How do I check if I have a 32-bit or a 64-bit OS?

I know at least 2 ways. Open a terminal(Ctrl+Alt+T) and type:

1. uname -a

   Result for 32-bit Ubuntu:

   Linux discworld 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:50 UTC 2011 i686 i686 i386 GNU/Linux

   whereas the 64-bit Ubuntu will show:

   Linux discworld 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:50 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux

   Shorter version:

   $ uname -i
   x86_64
   

   or

2. file /sbin/init

   Result for 32-bit Ubuntu:

   /sbin/init: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.15, stripped

   whereas for the 64-bit version it would look like:

   /sbin/init: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.15, stripped

   Same for systems using systemd (16.04):

   file /lib/systemd/systemd

   Result for 64-bit:

   /lib/systemd/systemd: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=54cc7ae53727d3ab67d7ff5d66620c0c589d62f9, stripped

Ubuntu 12.04+ with Unity

• Hit Command(mac) or Window key.
• Type Details, and select "Details" icon
• Read "OS type" field
• 64 bit OS will read "64-bit"

Alternative to get the above screen:

• click System Menu (gear at top right corner)
• click "About this Computer"

I know the terminal responses are good but I guess this is the GUI answer. :)

Ubuntu 11.04 with Unity

• Hit Command(mac) or Window key.
• Type System info, and select System Info icon
• Read "OS type" field
• 64 bit OS will read "64-bit"

A very easy and short way is:

Open the Terminal, write the following and press Enter.

getconf LONG_BIT

The resulting number (in my case 64) is the answer.