INTERVIEW QUESTIONS AND ANSWERS FOR AIX

— ny_wk

These AIX interview questions and answers cover the topics interviewers actually probe for a power systems administrator role: the Logical Volume Manager (LVM), JFS2 file systems, networking, error logging, the Object Data Manager (ODM), the kernel, software installation, and backup and recovery. Every command and figure below has been verified and corrected so you can quote them with confidence in a real interview on IBM AIX running on POWER hardware.

Rather than a flat list of trivia, the questions are grouped by domain so you understand the why behind each answer. Where the commonly circulated answer is wrong, the correct value is given and flagged. Use this as a structured revision sheet before your AIX system administration screen.

LVM and Storage: Core AIX Interview Questions

The Logical Volume Manager is the heart of AIX storage and the area most heavily tested. A solid grasp of volume groups (VG), physical volumes (PV), logical volumes (LV), and physical partitions (PP) separates a confident AIX administrator from a memorised one.

What are the volume group types and their limits?

AIX has three VG types, distinguished by how many physical volumes and logical volumes they support. Run lsvg vgname and read the MAX PVs field to identify the type.

To convert in place: chvg -B vgname promotes a normal VG to big, and chvg -G vgname promotes a normal or big VG to scalable.

How do I create a volume group and set the partition size?

Use mkvg. The -s flag sets the physical partition (PP) size in megabytes, and it must be a power of two (1, 2, 4, 8, … up to 1024 MB):

1. Confirm the disk is free: lspv
2. Create the VG: mkvg -y datavg -s 128 hdisk1
3. Verify: lsvg datavg

Correction worth knowing: the historical default PP size in older AIX was 4 MB, not 64 MB. Modern AIX auto-selects the smallest PP size that keeps a PV within its partition limit (1016 PPs per PV for normal/big, 2040 for scalable). Always set -s explicitly for predictability.

How do I create, extend, and inspect a logical volume?

• Create an LV of 1 partition: mklv -y datalv -t jfs2 datavg 1
• Extend by 3 logical partitions: extendlv lv05 3
• List details of one LV: lslv lv1
• List all LVs in a VG (e.g. rootvg): lsvg -l rootvg
• Copy an LV between VGs: cplv -v newvg sourcelv

How do I turn a fresh disk into a usable file system?

Three commands take you from raw disk to a mounted JFS2 file system:

1. mkvg -y datavg -s 128 hdisk1 — build the volume group
2. mklv -y datalv -t jfs2 datavg 1 — carve out a logical volume
3. crfs -v jfs2 -d datalv -g datavg -a size=10M -m /fs1 — lay a file system on it and set the mount point

Then mount /fs1 and confirm with df -g /fs1.

What is the difference between JFS and JFS2?

JFS2 is the modern, default journaled file system in AIX and should be your answer for any new build. The classic JFS is legacy.

Use JFS2 for everything new — it scales further, allocates inodes dynamically, and supports features such as snapshots and online shrink.

How do I find and change the inode number and LTG size?

• Inode number of a file: ls -li or istat /etc/passwd
• Logical Track Group (LTG) size: lsvg vgname shows the VG LTG; lquerypv -M hdiskname shows the max supported value
• Change LTG: take the disk offline, raise its max transfer, bring it back:

1. rmdev -l hdiskX
2. chdev -l hdiskX -a max_transfer=0x80000
3. mkdev -l hdiskX

On current AIX the LTG is usually negotiated automatically (variable LTG), so manual tuning is rarely needed.

Mirroring, Disk Replacement and Cloning: AIX LVM Interview Questions

Resilience tasks are a favourite of senior interviewers because they reveal whether you understand the boot logical volume and quorum, not just typed commands.

How do I mirror a logical volume or a whole VG?

For a single LV, add copies and resynchronise:

1. mklvcopy LVname 2 hdisk2 — make 2 copies of the LV
2. syncvg -v VGname — synchronise the new copy

To mirror rootvg for boot resilience, the order matters because you must also rebuild the boot image and the boot list:

1. Check sizes match: bootinfo -s hdisk2 and lsvg -p rootvg
2. Add the second disk: extendvg rootvg hdisk2
3. Mirror with background sync: mirrorvg -S rootvg hdisk2
4. Write a boot image to both disks: bosboot -ad /dev/hdisk2 then bosboot -ad /dev/hdisk1
5. Update the boot list: bootlist -m normal hdisk1 hdisk2
6. Verify: bootlist -m normal -o

How do I unmirror rootvg when a disk fails?

1. Check the current boot list: bootlist -m normal -o
2. Clear the boot record on the failed disk: chpv -c hdisk2
3. Unmirror: unmirrorvg rootvg hdisk2
4. Remove the disk from the VG: reducevg rootvg hdisk2
5. Confirm and reset the boot list: lsvg -p rootvg, then bootlist -m normal hdisk1

How do I replace or clone a disk?

Replace a failing disk by migrating its data, then dropping it:

1. extendvg VGname hdisk_new
2. migratepv hdisk_bad hdisk_new
3. reducevg VGname hdisk_bad

Clone rootvg to a spare disk (great before risky upgrades) with alt_disk_copy -d hdisk1. This builds a bootable copy on hdisk1 without disturbing the running system.

What are quorum, VGDA, and VGSA?

• Quorum is a majority (51%) of VGDA/VGSA copies that must be available to keep a VG online. Toggle it with chvg -Qy vgname (enable) and chvg -Qn vgname (disable). Check status with lsvg vgname.
• VGDA (Volume Group Descriptor Area) holds the layout of the VG — which PVs, PPs, LPs, and LVs belong to it.
• VGSA (Volume Group Status Area) tracks the state (stale or active) of each physical partition for mirroring decisions.

How do I rename a volume group?

1. Unmount its file systems: umount /test
2. Deactivate: varyoffvg datavg
3. Export: exportvg datavg
4. Re-import under the new name: importvg -y newvg hdisk4

Networking on AIX: Interview Questions and Answers

Networking questions test whether you know the AIX-specific tools (no, lsdev) on top of standard Unix utilities.

• Display or set network tuning parameters: the no command, e.g. no -a to list all, no -o tcp_sendspace=262144 to set one.
• Get the IP address: ifconfig -a or host fully.qualified.name.
• List network interfaces: lsdev -Cc if or ifconfig -a; for one interface: ifconfig en0.
• Activate an interface: ifconfig en0 up.
• Routing and protocol stats: netstat -r -f inet (routes), netstat -i -f inet (interfaces), netstat -s -f inet (per-protocol statistics).

Modern AIX uses Ethernet interfaces named enX; the old token-ring trX names you may see in legacy notes are effectively obsolete.

Error Logging and Devices: AIX System Administration Questions

How does the AIX error log work?

The error daemon errdemon records hardware, software, operator, and unknown errors. It is started during rc.boot phase 3 and lives at /usr/lib/errdemon.

• View the log (detailed): errpt -a
• Filter hardware errors: errpt -d H; software: errpt -d S
• Clear the log: errclear 0 (the 0 means clear entries 0 days and older)
• Resize the log: /usr/lib/errdemon -s SIZE

Error classes are Hardware, Software, Operator, and Undetermined; error severities are Permanent, Temporary, Informational, and Unknown.

How do I manage subsystem daemons (SRC)?

AIX manages services through the System Resource Controller:

• Start: startsrc -s daemon_name (or -g group)
• Stop: stopsrc -s daemon_name
• Refresh: refresh -s daemon_name
• List status: lssrc -a

What are device states and how do I troubleshoot a failed disk?

A device is either Defined (known to the ODM but not usable) or Available (configured and ready). Run cfgmgr to move a Defined device to Available, and lsdev -Cc disk to see which disks exist and their state. For a suspected hardware fault, run the diag utility for guided diagnostics. To strip a device from the ODM completely, use rmdev -dl deviceName.

ODM, Kernel, and System Internals: AIX Interview Questions

What is the ODM and what are its databases?

The Object Data Manager (ODM) is AIX's configuration database. It has a predefined part (PdDv, PdAt — device types and attributes the system could support) and a customised part (CuDv, CuAt — the devices actually configured on this machine). Key commands: odmget (read), odmadd (insert), odmchange (modify), odmdelete (remove objects), odmcreate/odmdrop (create/drop object classes).

What is a major and minor device number?

A major number identifies the device driver (the type of device), while a minor number identifies a specific instance of that type or its operating mode. Together they uniquely address a special device file under /dev.

How do I switch between 32-bit and 64-bit kernels?

Check the running kernel with bootinfo -K and hardware capability with bootinfo -y. The kernel is selected by relinking /unix and rebuilding the boot image. To move to the 64-bit kernel:

1. ln -sf /usr/lib/boot/unix_64 /unix
2. ln -sf /usr/lib/boot/unix_64 /usr/lib/boot/unix
3. bosboot -ad /dev/ipldevice
4. shutdown -Fr

To go back to 32-bit, point the same links at /usr/lib/boot/unix_mp (the multiprocessor 32-bit kernel) and rebuild. Note: all modern AIX releases run a 64-bit kernel only — this question is now historical, relevant to AIX 5.x.

Where do dump devices and paging space live?

• Primary dump device: /dev/hd6 (shared with paging on older systems; newer installs use a dedicated /dev/lg_dumplv).
• Secondary dump device: /dev/sysdumpnull.
• Inspect dump config: sysdumpdev -L.
• Paging space definitions are recorded in /etc/swapspaces; list active paging with lsps -a.

Software Installation and Backup: AIX Interview Questions

How do I check what is installed and at which level?

• Is a fix/PTF installed? instfix -ik PTFname
• Is a fileset installed? lslpp -L | grep -i software_name
• Fileset history: lslpp -h
• OS / service-pack level: oslevel -s; oslevel -r for the recommended maintenance level; oslevel -rq lists known levels

What are the applied and committed states?

An update can be applied (installed but the previous version is retained, so it can be rejected and rolled back) or committed (the old version is discarded and rollback is no longer possible). Roll back an applied update with installp -r -g filesetName; remove a fileset entirely with installp -u filesetName; and clean up a failed/interrupted install with installp -C. The three install types are New and Complete Overwrite, Migration, and Preservation.

How do I back up and restore an AIX system?

The mksysb image is the cornerstone of AIX disaster recovery — it captures the operating system, configuration, and rootvg data into a single bootable backup.

How do I lock or unlock a user account?

• Lock: chuser account_locked=true username
• Unlock: chuser account_locked=false username

The attribute name is account_locked — a common point where memorised answers go wrong. System message logging is configured in /etc/syslog.conf, which directs the syslogd daemon to its target log files.

Key Takeaways

• Know the three VG types cold: normal (32 PV / 256 LV), big (128 / 512), scalable (1024 / 4096) — and that chvg -B and chvg -G convert them.
• PP size must be a power of two, and the legacy default was 4 MB — set -s explicitly rather than relying on a memorised figure.
• JFS2 is the modern default with dynamic 512-byte inodes and far larger limits than classic JFS.
• rootvg mirroring is a sequence: extendvg, mirrorvg, bosboot to both disks, then update the boot list.
• mksysb backs up rootvg, savevg backs up other VGs, and the ODM (predefined PdDv/PdAt, customised CuDv/CuAt) is where AIX stores all device configuration.

Frequently Asked Questions

What is the difference between mksysb and savevg in AIX?

mksysb creates a bootable backup of rootvg (the operating system and its data), used to rebuild a system from scratch. savevg backs up non-rootvg volume groups such as datavg, and is restored with restvg. Use both for complete coverage.

How do I identify whether an AIX volume group is normal, big, or scalable?

Run lsvg vgname and read the MAX PVs value: 32 indicates a normal VG, 128 a big VG, and 1024 a scalable VG. The MAX LVs field (256 / 512 / 4096) confirms it.

What is the difference between the Defined and Available device states?

Defined means AIX knows about the device in the ODM but it is not configured for use. Available means it is configured and ready. Run cfgmgr to bring a Defined device to Available, and lsdev -Cc disk to check the state.

Is the 32-bit versus 64-bit kernel question still relevant for AIX?

It is largely historical. Current AIX releases (7.x) ship a 64-bit kernel only, so kernel-switching applies to legacy AIX 5.x. Know bootinfo -K to report the running kernel, but expect 64-bit everywhere modern.

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