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uname -m gives i686 and uname -m gives i686 i386 output in Red Hat Enterprise Linux Server release 5.4 (Tikanga) machine. I need to install Oracle Database 10g Release 2 on that machine. So, how can I decide whether kernel architecture is 32bit or 64bit?

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Is that a typo on the first sentence: uname -m and uname -m? – Tshepang May 2 '11 at 17:34
See also Linux command to return number of bits (32 or 64)?. If uname -m shows i?86, you have a 32-bit system. – Gilles May 2 '11 at 21:29
See also Get Distribution Name and Version Number – Mikel May 2 '11 at 23:07
The question Gilles links to gives an interesting solution: getconf WORD_BIT. – Mikel May 2 '11 at 23:11
getconf WORD_BIT returns 32 on my 64-bit Ubuntu – minaev May 4 '11 at 8:53

4 Answers

up vote 14 down vote

i386 and i686 are both 32-bit.
x86_64 is 64-bit

example for 64 bit: 

behrooz@behrooz:~$ uname -a  
Linux behrooz 2.6.32-5-amd64 #1 SMP Mon Mar 7 21:35:22 UTC 2011 **x86_64** GNU/Linux
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up vote 10 down vote

@behrooz is correct. Unfortunately uname requires you to know architectures. Actually, I was looking for a list of architectures and I found this article that answers your question. In regards to uname -m:

x86_64 GNU/Linux indicates that you've a 64bit Linux kernel running. If you use see i386/i486/i586/i686 it is a 32 bit kernel.

To determine if the hardware is capable of running a 64-bit kernel

grep flags /proc/cpuinfo

Look for the following in the output (all flags retrieved from this stackoverflow answer for the same question )

  • lm flag means Long mode cpu - 64 bit CPU
  • tm flag means Protected mode - 32-bit CPU
  • rm flag means Real Mode - 16 bit CPU
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Does the lm flag simply mean the CPU supports 64-bit or does it mean that it's running in 64-bit. I recommend relying on the arch knowing that it will be x86_64 for 64-bit or i?86 for 32-bit. – penguin359 May 2 '11 at 21:45
@penguin359 it means that the cpu supports 64-bit. – xenoterracide♦ May 2 '11 at 22:57
@xeno so then is can't be used to determine the kernel architecture. – penguin359 May 2 '11 at 23:58
@penguin359 no, was that unclear in the answer? – xenoterracide♦ May 3 '11 at 8:55
@xeno When I first read your answer, I took it as implying an alternative to looking at the kernel architecture. On a re-read, I do notice you were specifying the CPU architecture, but I wanted to clarify that that does not help with the user's question which is specifically whether the kernel is 64-bit. – penguin359 May 3 '11 at 11:01
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up vote 3 down vote

It's simple! Use arch command.

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up vote 0 down vote

Another way is to check the architecture some system file was compiled for, like

$ file /usr/bin/ld
/usr/bin/ld: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.15, stripped
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That's the system architecture, which isn't always the kernel architecture. See this answer at SU for more variations. – Gilles May 4 '11 at 9:47
Theoretically, they may differ, but is there a chance they would mismatch on any real-life installation? – minaev May 5 '11 at 11:30
Some distributions ship an amd64 kernel on the x86 version. I don't know how many people use them, I checked Debian popcon but it doesn't correlate between the various stats. I think the main use case is having a 32-bit main OS and running a 64-bit OS in a chroot or in a VM. – Gilles May 5 '11 at 20:00

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