/dev/chat

9:01 AM

An informal poll. Who here builds his/her own computer, or have it built for him/her? And who buys off the shelf computer?

terdon

I build desktops, I've never bought one of those. But I buy laptops, never built one of those.

fra-san

10:10 AM

@FaheemMitha Same here. I've never even started exploring the possibility of building a laptop, while in the last (almost) fifteen years I kept replacing parts (as they got too old) in the desktop computer I had assembled.

Faheem Mitha

10:37 AM

@terdon @fra-san So you both build your own desktop computers?

Is it hard? It seems hard to me. But I've never tried.

terdon

It's easy enough. Takes some time at first, but it boils down to screwing a few screws. The only tricky bit is the CPU and even that is just a question of being careful, applying thermal paste and not forcing anything.

fra-san

@FaheemMitha I wouldn't say it's hard. Sure, practicing with some old piece of junk before putting your brand new components together would be a good idea. Sometimes I broke things, though it was never completely unexpected.

Faheem Mitha

11:02 AM

@terdon @fra-san Hmm. I see. Maybe I'll give it a shot with some assistance. Did you use a book? Or books? Or help from the internet?

Labor is cheaper in India, and help possibly easier to find than in other places.

Oh, and do you need a specially clean place to assemble the computer?

I wasn't thinking of laptops at all. I've never heard of anyone building his/her own. It may not be possible.

Also, how long did it take you to build a desktop computer from sratch, assuming you did?

Also, is there any soldering involved?

Andras Deak

11:24 AM

@FaheemMitha hell no

I put together a desktop to use as a NAS, from scratch. First time in my life. It was easy. It's mostly like this:

terdon

@FaheemMitha Good grief no. You just need a regular flat surface to lay the thing down, a Phillips screwdriver and, if you're also installing a CPU, a tube of thermal paste and a plastic card (usually included when you buy the paste, if not any membership card or expired credit card will do). No other tools or special equipment needed at all.

Andras Deak

Hardest part was deciding on what exact components to buy.

terdon

I haven't done this in a while, but I don't think I used help from the internet. I did know the basics, however. But still, most of what I needed was "which cable connects to which port on the motherboard" and that is in the motherboard's manual.

Andras Deak

And my desktop casing didn't come with enough screws to secure two HDDs. That was annoying.

And finding a screwdriver with a non-magnetic tip.

terdon

@AndrasDeak Why?

Andras Deak

11:30 AM

Because I'm not putting anything magnetic near my new HDDs :P

Faheem Mitha

@AndrasDeak @terdon OK. Thank you for the assurance. Certainly, the hardest part will be finding suitable components at a reasonable price.

terdon

The magnet on the screwdriver is not going to affect your HDD, surely. At least, every single build I've made in the past 25 years or so used magnetic screwdrivers.

Andras Deak

@terdon indeed, and yet

terdon

If they can't deal with that level of magnetism, you might as well throw them out now.

Faheem Mitha

@AndrasDeak You don't use SSDs? Also, don't magnets need to be really powerful to affect HDDs?

Andras Deak

11:31 AM

@FaheemMitha no and maybe (depends on the distance)

For my NAS I absolutely want persistent storage. And SSDs are too expensive. I needed at least two 2 TB disks for raid.

terdon

74

Q: Can Screwdrivers With Magnetic Tips Cause Damage To Electronics?

While it is convenient to pick screws with magnetized tips I wonder if the magnetism can cause any damage to electronics?

magnet

Andras Deak

@terdon neat

Faheem Mitha

While we're on the subject, are computers sensitive to heat? One computer person told me that I should keep it at 24C. Or possibly below.

terdon

I found several such discussions and they all agree that it isn't an issue.

Faheem Mitha

I don't quite achieve that, but I do leave the A/C on in the room where I have my computer.

Andras Deak

11:33 AM

> These are simple physics, the magnetic tip has a magnetic field which will induce ferromagnetic wave into the conductive materials around it

Oof

terdon

@FaheemMitha BS. I mean, yes, the colder the room holding your computer, the better the computer will be cooled and the better it will work. So servers tend to be kept in refrigerated (air conditioned) rooms. But there is no need to do so unless you are building a server.

Andras Deak

@FaheemMitha working temperatures are higher anyway. You only have to worry about the PC's own heat if it's doing a lot of work. Hence ACs in server rooms.

Faheem Mitha

@terdon I see. Does that apply even to places where the temperature can reach 40C and above, and which are also very humid?

terdon

@AndrasDeak Yes, but so what? Everything is protected, you won't get anywhere near anything that could be affected.

Andras Deak

@terdon I mean that quote is utter bullshit

terdon

11:35 AM

@AndrasDeak Ah, better :)

Faheem Mitha

@AndrasDeak My computer seems to get quite warm easily. It might be partly age. Or something else. I think it has adequate ventilation. We also cleaned it recently.

terdon

@FaheemMitha Yes. Your machine will regularly reach temperatures approaching 100 degrees Celsius. And yes, when it is very hot outside, that does mean the internal temperature of the machine can go up but, again, unless you're doing something very intense, I doubt it will matter.

Faheem Mitha

@terdon OK.

terdon

More importantly, haven't you been using computers in that climate for years? Surely you'd have noticed if they can't work outside an air conditioned room.

Andras Deak

@terdon All evidence seems to be of the anecdata kind. Which is fine, but I won't stop being careful when I build a PC every few decades.

terdon

11:36 AM

@FaheemMitha Change the thermal paste on the CPU.

Faheem Mitha

@terdon I've never used them outside an air-conditioned room, so no.

I don't get out much.

terdon

@AndrasDeak All evidence on both sides.

Andras Deak

What both sides?

terdon

@FaheemMitha Then the question is moot anyway: you will be using this one in the same room.

Faheem Mitha

@terdon I'd rather change the CPU, in that case. But on a MB this old, I'm not sure that would be practical. Or worth it.

@terdon Well, I could turn the A/C off. :-)

terdon

11:38 AM

@AndrasDeak Nobody is suggesting it actually does cause harm, at best it's people who worry about it for no specific reason. So the evidence on both sides is weak. I'm pretty sure we can find a good answer if we look though. I can guarantee it has never been a problem for me and seriously, if that were an issue our machines would be breaking all the time.

Andras Deak

@terdon yes, I'm not aware of cases where magnetic screwdrivers did any harm.

And I never said they can

Faheem Mitha

I always had the impression that HDDs are pretty robust. And they must be exposed to magnetism from time to time, one way or the other.

user3342816

3:01 PM

@StéphaneChazelas Notice you use space in the shebang for scripts in some posts. Any particular reason for this? (Ignore if you like ;))

I liked this comment :P unix.stackexchange.com/questions/276751/…

terdon

@user3342816 A lot of people do it that way. You mean "#! /bin/bash" instead of "#!/bin/bash", right?

It makes no difference to anything other than what you personally find easier to uise and/or more readable/clearer.

user3342816

Yes, that is what I mean

I have never used space, but yes, find it more clear

terdon

Of course, Stéphane being Stéphane, there may be some sort of obscure shell or system or other edge case that can support only one of the two.

@user3342816 Go for it then.

user3342816

Yup. And, yes, lol, that was why I @'tted him

terdon

Ah. I just read the comment you linked to. Apparently systemd doesn't like it, huh? Sigh.

user3342816

3:05 PM

I searched systemd on github for a bug report on it, but could not find one

Only about shebang not being on line 1

terdon

According to wikipedia, this was even in the very first implementation:

> Dennis Ritchie introduced kernel support for interpreter directives in January 1980, for Version 8 Unix, with the following description:[25]

> 5) It will allow other interpreters to fit in more smoothly.

To take advantage of this wonderful opportunity,
put

#! /bin/sh

at the left margin of the first line of your shell scripts.
Blanks after ! are OK.

Shebang (Unix)

In computing, a shebang is the character sequence consisting of the characters number sign and exclamation mark (#!) at the beginning of a script. It is also called sha-bang, hashbang, pound-bang, or hash-pling.When a text file with a shebang is used as if it is an executable in a Unix-like operating system, the program loader mechanism parses the rest of the file's initial line as an interpreter directive. The loader executes the specified interpreter program, passing to it as an argument the path that was initially used when attempting to run the script, so that the program may use the file as...

user3342816

Yes, limited by size iirc

There it was, hah. A few lines above the comment I linked «Note that early versions of Unix had a limit of 16 characters in this interpreter line, so you couldn’t have an arbitrary amount of whitespace there. This restriction no longer applies in modern kernels.»

terdon

That doesn't make sense though. I mean, granted, the extra space would eat an extra character, but if the stuff on wikipedia is right, the very first version to ever support a shebang, explicitly allowed and even suggested (the example had it) a space.

jesse_b

a space isn't an arbitrary amount of space though

Jeff Schaller

@AndrasDeak it seems to me that "new hard drive" and "expired hard drive" are the two times I'd be OK with a magnet being near it.

@terdon probably someone had #! /usr/bin/env /usr/local/bin/oh-my-zsh :)

Andras Deak

3:17 PM

@JeffSchaller yeah, that's fair

Jeff Schaller

@AndrasDeak not trying to polarize the discussion, just thought I'd throw my two bits in ;)

2

jesse_b

Jeff Schaller

whew, stopped short of a table flip

jesse_b

:)

terdon

@JeffSchaller you should be ashamed of yourself. And I snickered, so I should be too.

Jeff Schaller

3:21 PM

@terdon if you find yourself snickering too much, maybe put the magnetized screwdriver down for a bit -- you might be inducing a current in your fillings

Stéphane Chazelas

@user3342816 mostly a matter of taste. See also unix.stackexchange.com/q/351729/22565

terdon

@StéphaneChazelas Apparently, it breaks systemd though.

At least according to this:

8

A: Is space allowed between #! and /bin/bash in shebang?

FYI, systemd fails to parse shebangs with a space. With a service like this: [Service] Type=oneshot ExecStart=/root/foo.sh ... and a shebang like this: #! /bin/bash ... you get an error like this: systemd[32834]: foo.service: Failed at step EXEC spawning /root/foo.sh: Exec format error ...

Stéphane Chazelas

Then, that's just a bug in systemd

terdon

Yep.

jesse_b

Don't most people considering using bug and systemd in one sentence redundant?

Stéphane Chazelas

3:25 PM

I always put a space myself and have for decades.

Jeff Schaller

If there's an existing bug report in systemd, it'd be nice to link it to that answer, just so we have a chance of staying current.

user3342816

@StéphaneChazelas Nice, thanks. And I like it and will try to start to adapt it. But old habits and all that

@terdon From the looks of it v8 had 32 char,
`#define SHSIZE 32` and
`char ux_shell[SHSIZE]; /* #! and name of interpreter */`

Jeff Schaller

couldn't find an existing (open) bug searching their github open issues for "space"; I only scanned the titles, so I either missed it, or it's a closed issue, or it hasn't been reported yet

user3342816

Yes, looked for it as well a while back. Could not find any

(Or guess that might have been 31 char if NULL was included in that)

Stéphane Chazelas

3:40 PM

I can't reproduce the systemd issue on Ubuntu 20.04. The ENOEXEC error message in that answer also suggests the issue is elsewhere. I'd expect a ENOENT error if systemd tried to execute " /bin/bash" instead of "/bin/bash".

Andras Deak

user3342816

3:56 PM

If interested in v8 shell:
https://github.com/Alhadis/Research-Unix-v8/blob/master/v8/usr/sys/h/user.h#L24
https://github.com/Alhadis/Research-Unix-v8/blob/master/v8/usr/sys/sys/sys1.c#L260

Stéphane Chazelas

In case it's not been mentioned already (other than the Q&A I referenced above), one of the best references about Unix shebang is in-ulm.de/~mascheck/various/shebang

user3342816

Ah, nice. It's rather fun, (when having the time), to look et these things.

terdon

4:15 PM

I'm not sure why systemd would want to parse shebangs by itself. Also, I'd expect a "no such file or directory" error if systemd tried to execute " /bin/bash" instead of "/bin/bash". It all suggests systemd is fine but your issue was elsewhere. Maybe you had a UTF-8 BOM at the start of your #! /bin/bash script? — Stéphane Chazelas 19 mins ago

^^ That's the main issue isn't it? That's what I found surprising anyway, why would systemd be reinventing the wheel?

Jeff Schaller

@terdon it has picked up a bit of a reputation for reinventing squares, rectangles, and triangles, so maybe wheels aren't far behind

terdon

Ah, but if it were, then surely the error wouldn't be mentioning kernel calls (EXEC) right?

Jeff Schaller

4:36 PM

I find Stéphane's comment plausible; perhaps there was some other kind of space there (tab/vertical-tab, etc). Untested hypothesis. Too many other problems at the moment to generate & troubleshoot this one :)

user3342816

@terdon I read it as I'm not sure why systemd would want to parse shebangs by itself. = I have not seen any indication that systemd is parsing the shebang, and why would it - but I might be wrong.

Jeff Schaller

I mean, from a simplicity standpoint, why would systemd dig into the script/executable pointed at? Why not just exec() it and be transparent about the results?

user3342816

Believe it is from here: github.com/systemd/systemd/blob/… and tried to backtrack it, but not there (yet) and might not be

Jeff Schaller

heh! not laying any blame at all, but as I went backwards and landed in exec_command_line, the comment FIXME: this doesn't really handle arguments that have spaces and ticks in them caught my eye

(man, that's a lot of work they do in systemd to execute things)

user3342816

Good catch. exec_child with 14 arguments and I almost stopped there.

jesse_b

4:51 PM

my wife and I did exec_child a while back but I think 14 arguments is a bit low

user3342816

lol

There are some structs and pointers in there

Jeff Schaller

children, arguments, instructions, pointers ... what is this, Interpersonal SE?

user3342816

Retrospective introspection

/me is back to Lisey's Story to get some pointers on booleans

Faheem Mitha

7:01 PM

Has anyone tried github.com/gruns/icecream? Looks relatively new. Just read an articla about it which came up in my news feed.

Andras Deak

7:14 PM

@FaheemMitha half the functionality is provided by f-strings in newer python versions

In [320]: d = {'potato': {'pot', 'at', 'o'}}
     ...: print(f'{d["potato"]=}')
d["potato"]={'pot', 'at', 'o'}

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