UNIX for Dummies Questions & Answers

I am trying to figure out the OS version of my Linux box. I got three commands:

Code:

# uname -a
Linux test01     2.6.18-238.el5 #1 SMP Thu Jan 13 15:51:15 EST 2011 x86_64 x86_64 x86_64

# cat /proc/version
Linux version 2.6.18-238.el5 (mockbuild@builder10.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)) #1 SMP Thu Jan 13 15:51:15 EST 2011

# cat /etc/redhat-release
CentOS release 5.6 (Final)

What are the difference of these three commands?

Well, for starters, redhat-release only exists on redhat. it's also only a file, so might lie or be missing.

More distributions have /etc/release but it's not impossible they won't, or be incorrect.

/proc/version is more general but only a Linux thing as far as I know.

uname exists almost everywhere.

Mainly the amount of information they give you, and the availability.
uname is defined by the POSIX standard and is available on every Unix and Unix-like OS, and gives you information on the OS type, version, and architecture.
/proc/version, as part of the proc pseudo-fs is only available on Linux, and gives you some more detailed information about the kernel, and where and when it was built.

/etc/redhat-release is Red Hat (and derivates) specific, probably not available on any other distribution, and tells you the brand and version of the Linux distribution (not the OS) you're running.

Thanks above!

I was running the commands on a virtual machine. It is supposed that the VM with CentOS5.6 running on a Linux machine. So with the output of "cat /etc/redhat-release", can I say the VM was set up with right CentOS?

yes !!

FYI :

cat /proc/version :
displays additional information like Name of the user who compiled your kernel, and also a host name where it happened and GCC version used.

the info about the kernel version uname -v , about machine uname -m ..etc.. all can be combined together as #uname -msrnv or #uname -a simply