Orienting on an unfamiliar AIX LPAR before you type anything else

What it is

An AIX LPAR (logical partition on IBM Power hardware) shares a Unix ancestry with Linux but diverges in ways that break assumptions carried over from GNU/Linux systems. Before changing anything, gather:

• oslevel -s — the installed Release-TechnologyLevel-ServicePack-Build string (for example 7300-01-02-2320), the standard way to state the AIX level. Compare it against the level you expect for the workload.
• prtconf — a plain-text hardware/firmware inventory: System Model, Machine Serial Number, processor type and count, memory size, network and paging information in one report.
• lsattr -El sys0 — the attributes of the pseudo-device sys0, which represents overall system tunables (realmem, maxuproc, and similar) stored in the ODM, not in a config file.
• uname -a — prints AIX-specific fields (OS name, node name, AIX version and release, machine ID); the field order and meaning differ from Linux uname -a and there is no kernel build string to read.
• bootinfo -b — the last boot device; useful when diagnosing why a system came up from an unexpected disk.
• lparstat -i — partition configuration from the hypervisor's point of view: partition name/number, type (dedicated or shared processor), entitled capacity, virtual CPUs and memory; distinct from vmstat/top-style utilization.

Why it matters

Two habits from Linux cause the most friction. First, AIX's default interactive and login shell is the Korn shell (/usr/bin/ksh), not bash. On AIX 7.2/7.3 /usr/bin/ksh is ksh88 (ksh93 is a separate binary, /usr/bin/ksh93), so bash-only syntax such as arr=(a b) array assignment, {1..5} brace expansion, $'...' quoting or local is absent or behaves differently. Second, standard AIX commands (ls, ps, df, tar, …) are the historical Unix/POSIX ones: long GNU-style --flag options are generally not accepted. Scripts written against GNU tools silently fail or behave differently unless a GNU toolset has been installed separately (see the AIX Toolbox article in this series).

How to apply

• Run the six commands above, read-only, before making any change; keep the output as your baseline.
• Note the AIX level from oslevel -s and check it against IBM's supported/EOS status for that release before assuming any behaviour.
• Treat sys0 and other ODM-backed attributes as configuration to inspect with lsattr, not files to grep.
• When a script must run on both Linux and AIX, test its exact command line on AIX first; do not assume a flag exists.

Pitfalls

• Assuming bash is present or is the login shell; even where installed (often under /opt/freeware/bin or /usr/bin via the AIX Toolbox), the system default remains ksh.
• Reading uname -a output with Linux field positions in mind and misidentifying the version.
• Treating lparstat -i and vmstat/topas as interchangeable; -i is a one-shot configuration snapshot, not a utilization sample.