Understanding AIX Versions

If you're planning to update AIX, the method you use will depend on the version you're currently running. You can find that using the command “oslevel -s” (see Figure 1).

In this article I'll answer a few questions about AIX levels and the oslevel command:

• What's a TL? What's a Service Pack?
• When you run “oslevel -s”, what do all the numbers mean?
• Should you do a migration or a smitty update_all?
• What's the difference between applying and committing updates?

Armed with the answers to these, you can start planning your AIX updates. You can find excellent material on updating your AIX systems in the links below, but before you begin, you'll need to know your starting point.

Unraveling the Numbers

After the release of AIX base levels, such as AIX 5.3, 6.1 or 7.1, IBM regularly releases updates. These are packed together as Technology Levels (TLs) or Service Packs (SPs). The oslevel command reports the base and TL levels you have installed, and the “-s” flag includes service pack information.

If your system is running AIX 5.3 TL 6 or anything later, “oslevel -s” will look something like this: 6100-02-06-0943. Breaking that down, the first four numbers show the AIX base level. In this example, it's 6100, which means we're running AIX 6.1. Next is the Technology Level (TL), followed by the number of the Service Pack (SP). he last four digits show the release date of the Service Pack using the format YYWW (YY for the year, then WW for the week of the year). So, if your “oslevel -s” command reports 6100-02-06-0943, then you know you're on AIX 6.1, running TL 2, with SP 6. The “0943” tells you that Service Pack came out in week 43 of 2009. It’s time to update your system. See Figure 1 for some examples.

AIX TLs and SPs

A TL contains new functions and features. For example, when AIX 7.1 was released, some of its features–such as volume groups exclusively for solid state disks–were included in a new TL for AIX 6.1: TL 6. If you were already running AIX 6.1 but were on an older TL, you'd need to update to TL 6 to take advantage of those features.

A TL gives new features, while a SP contains fixes for problems that are critical and can't wait until the next TL. Service Packs are limited to minimal corrections that don't change the way things work or add any new functionality. (There are also interim fixes, which can't wait for the next SP to be released. Find out more about them in the AIX Service Strategy Details and Best Practices in the links below.)

Migration or Update?

Once you know what AIX version you're starting from, you can determine how to move to a new version. Moving to a new base level of AIX is always a migration. So, if you're going from AIX 6.1 to AIX 7.1 or even from AIX 5.3 to AIX 7.1 (no need to do it in two stages), you're migrating to a new release. On the other hand, if you're moving to a version within the same release, referred to as “patching,” it's an update. That means it can be done using “smitty update_all,” even if it does require a reboot at the end of the update.

You may be updating to a later TL, or just to another Service Pack within the same TL. Installing a new TL is an “all or nothing” operation.

If you're downloading the updates yourself from the IBM Support Portal, you'll need to know whether you're going to a new TL or just updating to a later Service Pack on the same TL. The TL is a separate download and significantly larger than the SP.

Apply or Commit?

When you install updates, you commit them or simply apply them. When fileset updates are committed, the older versions are removed. When fileset updates are only applied, the previous version is saved. Applying them rather than committing them has this advantage: In the unlikely event that you want to roll back those new updates, you can reject them later without having to restore your OS from a backup. Once you're sure you're not going to back out the new filesets, you can commit them, which will save you some disk space.

TL updates can't be rejected in the way Service Packs can so the recommendation is to commit them, rather than apply them.

Figure 2 shows some examples of the different upgrade paths, depending on the version of AIX you're starting from.

Going Backwards Fast

If you find that “oslevel -s” reports that you're on an older TL than you were before, it's probably because new software has been installed at a lower level than the TL. If you encounter this oslevel regression, you need to determine which filesets are the culprits and install their updates as well. You can identify them by running “oslevel -s -l Level” (see Figure 3). The level you enter has to be known to the OS, even if its updates haven't been installed. Run “oslevel -qs” to see the known versions (Figure 4).

After installing a SP, the Reliable Scalable Cluster Technology (RSCT) filesets typically drag your oslevel backwards in this way. The teams that look after RSCT and CSM filesets match the AIX TL schedules, but not the SPs, so you'll have to download the RSCT updates yourself.

Staying Current

It's worthwhile getting familiar with the oslevel command syntax (see links). Understanding your AIX levels will help you stay up-to-date with important new features, which in turn will protect your systems by including fixes for critical problems.

Links

AIX Technology Level Update Strategies
http://www.ibm.com/developerworks/aix/library/au-aixtlupdate/index.html
http://www14.software.ibm.com/webapp/set2/sas/f/best/home.html

AIX Service and Support Best Practices for Power Systems
http://www14.software.ibm.com/webapp/set2/sas/f/best/home.html

AIX 6.1 Installation and Migration
http://publib.boulder.ibm.com/infocenter/aix/v6r1/topic/com.ibm.aix.install/doc/insgdrf/bos_migration_installation.htm

AIX oslevel Command Documentation
http://publib.boulder.ibm.com/infocenter/aix/v7r1/index.jsp?topic=/com.ibm.aix.cmds/doc/aixcmds4/oslevel.htm