How can I reliably get the operating system's name?

lsb_release -a is likely going to be your best option for finding this information out, and being able to do so in a consistent way.

History of LSB

The lsb in that command stands for the project Linux Standards Base which is an umbrella project sponsored by the Linux Foundation to provide generic methods for doing basic kinds of things on various Linux distros.

The project is voluntary and vendors can participate within the project as just a user and also as facilitators of the various specifications around different modules that help to drive standardization within the different Linux distributions.

excerpt from the charter

The LSB workgroup has, as its core goal, to address these two concerns. We publish a standard that describes the minimum set of APIs a distribution must support, in consultation with the major distribution vendors. We also provide tests and tools which measure support for the standard, and enable application developers to target the common set. Finally, through our testing work, we seek to prevent unnecessary divergence between the distributions.

Useful links related to LSB

• LSB Charter
• LSB Workgroup
• LSB Roadmap
• LSB Mailing List (current activity is here!)
• List of certified LSB products
• LSB Wikipedia page

Criticisms

There are a number of problems with LSB that make it problematic for distros such as Debian. The forced usage of RPM being one. See the Wikipedia article for more on the matter.

Novell

If you search you'll possibly come across a fairly dated looking page titled: Detecting Underlying Linux Distro from Novell. This is one of the few places I"ve seen an actual list that shows several of the major distros and how you can detect what underlying one you're using.

excerpt

Novell SUSE         /etc/SUSE-release
Red Hat             /etc/redhat-release, /etc/redhat_version
Fedora              /etc/fedora-release
Slackware           /etc/slackware-release, /etc/slackware-version
Debian              /etc/debian_release, /etc/debian_version,
Mandrake            /etc/mandrake-release
Yellow dog          /etc/yellowdog-release
Sun JDS             /etc/sun-release
Solaris/Sparc       /etc/release
Gentoo              /etc/gentoo-release
UnitedLinux         /etc/UnitedLinux-release
ubuntu              /etc/lsb-release

This same page also includes a handy script which attempts to codify for the above using just vanilla uname commands, and the presence of one of the above files.

NOTE: This list is dated but you could easily drop the dated distros such as Mandrake from the list and replace them with alternatives. This type of a script might be one approach if you're attempting to support a large swath of Solaris & Linux variants.

Linux Mafia

More searching will turn up the following page maintained on Linuxmafia.com, titled: /etc/release equivalents for sundry Linux (and other Unix) distributions. This is probably the most exhaustive list to date that I've seen. You could codify this list with a case/switch statement and include it as part of your software distribution.

In fact there is a script at the bottom of that page that does exactly that. So you could simply download and use the script as 3rd party to your software distribution.

script

#!/bin/sh
# Detects which OS and if it is Linux then it will detect which Linux
# Distribution.

OS=`uname -s`
REV=`uname -r`
MACH=`uname -m`

GetVersionFromFile()
{
    VERSION=`cat $1 | tr "\n" ' ' | sed s/.*VERSION.*=\ // `
}

if [ "${OS}" = "SunOS" ] ; then
    OS=Solaris
    ARCH=`uname -p` 
    OSSTR="${OS} ${REV}(${ARCH} `uname -v`)"
elif [ "${OS}" = "AIX" ] ; then
    OSSTR="${OS} `oslevel` (`oslevel -r`)"
elif [ "${OS}" = "Linux" ] ; then
    KERNEL=`uname -r`
    if [ -f /etc/redhat-release ] ; then
        DIST='RedHat'
        PSUEDONAME=`cat /etc/redhat-release | sed s/.*\(// | sed s/\)//`
        REV=`cat /etc/redhat-release | sed s/.*release\ // | sed s/\ .*//`
    elif [ -f /etc/SuSE-release ] ; then
        DIST=`cat /etc/SuSE-release | tr "\n" ' '| sed s/VERSION.*//`
        REV=`cat /etc/SuSE-release | tr "\n" ' ' | sed s/.*=\ //`
    elif [ -f /etc/mandrake-release ] ; then
        DIST='Mandrake'
        PSUEDONAME=`cat /etc/mandrake-release | sed s/.*\(// | sed s/\)//`
        REV=`cat /etc/mandrake-release | sed s/.*release\ // | sed s/\ .*//`
    elif [ -f /etc/debian_version ] ; then
        DIST="Debian `cat /etc/debian_version`"
        REV=""

    fi
    if [ -f /etc/UnitedLinux-release ] ; then
        DIST="${DIST}[`cat /etc/UnitedLinux-release | tr "\n" ' ' | sed s/VERSION.*//`]"
    fi

    OSSTR="${OS} ${DIST} ${REV}(${PSUEDONAME} ${KERNEL} ${MACH})"

fi

echo ${OSSTR}

NOTE: This script should look familiar, it's an up to date version of the Novell one!

Legroom script

Another method I've seen employed is to roll your own script, similar to the above Novell method but making use of LSB instead. This article titled: Generic Method to Determine Linux (or UNIX) Distribution Name, shows one such method.

# Determine OS platform
UNAME=$(uname | tr "[:upper:]" "[:lower:]")
# If Linux, try to determine specific distribution
if [ "$UNAME" == "linux" ]; then
    # If available, use LSB to identify distribution
    if [ -f /etc/lsb-release -o -d /etc/lsb-release.d ]; then
        export DISTRO=$(lsb_release -i | cut -d: -f2 | sed s/'^\t'//)
    # Otherwise, use release info file
    else
        export DISTRO=$(ls -d /etc/[A-Za-z]*[_-][rv]e[lr]* | grep -v "lsb" | cut -d'/' -f3 | cut -d'-' -f1 | cut -d'_' -f1)
    fi
fi
# For everything else (or if above failed), just use generic identifier
[ "$DISTRO" == "" ] && export DISTRO=$UNAME
unset UNAME

This chunk of code could be included into a system's /etc/bashrc or some such file which would then set the environment variable $DISTRO.

gcc

Believe it or not another method is to make use of gcc. If you query the command gcc --version you'll get the distro that gcc was built for, which is invaribly the same as the system it's running on.

Fedora 14

$ gcc --version
gcc (GCC) 4.5.1 20100924 (Red Hat 4.5.1-4)
Copyright (C) 2010 Free Software Foundation, Inc.

CentOS 5.x

$ gcc --version
gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-54)
Copyright (C) 2006 Free Software Foundation, Inc.

CentOS 6.x

$ gcc --version
gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-3)
Copyright (C) 2010 Free Software Foundation, Inc.

Ubuntu 12.04

$ gcc --version
gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3
Copyright (C) 2011 Free Software Foundation, Inc.

TL;DR;

So which one should I use? I would tend to go with lsb_release -a for any Linux distributions that I would frequent (RedHat, Debian, Ubuntu, etc.). For situations where you're supporting systems that don't provide lsb_release I'd roll my own as part of the distribution of software that I'm providing, similar to one of the above scripts.

UPDATE #1: Follow-up with SuSE

In speaking with @Nils in the comments below it was determined that for whatever reason, SLES11 appeared to drop LSB from being installed by default. It was only an optional installation, which seemed counter for a package that provides this type of key feature.

So I took the opportunity to contact someone from the OpenSuSE project to get a sense of why.

excerpt of email

Hi Rob,

I hope you don't mind me contacting you directly but I found your info here: 
https://en.opensuse.org/User:Rjschwei. I participate on one of the StackExchange 
sites, Unix & Linux and a question recently came up regarding the best option 
for determining the underlying OS.

http://unix.stackexchange.com/questions/92199/how-can-i-reliably-get-the-operating-systems-name/92218?noredirect=1#comment140840_92218

In my answer I suggested using lsb_release, but one of the other users mentioned 
that this command wasn't installed as part of SLES11 which kind of surprised me. 
Anyway we were looking for some way to confirm whether this was intentionally 
dropped from SLES or it was accidental.

Would you know how we could go about confirming this one way or another?

Thanks for reading this, appreciate any help and/or guidance on this.

-Sam Mingolelli
http://unix.stackexchange.com/users/7453/slm

Here's Rob's response

Hi,

On 10/01/2013 09:31 AM, Sam Mingo wrote:
- show quoted text -

lsb_release was not dropped in SLES 11. SLES 11 is LSB certified. However, it 
is not installed by default, which is consistent with pretty much every other
distribution. The lsb_release command is part of the lsb-release package.

At present almost every distribution has an entry in /etc such as 
/etc/SuSE-release for SLES and openSUSE. Since this is difficult for ISVs and 
others there is a standardization effort going on driven by the convergence to 
systemd. The standard location for distribution information in the future will 
be /etc/os-release, although Ubuntu will probably do something different.

HTH,    
Robert

--  Robert Schweikert                           MAY THE SOURCE BE WITH YOU    
SUSE-IBM Software Integration Center                   LINUX    
Tech Lead    
Public Cloud Architect 

Since you probably won't be able to install facter on a remote server, you can mimic what it does to find the OS name. The Ruby code for the operatingsystem fact can be found here on pastebin. Basically, it looks through the different *-release files and others to determine the OS name.

Some of the files it looks at:

/etc/debian_version
/etc/gentoo-release
/etc/fedora-release
/etc/mandriva-release
/etc/mandrake-release
/etc/meego-release
/etc/arch-release
/etc/oracle-release
/etc/enterprise-release
/etc/ovs-release
/etc/vmware-release
/etc/redhat-release
/etc/SuSE-release
/etc/bluewhite64-version
/etc/slamd64-version
/etc/slackware-version
/etc/alpine-release
/etc/system-release
/etc/centos-release

I'm sorry if you find duplicates in this list, I produced it quickly with grep. Should be fairly easy (albeit a bit tedious) to port this to a POSIX shell script.

In case you have python installed (doesn't matter whether Python 3 or Python 2), you can find out the distribution name without reinventing the wheel:

python -c "import platform;print(platform.linux_distribution()[0])"