[Server-devel] /tmp, /var/tmp and tmpfs (was: Re: [PATCH] ds_backup - major rework)

[John Watlington]

These comment apply equally to school server developers and laptop  
developers,
as we hope to start supporting school servers with 1GB Flash drives  
for the / and
boot partitions, and disk partitions (e.g. /library/) for supported  
services.  The goal
is to support OS, networking, and critical services in the presence  
of a disk failure.

wad

On Jun 18, 2008, at 1:52 PM, Martin Langhoff wrote:

> Michael Stone's review of my recent patches to ds-backup raised some
> issues about creating temp files (that wear NAND out) and about
> successful backups on a full or otherwise RO NAND. See below...
>
> On Mon, Jun 16, 2008 at 5:45 PM, Martin Langhoff
> <martin.langhoff at gmail.com> wrote:
>
>>> Are we concerned about the cleanup code failing, for example because
>>> permissions were changed on the ds_path dir? If it permanently  
>>> failed
>>> then I think our backup script would also permanently fail, which
>>> doesn't seem quite right. (If something's broken with my  
>>> permissions,
>>> then I _want_ my backup script to take what data it can get and  
>>> move it
>>> off the system, right?)
>>
>> Good point. This part of the code is removed, but I haven't made it a
>> point to ensure that the code can backup a RO homedir. Actually, we
>> aren't well setup for a RO root fs at all (should an error kick us
>> into ro), /tmp is not a tmpfs!
>
> To address both issues - RO/fulldisk-tolerant backup and less NAND
> wear, we need /tmp to be a tmpfs. There are some risks in that -
> namely, that programs might be using /tmp to write large stuff. That
> is a pretty common bug in the unix world - mkstemp and friends to
> straight for /tmp but for large stuff, /var/tmp is the place. Many
> systems, old and new, use some kind of ramdisk for /tmp -
>
> I would suggest a quick audit of likely suspects that we don't want to
> see break (ie: olpc-update).
>
> In any case, here's the bug:
>
>      http://dev.laptop.org/ticket/7300
>
> cheers,
>
>
>
> m
> -- 
>  martin.langhoff at gmail.com
>  martin at laptop.org -- School Server Architect
>  - ask interesting questions
>  - don't get distracted with shiny stuff  - working code first
>  - http://wiki.laptop.org/go/User:Martinlanghoff
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