Re: Network Time Protocol Daemon needed for zLinux?

[Alan Altmark]

On Wednesday, 03/18/2015 at 06:04 EDT, Rob van der Heij
 wrote:
> Sorry to complicate it, but that check is not conclusive. When Linux
does
> not run ntpd, the time on Linux will match the time on z/VM (give or
take
> time zones). But when they still match the wall clock time a few weeks
> after the IPL of z/VM, you know STP is steering the clock.

Someone said to me that they thought zLinux will still use jiffies in
certain cases, which can cause "now" to have some significant variation.
Perhaps Those Who Know will speak up.

I've done more thinking, studying, and talking to Development about this,
and I now believe that TOD clock steering does NOT deal with leap seconds.
 This is because the TOD clock is steered to Coordinated Server Time
(CST), not UTC, and CST is computed by adding the leap seconds to UTC. UTC
can be determined by manual input or from NTP.  So if you set leap seconds
to zero, you have UTC but only until the next leap second.  But
Development is inquiring of PE to verify.

Architecturally, the z TOD clock is ahead of UTC by the number of leap
seconds contained in the UTC clock.

And please know, too, that it is the STP feature that steers the TOD clock
to the external time source.  Without it, you have to re-IPL z/VM to get
the LPAR TOD clock resync'd with the physical TOD clock, which is adjusted
to match the time obtained by the SE from the external time source at
model-dependent intervals.

Leap seconds become important when you start reaching back in the time. If
you reach past the most recent leap second insertion point, the wall clock
or TOD clock conversations start being off by one second per insertion.
For many things, that's close enough.  For others (e.g. financial
institutions) the time standards are established by regulatory agencies.

But you must be careful.  If you think about this too hard, you will
create a tear in the time-space continuum and fall in.  Just remember that
"The music is reversible, but time is not.   Kcab nrut, kcab nrut, "

Alan Altmark

Senior Managing z/VM and Linux Consultant
Lab Services System z Delivery Practice
IBM Systems & Technology Group
ibm.com/systems/services/labservices
office: 607.429.3323
mobile; 607.321.7556
alan_altm...@us.ibm.com
IBM Endicott

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Re: Network Time Protocol Daemon needed for zLinux?

[Scott Rohling]

hehe  ..   I do wonder if hypervisors on other platforms deal wiith this
-- my guess is they just shrug and run ntpd on their guests.   I do
understand the mentality of running the same setup on every platform ..
but it isn't that difficult to allow for the fact that you don't want
packages installed and running that aren't necessary for the platform.
And ..  (IMO) there should be a difference between a virtual setup and a
physical one.

As you say - se la vi :)

Scott Rohling

On Wed, Mar 18, 2015 at 3:19 PM, Rob van der Heij  wrote:

> On 18 March 2015 at 23:02, Scott Rohling  wrote:
>
> > Not sure how strongly you were asked  :)  --  but I would explain that
> > z/VM-Linux are already synced with whatever NTP server the z is using..
> >  and I would ask why it should then be necessary.   Put the burden of
> > explanation on them to tell you why it doesn't satisfy the time synch
> > requirement.
> >
> > Scott Rohling
> >
> > Such is life. I remember a discussion with the Linux admin that went like
> this :-)
>
> R: You're running ntpd - you shouldn't when the hypervisor is already
> synchronized
> A: But I need the exact time, and that requires ntpd
> R: No, it does not. It's wasting resources and does not do you any good.
> A: I need it anyway, for exact time.
> R: Your time on z/Linux will be less exact with ntpd than without
> A: I does not have to be that exact, so I will run ntpd anyway
>
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Re: Network Time Protocol Daemon needed for zLinux?

[Rob van der Heij]

On 18 March 2015 at 23:02, Scott Rohling  wrote:

> Not sure how strongly you were asked  :)  --  but I would explain that
> z/VM-Linux are already synced with whatever NTP server the z is using..
>  and I would ask why it should then be necessary.   Put the burden of
> explanation on them to tell you why it doesn't satisfy the time synch
> requirement.
>
> Scott Rohling
>
> Such is life. I remember a discussion with the Linux admin that went like
this :-)

R: You're running ntpd - you shouldn't when the hypervisor is already
synchronized
A: But I need the exact time, and that requires ntpd
R: No, it does not. It's wasting resources and does not do you any good.
A: I need it anyway, for exact time.
R: Your time on z/Linux will be less exact with ntpd than without
A: I does not have to be that exact, so I will run ntpd anyway

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Re: Network Time Protocol Daemon needed for zLinux?

[Scott Rohling]

Not sure how strongly you were asked  :)  --  but I would explain that
z/VM-Linux are already synced with whatever NTP server the z is using..
 and I would ask why it should then be necessary.   Put the burden of
explanation on them to tell you why it doesn't satisfy the time synch
requirement.

Scott Rohling

On Wed, Mar 18, 2015 at 1:00 PM, Vitale, Joseph  wrote:

> Using  STP to set clock for zVM LPAR.  zVM and zLinux guest show time,
> both in sync.  Trying to avoid setting up NTPD and starting on all zLinux
> if not necessary.
>
> Came about due to checks comparing zLinux software configuration vs  X86
> configuration, they run NTPD. So, I was asked to do same.  Never seen an
> issue with time under zLinux.
>
>
> Thank you for your assistance
> Joe
>
>
> Joseph Vitale
> Technology Services Group
> Mainframe Operating Systems
>
> Pershing Plaza
> 95 Christopher Columbus Drive
> Floor 14
> Jersey City,  N.J.  07302
> Work  201-395-1509
> Cell917-903-0102
>
>
> -Original Message-
> From: Linux on 390 Port [mailto:LINUX-390@VM.MARIST.EDU] On Behalf Of Rob
> van der Heij
> Sent: Wednesday, March 18, 2015 3:54 PM
> To: LINUX-390@VM.MARIST.EDU
> Subject: Re: Network Time Protocol Daemon needed for zLinux?
>
> On 18 March 2015 at 20:04, Vitale, Joseph 
> wrote:
>
>
> > My Linux runs under zVM, not in a stand alone LPAR.  So, NTP or STP
> > not required, correct ?
> >
>
> That depends on whether you have STP steer the clock for the LPARs. It's a
> priced feature. If Q TIME on z/VM is now very accurate, then you're most
> likely steering and your Linux guests will follow. When z/VM is not running
> on time, then all Linux guests will get a clock (the same) that is slightly
> off as well. If that bothers you (your applications rather) then you can
> either implement STP or have each guest synchronize it's won clock with
> ntpd etc. If you frequently reboot, then ntpdate during startup might be
> enough to stay somewhat on time (eg 3 seconds per week). Some things like
> Kerberos expect you to be sort-of on time (10's of seconds, iirc).
>
> My experience is that the quality of the clock with ntpd is somewhat less,
> but that's a moot point when it's your only option. Yes, it's true that
> running ntpd takes resources. But much middleware does too and we're not on
> G3 anymore.
>
> PS Yes, I did do an "ntpq" for CMS a while back, but the year does not
> have nearly enough Friday nights to come up with an alternative for STP.
>
> Rob
>
> --
> For LINUX-390 subscribe / signoff / archive access instructions, send
> email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit
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> For more information on Linux on System z, visit http://wiki.linuxvm.org/
>
> The information contained in this e-mail, and any attachment, is
> confidential and is intended solely for the use of the intended recipient.
> Access, copying or re-use of the e-mail or any attachment, or any
> information contained therein, by any other person is not authorized. If
> you are not the intended recipient please return the e-mail to the sender
> and delete it from your computer. Although we attempt to sweep e-mail and
> attachments for viruses, we do not guarantee that either are virus-free and
> accept no liability for any damage sustained as a result of viruses.
>
> Please refer to http://disclaimer.bnymellon.com/eu.htm for certain
> disclosures relating to European legal entities.
>
> --
> For LINUX-390 subscribe / signoff / archive access instructions,
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> http://wiki.linuxvm.org/
>

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Re: Network Time Protocol Daemon needed for zLinux?

[Rob van der Heij]

On 18 March 2015 at 21:00, Vitale, Joseph 
wrote:

Using  STP to set clock for zVM LPAR.  zVM and zLinux guest show time, both
> in sync.  Trying to avoid setting up NTPD and starting on all zLinux if not
> necessary.


Sorry to complicate it, but that check is not conclusive. When Linux does
not run ntpd, the time on Linux will match the time on z/VM (give or take
time zones). But when they still match the wall clock time a few weeks
after the IPL of z/VM, you know STP is steering the clock.

Rob

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Re: Network Time Protocol Daemon needed for zLinux?

[Marcy Cortes]

We run NTP on all the Linux guests under zVM (and we have STP for VM).
There were just too many things that require it and it wasn't worth the effort 
to make them believe that it wasn't necessary.

-Original Message-
From: Linux on 390 Port [mailto:LINUX-390@VM.MARIST.EDU] On Behalf Of Vitale, 
Joseph
Sent: Wednesday, March 18, 2015 1:00 PM
To: LINUX-390@VM.MARIST.EDU
Subject: Re: [LINUX-390] Network Time Protocol Daemon needed for zLinux?

Using  STP to set clock for zVM LPAR.  zVM and zLinux guest show time, both in 
sync.  Trying to avoid setting up NTPD and starting on all zLinux if not 
necessary.

Came about due to checks comparing zLinux software configuration vs  X86 
configuration, they run NTPD. So, I was asked to do same.  Never seen an issue 
with time under zLinux.


Thank you for your assistance
Joe


Joseph Vitale
Technology Services Group
Mainframe Operating Systems

Pershing Plaza
95 Christopher Columbus Drive
Floor 14   
Jersey City,  N.J.  07302
Work  201-395-1509
Cell917-903-0102


-Original Message-
From: Linux on 390 Port [mailto:LINUX-390@VM.MARIST.EDU] On Behalf Of Rob van 
der Heij
Sent: Wednesday, March 18, 2015 3:54 PM
To: LINUX-390@VM.MARIST.EDU
Subject: Re: Network Time Protocol Daemon needed for zLinux?

On 18 March 2015 at 20:04, Vitale, Joseph 
wrote:


> My Linux runs under zVM, not in a stand alone LPAR.  So, NTP or STP 
> not required, correct ?
>

That depends on whether you have STP steer the clock for the LPARs. It's a 
priced feature. If Q TIME on z/VM is now very accurate, then you're most likely 
steering and your Linux guests will follow. When z/VM is not running on time, 
then all Linux guests will get a clock (the same) that is slightly off as well. 
If that bothers you (your applications rather) then you can either implement 
STP or have each guest synchronize it's won clock with ntpd etc. If you 
frequently reboot, then ntpdate during startup might be enough to stay somewhat 
on time (eg 3 seconds per week). Some things like Kerberos expect you to be 
sort-of on time (10's of seconds, iirc).

My experience is that the quality of the clock with ntpd is somewhat less, but 
that's a moot point when it's your only option. Yes, it's true that running 
ntpd takes resources. But much middleware does too and we're not on
G3 anymore.

PS Yes, I did do an "ntpq" for CMS a while back, but the year does not have 
nearly enough Friday nights to come up with an alternative for STP.

Rob

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damage sustained as a result of viruses. 

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relating to European legal entities.

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Re: Network Time Protocol Daemon needed for zLinux?

[Vitale, Joseph]

Using  STP to set clock for zVM LPAR.  zVM and zLinux guest show time, both in 
sync.  Trying to avoid setting up NTPD and starting on all zLinux if not 
necessary.

Came about due to checks comparing zLinux software configuration vs  X86 
configuration, they run NTPD. So, I was asked to do same.  Never seen an issue 
with time under zLinux.


Thank you for your assistance
Joe


Joseph Vitale
Technology Services Group
Mainframe Operating Systems

Pershing Plaza
95 Christopher Columbus Drive
Floor 14   
Jersey City,  N.J.  07302
Work  201-395-1509
Cell917-903-0102


-Original Message-
From: Linux on 390 Port [mailto:LINUX-390@VM.MARIST.EDU] On Behalf Of Rob van 
der Heij
Sent: Wednesday, March 18, 2015 3:54 PM
To: LINUX-390@VM.MARIST.EDU
Subject: Re: Network Time Protocol Daemon needed for zLinux?

On 18 March 2015 at 20:04, Vitale, Joseph 
wrote:


> My Linux runs under zVM, not in a stand alone LPAR.  So, NTP or STP 
> not required, correct ?
>

That depends on whether you have STP steer the clock for the LPARs. It's a 
priced feature. If Q TIME on z/VM is now very accurate, then you're most likely 
steering and your Linux guests will follow. When z/VM is not running on time, 
then all Linux guests will get a clock (the same) that is slightly off as well. 
If that bothers you (your applications rather) then you can either implement 
STP or have each guest synchronize it's won clock with ntpd etc. If you 
frequently reboot, then ntpdate during startup might be enough to stay somewhat 
on time (eg 3 seconds per week). Some things like Kerberos expect you to be 
sort-of on time (10's of seconds, iirc).

My experience is that the quality of the clock with ntpd is somewhat less, but 
that's a moot point when it's your only option. Yes, it's true that running 
ntpd takes resources. But much middleware does too and we're not on
G3 anymore.

PS Yes, I did do an "ntpq" for CMS a while back, but the year does not have 
nearly enough Friday nights to come up with an alternative for STP.

Rob

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The information contained in this e-mail, and any attachment, is confidential 
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do not guarantee that either are virus-free and accept no liability for any 
damage sustained as a result of viruses. 

Please refer to http://disclaimer.bnymellon.com/eu.htm for certain disclosures 
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Re: Network Time Protocol Daemon needed for zLinux?

[Rob van der Heij]

On 18 March 2015 at 20:04, Vitale, Joseph 
wrote:


> My Linux runs under zVM, not in a stand alone LPAR.  So, NTP or STP not
> required, correct ?
>

That depends on whether you have STP steer the clock for the LPARs. It's a
priced feature. If Q TIME on z/VM is now very accurate, then you're most
likely steering and your Linux guests will follow. When z/VM is not running
on time, then all Linux guests will get a clock (the same) that is slightly
off as well. If that bothers you (your applications rather) then you can
either implement STP or have each guest synchronize it's won clock with
ntpd etc. If you frequently reboot, then ntpdate during startup might be
enough to stay somewhat on time (eg 3 seconds per week). Some things like
Kerberos expect you to be sort-of on time (10's of seconds, iirc).

My experience is that the quality of the clock with ntpd is somewhat less,
but that's a moot point when it's your only option. Yes, it's true that
running ntpd takes resources. But much middleware does too and we're not on
G3 anymore.

PS Yes, I did do an "ntpq" for CMS a while back, but the year does not have
nearly enough Friday nights to come up with an alternative for STP.

Rob

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Re: Network Time Protocol Daemon needed for zLinux?

[Scott Rohling]

I don't think anybody will answer that question :-)That depends on what
your requirements are..   are you communicating with a non-z database for
example where time synching must be assured?  Are they actually in the same
stratum as the other platform servers?

What requirement are you trying to satisfy here?

Scott Rohling

On Wed, Mar 18, 2015 at 12:04 PM, Vitale, Joseph <
joseph.vit...@bnymellon.com> wrote:

> My Linux runs under zVM, not in a stand alone LPAR.  So, NTP or STP not
> required, correct ?
>
> Thanks
>
> Joseph Vitale
> Technology Services Group
> Mainframe Operating Systems
>
> Pershing Plaza
> 95 Christopher Columbus Drive
> Floor 14
> Jersey City,  N.J.  07302
> Work  201-395-1509
> Cell917-903-0102
>
>
> -Original Message-
> From: Linux on 390 Port [mailto:LINUX-390@VM.MARIST.EDU] On Behalf Of Rob
> van der Heij
> Sent: Wednesday, March 18, 2015 2:53 PM
> To: LINUX-390@VM.MARIST.EDU
> Subject: Re: Network Time Protocol Daemon needed for zLinux?
>
> Just a warning: my understanding is that this quote is talking about Linux
> in LPAR; that z/VM does not virtualize the ETR/STP.
>
> For the rest of us: When you have STP steer the LPAR TOD to keep z/VM on
> time, Linux will inherit the same (UTC) TOD and runs better on time than
> anything you can do with ntpd. This will cover the leap second in that the
> TOD appears to slow down for a few hours, to be on time in the morning.
>
>
> On 18 March 2015 at 19:33, John McKown 
> wrote:
>
> > On Wed, Mar 18, 2015 at 10:46 AM, Vitale, Joseph
> >  wrote:
> > > Hello,
> > >
> > > Currently not running  NTPD  under RedHat, is that necessary or does
> > > zVM
> > present time adjustment via Sysplex Timer?
> >
> > I think this answers that question:
> >
> > http://www-01.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux
> > .z.lgdd/lgdd_r_feature_time.html
> >
> > 
> >
> > ETR- and STP-based clock synchronization
> >
> > Your Linux instance might be part of an extended remote copy (XRC)
> > setup that requires synchronization of the Linux time-of-day (TOD)
> > clock with a timing network.
> >
> > Linux on z Systems supports external time reference (ETR) and system
> > time protocol (STP) based TOD synchronization. ETR and STP work
> > independently of one another. If both ETR and STP are enabled, Linux
> > might use either to synchronize the clock.
> >
> > For more information about ETR, see the IBM(r) Redbooks(r) technote at
> >
> > www.ibm.com/redbooks/abstracts/tips0217.html
> >
> > For information about STP, see
> >
> > www.ibm.com/systems/z/advantages/pso/stp.html
> >
> > Both ETR and STP support are included in the Linux kernel. No special
> > build options are required.
> >
> > ETR requires at least one ETR unit that is connected to an external
> > time source. For availability reasons, many installations use a second
> > ETR unit. The ETR units correspond to two ETR ports on Linux. Always
> > set both ports online if two ETR units are available.
> >
> > Attention: Be sure that a reliable timing signal is available before
> > enabling clock synchronization. With enabled clock synchronization,
> > Linux expects regular timing signals and might stop indefinitely to
> > wait for such signals if it does not receive them.
> >
> > Enabling clock synchronization when booting Use kernel parameters to
> > enable clock synchronization when booting.
> > Enabling and disabling clock synchronization You can use the sysfs
> > interfaces of ETR and STP to enable and disable clock synchronization
> > on a running Linux instance.
> >
> > Parent topic: System resources
> > 
> >
> > >
> > > Thanks
> > > Joe
> >
> > --
> > If you sent twitter messages while exploring, are you on a textpedition?
> >
> > He's about as useful as a wax frying pan.
> >
> > 10 to the 12th power microphones = 1 Megaphone
> >
> > Maranatha! <><
> > John McKown
> >
> > --
> > For LINUX-390 subscribe / signoff / archive access instructions, send
> > email to lists...@vm.marist.edu with the message: INFO LINUX-390 or
> > visit
> > http://www.marist.edu/htbin/wlvindex?LINUX-390
> > --
> > For more information on Linux on System z, visit
> > http://wiki.linuxvm.org/
> >
>
> --
> For LINUX-390 subscribe / signoff / archive access instructions, send
> email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit
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> For more information on Linux on System z, visit http://wiki.linuxvm.org/
>
> The information contained in this e-mail, and any attachment, is
> confidential and is intended solely for the use of the intended recipient.
> Access, copying or re-use of the e-mail or any attachment, or any
> information contained therein, by any other p

Re: Network Time Protocol Daemon needed for zLinux?

[Vitale, Joseph]

My Linux runs under zVM, not in a stand alone LPAR.  So, NTP or STP not 
required, correct ?

Thanks

Joseph Vitale
Technology Services Group
Mainframe Operating Systems

Pershing Plaza
95 Christopher Columbus Drive
Floor 14   
Jersey City,  N.J.  07302
Work  201-395-1509
Cell917-903-0102


-Original Message-
From: Linux on 390 Port [mailto:LINUX-390@VM.MARIST.EDU] On Behalf Of Rob van 
der Heij
Sent: Wednesday, March 18, 2015 2:53 PM
To: LINUX-390@VM.MARIST.EDU
Subject: Re: Network Time Protocol Daemon needed for zLinux?

Just a warning: my understanding is that this quote is talking about Linux in 
LPAR; that z/VM does not virtualize the ETR/STP.

For the rest of us: When you have STP steer the LPAR TOD to keep z/VM on time, 
Linux will inherit the same (UTC) TOD and runs better on time than anything you 
can do with ntpd. This will cover the leap second in that the TOD appears to 
slow down for a few hours, to be on time in the morning.


On 18 March 2015 at 19:33, John McKown  wrote:

> On Wed, Mar 18, 2015 at 10:46 AM, Vitale, Joseph 
>  wrote:
> > Hello,
> >
> > Currently not running  NTPD  under RedHat, is that necessary or does 
> > zVM
> present time adjustment via Sysplex Timer?
>
> I think this answers that question:
>
> http://www-01.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux
> .z.lgdd/lgdd_r_feature_time.html
>
> 
>
> ETR- and STP-based clock synchronization
>
> Your Linux instance might be part of an extended remote copy (XRC) 
> setup that requires synchronization of the Linux time-of-day (TOD) 
> clock with a timing network.
>
> Linux on z Systems supports external time reference (ETR) and system 
> time protocol (STP) based TOD synchronization. ETR and STP work 
> independently of one another. If both ETR and STP are enabled, Linux 
> might use either to synchronize the clock.
>
> For more information about ETR, see the IBM(r) Redbooks(r) technote at
>
> www.ibm.com/redbooks/abstracts/tips0217.html
>
> For information about STP, see
>
> www.ibm.com/systems/z/advantages/pso/stp.html
>
> Both ETR and STP support are included in the Linux kernel. No special 
> build options are required.
>
> ETR requires at least one ETR unit that is connected to an external 
> time source. For availability reasons, many installations use a second 
> ETR unit. The ETR units correspond to two ETR ports on Linux. Always 
> set both ports online if two ETR units are available.
>
> Attention: Be sure that a reliable timing signal is available before 
> enabling clock synchronization. With enabled clock synchronization, 
> Linux expects regular timing signals and might stop indefinitely to 
> wait for such signals if it does not receive them.
>
> Enabling clock synchronization when booting Use kernel parameters to 
> enable clock synchronization when booting.
> Enabling and disabling clock synchronization You can use the sysfs 
> interfaces of ETR and STP to enable and disable clock synchronization 
> on a running Linux instance.
>
> Parent topic: System resources
> 
>
> >
> > Thanks
> > Joe
>
> --
> If you sent twitter messages while exploring, are you on a textpedition?
>
> He's about as useful as a wax frying pan.
>
> 10 to the 12th power microphones = 1 Megaphone
>
> Maranatha! <><
> John McKown
>
> --
> For LINUX-390 subscribe / signoff / archive access instructions, send 
> email to lists...@vm.marist.edu with the message: INFO LINUX-390 or 
> visit
> http://www.marist.edu/htbin/wlvindex?LINUX-390
> --
> For more information on Linux on System z, visit 
> http://wiki.linuxvm.org/
>

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Re: Network Time Protocol Daemon needed for zLinux?

[Rob van der Heij]

Just a warning: my understanding is that this quote is talking about Linux
in LPAR; that z/VM does not virtualize the ETR/STP.

For the rest of us: When you have STP steer the LPAR TOD to keep z/VM on
time, Linux will inherit the same (UTC) TOD and runs better on time than
anything you can do with ntpd. This will cover the leap second in that the
TOD appears to slow down for a few hours, to be on time in the morning.


On 18 March 2015 at 19:33, John McKown  wrote:

> On Wed, Mar 18, 2015 at 10:46 AM, Vitale, Joseph
>  wrote:
> > Hello,
> >
> > Currently not running  NTPD  under RedHat, is that necessary or does zVM
> present time adjustment via Sysplex Timer?
>
> I think this answers that question:
>
> http://www-01.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux.z.lgdd/lgdd_r_feature_time.html
>
> 
>
> ETR- and STP-based clock synchronization
>
> Your Linux instance might be part of an extended remote copy (XRC)
> setup that requires synchronization of the Linux time-of-day (TOD)
> clock with a timing network.
>
> Linux on z Systems supports external time reference (ETR) and system
> time protocol (STP) based TOD synchronization. ETR and STP work
> independently of one another. If both ETR and STP are enabled, Linux
> might use either to synchronize the clock.
>
> For more information about ETR, see the IBM® Redbooks® technote at
>
> www.ibm.com/redbooks/abstracts/tips0217.html
>
> For information about STP, see
>
> www.ibm.com/systems/z/advantages/pso/stp.html
>
> Both ETR and STP support are included in the Linux kernel. No special
> build options are required.
>
> ETR requires at least one ETR unit that is connected to an external
> time source. For availability reasons, many installations use a second
> ETR unit. The ETR units correspond to two ETR ports on Linux. Always
> set both ports online if two ETR units are available.
>
> Attention: Be sure that a reliable timing signal is available before
> enabling clock synchronization. With enabled clock synchronization,
> Linux expects regular timing signals and might stop indefinitely to
> wait for such signals if it does not receive them.
>
> Enabling clock synchronization when booting
> Use kernel parameters to enable clock synchronization when booting.
> Enabling and disabling clock synchronization
> You can use the sysfs interfaces of ETR and STP to enable and disable
> clock synchronization on a running Linux instance.
>
> Parent topic: System resources
> 
>
> >
> > Thanks
> > Joe
>
> --
> If you sent twitter messages while exploring, are you on a textpedition?
>
> He's about as useful as a wax frying pan.
>
> 10 to the 12th power microphones = 1 Megaphone
>
> Maranatha! <><
> John McKown
>
> --
> For LINUX-390 subscribe / signoff / archive access instructions,
> send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or
> visit
> http://www.marist.edu/htbin/wlvindex?LINUX-390
> --
> For more information on Linux on System z, visit
> http://wiki.linuxvm.org/
>

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Re: Network Time Protocol Daemon needed for zLinux?

[John McKown]

On Wed, Mar 18, 2015 at 10:46 AM, Vitale, Joseph
 wrote:
> Hello,
>
> Currently not running  NTPD  under RedHat, is that necessary or does zVM 
> present time adjustment via Sysplex Timer?

I think this answers that question:
http://www-01.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux.z.lgdd/lgdd_r_feature_time.html



ETR- and STP-based clock synchronization

Your Linux instance might be part of an extended remote copy (XRC)
setup that requires synchronization of the Linux time-of-day (TOD)
clock with a timing network.

Linux on z Systems supports external time reference (ETR) and system
time protocol (STP) based TOD synchronization. ETR and STP work
independently of one another. If both ETR and STP are enabled, Linux
might use either to synchronize the clock.

For more information about ETR, see the IBM® Redbooks® technote at

www.ibm.com/redbooks/abstracts/tips0217.html

For information about STP, see

www.ibm.com/systems/z/advantages/pso/stp.html

Both ETR and STP support are included in the Linux kernel. No special
build options are required.

ETR requires at least one ETR unit that is connected to an external
time source. For availability reasons, many installations use a second
ETR unit. The ETR units correspond to two ETR ports on Linux. Always
set both ports online if two ETR units are available.

Attention: Be sure that a reliable timing signal is available before
enabling clock synchronization. With enabled clock synchronization,
Linux expects regular timing signals and might stop indefinitely to
wait for such signals if it does not receive them.

Enabling clock synchronization when booting
Use kernel parameters to enable clock synchronization when booting.
Enabling and disabling clock synchronization
You can use the sysfs interfaces of ETR and STP to enable and disable
clock synchronization on a running Linux instance.

Parent topic: System resources


>
> Thanks
> Joe

-- 
If you sent twitter messages while exploring, are you on a textpedition?

He's about as useful as a wax frying pan.

10 to the 12th power microphones = 1 Megaphone

Maranatha! <><
John McKown

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Re: Network Time Protocol Daemon needed for zLinux?

[Rick Troth]

On 03/18/2015 11:46 AM, Vitale, Joseph wrote:
> Currently not running  NTPD  under RedHat, is that necessary or does zVM 
> present time adjustment via Sysplex Timer?

Given the stability of the z System clock, good practice is to run
'ntpdate' shortly after Linux boots and then perhaps at (long) intervals.

Performance opinions vary. I found that 'ntpd' is one of the better
behaved daemons in terms of load. Originally I told customers "kill it".
But I no longer insist on this. (Always a good idea to minimize the
number of tasks running on a guest.) My teammate Rob van der Heij may
have additional details to share.

Alan Altmark explained some of the STP behavior over on the IBMVM list
just last week. Perhaps he can chime in on this too.



--

Rick Troth
Senior Software Developer

Velocity Software Inc.
Mountain View, CA 94041
Main: (877) 964-8867
Direct: (614) 594-9768
ri...@velocitysoftware.com 


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Network Time Protocol Daemon needed for zLinux?

[Vitale, Joseph]

Hello,

Currently not running  NTPD  under RedHat, is that necessary or does zVM 
present time adjustment via Sysplex Timer?

Thanks
Joe

Joseph Vitale
Technology Services Group
Mainframe Operating Systems

Pershing Plaza
95 Christopher Columbus Drive
Floor 14
Jersey City,  N.J.  07302
Work  201-395-1509
Cell917-903-0102


The information contained in this e-mail, and any attachment, is confidential 
and is intended solely for the use of the intended recipient. Access, copying 
or re-use of the e-mail or any attachment, or any information contained 
therein, by any other person is not authorized. If you are not the intended 
recipient please return the e-mail to the sender and delete it from your 
computer. Although we attempt to sweep e-mail and attachments for viruses, we 
do not guarantee that either are virus-free and accept no liability for any 
damage sustained as a result of viruses. 

Please refer to http://disclaimer.bnymellon.com/eu.htm for certain disclosures 
relating to European legal entities.

--
For LINUX-390 subscribe / signoff / archive access instructions,
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