Re: Unnecessary hard drive spin-ups

2020-02-13 Thread George N. White III
On Thu, 13 Feb 2020 at 11:35, Andy Paterson via users <
users@lists.fedoraproject.org> wrote:

> Except the system call version doesn't need you to include any header
> files!
> Which is NOT clear from the man page!
>

The man page says "On Linux, the kernel provides a getcwd() system call,
which the functions
described in this page will use if possible." so it seems applications are
meant to use the
header files and let the library do the system call "if possible".


>
> On 13 Feb 2020, at 13:53, George N. White III  wrote:
>
> 
> On Thu, 13 Feb 2020 at 06:40, Andy Paterson via users <
> users@lists.fedoraproject.org> wrote:
>
>> [...]
>>
>> I am a little confused by getcwd(), on linux it is supposed to be a
>> system call .. I expect to find a manual page for it in section 2 (man 2
>> getcwd)
>>
>> instead it gives me the library function manual page from section 3 (man
>> 3 getcwd)
>>
>
> $ man -k getcwd
> getcwd (2)   - get current working directory
> getcwd (3)   - get current working directory
> getcwd (3p)  - get the pathname of the current working directory
> $ gzip -dc /usr/share/man/man2/getcwd.2.gz
> .so man3/getcwd.3
>
>
>
>> I would fully expect a libc version of getcwd to make many system calls
>> to traverse the current path but here getcwd() is a system call with all
>> work done internally in the kernel, so I wouldnt expect anything to probe
>> the path elements.
>>
>> When I knock up a simple program to do a getcwd() and strace it I find
>> that getcwd (on FC31 anyway) IS a system call.
>>
>> Why does "man getcwd" give me a page from section 3?
>>
>
> The man page explains the differences, so it makes sense that "man 2" and
> "man 3" give the same text:
>
>  C library/kernel differences
>On Linux, the kernel provides a getcwd() system call, which  the
>  func‐
>tions  described  in  this  page will use if possible.  The system
> call
>takes the same arguments as the library function of the same name,
>  but
>is  limited  to  returning at most PATH_MAX bytes.
>
>
> The getcwd() system call saves overhead but should make the same storage
> accesses as the
> library version.
>
> --
> George N. White III
>
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Re: Unnecessary hard drive spin-ups

2020-02-13 Thread Andy Paterson via users
Except the system call version doesn't need you to include any header files!
Which is NOT clear from the man page!

> On 13 Feb 2020, at 13:53, George N. White III  wrote:
> 
> 
>> On Thu, 13 Feb 2020 at 06:40, Andy Paterson via users 
>>  wrote:
> 
>> [...] 
>> I am a little confused by getcwd(), on linux it is supposed to be a system 
>> call .. I expect to find a manual page for it in section 2 (man 2 getcwd)
>> instead it gives me the library function manual page from section 3 (man 3 
>> getcwd)
> 
> $ man -k getcwd
> getcwd (2)   - get current working directory
> getcwd (3)   - get current working directory
> getcwd (3p)  - get the pathname of the current working directory
> $ gzip -dc /usr/share/man/man2/getcwd.2.gz
> .so man3/getcwd.3
>  
>> I would fully expect a libc version of getcwd to make many system calls to 
>> traverse the current path but here getcwd() is a system call with all work 
>> done internally in the kernel, so I wouldnt expect anything to probe the 
>> path elements.
>> When I knock up a simple program to do a getcwd() and strace it I find that 
>> getcwd (on FC31 anyway) IS a system call.
>> Why does "man getcwd" give me a page from section 3?
> 
> The man page explains the differences, so it makes sense that "man 2" and 
> "man 3" give the same text:
> 
>  C library/kernel differences
>On Linux, the kernel provides a getcwd() system call, which  the  func‐
>tions  described  in  this  page will use if possible.  The system call
>takes the same arguments as the library function of the same name,  but
>is  limited  to  returning at most PATH_MAX bytes. 
> 
> The getcwd() system call saves overhead but should make the same storage 
> accesses as the
> library version.
> 
> -- 
> George N. White III
> 
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Re: Unnecessary hard drive spin-ups

2020-02-13 Thread George N. White III
On Thu, 13 Feb 2020 at 06:40, Andy Paterson via users <
users@lists.fedoraproject.org> wrote:

> [...]
>
> I am a little confused by getcwd(), on linux it is supposed to be a system
> call .. I expect to find a manual page for it in section 2 (man 2 getcwd)
>
> instead it gives me the library function manual page from section 3 (man 3
> getcwd)
>

$ man -k getcwd
getcwd (2)   - get current working directory
getcwd (3)   - get current working directory
getcwd (3p)  - get the pathname of the current working directory
$ gzip -dc /usr/share/man/man2/getcwd.2.gz
.so man3/getcwd.3



> I would fully expect a libc version of getcwd to make many system calls to
> traverse the current path but here getcwd() is a system call with all work
> done internally in the kernel, so I wouldnt expect anything to probe the
> path elements.
>
> When I knock up a simple program to do a getcwd() and strace it I find
> that getcwd (on FC31 anyway) IS a system call.
>
> Why does "man getcwd" give me a page from section 3?
>

The man page explains the differences, so it makes sense that "man 2" and
"man 3" give the same text:

 C library/kernel differences
   On Linux, the kernel provides a getcwd() system call, which  the
 func‐
   tions  described  in  this  page will use if possible.  The system
call
   takes the same arguments as the library function of the same name,
 but
   is  limited  to  returning at most PATH_MAX bytes.


The getcwd() system call saves overhead but should make the same storage
accesses as the
library version.

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Re: Unnecessary hard drive spin-ups

2020-02-13 Thread Andy Paterson via users
On Thursday, 13 February 2020 01:09:20 GMT Roger Heflin wrote:
> It may be the pwd command doing it.  It works like this:
> 
> if something runs pwd when its cwd is under say /var/log then pwd goes
> through all files in /var/log until it finds .. then it goes up a
> directory and repeats, until it gets to /.
> 
> Assuming that is the case your solution would be expected to work, if
> you put it under /mnt/backups then any other pwd anywhere under mnt
> may also cause the spinup.  On nfs mounts an nfs mount that is hanging
> of say /mnt/host1 can hang everything else in /mnt even coming from
> other responding hosts.  the trick there is to
> /mnt/host1/host1mntpoint and put each separate host in a separate top
> level directory to isolate them from each other.  You may not need to
> do that so long as you don't have other things in /mnt being used that
> may cause a pwd.
> 
> if you run ls -l /proc/*/cwd | more it will show you everything
> running's cwd.  I see /var/spool/at (atd process) with that as a home
> dir, so atd doing a pwd would cause a spinup.
> 
> I don't actively use atd for anything and strace does not show atd
> doing anything on my machine.  If you use atd then it may be what is
> doing it. nfs's statd also its cwd under var and is used on nfs
> servers.
> 
> On Wed, Feb 12, 2020 at 1:11 PM Dave Ulrick  wrote:
> 
> >
> >
> > On 2/12/20 7:53 AM, Dave Ulrick wrote:
> > 
> > > Interesting thought. I can envision how a lookup for /var/xyz could
> > > cause everything under /var to be looked up, and I can see how
> > > /var/cache or /var/run would be frequently read.  I'll try mounting a
> > > green USB drive's file system at a third-level directory (e.g.,
> > > /var/backups/0) or under a less popular directory (e.g., /mnt/backups)
> > > and see if that behaves any differently.
> >
> >
> >
> > I ran 'strace' on 'ls' but nothing interesting showed up. Then, I ran
> > 'strace' on 'bash'. I ran 'ls' from 'bash' and then exited. The strace
> > log shows two connect()s to a socket file under /var/run:
> >
> >
> >
> > socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
> > connect(3, {sa_family=AF_UNIX, sun_path="/var/run/nscd/socket"}, 110) =
> > -1 ENOEN
> > T (No such file or directory)
> > close(3)
> >
> >
> >
> > /var/run/nscd/socket appears to be related to the 'nscd' DNS cache which
> > I am not running on my PCs.
> >
> >
> >
> > So, it looks likely that reading /var/run caused the contents of /var to
> > be read. This would have triggered a wakeup of the device hosting
> > /var/backups which would be a cause of its hard drive spinning up.
> >
> >
> >
> > In addition to one PC that mounted a green USB drive under /var I had
> > several other PCs that mounted a NAS under /var. That NAS is intended to
> > store backup files so its hard drive is configured to spin down after 10
> > idle minutes.
> >
> >
> >
> > In view of these findings, I've reconfigured my PCs to mount the backups
> > directory under /mnt instead of /var. So far since doing so I've not
> > noticed any spin-up delays related to a USB hard drive or the backup NAS.
> >
> >
> >
> > Thanks, Tim!
> >
> >
> >
> > Dave
> >
> >
> >
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 List
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> > rg
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I am a little confused by getcwd(), on linux it is supposed to be a system call 
.. I expect to find a 
manual page for it in section 2 (man 2 getcwd)
instead it gives me the library function manual page from section 3 (man 3 
getcwd)
I would fully expect a libc version of getcwd to make many system calls to 
traverse the current 
path but here getcwd() is a system call with all work done internally in the 
kernel, so I wouldnt 
expect anything to probe the path elements.
When I knock up a simple program to do a getcwd() and strace it I find that 
getcwd (on FC31 
anyway) IS a system call.
Why does "man getcwd" give me a page from section 3?
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Re: Unnecessary hard drive spin-ups

2020-02-12 Thread Samuel Sieb

On 2/12/20 7:00 PM, Tim via users wrote:

Gnome (or Gnome-based) things, will put temporary auto-mounting
things (flash drives, etc) inside of /var/run/, then give you an
apparently separate mount point.  You'll get a desktop icon for it, and
no immediate indication that it's accessed through /var/run.


Actually, the mount point is /run/media//.
/var/run is a symlink to /run.
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Re: Unnecessary hard drive spin-ups

2020-02-12 Thread Cameron Simpson

On 12Feb2020 19:09, Roger Heflin  wrote:

It may be the pwd command doing it.  It works like this:

if something runs pwd when its cwd is under say /var/log then pwd goes
through all files in /var/log until it finds .. then it goes up a
directory and repeats, until it gets to /.


getcwd() is a system call on Linux since 2.1.92. It doesn't need to 
perform the expensive ".. then stat everything for a match" loop.


[... snip arranging mounts to be in more out-of-the-way places ...]

On Wed, Feb 12, 2020 at 1:11 PM Dave Ulrick  
wrote:

I ran 'strace' on 'ls' but nothing interesting showed up. Then, I ran
'strace' on 'bash'. I ran 'ls' from 'bash' and then exited. The strace
log shows two connect()s to a socket file under /var/run:

socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_UNIX, sun_path="/var/run/nscd/socket"}, 110) =
-1 ENOEN
T (No such file or directory)
close(3)

/var/run/nscd/socket appears to be related to the 'nscd' DNS cache which
I am not running on my PCs.


Aye.


So, it looks likely that reading /var/run caused the contents of /var to
be read. This would have triggered a wakeup of the device hosting
/var/backups which would be a cause of its hard drive spinning up.


This would surprise me; accessing a direct name doesn't require stating 
everything adjacent.


You can test this:

- wait for the drive to spin down
- type ">>var/run/nscd/socket" and preess  (do NOT filecomplete 
 that path, your shell will do unwanted filesystem access)

- see if/when the drive spins up

Cheers,
Cameron Simpson 
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Re: Unnecessary hard drive spin-ups

2020-02-12 Thread Dave Ulrick

On 2/12/20 7:09 PM, Roger Heflin wrote:

It may be the pwd command doing it.  It works like this:

if something runs pwd when its cwd is under say /var/log then pwd goes
through all files in /var/log until it finds .. then it goes up a
directory and repeats, until it gets to /.
That makes sense. Just occurred to me: a typical shell prompt displays 
the cwd, so 'pwd' or something like it must get run just before a shell 
prompt is displayed. This likely explains why I'd sometimes experience 
the spin-up delay after running a command: it wasn't the command itself 
necessarily that triggered the spin-up but the pwd afterwards.

Assuming that is the case your solution would be expected to work,
It seemed to work earlier today when I fired up the green USB hard drive 
in that I experienced no spin-up delays, but...



  if you put it under /mnt/backups then any other pwd anywhere under mnt
may also cause the spinup.  On nfs mounts an nfs mount that is hanging
of say /mnt/host1 can hang everything else in /mnt even coming from
other responding hosts.  the trick there is to
/mnt/host1/host1mntpoint and put each separate host in a separate top
level directory to isolate them from each other.  You may not need to
do that so long as you don't have other things in /mnt being used that
may cause a pwd.

That's a great idea. I've gone ahead and implemented it on my PCs.

if you run ls -l /proc/*/cwd | more it will show you everything
running's cwd.  I see /var/spool/at (atd process) with that as a home
dir, so atd doing a pwd would cause a spinup.

I don't actively use atd for anything and strace does not show atd
doing anything on my machine.  If you use atd then it may be what is
doing it. nfs's statd also its cwd under var and is used on nfs
servers.


There certainly are a lot of processes on my PC running cwd. Interesting...

Thanks!
Dave
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Re: Unnecessary hard drive spin-ups

2020-02-12 Thread Tim via users
On Wed, 2020-02-12 at 13:10 -0600, Dave Ulrick wrote:
> In addition to one PC that mounted a green USB drive under /var I
> had several other PCs that mounted a NAS under /var. That NAS is
> intended to store backup files so its hard drive is configured to
> spin down after 10 idle minutes.
> 
> In view of these findings, I've reconfigured my PCs to mount the
> backups directory under /mnt instead of /var. So far since doing so
> I've not noticed any spin-up delays related to a USB hard drive or
> the backup NAS.
> 
> Thanks, Tim!

Glad to help, even if I'm not quite sure how I steered things in the
right way.  ;-)  It was one of those "in the back of my mind" ideas.

Gnome (or Gnome-based) things, will put temporary auto-mounting
things (flash drives, etc) inside of /var/run/, then give you an
apparently separate mount point.  You'll get a desktop icon for it, and
no immediate indication that it's accessed through /var/run.

I'm not sure if the same applies to KDE.
 
-- 
 
uname -rsvp
Linux 3.10.0-1062.12.1.el7.x86_64 #1 SMP Tue Feb 4 23:02:59 UTC 2020 x86_64
 
Boilerplate:  All unexpected mail to my mailbox is automatically deleted.
I will only get to see the messages that are posted to the mailing list.
 
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Re: Unnecessary hard drive spin-ups

2020-02-12 Thread Roger Heflin
It may be the pwd command doing it.  It works like this:

if something runs pwd when its cwd is under say /var/log then pwd goes
through all files in /var/log until it finds .. then it goes up a
directory and repeats, until it gets to /.

Assuming that is the case your solution would be expected to work, if
you put it under /mnt/backups then any other pwd anywhere under mnt
may also cause the spinup.  On nfs mounts an nfs mount that is hanging
of say /mnt/host1 can hang everything else in /mnt even coming from
other responding hosts.  the trick there is to
/mnt/host1/host1mntpoint and put each separate host in a separate top
level directory to isolate them from each other.  You may not need to
do that so long as you don't have other things in /mnt being used that
may cause a pwd.

if you run ls -l /proc/*/cwd | more it will show you everything
running's cwd.  I see /var/spool/at (atd process) with that as a home
dir, so atd doing a pwd would cause a spinup.

I don't actively use atd for anything and strace does not show atd
doing anything on my machine.  If you use atd then it may be what is
doing it. nfs's statd also its cwd under var and is used on nfs
servers.

On Wed, Feb 12, 2020 at 1:11 PM Dave Ulrick  wrote:
>
> On 2/12/20 7:53 AM, Dave Ulrick wrote:
> > Interesting thought. I can envision how a lookup for /var/xyz could
> > cause everything under /var to be looked up, and I can see how
> > /var/cache or /var/run would be frequently read.  I'll try mounting a
> > green USB drive's file system at a third-level directory (e.g.,
> > /var/backups/0) or under a less popular directory (e.g., /mnt/backups)
> > and see if that behaves any differently.
>
> I ran 'strace' on 'ls' but nothing interesting showed up. Then, I ran
> 'strace' on 'bash'. I ran 'ls' from 'bash' and then exited. The strace
> log shows two connect()s to a socket file under /var/run:
>
> socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
> connect(3, {sa_family=AF_UNIX, sun_path="/var/run/nscd/socket"}, 110) =
> -1 ENOEN
> T (No such file or directory)
> close(3)
>
> /var/run/nscd/socket appears to be related to the 'nscd' DNS cache which
> I am not running on my PCs.
>
> So, it looks likely that reading /var/run caused the contents of /var to
> be read. This would have triggered a wakeup of the device hosting
> /var/backups which would be a cause of its hard drive spinning up.
>
> In addition to one PC that mounted a green USB drive under /var I had
> several other PCs that mounted a NAS under /var. That NAS is intended to
> store backup files so its hard drive is configured to spin down after 10
> idle minutes.
>
> In view of these findings, I've reconfigured my PCs to mount the backups
> directory under /mnt instead of /var. So far since doing so I've not
> noticed any spin-up delays related to a USB hard drive or the backup NAS.
>
> Thanks, Tim!
>
> Dave
>
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Re: Unnecessary hard drive spin-ups

2020-02-12 Thread Tom Horsley
The most irritating spin-up for me occurs on a reboot.
I have a really slow USB drive that isn't even mounted,
just plugged in (in case I want to mount it). The reboot
always hangs for several seconds, and I can hear the
drive spin up before the reboot proceeds.
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Re: Unnecessary hard drive spin-ups

2020-02-12 Thread Dave Ulrick

On 2/12/20 7:53 AM, Dave Ulrick wrote:
Interesting thought. I can envision how a lookup for /var/xyz could 
cause everything under /var to be looked up, and I can see how 
/var/cache or /var/run would be frequently read.  I'll try mounting a 
green USB drive's file system at a third-level directory (e.g., 
/var/backups/0) or under a less popular directory (e.g., /mnt/backups) 
and see if that behaves any differently.


I ran 'strace' on 'ls' but nothing interesting showed up. Then, I ran 
'strace' on 'bash'. I ran 'ls' from 'bash' and then exited. The strace 
log shows two connect()s to a socket file under /var/run:


socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_UNIX, sun_path="/var/run/nscd/socket"}, 110) = 
-1 ENOEN

T (No such file or directory)
close(3)

/var/run/nscd/socket appears to be related to the 'nscd' DNS cache which 
I am not running on my PCs.


So, it looks likely that reading /var/run caused the contents of /var to 
be read. This would have triggered a wakeup of the device hosting 
/var/backups which would be a cause of its hard drive spinning up.


In addition to one PC that mounted a green USB drive under /var I had 
several other PCs that mounted a NAS under /var. That NAS is intended to 
store backup files so its hard drive is configured to spin down after 10 
idle minutes.


In view of these findings, I've reconfigured my PCs to mount the backups 
directory under /mnt instead of /var. So far since doing so I've not 
noticed any spin-up delays related to a USB hard drive or the backup NAS.


Thanks, Tim!

Dave

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Re: Unnecessary hard drive spin-ups

2020-02-12 Thread Dave Ulrick
Interesting thought. I can envision how a lookup for /var/xyz could 
cause everything under /var to be looked up, and I can see how 
/var/cache or /var/run would be frequently read.  I'll try mounting a 
green USB drive's file system at a third-level directory (e.g., 
/var/backups/0) or under a less popular directory (e.g., /mnt/backups)  
and see if that behaves any differently.


Thanks,
Dave



On 2/12/20 7:11 AM, Tim via users wrote:

On Tue, 2020-02-11 at 19:53 -0600, Dave Ulrick wrote:

I'm logged in as a non-root user with my home directory as my
current working directory. The file system containing my home
directory is mounted at /home. I'm using a shell prompt via a
graphical terminal emulator (xfce4-terminal, in my case). Now, I
enter an 'ls' command at a bash prompt. The output doesn't appear
until after my USB hard drive spins up. Note that neither
/var/backups nor any directory under it is in my shell's PATH, nor is
there any symlink to /var/backups in my current working directory.
Thus, there should be no need to read /var/backups, yet evidently
this exactly what happens.

Just a stab in the dark:  Is something poking about /var/run or
/var/cache?  Perhaps that's enough to look through /var.  I wonder if
you could try another terminal program, just to see if it's the
terminal, itself.

Maybe strace ls, to see what it's up to.

I know with GUI programs, I had to move mountable thing to be inside a
sub-directory of my homespace.  Otherwise, anything that listed ~/
would wake up the drives to count the number of files in them.  So, I
feel your pain.
  

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Re: Unnecessary hard drive spin-ups

2020-02-12 Thread Tim via users
On Tue, 2020-02-11 at 19:53 -0600, Dave Ulrick wrote:
> I'm logged in as a non-root user with my home directory as my
> current working directory. The file system containing my home
> directory is mounted at /home. I'm using a shell prompt via a
> graphical terminal emulator (xfce4-terminal, in my case). Now, I
> enter an 'ls' command at a bash prompt. The output doesn't appear
> until after my USB hard drive spins up. Note that neither
> /var/backups nor any directory under it is in my shell's PATH, nor is
> there any symlink to /var/backups in my current working directory.
> Thus, there should be no need to read /var/backups, yet evidently
> this exactly what happens.

Just a stab in the dark:  Is something poking about /var/run or
/var/cache?  Perhaps that's enough to look through /var.  I wonder if
you could try another terminal program, just to see if it's the
terminal, itself.

Maybe strace ls, to see what it's up to.

I know with GUI programs, I had to move mountable thing to be inside a
sub-directory of my homespace.  Otherwise, anything that listed ~/
would wake up the drives to count the number of files in them.  So, I
feel your pain.
 
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