/dev/chat - 2015-11-28

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2:45 AM

hey guys, anyone here?

2 hours later…

4:24 AM

just one more unix.stackexchange.com/q/245780/41104

I wonder my question unix.stackexchange.com/q/246026/38906 is too broad?

nah, that is designed to accomplish a very specific (and even programy) task, determining the type of a variable

@Braiam: The bourne-shell tag is not good

bourne-like shell is not the same as bourne-shell

weird, most of those tags (ie, debian) we assume is X or X-like

You can read unix.stackexchange.com/tags/bourne-shell/info

> Use this tag only for questions about genuine Bourne shells. For questions about Bourne/POSIX-style shells in general, use shell.

4:34 AM

ain't bash and zsh bourne shells implementations?

@Braiam: No, they're bourne like shell

not genuine Bourne shells

well, but having a explosion of all shell tags isn't good either

@Braiam: Maybe, but I only include the main shells tag, which (I guess) the solution for each of them will be specified

I really expect determining the type of a variable to be defined

and my hopes are crushed, you may have to rely on regexes or tr [:alpha:] stuff

@cuonglm - interesting question but it's hard to imagine a scenario in sh/bash where you'd need to determine whether a var is an array or not. differentiating between scalar and list is common in perl and other languages, but where and how would you use it in sh?

4:45 AM

umm... actually I just read over it... tldp.org/LDP/Bash-Beginners-Guide/html/sect_10_01.html

in bash at least you have declare -p, lets see others

@casey: I have it in mind when I intend to add a feature to oh-my-zsh

imaging you have a variable called theme

you can load a theme by its value

theme=cuonglm.theme

then zsh will load cuonglm.theme

if theme=random

then each time a zsh session start, zsh will pick a random theme from themes/ directory

now I want zsh can load themes from a list of predifine themes

theme=(cuonglm.theme cas.theme)

then if theme == random or theme is an array

zsh will pick a random theme from them

@Braiam: As I shown in my question, doing some parsing can do this task

but I want to know there's easier ways?

@cas: scalar and list context also important in shell, as mention too many times in U&L site

> Do not touch the Oscillator upon starting; it will cause you to feel pain.

list context will cause split+glob

while scalar context isn't

in sh you generally know whether you've got a scalar or a list....and/or you write defensively and assume list because list includes one-or-more elements.

2 hours later…

6:24 AM

@Braiam Looks like we did talk about it 2 years ago. How time flies.

3 hours later…

9:06 AM

Here's a fairly comprehensive review of backup solutions: gist.github.com/drkarl/739a864b3275e901d317

There is certainly no shortage of choices.

2 hours later…

10:53 AM

while :
    do
        eject -T
done

1 hour later…

12:22 PM

I see what you mean now, yes these kinds of people certainly do exist. My real point of argument was that often people are called out as this type, when they're really just that new to everything that they don't realize that a google search would give them the answer, or don't realize that they are asking the same question over and over again.

Then again though, I've been there with entrylevel programmers in college who have practically no computer skills when they get there, they often fail to realize the first time around that they can use the same method as used to solve one of their ol…

1:10 PM

@Cestarian the thing that seems to provoke hostility (or, at least, an "i give up" reaction) around here is when someone asks minor variations of the same question and doesn't learn anything from the answers they've been given.

1:53 PM

@Cestarian I've been around this site for awhile, and in general, I would not call it unfriendly or unhelpful. Forums get much worse than this, on SE and elsewhere.

People here do understandably get tired of dealing with the many clueless, often garbage questions that pass through here, but you can't blame them. Nobody is getting paid for this. And that isn't unfriendly, nor elitist.

2:21 PM

Looking at backup options is really confusing. For example, bup, attic, obnam, and duplicity. All of them similar. How does one choose. And that's only a selection from the tech side of things.

2:38 PM

@Cestarian I agree that the Linux community is often unfriendly to newbies. I submit, however, that this site isn't. I certainly try not to be and so do most of the regulars. If you happen to come across newbie bashing, please flag the comment or answer for mod attention and it will be dealt with.

We are open to all levels of expertise here, from the newbie to the guru. You'll find many very basic questions asked and answered. Indeed, knowledge level is not really related to help vampirism at all. I've seen quite knowledgeable people post questions here whose answer is the first hit on any search engine if they had bothered to simply paste their question's title as a search query.

That bugs me. As do people who can't be bothered to understand answers and instead post the same thing over and over again with tiny variations. Yes, we do expect users to put some effort into it. But please don't confuse newbies with help vampires. The former will learn, the latter are often beyond help.

1 hour later…

4:04 PM

@cas Do you have any thoughts about backups? This is clearly a vexing topic.

This guy has three answers, all advertising his own service. Are there no rules against this?

111 3

backup windows windows-7 windows-server file-management ftp sftp

1 hour later…

5:28 PM

John Goerzen's take on backup systems - changelog.complete.org/archives/…

6:08 PM

Borg looks interesting. It's a fork of attic, after it's author decided he didn't want to play with others. See for example github.com/borgbackup/borg/issues/216

Also in Debian unstable.

Does anyone have experience with these programs? As of a couple of days ago, I'd not heard of them.

4 hours later…

10:03 PM

Does anyone know of a Linux application that can open .pmx files. It was created by PrintMaster on windows, but from my research it appears to be an adobe pagemaker file.

Borkbackup definitely looks interesting.

@TinyGiant If it's proprietary, that would be hard. Unless Adobe has released the specs.

That's what I figured. Just thought I would see if anyone had specific knowledge.

The proprietary program in question is a PITA to use for exporting the images.

10:29 PM

The only other option would be reverse-engineering. Which might be illegal.

I'm thinking that may be more of a PITA than using the proprietary program.

But, I can make using the proprietary program less of a PITA if I make someone else do it.

@FaheemMitha reverse engineering is legal if it's done for the purpose of interoperability, at least in France and in the US

@Gilles Oh. I remember the creator of Bitkeeper created a situation involving that. But maybe there was something else going on.

@FaheemMitha - i used to use amanda then my tape drive died at home and at my last employer it was easier to make use of the university's offsite backup. at home I use a combination of rsync and zfs send to backup my various machines to an 8TB zfs pool called backup, with snapshots of each backup.

@cas Does it work well?

10:33 PM

Hey @Gilles. How's it going today?

it works for me. i have no off-site backup, so i'm f***ed if there's a fire or something.

@cas This pool is part of your local machines then?

yep.

This Borgbackup thing seems promising. I was just chatting to the main dev on IRC.

my main machine has two zpools, one for normal use. and one for backups.

10:34 PM

Unfortunately it requires server support as of now. S3 for example doesn't work right now.

all other machines on the network also backup to the backup pool.

Anyway, I'll test it with my VPS.

The zpool is on one machine?

there are two zpools on that machine. and another zpool on my myth box (which i don't bother backing up).

Ok

The backup pool has 4 x 4TB drives, in two mirrors (i.e. raid-10):

zpool status backup
pool: backup
state: ONLINE
scan: scrub repaired 0 in 4h12m with 0 errors on Sat Nov 28 05:29:14 2015
config:

NAME STATE READ WRITE CKSUM
backup ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
sdb ONLINE 0 0 0
sdi ONLINE 0 0 0
mirror-1 ONLINE 0 0 0
sdd ONLINE 0 0 0
sdc ONLINE 0 0 0

errors: No known data errors

10:45 PM

@cas Do you make incremental backups?

yep. with rsync and with zfs send (which sends the difference between one snapshot and another).

@cas Ok. Is zfs reliable?

of course not, i'd never want to use a reliable filesystem for my files. that would be silly. :-)

Well, I've heard mixed things about it.

That was originally a Sun project. I've heard talk about it over the years. But I've not seen it widely used.

Hmm, it implements sw RAID. Interesting.

Do you think it is better than ext4?

it combines the features of raid and lvm and a lot more, including snapshots, and error detection and correction.

much better. better (and more reliable) than btrfs too.

10:51 PM

So a Zpool is like LVM then?

@cas Oh. Surprising more people are not using it then.

Wonder where Anthony is. Haven't seen him around in a while.

sort of. from the admin pov you mostly work with filesystems (subvolumes in btrfs-speak). you can create them as easily as you can create a directory. and unlike lvm, the quota allocated from the pool can be a soft of hard quota and is shared by all filesystems.

this is scary

the license is a minor problem. it's CDDL which isn't compatible with GPL.

Maybe VTC this one?

0

Q: Upgrading wheezy to jessie - packages missing

I'm trying to upgrade wheezy to jessie. apt-get update works fine apt-get upgrade results in this series of errors: Extracting templates from packages: 100% Preconfiguring packages ... dpkg: warning: files list file for package 'libxau6:armhf' missing; assuming package has no files currently ...

@cas Ok

distributing the source as a dkms module for the user to install avoids any licensing issues (you can't distribute CDDL+GPL binaries but there's nothing stopping the end user from combining CDDL and GPL code themselves)

10:54 PM

@cas Why is it is a problem?

@cas Oh. I see. So it can't be included in the kernel. Bummer.

it's a problem because CDDL is incompatible with GPL.

Ok

it's not a big deal because installing it is as simple as installing any other dkms package.

zfsonlinux.org

currently zfsonlinux.org provides an external repo of zfs and related packages. it will be in debian repo sometime over the next few months. and, of course, debian kfreebsd already supports zfs.

@cas Does the Debian installer support ZFS?

on kfreebsd it does. not yet on linux kernel.

10:57 PM

@cas Oh. I guess not, then.

@cas Ok.

Doesn't that make it a bit harder to install Debian on it?

one of these days i'll get around to converting my rootfs to zfs - currently i'm still using mdadm RAID-1 and XFS....but i want to be able to do snapshots and backups of / with zfs send, same as i can for my home dirs etc.

@cas Ok. Is ZFS better than XFS too?

no, it's not particularly difficult. there are numerous howtos on doing a zfs rootfs install on debian.

Ok

yes, much better. ext4 and xfs are old-school filesystems. zfs is modern COW with snapshots and error correction and subvolumes and more.

11:01 PM

@cas Ah, Ok. Making a mental note of that.

This is an opinion based question: What is the benefit of using an external smtp with sendmail instead of using your own server? For example the ones provided by gmail, gandhi, or namecheap. I couldn't find any answers on this other than people saying outright that it is "better." Would be very very appreciative of scratching this curiousity itch

@Cenoc Well, you control it, for one thing.

as well as filesystems, zfs can also create zvols - which are kind of like partitions, useful for e.g. virtualisation. e.g. create a 10GB zvol to be the virtual hard disk for a kvm VM...install debian or whatever on it, and then zfs clone it to make duplicate VMs. the copy-on-write nature of zfs ensures each VM only takes as much disk space as is needed to differentiate it from the original.

You can make it behave as you want. Of course, the flip side is that if it breaks, it's solely your problem.

@cas Wow. Sounds super flexible.

What's the current maintainance situation of ZFS? Since it isn't in the kernel?

@FaheemMitha so that's the benefit for using your own server, but it seems more common to use the external ones - was wondering if this is to avoid emails being tagged as spam?

11:07 PM

@Cenoc Well, lots of people run local servers. It's not that uncommon. This isn't the same as managing your own email, necessarily.

see the zfsonlinux.org web site. there are several developers working on it.

You might just use it to send email from local machines.

@cas Ok

btw, i've been using zfsonlinux since around 2010 or 2011. no data loss, no corruption, no major problems - even with a few disk failures.

@cas That's impressive. Did someone recommend it to you, or did you know about it from before?

i read about it and decided to try it.

11:12 PM

Ok. Do you have deduplication turned on?

@FaheemMitha well i meant this for managing short spurts of informational emails for a small group of people - what is the advantage of sending external v. using your own server running an app

(thanks for all the answers btw)

nope. requires too much memory, so costs too much. much cheaper to just have more/bigger disks. de-duplication is a nice idea but just can't compete economically with adding more storage.

@Cenoc You might be sending an email from some local app. E.g. Debian's reportbug.

@cas Ok.

@Cenoc You'd have logs of what was going on.

A remote server is basically a black box.

approx $50/TB for disk, or approx $40/4G for RAM - and you need anywhere from 1-5GB of RAM for every TB of storage if you enable de-duplication, depending on the nature of your data.

I personally run a local exim, which hands off to a remote smarthost. Which does the actual delivery.

That's quite common, I think.

And I run POP via fetchmail to pull from the same smarthost periodically.

11:16 PM

if you had a static IP you could have your domain's mail delivered direct to your exim host.....but it's not reliable to do that if you have a dynamic IP.

Oh, and if you hand off to a remote machine directly, your app has to know how to that. Not all of them do, obviously. Whereas pretty much any app can just send mail locally.

@cas True. Also, a local machine isn't as reliable as a big server.

If it gets delivered to a big remote mailhost, it will just sit there till I get around to fetching it.

I think most machines will give up on mail deliveries after a few days.

i'd disagree with that. i've been running my own mail servers since the early 90s. wouldn't trust an ISP (or google etc) to handle my mail.

@cas Disagree with which part?

disagree with "Also, a local machine isn't as reliable as a big server"

@cas So, your CPU would be running constantly trying to keep up with the deduplication?

@cas Depends on the local machine.

And the adminstrator.

Sure, if you know what you are doing, that's fine. But lots of people don't.

I'm thinking of a situation where your local machine breaks down, or your basement gets flooded. Or something.

I use Luxsci, based outside Boston. I'm pretty sure their servers are up all the time.

Take care, everyone. Sleep time.

11:23 PM

de-dupe on zfs works by keeping a checksum of every block, so zfs can tell if the checksums are the same or not. zfs also uses that checksum for error detection and correction, but it doesn't need to keep it in RAM all the time if it's not doing de-dupe. so cpu utilisation is similar with or without de-dupe. RAM usage goes through the roof with de-dupe. of course, it can also use L2ARC (a block caching device such as an SSD) but that's a LOT slower than RAM.

@cas I see. So nice in theory, but not so much in practice.

in my experience, ISP mail servers going down is far more common than flooded basesments (i don't even have a basement).

@cas :-)

Luxsci seems quite reliable, though. And I chose them because the worst thing anyone seemed to be able to say about them is that they cost too much.

some ISPs have a clue, some don't. the bigger they are, the less clue they have. small to medium ISPs run by geeks are best, at least until they get bought out by a giant clueless corporation.

@cas Agreed. I think Luxsci is quite small. Are you familiar with it?

11:27 PM

nope

ok

no need. i live in .au not boston. and all i really need is a cheap fast reliable pipe, i can (and do) run all my own services myself.

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