Solving the ext3 latency problem [LWN.net]

Solving the ext3 latency problem

Posted Apr 14, 2009 17:55 UTC (Tue) by mgb (guest, #3226)
Parent article: Solving the ext3 latency problem

"multiuser Linux systems are relatively scarce in 2009"

We run a bunch of Linux mail servers, and we ain't the only ones.

Maybe somebody should tell Linus how Linux is being used.

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Solving the ext3 latency problem

Posted Apr 14, 2009 18:11 UTC (Tue) by malor (guest, #2973) [Link] (5 responses)

It can be argued that most servers that provide more than one service are 'multiuser' machines.

Solving the ext3 latency problem

Posted Apr 14, 2009 20:10 UTC (Tue) by drag (guest, #31333) [Link] (4 responses)

Personally I would think that multiuser actually means having multiple people with users using the computer at the same time.

That is they are logged onto the machine and are doing something on them.. programming, editing, web browsing, etc.

So your dealing with computers with multiple monitors with multiple users logged in at once, or LTSP, or people that still sell shell accounts. All of which are fairly rare compared to personal desktops, embedded systems, or most server systems.

Solving the ext3 latency problem

Posted Apr 14, 2009 23:24 UTC (Tue) by ktanzer (guest, #6073) [Link] (1 responses)

Multi-user systems may be relatively rare, but as someone who was responsible for multiple LTSP deployments, I shudder at the thought that security in such cases would be cast aside or relegated to an afterthought. LTSP is a great way to use old hardware. For that matter, any home machine used by the whole family would also be multi-user (assuming people set up their own logins).

On a more general note, Linux has inherited rich multi-user capabilities from Unix, and I hate to see that atrophy over time. As one example, it is very easy to find information on how to configure popular programs such as Firefox, KDE, OpenOffice, etc. for a single user, but often maddeningly hard to determine how to configure on a system-wide basis. The fact that FF can't run multiple instances from a single profile is not technically a multi-user issue, but also drives me up the wall...

Solving the ext3 latency problem

Posted Apr 15, 2009 1:25 UTC (Wed) by drag (guest, #31333) [Link]

Well I can agree with that.

I don't know exactly why, but I have a feeling that multiuser systems will become increasingly important in the future.

Something will come along... like the acceptance of IPv6 and the decline of the "Personal Computer"-ing inflicted client-server relationship and the internet will return to it's P2P roots. (for reasons of scalability, robustness, expense). If something like that were to happen and people realized that having mobile computers could become essentially disposible if they turned into little more then terminals for the 'big' computer at home or clusters at work... Then multiuser systems could become common place again.

Weirder things have happenned.

Solving the ext3 latency problem

Posted Apr 15, 2009 4:35 UTC (Wed) by malor (guest, #2973) [Link]

Typically, different services run under different user accounts, and rely on the system's security features to keep the two separate.

It would be bad if a bug in the mail server gave access to, say, deleted .htaccess files, or part of a SQL database.

All Unix systems are inherently multiuser, and sabotaging inter-account security features is deliberately cutting away one layer of the net that can catch you if a bug exposes an attack vector.

Solving the ext3 latency problem

Posted Apr 15, 2009 5:55 UTC (Wed) by hawk (subscriber, #3195) [Link]

It may not be "multi-user" by that definition but the exact definition of "multi-user" isn't really that interesting for the actual argument, is it?

Isn't the point that as soon as soon as there are multiple users (no matter if they are logged in using a system account or accessing the system through some other means, eg HTTP, authenticated in some way or even anonymously), there would be a chance that one user's data (or data "belonging to the system") could leak into a file which will be accessible by another user.

So in the case of the the system crashing, a file publicly available on the web, or some logged in user(s), might end up containing anything that has previously been deallocated if that file was being modified, be it by the site administrator, or by a random user on a site where you can for instance upload an image to include in your content.

I would think this definitely falls within the "common usage"-realm for Linux systems and that whoever made the argument may not have really thought it through.

(Or I'm just not understanding in what scenarios something like this could actually happen.)

Solving the ext3 latency problem

Posted Apr 14, 2009 18:16 UTC (Tue) by smoogen (subscriber, #97) [Link] (1 responses)

You may run such a server (I do too... ) but nowadays it is a blip in the data compared to routers, switches, music boxes, GPS systems, laptops, desktops, workstations that run Linux. In those cases, worrying about data from some other user is less likely.

Also I think it was the editor not Linus who said that.

Solving the ext3 latency problem

Posted Apr 17, 2009 18:21 UTC (Fri) by giraffedata (guest, #1954) [Link]

nowadays it is a blip in the data compared to routers, switches, music boxes, GPS systems, laptops, desktops, workstations that run Linux.

I was going to say the opposite. I think you're making a statement about the number of Linux kernel images running, but I don't think that's a useful measure of prevalence as it relates to the cost of assuming a system is single-user.

On the contrary, I believe the great majority of Linux is multiuser servers and the personal computers and appliances you mention are a blip. I'm looking at the amount of filesystem access that happens.

When I say "multiuser" I'm considering a user to be a person, not a uid.

Incidentally, routers and switches (from your list) are multiuser systems. Consequently, there is a security issue in sending data to the wrong user.

Multiuser quite important still: remote users on Windows PC:s

Posted Apr 15, 2009 3:53 UTC (Wed) by eru (subscriber, #2753) [Link] (4 responses)

The big company I'm working for actually has most of its interactive Linux users on multi-user servers: This is because everyone is "of course" supplied with a Windows PC, but Linux is preferred for software development for several products, so the developers access Linux servers with X11 emulator or VNC running on the PC. This also makes it easier to maintain a consistent development environment for the users. Some people do have Linux workstations, but these are a minority.

I don't know how typical this kind of use is, but I suspect it common in technology companies needing a Linux development environment for some users but not wanting or being able to go all the way to Linux desktops.

Multiuser quite important still: remote users on Windows PC:s

Posted Apr 15, 2009 16:05 UTC (Wed) by chema (subscriber, #32636) [Link]

Same here.

Our development environment is a mixture of Windows desktop PCs (running some development tools + "corporate" applications) and Linux servers (providing: ssh + X11 fwd + http + samba + ...).

It used to be HP-UX/Solaris <-> Windows but we happily migrated to linux a year ago.

Multiuser quite important still: remote users on Windows PC:s

Posted Apr 15, 2009 20:18 UTC (Wed) by PhracturedBlue (subscriber, #4193) [Link] (2 responses)

Yes, but are you using EXT3 as the filesystem on those machines? In many (most?) multi-user systems, you're likely to have a big fileserver serving files via NFS or equivalent to various servers. I don't know if your company is set up that way, but I'd think it would be common for large corporations with many users.

Multiuser quite important still: remote users on Windows PC:s

Posted Apr 15, 2009 20:29 UTC (Wed) by mgb (guest, #3226) [Link]

We used NFS like that back around '95 or '97 but it's way too slow for general use these days although there are undoubtedly still specialized applications where it's useful.

So yes, we use ext3 for mail servers and web servers etc. All of which are multi-remote-user.

Multiuser quite important still: remote users on Windows PC:s

Posted Apr 16, 2009 4:29 UTC (Thu) by eru (subscriber, #2753) [Link]

Yes, but are you using EXT3 as the filesystem on those machines? In many (most?) multi-user systems, you're likely to have a big fileserver serving files via NFS or equivalent to various servers.

Yes and no: The home directories of the users are normally mounted via NFS (the NFS servers are not always Linux: NetApps and and Solaris boxes are also used), but the Linux servers (usually RHEL) to which people log in use ext3. Because of the various local shared directories, multiuser issues in ext3 are still relevant.

Solving the ext3 latency problem

Posted Apr 16, 2009 0:46 UTC (Thu) by hazelsct (guest, #3659) [Link]

Indeed.

Another "multi-user" use case on my "single-user" laptop is having a separate account for downloaded software (government contracts sometimes require such things), for which I don't want to take the risk of polluting the rest of my system. I install in wine in this separate account, and share (minimal) data as necessary. Security matters.

[OT: it's astounding to me how well wine runs a *lot* of Windoze software these days!!]