Can we boot the linux kernel in 32-bit mode?

[GnanaShekar]

Hi,

We have installed RHEL AS4 on an AMD server.
I have the following queries:

1. How can we find out if the Linux OS is 32-bit / 64-bit?

2. If the Linux OS is 64-bit, can we do some setting and boot the kernel in 32-bit mode?

[root@bgpcem15 ~]# more /etc/redhat-release
Red Hat Enterprise Linux AS release 4 (Nahant Update 3)

[root@bgpcem15 ~]# uname -m
x86_64

[root@bgpcem15 ~]# more /proc/cpuinfo | grep "model name"
model name : Dual Core AMD Opteron(tm) Processor 275

Please suggest,
Thanks & Regards.

[Jean-Yves Picard]

Hello,

#1
as mention in http://www.unixguide.net/unixguide.shtml

getconf LONG_BIT

#2
sorry can't answer I don't have any 64 bit running ....

Jean-Yves Picard

[Alpha977]

Hello!

1) Usually the last AMD server are all at 64 Bit. Try with "uname -a"

2) I don't mind is possible, because the entire server is at 64 (cpu, chipset...)and kernel is compiled at 64 bit.

[Matti_Kurkela]

1.)
If your "uname -m" reports "x86_64", you are running a 64-bit kernel. It would report something like "i686" if you were running a 32-bit kernel.

2.)
There is no such a setting.
If you have installed a 64-bit distribution, even replacing just the kernel would not help: all the 64-bit system binaries would be totally incompatible with a 32-bit kernel. The 32-bit kernel would start, but if /sbin/init is 64-bit, the kernel would panic after an unsuccessful attempt to start the "init" process.

Fortunately, the 64-bit kernel can run 32-bit binaries. You need to ensure you have 32-bit versions of any necessary libraries available: the 32-bit binaries can use only 32-bit libraries. Other than that, you don't need to do anything special: the kernel detects the binary format automatically and does the right thing.

The RHEL AS/ES 4 distribution has several 32-bit library packages available for x86_64 architecture: I think they were named like "compat-*.rpm".