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Debian's apt-get update fetches and updates the package index. Because I'm used to this way of doing things, I was surprised to find that yum update does all that and upgrades the system. This made me curious of how to update the package index without installing anything.

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The check-update command will refresh the package index and check for available updates:

yum check-update
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    This command allows you to determine whether any updates are available for your installed packages. yum returns a list of all package updates from all repositories if any are available. apt-get update refresh index files but yum check-update does not. – SuB Apr 15 '17 at 10:56
  • This doesn't work if yum has already been run recently, see some of the other answers for alternatives... – rogerdpack Jun 21 '17 at 21:59
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While yum check-update will check updates for installed packages, if it needs to be refreshed, so will most other commands.

The command that's strictly the equivalent of apt-get update is yum makecache ... however it's generally not recommended to run that directly, in yum.

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    I don't understand the first sentence. Can you rephrase maybe? – tshepang Feb 8 '11 at 18:06
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    It means that other yum commands, e.g. yum upgrade will automatically run yum check-update if necessary. In other words, yum upgrade is basically the same as apt-get update; apt-get upgrade. – Mikel Feb 8 '11 at 21:02
  • Thank you! yum check-update did not helps me against 404 errors. But yum makecache helps! HUGE thanks! – socketpair Jun 6 '14 at 11:41
  • The original was about automatically updating repodata to present the latest information (something apt-get doesn't do, or at least didn't in 2011). After the edit it's now kind of weirdly meaningless :(. – James Antill Apr 19 '17 at 16:23
  • Why isn't it recommended to run yum makecache? It's listed in the man page and seems to work like apt-get update... also note that yum check-update doesn't always perform a refresh, see other answers, FWIW :) – rogerdpack Jun 7 at 16:23
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Unfortunately yum check-update by default doesn't pull down changes from remote repositories until yum.conf's metadata_expire parameter has elapsed (default 90m). Apparently its purpose is "know if your machine had any updates that needed to be applied without running it interactively" so basically it's "check if any packages are update-able" not "refresh the list of packages that I could update to" as you'd expect.

So if you run yum check-update and get this:

$ sudo yum check-update
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile

packagename      version     repo

This means that check-update is not performing an update, like apt-get update does.

You can see how long it will take before doing the "auto refresh" that all commands do underneath, by running this: yum repolist enabled -v

Work around:

use yum clean expire-cache (or yum clean all) first, then any future yum commands will auto-refresh the cache "when run." . Because future yum commands refresh the cache, this is in practice the same as apt-get update.

Or change the metadata_expire parameter of yum.conf to less than the default 90min, I guess.

Or run yum makecache (from the other answers) which seems to remove the cache and pull down fresh copies right then. But it seems to take longer than clean all (?) FWIW.

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    Not sure why this answer is languishing at the bottom. This seems like the obvious and simple answer. – cbmanica Aug 27 '18 at 22:46
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That is the command to update the local cache, hence

yum makecache

seems to be the command you are looking for, according to Working with Yum cache.

Normally you shouldn't need to run this command directly as yum already checks and refreshes metadata based on metadata_expire value in yum.conf, default being 6 hours.

However, there might be at least one use case, which is in an Ansible playbook, as you don't have a way in an Ansible playbook to only update the cache without installing any packages (See Ansible issues 33461 and 40068, which seems to be fixed in version 2.8, 46183). Ansible yum module requires a package name for 'update_cache: yes' option to have an effect. So, as an alternative 'command: yum makecache' can be used in the playbook.

dnf also has a makecache command, although it is also possible to force metadata synchronization with the --refresh switch.

  • This existing answer already mentions yum makecache; perhaps you could expand your answer to make it more useful, for example by explaining why yum makecache isn’t recommended, or what the dnf equivalent is. – Stephen Kitt May 3 at 13:39

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