Wednesday, December 14, 2011

New features of yum in RHEL-6.1 now that it's released

A few things you might not know about RHEL-6.1+ yum

  • Search is more user friendly

    As we maintain yum we are always looking for the "minor" changes that can make a big difference to the user, and this is probably one of the biggest minor changes. As of late RHEL-5 and RHEL-6.0 "yum search" was great for finding obscure things that you knew something about but with 6.1 we've hopefully made it useful for finding the "everyday" packages you can't remember the exact name of. We did this by excluding a lot of the "extra" hits, when you get a large search result. For instance "yum search kvm manager" is pretty useless in RHEL-6.0, but in RHEL-6.1 you should find what you want very quickly.
    Example commands:

    yum search kvm manager
    yum search python url
  • The updateinfo command The "yum-security" or "yum-plugin-security" package has been around since early RHEL-5, but the RHEL-6.1 update has introduced the "updateinfo" command to make things a little easier to use, and you can now easily view installed security errata (to more easily make sure you are secure). We've also added a few new pieces of data to the RHEL updateinfo data. Probably the most significant is that as well as errata being marked "security" or not they are now tagged with their "severity". So you can automatically apply only "critical" security updates, for example.
Example commands:

yum updateinfo list security all
yum update-minimal --sec-severity=critical

The versionlock command As with the previous point we've had "yum-plugin-version" for a long time, but now we've made it easier to use and put all it's functions under a single "versionlock" sub-command. You can now also "exclude" specific versions you don't want, instead of locking to known good specific ones you had tested.
Example commands:

# Lock to the version of yum currently installed.
yum versionlock add yum
# Opposite, disallow versions of yum currently available:
yum versionlock exclude yum
yum versionlock list
yum versionlock delete yum\*
yum versionlock clear
# This will show how many "excluded" packages are in each repo.
yum repolist -x .

Manage your own .repo variables This is actually available in RHEL-6.0, but given that almost nobody knows about it I thought I'd share it here. You can put files in "/etc/yum/vars" and then use the names of those files are variables in any yum configuration, just like $basearch or $releasever. There is also a special $uuid variable, so you can track individual machines if you want to.

yum has it's own DB
Again, this something that was there in RHEL-6.0 but has improved (and is likely to improve more over time). The most noticeable addition is that we now store the "installed_by" and "changed_by" attributes, this could be worked out from "yum history" before, but now it's easily available directly from the installed package.
  • Example commands:
    yumdb info yum 
    yumdb set installonly keep kernel-2.6.32-71.7.1.el6 
    yumdb sync
  • Additional data in "yum history" Again, this something that was there in RHEL-6.0 but has improved (and is likely to improve more over time). The most noticeable additions are that we now store the command line and we store a "transaction file" that you can use on other machines.
    Example commands:

    yum history
    yum history pkgs yum
    yum history summary
    yum history undo last
    yum history addon-info 1    config-main
    yum history addon-info last saved_tx
    "yum install" is now fully kickstart compatible As of RHEL-6.0 there was one thing you could do in a kickstart package list that you couldn't do in "yum install" and that was to "remove" packages with "-package". As of the RHEL-6.1 yum you can do that, and we also added that functionality to upgrade/downgrade/remove. Apart from anything else, this should make it very easy to turn the kickstart package list into "yum shell" files (which can even be run in kickstart's %post).
    Example commands:

     yum install 'config(postfix) >= 2.7.0'
     yum install MTA
     yum install '/usr/kerberos/sbin/*'
     yum -- install @books -javanotes
    Easier to change yum configuration We tended to get a lot of feature requests for a plugin to add a command line option so the user could change a single yum.conf variable, and we had to evaluate those requests for general distribution based on how much we thought all users would want/need them. With the RHEL-6.1 yum we created the --setopt so that any option can be changed easily, without having to create a specific bit of code. There were also some updates to the yum-config-manager command.
    Example commands:
    yum --setopt=alwaysprompt=false upgrade yum yum-config-manager yum-config-manager --enable myrepo yum-config-manager --add-repo
    Working towards managing 10 machines easily yum is the best way to manage a single machine, but it isn't quite as good at managing 10 identical machines. While the RHEL-6.1 yum still isn't great at this, we've made a few improvements that should help significantly. The biggest is probably the "load-ts" command, and the infrastructure around it, which allows you to easily create a transaction on one machine, test it, and then "deploy" it to a number of other machines. This is done with checking on the yum side that the machines started from the same place (via. rpmdb versions), so that you know you are doing the same operation.
    Also worth noting is that we have added a plugin hook to the "package verify" operation, allowing things like "puppet" to hook into the verification process. A prototype of what that should allow those kinds of tools to do was written by Seth Vidal here.
    Example commands:

    # Find the current rpmdb version for this machine (available in RHEL-6.0)
    yum version nogroups
    # Completely re-image a machine, or dump it's "package image"
    # This is the easiest way to get a transaction file without modifying the rpmdb
    echo | yum update blah
    ls ${TMPDIR:-/tmp}/yum_save_tx-* | sort | tail -1
    # You can now load a transaction and/or see the previous transaction from the history
    yum load-ts /tmp/yum_save_tx-2011-01-17-01-00ToIFXK.yumtx
    yum -q history addon-info last saved_tx > my-yum-saved-tx.yumtx