Top 5 Starter Tips for AIX Whizzes Who Want to Be Linux Legends

I’ve been an AIX administrator since the MicroChannel days — my first AIX was version 3 — and I’m not expecting AIX to vanish any time soon, but lately I’m hearing a lot about Linux, and it’s looking more and more like my AIX skill set is going to need to be extended to include Linux skills, too. In this post I’m going to address five questions that seem to me likely to arise during this process.

1. How do I get Linux installed?
   In the AIX world, I use Network Installation Manager (NIM) for AIX installation, backups and patching, but I have yet to find a true equivalent to NIM in the Linux world. If you are installing Linux to a standalone server, the most common method involves booting from optical media, or a USB-based boot image. In virtualized environments, the install media is usually provided as a virtual device backed by an .iso format disk image file. From that media, you will boot a kernel and device drivers for disk and network devices. If your boot media image includes the source for the entire installation, you just continue to install from media. Otherwise, you can set up what Linux calls an “install server,” which is just a file server used to provide the installation source data over the network via standard protocols such as NFS, FTP or HTTP. If your Intel hardware supports PXE, a true network boot is possible; if your hardware can do bootp+tftp, then you can modify a NIM server to support a more AIX-style network boot for Linux. If you’re installing Linux on a Power server, it is worth looking up the IBM Installation Toolkit for Linux on POWER.
2. How Does Linux Enable Package Management?
   Now that you have Linux installed, you will find that you do not have the AIX installp command; instead you have rpm, and it’s the same rpm that has been included in AIX since AIX5. Most of the major Linux distributions (except Ubuntu, which uses dpkg) use rpm, so your best starting point is doing a man on rpm. You will find that rpm and installp are very similar in functionality; although the syntax is of course different and I find rpm doesn’t handle prerequisites as well as installp. In the open source world, there seem to be more packages to manage and they seem to have more pre– and co– requisites than in the more controlled AIX world.
3. Where is the Object Data Manager (ODM) in Linux?
   Sadly, there is no concept of a centralized, consistent database of configuration data in Linux. Instead, the data AIX stores neatly and consistently organized into ODM object classes is stored in different places and in different forms within Linux. Most can be found in the form of ASCII text flat files located in the /etc filesystem, but there are exceptions. The details vary from distribution to distribution, but to get you started, if you’re looking for device data, try a man on the udev command, and then start looking in the /etc/udev directory. For network configuration, try /etc/sysconfig/network, /etc/sysconfig/network-scripts, or just /etc/network. Like AIX, however, Linux does store user account data in the traditional UNIX files (/etc/passwd and /etc/group), although /etc/security and it’s extended security configuration functionality is not going to be found on your Linux server. To implement password aging and similar controls, Linux uses the Pluggable Authentication Modules (PAM) framework. AIX also implements PAM, but in AIX, the PAM configuration internals are managed under the covers. For Linux, each distribution handles PAM configuration differently, so you’ll need to start researching that.
4. What about Logical Volumes in Linux?
   AIX has always enforced a logical volume management (LVM) methodology — in Linux it’s optional. At installation time, you will be offered the choice between traditional fixed disk partition style or LVM style. If you opt for LVM, there is a single implementation that is used pretty consistently by most distributions. It was originally based on the HP-UX LVM and retains similar command names, so you will see vgdisplay instead of lsvg, and lvcreate in place of mklv, for example. The Wikipedia page gives a good overview. There are also numerous LVM command cheat sheets available on the net.
5. What are the Choices for Shells in Linux?
   After logging in to your new Linux system, you will probably be running the Bourne-Again (bash) shell. Like the AIX default Korn shell (ksh), bash is a superset of the old Bourne shell (bsh), so bsh syntax will all work. The bash is going to look very similar to ksh in most other expects too, except that recalling command history uses the up/down arrow keys, and recalling and editing previous commands is not as functional as it is in ksh. There is a good overview of bash here. Jump to the appendix for a useful table of bash and ksh differences.

This is a starting point, and so of course more questions will pop up as you spend more time at your new Linux console and you will be doing a lot more reading. As you do, keep these three points in mind:

1. Always go to the documentation for your distribution (Red Hat, SuSE, Ubuntu, etc.) first. There are very often different ways to do things in the Linux world, in some cases most distributions will be similar, but not always. Some functions are implemented mostly by the distribution itself independent of the broader Linux world.
2. Always check the date on anything you read. The rate of change in the Linux world is faster than it is in the AIX world. The Linux distributors try to bring some order to it but you still need to make sure that the article you’re reading is relevant to the version of the Linux utility you’re dealing with now.
3. Have Fun!

 
ABOUT THE AUTHOR
Iain Campbell is a Mechanical Engineer. While managing several production automation labs at Ryerson Polytechnic University in Toronto he became distracted by UNIX operating systems. His first experience of AIX was a PC RT used in the lab as a machine cell controller. Iain has been teaching and consulting in AIX and Linux since 1997. He is the author of Reliable Linux (Wiley, New York, 2002), as well as several technical papers and curriculum material. He holds LPI and Novell certifications in Linux administration, and is an IBM certified AIX Specialist.