How to find if its VM or Real host

Linux -

    dmidecode | grep -i vmware

AIX -

    nonlpar# umame -L
    -1 NULL

    lparhost# uname -L
    5 lparhost

Solaris -

    bash-3.00# prtdiag -v | head -3
    System Configuration: VMware, Inc. VMware Virtual Platform
    BIOS Configuration: Phoenix Technologies LTD 6.00 10/13/2009

    bash-3.00# modinfo | grep -i vm
    148 fffffffff7e71000 3b38 244 1 vmxnet3s (VMware EtherAdapter v3 b341836)
    205 fffffffff78e7000 21b0 230 1 vmmemctl (VMware Memory Control b341836)

Determine if your OS is 64-bit or 32-bit?

Windows:

Run> msinfo32.exe

Windows

Click Start -> Run, and type dxdiag. If a Windows dialog box is displayed asking if you want to verify your drivers, you can safely click no and continue. When the program has finished loading, you should see something similar to one of the following images:
The Operating System line, refers to Windows x64 or 64-bit edition. The last window specifies the processor Itanium, which is a 64-bit processor.

Macintosh

You must be running Mac OS X 10.5 (Leopard) or newer and have a Core 2 Duo or G5 processor for 64-bit support.* To determine if your computer meets both requirements, select About This Mac from the Apple menu. A window will appear from which you can determine the version of Mac OS X and the processor type installed on your computer.

* A 64-bit version of Stata 10 for the Macintosh is expected to be available during the second half of 2008. An announcement will be made once it is available.

Unix (IBM-AIX, Sun Solaris)

• IBM-AIX
  
  The getconf command will return the configuration of your machine. Since you are looking only for the kernel parameters, you should type

[cph@anna ~]$ getconf -a | grep KERN
KERNEL_BITMODE: 64

If that fails or does not return a result, try the file command.

[cph@anna ~]$ file /usr/lib/boot/unix*
/usr/lib/boot/unix: 64-bit XCOFF executable or object module not stripped
/usr/lib/boot/unix_64: 64-bit XCOFF executable or object module not stripped
/usr/lib/boot/unix_mp: executable (RISC System/6000) or object module not stripped
/usr/lib/boot/unix_up: executable (RISC System/6000) or object module not stripped

[cph@ozona ~]$ file /usr/lib/boot/unix*
/usr/lib/boot/unix: symbolic link to /usr/lib/boot/unix_up.
/usr/lib/boot/unix_kdb: executable (RISC System/6000) or object module not stripped
/usr/lib/boot/unix_up: executable (RISC System/6000) or object module not stripped

We can see that 'anna' is a 64-bit capable platform, and 'ozona' is only 32-bit.

Sun Solaris

eden:/home/cph: isainfo -v
64-bit sparcv9 applications
32-bit sparc applications

You can see that this Solaris machine is capable of running 32-bit as well as 64-bit applications. If isainfo fails, running a 64-bit application on your Sun will generally not be possible, unless of course isainfo is not in your path or has not been installed. You can also use the uname command to glean more information:

eden:/home/cph: uname -a
SunOS eden 5.8 Generic_108528-05 sun4u sparc SUNW,Ultra-5_10

lagrange:/usr/users/cph: uname -a
SunOS lagrange 5.5.1 Generic_103640-29 sun4u sparc SUNW,Ultra-1

How to check Solaris kernel on x86 (Intel) platform :

bash-3.00# uname –m
i86pc
bash-3.00# /usr/bin/isainfo -kv
32-bit i386 kernel modules

Linux

Linux users should type the uname command. Depending on the platform, you may see

[cph@gaylord ~]$ uname -a
Linux gaylord.stata.com 2.6.11-1.27_FC3 #1 Tue May 17 20:24:57 EDT 2005 x86_64 x86_64 x86_64 GNU/Linux

[cph@caddo ~]$ uname -a
Linux caddo.stata.com 2.6.9-5.0.5.EL #1 SMP Fri Apr 8 14:20:58 EDT 2005 ia64 ia64 ia64 GNU/Linux

[cph@tango ~]$ uname -a
Linux tango.stata.com 2.6.10-1.771_FC2smp #1 SMP Mon Mar 28 01:10:51 EST 2005 i686 i686 i386 GNU/Linux

In the above listing, 'gaylord' (x86_64 GNU/Linux) and 'caddo' (ia64 GNU/Linux) are 64-bit compliant. 'tango' (i386 GNU/Linux) is only a 32-bit platform

Different RUN levels in Linux,Solaris and AIX

RedHat Linux - Run Levels

0: Halt

1: Single user mode

2: Multiuser, without NFS

3: Full multiuser mode

4: Unused

5: X11

6: Reboot

Solaris - Run Level

S: Single user state (useful for recovery)

0: Access Sun Firmware ( ok> prompt)

1: System administrator mode

2: Multi-user w/o NFS

3: Multi-user with NFS ( default run level)

4: Unused

5: Completely shutdown the host (like performing a power-off @ OBP) [ thanks to Marco ]

6: Reboot but depend upon initdefault entry in /etc/inittab

AIX - Run Levels

0-1: Reserved for future use

2: Multiuser mode with NFS resources shared (default run level)

3-9: Defined according to the user's preferences

m,M,s,S: Single-user mode (maintenance level)

a,b,c: Starts processes assigned to the new run levels while leaving the existing processes at the current level running

Q,q: init command to reexamine the /etc/inittab file

Command to see Run level:-

$ who -r

Output:

. run-level 3 Mar 3 14:04 3 0 S

Solaris/Linux changing runlevels after bootup

You need to use init command, for example change runlevel to 2.

# /sbin/init 2

Solaris changing the default runlevel

An entry with initdefault (in /etc/inittab file) is scanned only when init is initially invoked. init uses this entry to determine which run level to enter initially.

Open /etc/inittab file:

# vi /etc/inittab

Find out this entry:

is:3:initdefault:

Change is:3 to number you want, don't use S, 0, 6 ;). Save file.