Traversing Linux is usually a shock to most AIX administrators. While Linux is in many ways just another variant of UNIX®, in other ways it is a very different beast. For UNIX administrators who have moved to AIX from Solaris or HP-UX, you'll understand what I'm talking about. If UNIX is not always UNIX (look at the differences between Solaris, HP-UX, and AIX), how more-so will Linux not be AIX. Futhermore, with Linux, you won't have smitty to fall back on.
Generally speaking, it is easier for Solaris administrators to make the transition to Linux than AIX administrators because there are more files that need editing on both Solaris and Linux. Both Solaris and Linux are also more command-line driven than AIX. One advantage you will have as an AIX administrator is that the hardware is the same, so if you're familiar with Virtualization using AIX on System p, you'll find a lot of similarities. If you were using Red Hat Enterprise Linux 5 (RHEL5) on an x86 box, you would be using Red Hat's Xen-based virtualization process (see Resources for more information on Xen). On System p, you'll be using the same PowerVM™ that you are using on AIX. While virtualization is outside the scope of this article, this is an important concept to understand and a big plus for you (see the Resources section for some good articles on the topic).
AIX administrators know that while their environment has a rich set of command-line tools, many of the commands will not hold without a reboot, which is one of the primary reasons for their reliance on smit. With Linux, there are many more files that have to be edited manually and, generally speaking, more commands need to be run to complete the same tasks. Red Hat also has a front end, which is a combination of various system-config-* commands, including: system-config-display, system-config-printer, system-config-network, system-config-network, systems-config-packages, systems-config-authentication, system-config-users, and system-config-lvm. Some of them will work in text mode, and some of them will require you to get your X environment working. I strongly suggest you do so, because the GUI tools on RHEL5 add a lot of value in addition to being well designed.
While RHEL5 has a feature-rich GUI environment that you may learn to like, it is not as productive as smitty. With AIX you can use smit or smitty; you don't always have the option of going text or GUI with Linux. With Linux you also won't have the Object Data Manager (ODM), which AIX utilizes for managing devices and configuration files. With Linux, you'll rely on editing text-based files. For the purposes of this article, I'll use AIX V6.1 - TL 0 and SP2 and Red Hat Enterprise Linux Server release 5.1, with kernel Linux version 2.6.18-53.el5. Both are running on an IBM System p 570 with one CPU and 2GB RAM.
Next, you will see the tools used to get information about the system.
As an AIX administrator, you're probably used to running prtconf and a half-dozen or so lscfg or lsattr commands. With RHEL5, you go to /proc and cat files for this data. In AIX /proc, these files are are also virtual files like in Linux, showing hardware and some settings, for example, using interprocess communications. It is used more or less for the set of 'p' commands for retrieving useful data. For example, Listing 1 shows the AIX output of one such command, pstat.
Listing 1. Output for pstat command
lpar23ml16fd_pub[/] > pstat -a PROC TABLE: SLT ST PID PPID PGRP UID EUID TCNT NAME 0 a 0 0 0 0 0 1 swapper FLAGS:swapped_inno_swapfixed_prikproc 64bit
When you look at the directory structure for /proc on RHEL5, you'll see Listing 2.
Listing 2. Directory structure for /proc on RHEL5
root@172_29_140_173 proc]# ls 1 139 1551 2712 2955 6 driver kmsg self 10 142 1574 2713 2956 7 execdomains loadavg slabinfo 1015 143 170 2745 2989 8 fb locks stat 1016 144 1793 2746 2990 9 filesystems mdstat swaps 1047 1447 1810 2814 3 asound fs meminfo sys 1170 145 1814 2816 3031 buddyinfo ide misc sysrq-trigger 1174 1450 2 2817 350 bus interrupts modules sysvipc 1178 1462 205 284 378 cmdline iomem mounts tty 1182 1486 206 2850 379 cpuinfo ioports net uptime 1183 149 207 2852 380 crypto irq partitions version 1187 1507 208 2853 4 devices kallsyms ppc64 vmstat 1191 151 209 2888 403 device-tree kcore rtas zoneinfo 1201 1549 210 2892 432 diskstats keys schedstat 1202 1550 2710 2953 5 dma key-users scsi [root@172_29_140_173 proc]#
With AIX, you won't see all these text files to glean information from. On the RHEL5 partition, cat a file to get some information about our system. Listing 3 shows cpuinfo.
Listing 3. Using cpuinfo to get system information
cd /proc[root@172_29_140_173 /]# cd /proc[root@172_29_140_173 proc]# more cpuinfo processor : 0 cpu : POWER5 (gr) clock : 1654.344000MHz revision : 2.1 (pvr 003a 0201) processor : 1 cpu : POWER5 (gr) clock : 1654.344000MHz revision : 2.1 (pvr 003a 0201) timebase : 207050000 platform : pSeries machine : CHRP IBM,9117-570 [root@172_29_140_173 proc]# \
Other files worth 'cating' include meminfo, partitions, version, and filesystems. Another useful Linux command is dmesg, as shown in Listing 4.
Listing 4. Using dmesg
root@172_29_140_173 ~]# dmesg | more Using pSeries machine description Page orders: linear mapping = 24, virtual = 12, io = 12 Found initrd at 0xc000000002400000:0xc000000002679400 Partition configured for 2 cpus. Starting Linux PPC64 #1 SMP Wed Oct 10 16:38:58 EDT 2007 ----------------------------------------------------- ppc64_pft_size = 0x19 physicalMemorySize = 0x80000000 ppc64_caches.dcache_line_size = 0x80 ppc64_caches.icache_line_size = 0x80 htab_address = 0x0000000000000000 htab_hash_mask = 0x3ffff ----------------------------------------------------- Linux version 2.6.18-53.el5 (firstname.lastname@example.org) (gcc version 4.1.2 20070626 (Red Hat 4.1.2-14)) #1 SMP Wed Oct 10 16:38:58 EDT 2007
This command is similar to prtconf and is also used to log errors, similar to errpt. As you can see, there is also POWER specific information that is gleaned from the dmesg command.
Next, you'll see the tools needed for filesystem and Logical Volume Management (LVM).
Filesystem and disk management
The default JFS filesystem for AIX is JFS2 and for RHEL5 it is ext3, which is an enhanced version of ext2. A new RHEL5 command is resize2fs (replacing ext2onliner), which allows one to enlarge or shrink mounted filesystems on the fly. This is supported through the Linux 2.6 kernel. It's important to note that this command does not manipulate the size of partitions, so prior to enlarging filesystem you must ensure that the underlying partition is big enough to support this. This is a similar concept to AIX where you must make sure that your volume group is large enough to support this kind of operation.
This is something else you will need to get used to. As you are aware, with AIX everything is already managed outside of the box with LVM. With Linux you'll need to work with partitions before you can configure LVM. Everything is just much more tightly integrated within AIX.
To return to RHEL5, partition information can be gleaned using fdisk or parted (see Listing 5). I perfer parted, as it is simpler to use.
Listing 5. Using parted to get partition information
[root@172_29_140_173 sbin]# parted GNU Parted 1.8.1 Using /dev/sda Welcome to GNU Parted! Type 'help' to view a list of commands. (parted) print Model: AIX VDASD (scsi) Disk /dev/sda: 21.5GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 32.3kB 8225kB 8193kB primary boot, prep 2 8225kB 115MB 107MB primary ext3 3 115MB 19.3GB 19.2GB primary ext3 4 19.3GB 21.4GB 2089MB primary linux-swap
Creating Linux filesystems can also be performed using mkfs, which is a front end to the mke2fs tool. Listing 6 shows how to create an ext3 filesystem.
Listing 6. Using mkfs to create an ext3 filesystem
[root@172_29_140_173 sbin]# mkfs.ext3 /dev/sda1 mke2fs 1.39 (29-May-2006) Filesystem label= OS type: Linux Block size=1024 (log=0) Fragment size=1024 (log=0) 2000 inodes, 8000 blocks 400 blocks (5.00%) reserved for the super user First data block=1 Maximum filesystem blocks=8388608 1 block group 8192 blocks per group, 8192 fragments per group 2000 inodes per group Writing inode tables: done Creating journal (1024 blocks): done Writing superblocks and filesystem accounting information: done
Now try to resize the filesystem using the resize2fs utility referenced earlier (see Listing 7).
Listing 7. Attempting to resize the filesystem
root@172_29_140_173 sbin]# resize2fs /dev/sda1 1G resize2fs 1.39 (29-May-2006) The containing partition (or device) is only 8001 (1k) blocks. You requested a new size of 1048576 blocks.
As shown in Listing 7, it did not work because of the partition issue discussed earlier. Remember, your partition size must be able to support the new FS, similar to how with AIX you must have enough space on your volume group to increase space. Note that similar to AIX, you can now shrink an ext3 filesystem.
Figure 1 is a view of the RHEL5 LVM using the system-config-lvm tool.
Figure 1. RHEL5 LVM using the system-config-lvm tool
With Linux, before you can use LVM, you will need to initialize your partitions to support LVM. When that process is completed, the partition will be classified as an unallocated physical volume. From here, you can create a volume group, add to an existing volume group, or remove a volume from the LVM altogether. Command-line tools available for you include lvcreate, lvremove, and lvextend.
Packages and software
This section discusses the tools needed for software installation and overall package management.
Sorry AIX brethren, but you'll have to learn to live without lslpp. With Linux you have RPMs. Many AIX administrators already know these commands because AIX has had RPM capabilities since 5L.
Now query our systems for packages using the
-qa flag, as shown in Listing
Listing 8. Querying our systems for packages using the
root@172_29_140_173 sbin]# rpm -qa |more popt-1.10.2-47.el5 pcre-6.6-1.1 libICE-1.0.1-2.1 libattr-2.4.32-1.1 libxslt-1.1.17-2 libgfortran-4.1.2-14.el5 bc-1.06-21
To install packages, use the
-i flag to upgrade the
-U flag. RPM
is very powerful, but it isn't the simplest tool to learn. Make sure you take the time to
learn this tool or use more sophisticated and user-friendly front ends that may be
available to you. One such front end is the Yellow Dog Updated Modified (YUM). It is an
interactive, automated update program that can be used for maintaining systems using RPM.
RHEL4 used up2date package manager and RHEL5 uses YUM (see Resources for more information on YUM).
To activate daily YUM updates on a system using the chkconfig command (which I'll discuss
in the next section), you can use this command:
[root@172_29_140_173 sbin]# /sbin/chkconfig --level 345 yum on; /sbin/service yum start.
Next, you'll learn about the tools needed for network configuration.
To support networking with RHEL5, you can either edit files, use the command line, use the network administration utility system-config-network, or use the setup command. Here you'll use setup, which is really meant for initially configuring your systems. Once you launch setup, you will see the Choose a Tool dialog, which contains different configuration options including Authentication, Firewall, Keyboard, Network, System services, Timezone, and X configuration.
Select Network configuration from this dialog to bring up the TCP/IP configuration dialog shown in Figure 2.
Figure 2. Configure TCP/IP dialog
From here, you can set up the Network Interface Controller (NIC) with the appropriate IP information, address, netmask, gateway, and nameserver. With RHEL5 networking, you also have the standard UNIX commands you should already be accustomed to, such as route, the netstat commands, and other utilities like ping and traceroute.
Next, you'll learn about the tools needed for service management.
AIX has the System Resource Controller and you make use of commands such as lssrc and startsrc. RHELhas various utilities including the system-config-services command. You can also do some of the work with the setup command, as referenced earlier. Setup actually allows one to specify which services you want to start and to bring up on boot. Other methods are to use the service command and the chkconfig command.
Use the service command to get a status, as shown in Listing 9.
Listing 9. Using the service command
root@172_29_140_173 sbin]# service --status-all amd is stopped anacron is stopped arpwatch is stopped atd is stopped auditd is stopped automount is stopped
Alternatively, you can use the chkconfig service, which is also very handy with scripts (see Listing 10).
Listing 10. Using the chkconfig service
root@172_29_140_173 sbin]# chkconfig --list NetworkManager 0:off 1:off 2:off 3:off 4:off 5:off 6:off NetworkManagerDispatcher 0:off 1:off 2:off 3:off 4:off 5:off 6:off amd 0:off 1:off 2:off 3:off 4:off 5:off 6:off anacron 0:off 1:off 2:off 3:off 4:off 5:off 6:off
The text files that you can edit include /etc/sysconfig/network-scripts, /etc/resolv.conf, and /etc/hosts.
Now look at a table (see Table 1) that compares some of the most popular commands for AIX and RHEL5.
Table 1. Comparing commands on AIX and RHEL5
|Adding users||mkuser, chuser, lsuser||useradd, usermod|
|Adding filesystems||crfs, chfs||mke2fs, mkfs|
|Maintaining logical volumens||mklv, chlv||lvcreate, lvextend, lvdisplay|
|Adding swap space||lsps -a||swapon -s|
|Managing processes||Systems resourced controller (SRC) commands||chkconfig, services, setup|
|System-info||prtconf more||/proc/cpuinfo, mem|
|Kernal paramerts||vmo, ioo, schedo, no||more /etc/sysctl.conf|
|Virtualization||PowerVM||PowerVM - only on System p (Xen available in x86 versions)|
|Oslevel||oslevel -s||more redhat-release|
Having worked with many administrators who have transitioned to Linux from AIX, the general rule is that it is a lot easier to transition from Solaris to Linux and then AIX to Linux because Linux is more text driven and also because the text files themselves have more similar naming conventions. As an AIX administrator, you should already be very familiar with many command-line tools, which will be helpful when making the transition. While you won't find smit, you'll find enough GUI's out there to increase your comfort level.
Even though Linux has come a long way, it is simply not as mature of a product as AIX and there will be more you will need to do to document and keep your systems up and running. The good news is that today you can also sign up with IBM for a support contract with Linux, which even the most senior of AIX administrators continue to do on AIX. Linux continues to make huge inroads in terms of its reliability and scalability, particularly on the IBM System p platform. The IBM commitment to Linux is second to none in the industry, which is a huge selling point for businesses that want to start moving towards Linux.
I strongly suggest that AIX administrators receive appropriate training to ease the transition process. Don't be afraid to experiment and make mistakes. You will find that with Linux there are many more ways to accomplish the same task as with AIX. Just make sure you don't experiment in production. I always recommend that AIX administrators create a sandbox Linux partition on their System p server so that they can get a head start when the business wants to put something on the platform.
- The AIX and UNIX developerWorks zone provides a wealth of information relating to all aspects of AIX systems administration.
- PowerVM Virtualization on IBM System p: Introduction and Configuration Fourth Edition: Read this Redbook for an introduction to PowerVM virtualization technologies on IBM System p servers.
- "An Introduction to Virtualization" by Amit Singh is a great introduction to virtualization and the varying implementations that are available. In addition to Linux, this article also covers other operating system virtualization (Windows, Solaris) and other means of virtualization (such as network stack virtualization)
- Xen is an open source virtual machine monitor (hypervisor) developed by XenSource. Xen uses what is known as paravirtualization, which typically requires guest operating system modification, but Xen can take advantage of virtualization CPUs to support unmodified guest operating systems.
- Learn about the Yellow Dog Updater Modified (YUM) program in the article Using YUM in RHEL5 for RPM systems.
- Optimizing AIX 5L performance: Tuning network performance, Part 1 (Ken Milberg, developerWorks, November 2007): Read Part 1 of a three-part series on AIX networking, which focuses on the challenges of optimizing network performance.
- For a three-part series on memory tuning on AIX, see Optimizing AIX 5L performance: Tuning your memory settings, Part 1 (Ken Milberg, developerWorks, June 2007).
- For a comprehensive guide about the performance monitoring and tuning tools that are provided with AIX 5L Version 5.3, see the IBM Redbook AIX 5L Practical Performance Tools and Tuning Guide.
- The AIX 5L Differences Guide Version 5.3 Edition (developerWorks, December 2004) redbook focuses on the differences introduced in AIX 5L Version 5.3 when compared to AIX 5L Version 5.2.
- Visit the developerWorks Open source zone for extensive how-to information, tools, and project updates to help you develop with open source technologies, and use them with IBM products.
- developerWorks technical events and webcasts: Stay current with developerWorks technical events and webcasts.
- Podcasts: Tune in and catch up with IBM technical experts.
- Participate in the AIX and UNIX Forums.