it once in a while.
"Should" does not mean that you must run it.  If you leave it off
nothing that I know of will break.

/etc/sysconfig/prelink is sourced by /etc/cron.daily/prelink.
Scan both for flags and options.

Look also at /etc/prelink.conf.  Some rare folks will need to add or
delete directories there.  Some 3rd party packages verify the CRC of
their own binary so copy protection cannot be tinkered with.  These
should be excluded (see the comments on following links).  Tripwire
folks might notice that a set of rpm updates need to be validated
twice because prelink touches them.  The paranoid and cautious might
run prelink by hand rather than let cron do it.

I suspect that there would be no harm if you move
/etc/cron.daily/prelink to /etc/cron.weekly or even /etc/cron.monthly.
However, if you do this then after an OS update you might have both
/etc/cron.daily and /etc/cron.weekly active....  so add it to the
"next update" check list in your system notebook.

The improvement in startup time and the value of randomizing memory
slot assignments are real, so you should run it on occasion.


-- 
	T o m  M i t c h e l l 
	/dev/null the ultimate in secure storage.