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Old 06-28-2011, 03:59 PM
Petrus de Calguarium
 
Default gnu linux update question

It is common knowledge that one does not need to reboot for updates to take
effect in GNU Linux.

However, in actual practice, this is not so. I could cite many examples, but
this should suffice:

On Sunday evening, I installed a new updates-testing version of mesa and then I
suspended the machine for the night. The following Monday morning (yesterday),
I resumed the machine and suspended it again around noon. I again resumed the
machine at about suppertime and _powered_ _it_ _down_ about 2 hours later. An
hour or two after that, I powered it back up and the mesa testing update turned
out to be bad and I was not able to log in. I did not know which program was at
fault, because the bad program had been installed over 24 hours prior, but was
only showing itself to be bad after a power off.

Could someone explain how reboots are not needed in Linux for updates to
_take_, given the evidence to the contrary.

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Old 06-28-2011, 04:07 PM
Andrew Haley
 
Default gnu linux update question

On 06/28/2011 04:59 PM, Petrus de Calguarium wrote:
> It is common knowledge that one does not need to reboot for updates to take
> effect in GNU Linux.
>
> However, in actual practice, this is not so. I could cite many examples, but
> this should suffice:
>
> On Sunday evening, I installed a new updates-testing version of mesa and then I
> suspended the machine for the night. The following Monday morning (yesterday),
> I resumed the machine and suspended it again around noon. I again resumed the
> machine at about suppertime and _powered_ _it_ _down_ about 2 hours later. An
> hour or two after that, I powered it back up and the mesa testing update turned
> out to be bad and I was not able to log in. I did not know which program was at
> fault, because the bad program had been installed over 24 hours prior, but was
> only showing itself to be bad after a power off.
>
> Could someone explain how reboots are not needed in Linux for updates to
> _take_, given the evidence to the contrary.

If a process has a file open and that file is replaced with a new copy,
the process is still using the file handle for the old file. This is
normal UNIX, nothing new. How could it be otherwise?

Andrew.
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Old 06-28-2011, 04:14 PM
"Bryn M. Reeves"
 
Default gnu linux update question

On 06/28/2011 05:07 PM, Andrew Haley wrote:
> On 06/28/2011 04:59 PM, Petrus de Calguarium wrote:
>> It is common knowledge that one does not need to reboot for updates to take
>> effect in GNU Linux.
>>
>> However, in actual practice, this is not so. I could cite many examples, but
>> this should suffice:
>>
>> On Sunday evening, I installed a new updates-testing version of mesa and then I
>> suspended the machine for the night. The following Monday morning (yesterday),
>> I resumed the machine and suspended it again around noon. I again resumed the
>> machine at about suppertime and _powered_ _it_ _down_ about 2 hours later. An
>> hour or two after that, I powered it back up and the mesa testing update turned
>> out to be bad and I was not able to log in. I did not know which program was at
>> fault, because the bad program had been installed over 24 hours prior, but was
>> only showing itself to be bad after a power off.
>>
>> Could someone explain how reboots are not needed in Linux for updates to
>> _take_, given the evidence to the contrary.
>
> If a process has a file open and that file is replaced with a new copy,
> the process is still using the file handle for the old file. This is
> normal UNIX, nothing new. How could it be otherwise?

Or to put it in simpler terms: when you update a component you need to re-start
the application(s) that use that component. When that is a component of the
whole desktop environment (like mesa) you will need to log out of your session
and log back in again.

For a couple of releases now the graphical updater tools have supported the
ability to warn the user when this is the case. If you were using these tools
then you should have received such a warning.

Note that suspending and resuming does not count here since you are simply
suspending the running (old) copy and then resuming it with open files and other
state intact.

Regards,
Bryn.

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Old 06-28-2011, 04:18 PM
Petrus de Calguarium
 
Default gnu linux update question

Bryn M. Reeves wrote:

> For a couple of releases now the graphical updater tools have supported
> the ability to warn the user when this is the case. If you were using
> these tools then you should have received such a warning.

I run yum from the command line, as I feel I have both more control and am able
to see more clearly what is happening and why something fails, if it does.

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Old 06-28-2011, 04:21 PM
Petrus de Calguarium
 
Default gnu linux update question

Andrew Haley wrote:

> How could it be otherwise?

If a file has been deleted, the proper thing would be for the running process
to read the new copy into memory.

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Old 06-28-2011, 04:22 PM
Patrick O'Callaghan
 
Default gnu linux update question

On Tue, 2011-06-28 at 17:14 +0100, Bryn M. Reeves wrote:
> On 06/28/2011 05:07 PM, Andrew Haley wrote:
> > On 06/28/2011 04:59 PM, Petrus de Calguarium wrote:
> >> It is common knowledge that one does not need to reboot for updates to take
> >> effect in GNU Linux.
> >>
> >> However, in actual practice, this is not so. I could cite many examples, but
> >> this should suffice:
> >>
> >> On Sunday evening, I installed a new updates-testing version of mesa and then I
> >> suspended the machine for the night. The following Monday morning (yesterday),
> >> I resumed the machine and suspended it again around noon. I again resumed the
> >> machine at about suppertime and _powered_ _it_ _down_ about 2 hours later. An
> >> hour or two after that, I powered it back up and the mesa testing update turned
> >> out to be bad and I was not able to log in. I did not know which program was at
> >> fault, because the bad program had been installed over 24 hours prior, but was
> >> only showing itself to be bad after a power off.
> >>
> >> Could someone explain how reboots are not needed in Linux for updates to
> >> _take_, given the evidence to the contrary.
> >
> > If a process has a file open and that file is replaced with a new copy,
> > the process is still using the file handle for the old file. This is
> > normal UNIX, nothing new. How could it be otherwise?
>
> Or to put it in simpler terms: when you update a component you need to re-start
> the application(s) that use that component. When that is a component of the
> whole desktop environment (like mesa) you will need to log out of your session
> and log back in again.
>
> For a couple of releases now the graphical updater tools have supported the
> ability to warn the user when this is the case. If you were using these tools
> then you should have received such a warning.
>
> Note that suspending and resuming does not count here since you are simply
> suspending the running (old) copy and then resuming it with open files and other
> state intact.

After updating, I always run needs-restarting to see what running
processes are affected. I'm surprised more people don't seem to know
about this program.

BTW it's a Python script of only a couple of pages in length. Figuring
out how it works is a good exercise in understanding Linux (not to
mention Python :-)

poc

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Old 06-28-2011, 04:34 PM
Andrew Haley
 
Default gnu linux update question

On 06/28/2011 05:21 PM, Petrus de Calguarium wrote:
> Andrew Haley wrote:
>
>> How could it be otherwise?
>
> If a file has been deleted, the proper thing would be for the running process
> to read the new copy into memory.

That's not always possible. It's certainly not possible if one of
the changed files is an executable or a shared library.

Andrew.
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Old 06-28-2011, 04:38 PM
"Bryn M. Reeves"
 
Default gnu linux update question

On 06/28/2011 05:18 PM, Petrus de Calguarium wrote:
> Bryn M. Reeves wrote:
>
>> For a couple of releases now the graphical updater tools have supported
>> the ability to warn the user when this is the case. If you were using
>> these tools then you should have received such a warning.
>
> I run yum from the command line, as I feel I have both more control and am able
> to see more clearly what is happening and why something fails, if it does.

Then you should know to run needs-restarting when it has finished to check for
this yourself.

Regards,
Bryn.


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Old 06-28-2011, 04:41 PM
Patrick O'Callaghan
 
Default gnu linux update question

On Tue, 2011-06-28 at 10:21 -0600, Petrus de Calguarium wrote:
> Andrew Haley wrote:
>
> > How could it be otherwise?
>
> If a file has been deleted, the proper thing would be for the running process
> to read the new copy into memory.

And how is the process supposed to know? As for as it's concerned, the
file still exists. In fact it *does* still exist. It's a fundamental
feature of all Unix systems that a file only disappears when all
references to it go away. This includes both directory entries ("links")
and in-process open file descriptors.

To reinforce this principle, there is no "delete file" operation in Unix
(and Linux). There is only "unlink". Actually recovering space from the
file is a mere administrative detail that the system handles when
there's no longer any way to access the file contents.

The upshot is that if a process has a file open, and that file is
replaced by a different one (using unlink and creat) then the process
will continue to use the old file and all its attributes. When the
process closes the file, or terminates, the reference disappears and the
system then recovers the space. Meanwhile, a new directory entry with
the same name is pointing at the new contents.

On other systems you often see messages such as "Windows cannot update
until the following processes have exited". That's because Windows uses
the (broken) DOS model which doesn't distinguish between the file and
references to it.

If I had to pick out a single feature to demonstrate the superiority of
the Unix style of system, this would be it.

poc

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Old 06-28-2011, 05:12 PM
fred smith
 
Default gnu linux update question

On Tue, Jun 28, 2011 at 11:52:17AM -0430, Patrick O'Callaghan wrote:
> On Tue, 2011-06-28 at 17:14 +0100, Bryn M. Reeves wrote:
> > On 06/28/2011 05:07 PM, Andrew Haley wrote:
> > > On 06/28/2011 04:59 PM, Petrus de Calguarium wrote:
> > >> It is common knowledge that one does not need to reboot for updates to take
> > >> effect in GNU Linux.
> > >>
> > >> However, in actual practice, this is not so. I could cite many examples, but
> > >> this should suffice:
> > >>
> > >> On Sunday evening, I installed a new updates-testing version of mesa and then I
> > >> suspended the machine for the night. The following Monday morning (yesterday),
> > >> I resumed the machine and suspended it again around noon. I again resumed the
> > >> machine at about suppertime and _powered_ _it_ _down_ about 2 hours later. An
> > >> hour or two after that, I powered it back up and the mesa testing update turned
> > >> out to be bad and I was not able to log in. I did not know which program was at
> > >> fault, because the bad program had been installed over 24 hours prior, but was
> > >> only showing itself to be bad after a power off.
> > >>
> > >> Could someone explain how reboots are not needed in Linux for updates to
> > >> _take_, given the evidence to the contrary.
> > >
> > > If a process has a file open and that file is replaced with a new copy,
> > > the process is still using the file handle for the old file. This is
> > > normal UNIX, nothing new. How could it be otherwise?
> >
> > Or to put it in simpler terms: when you update a component you need to re-start
> > the application(s) that use that component. When that is a component of the
> > whole desktop environment (like mesa) you will need to log out of your session
> > and log back in again.
> >
> > For a couple of releases now the graphical updater tools have supported the
> > ability to warn the user when this is the case. If you were using these tools
> > then you should have received such a warning.
> >
> > Note that suspending and resuming does not count here since you are simply
> > suspending the running (old) copy and then resuming it with open files and other
> > state intact.
>
> After updating, I always run needs-restarting to see what running
> processes are affected. I'm surprised more people don't seem to know
> about this program.

wow! I never heard of that one before. I'll certainly be checking it out.

thanks, Patrick!

>
> BTW it's a Python script of only a couple of pages in length. Figuring
> out how it works is a good exercise in understanding Linux (not to
> mention Python :-)
>
> poc

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I can do all things through Christ
who strengthens me.
------------------------------ Philippians 4:13 -------------------------------
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