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#1 2018-10-09 06:12:19

StevenC21
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Registered: 2018-09-17
Posts: 59

Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

Hi. I'm afraid I just don't understand the idea. Isn't pacman -Sy just the same as, say, apt update? Why is it dangerous to do that on pacman but not many other package managers?

On a side note, is it safe to say "No" on changes when running pacman -Syu, or is that just like pacman -Sy?

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#2 2018-10-09 06:14:41

Scimmia
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Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

By itself it's not bad. It's the fact that it leads directly to partial updates that's the problem.

It's not a pacman issue, it's an Arch issue. Arch doesn't keep old libs around like most distros.

Stopping an update is the same as -Sy. You have to finish the update before you can do anything else.

Last edited by Scimmia (2018-10-09 06:15:11)

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#3 2018-10-09 06:18:21

jasonwryan
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Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

StevenC21 wrote:

Beyond it being a "partial upgrade"

That is precisely the issue. If you -Sy and then do not complete the upgrade, and later pacman -S $package, you run the risk of a partial update.

And saying "No" is exactly the same, you have run the -Sy and told pacman to forego the -u.

This was exacerbated a while back when several "helpful" install scripts included this as their default. People would then show up here whining about breakages.


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#4 2018-10-09 06:22:17

fukawi2
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From: .vic.au
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Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

1. You install your system.
2. Arch moves on, packages are updated, things change.
3. You use pacman -S to install the latest cool package you want.
4. Step 3 fails because your pacman database is out-of-date and the version of the package you want isn't in the repo anymore.
5. You run pacman -Sy to install the latest cool package you want.
6. pacman installs that package, and installs/upgrades it's dependencies.
7. Another package that you installed in step 1 depends on one of the same packages that your new program uses, but you just upgraded that package because it's a dependency of the new program. Old program is now broken.

Best case scenario, you can't open a minor program until you upgrade the rest of your packages. Worst case, you break a system level package like systemd without realizing it until you reboot and your system won't boot.

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#5 2018-10-09 08:34:22

Mr.Elendig
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Registered: 2004-11-07
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Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

https://gist.github.com/vodik/5660494  (also see the links on that page)

Last edited by Mr.Elendig (2018-10-09 08:34:36)


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#6 2018-10-09 09:55:32

madsravn
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Registered: 2013-05-12
Posts: 22

Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

I normally just do pacman -Syyu. Is that also bad?

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#7 2018-10-09 10:15:28

olive
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From: Belgium
Registered: 2008-06-22
Posts: 1,490

Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

@madsravn. No, pacman -Syyu is fine. The double "y" option force pacman to update the database even if it is not newer than the one you usually use. A single "y" option only update the database if it is newer than the one you usually use, which is normally sufficient.

The double "y" option may be needed in special cases. For example, if you use the Arch Linux Rollback Machine (https://wiki.archlinux.org/index.php/Arch_Linux_Archive) to point your mirror list to an older version of Archlinux, you can fully downgrade your distribution to an older version with pacman -Syyuu: double "y" to force pacman to "update" to the older database and double "u" to force pacman to "update" packages to an older version (aka. downgrade them).

I also sometimes use the double "y" if I change the mirror I use. So I can be sure to have the list of the mirror I have pointed to no matter what.

Last edited by olive (2018-10-09 10:26:58)

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#8 2018-10-09 14:00:58

Trilby
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Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

olive wrote:

@madsravn. No, pacman -Syyu is fine.

"Fine" is quite an overstatement.  This will do no harm to your system, but it definitely should not be your standard means of upgrading.  It is almost entirely pointless for your system, but it takes a little longer for no reason.  More importantly, though, it is essentially an abuse of the mirrors and if used regularly by many, a burden to other archers.

Do not use `pacman -Syyu` as a standard practice.  Use it when there is a specific condition for which you know you need to force a database syncronization.


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#9 2018-10-09 14:14:25

StevenC21
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Registered: 2018-09-17
Posts: 59

Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

Thanks guys, however, I have one relevant question.

Why doesn't Arch keep around old libraries like other distros? That seems like a rather serious issue.

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#10 2018-10-09 14:28:16

Trilby
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Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

Because arch is a rolling release, new software (libraries) are added to the repos as soon as they are available.  Debian, in contrast, is a point release.  Debian also doesn't keep around old libraries as they add newer ones - they *only* keep the old ones and don't add the new ones until the next release at which point the whole system must be upgraded (or reinstalled).

(There are exceptions where point releases do package multiple versions of some libs - but so too does arch.  The above still holds as the general difference between point and rolling releases.)

Last edited by Trilby (2018-10-09 14:29:39)


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#11 2018-10-09 15:08:36

StevenC21
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Registered: 2018-09-17
Posts: 59

Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

Yeah but Debian still has library updates? I am 99% sure that I've updated libraries on Debian systems, without a version upgrade.

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#12 2018-10-09 15:40:25

olive
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From: Belgium
Registered: 2008-06-22
Posts: 1,490

Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

StevenC21 wrote:

Yeah but Debian still has library updates? I am 99% sure that I've updated libraries on Debian systems, without a version upgrade.

Arch is not just another Debian. Debian has 3 branches (stable, testing, unstable) that follow some conventions that are not relevant to this forum. Any decision is a trade off with advantages and inconvenients.

Anyway, in general, you can't update libraries without updating the software that depends on them. From what I know, Debian keep dependencies between specific versions of software with specific version of libraries in a way that is more elaborate than Arch. Arch is just a rolling release that is supposed to be fully updated (partial upgrade are not supported). That offer the advantage to be much more simple and manageable.

Last edited by olive (2018-10-09 15:46:04)

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#13 2018-10-09 17:24:34

Slithery
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From: Norfolk, UK
Registered: 2013-12-01
Posts: 5,776

Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

StevenC21 wrote:

Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

That question is nonsensical, the reason why it is so bad is entirely because it results in a partial upgrade situation.

Last edited by Slithery (2018-10-09 17:25:23)


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#14 2018-10-09 20:25:06

Trilby
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Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

StevenC21 wrote:

Yeah but Debian still has library updates?

Does it?  Do you have examples?  They back port security patches, but they are not shipping new versions until there is a new release of the entire distro.


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#15 2018-10-10 00:23:50

fukawi2
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From: .vic.au
Registered: 2007-09-28
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Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

StevenC21 wrote:

Yeah but Debian still has library updates?

Updates to the same version are not the same as version upgrades.

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#16 2018-10-10 00:46:28

Trilby
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Registered: 2011-11-29
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Re: Why is pacman -Sy bad? (Beyond it being a "partial upgrade")

To complete the comparison, `pacman -Sy $package` would be basically like running Debian Wheezy for some time, then switching the urls in /etc/apt/sources.list to point to repos for Stretch then installing/upgrading a single package.  It would result in (potentially severe) breakage.  `pacman -Sy` is not directly comparable to apt-update.

Last edited by Trilby (2018-10-10 00:47:57)


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