How do I know if my linux kernel is running in 32bit or 64bit?

Question

When I do a cat in /proc/cpuinfo it shows a line with clflushsize : 64

Does this mean my kernel is running in 64 bits?

Answer 1

uname -a

will tell you the kernel - the end bit tells you the architecture.

Two examples:

My mac:

Darwin Mac.local 9.8.0 Darwin Kernel Version 9.8.0: Wed Jul 15 16:55:01 PDT 2009; root:xnu-1228.15.4~1/RELEASE_I386 i386

My Dreamhost hosting:

Linux ecco 2.6.24.5-serf-xeon-c6.1-grsec #1 SMP Tue Oct 7 06:18:04 PDT 2008 x86_64 GNU/Linux

i386 = 32 bit

x86_64 = 64 bit

Answer 2

uname -m will give you the architecture you kernel is compiled for. If it prints i686 then your kernel is 32 bit, if x86_64 then it's 64 bit, assuming you have an Intel/AMD chip.

Answer 3

I think the most precise way is

getconf LONG_BIT

here it exactly shows 64

found on this tip

getconf is from package libc-bin (on ubuntu)

Answer 4

If you want an easy but detailed report about your system (CPU, Kernel and Core OS software) and not just the kernel then here's a small bash script that will give you the answers swiftly.

If you know enough about the peculiarities of 32bit/64bit CPUs and S/W it's simply handy. If you don't know much and think that your "system" is either 32bit or 64bit then it will help you discover that the truth can be more complex (parts of your system may be 64bit while others 32bit) without confusing you.

Again this script (and answer) is not for the literal question "How do I know if my Linux kernel is running in 32bit or 64bit?" but for those who also want to know the arch of their CPU, and core OS SW.

Example reports

These are examples for a rather unusual case:

Report from mini-script (for experienced users)

You have a 64 bit CPU
Your kernel reports that the architecture is 32 bit
Your /sbin/init process is 64 bit
Your C compiler is configured to produce 32 bit executables

Report from larger script (for less experienced users)

You have a 64 bit CPU
Your kernel reports that the architecture is 32 bit
    If you are not the admin he can make a 64bit kernel report 32bit (see man setarch)
    In this case he has (because we have 64bit programs)
Your /sbin/init process is 64 bit
    Most other core OS programs will probably be 64 bits also.
    You may use the following command to check a specific program.
      file -L /path/to/program
Your C compiler is configured to produce 32 bit executables
    (Note that a 64bit compiler may be setup to produce 32bit code)

The scripts

Mini-script (for experienced admins)

These 4 lines gives all the essential information.

grep -w 'lm' /proc/cpuinfo > /dev/null && echo "You have a 64 bit CPU" || echo "You have a 32 bit CPU"
echo "Your kernel reports that the architecture is $(uname -m|sed -e 's/x86_64/64 bit/' -e 's/i.86/32 bit/')"
echo "Your /sbin/init process is $(file /sbin/init|sed -e 's/^.* \(32\|64\) bit.*$/\1bit/')"
echo "Your C compiler is configured to produce $(getconf LONG_BIT) bit executables"

Larger script (for less experienced users)

This script prints a lot of explanation and is useful if you don't have experience on the subject and are faced with a peculiar case.

#!/bin/bash

# collect system info
grep -w 'lm' /proc/cpuinfo > /dev/null && CPU=64 || CPU=32
ARCH=$(uname -m|sed -e 's/x86_64/64/' -e 's/i.86/32/')
INIT=$(file -L /sbin/init|sed -e 's/^.* \(32\|64\)-bit.*$/\1/')
COMPILER=$(getconf LONG_BIT)

# if all values are the same we set UNIFORM="YES"
! echo "$CPU $ARCH $INIT $COMPILER" | grep -q "$CPU $CPU $CPU $CPU" && UNIFORM="NO" || UNIFORM="YES"

# report to the user
echo "You have a $CPU bit CPU"
echo "Your kernel reports that the architecture is $ARCH bit"
if [ "$UNIFORM" = "NO" ] && [ "$ARCH" = "32" ] ; then
       echo "    If you are not the admin he can make a 64bit kernel report 32bit (see man setarch)"
       if  [ "$INIT" = "64" ] ||  [ "$COMPILER" = "64" ] ; then
           echo "    In this case he has (because we have 64bit programs)"
       else
           echo "    We don't see such signs so you most likely run a 32bit kernel"
           echo "    (A 64bit CPU can run 32bit kernels)"
       fi
fi
echo "Your /sbin/init process is $INIT bit"
if [ "$CPU" = "64" ] ; then
     echo "    Most other core OS programs will probably be $INIT bits also."
     echo "    You may use the following command to check a specific program."
     echo "      file -L /path/to/program"
fi
if [ "$UNIFORM" = "NO" ] && [ "$INIT" = "32" ] ; then
     echo "    (Note that a 64bit kernel may start a 32bit init process)"
fi
echo "Your C compiler is configured to produce $COMPILER bit executables"
if [ "$UNIFORM" = "NO" ] && [ "$COMPILER" = "32" ] ; then
        echo "    (Note that a 64bit compiler may be setup to produce 32bit code)"
fi

---

If you want to know more read these two pages from where I got most of the information a) https://stackoverflow.com/questions/246007/how-to-determine-whether-a-given-linux-is-32-bit-or-64-bit b) https://unix.stackexchange.com/a/134394/73271

Answer 5

If you want to see only the platform that you are running on, you can use

uname -i

The full list of supported options for uname is

$ uname --help
Usage: uname [OPTION]...
Print certain system information.  With no OPTION, same as -s.

  -a, --all                print all information, in the following order,
                             except omit -p and -i if unknown:
  -s, --kernel-name        print the kernel name
  -n, --nodename           print the network node hostname
  -r, --kernel-release     print the kernel release
  -v, --kernel-version     print the kernel version
  -m, --machine            print the machine hardware name
  -p, --processor          print the processor type or "unknown"
  -i, --hardware-platform  print the hardware platform or "unknown"
  -o, --operating-system   print the operating system
      --help     display this help and exit
      --version  output version information and exit

Answer 6

CLFLUSHSIZE doesn't tell you anything about the processor's operating mode. According to this answer, it refers to the smallest flushable unit of cache. In your case, cache lines are read/written in units of 64 bytes.

uname output varies too much to be useful, as a glance at Wikipedia's table of examples shows. The most reliable method is getconf LONG_BIT as show in Aquarius Power's answer. This works regardless of processor architecture, so is just at home on ARM, Power, or MIPS as on x86.