Bash – How to find out what version of RHEL I’m using

bashrhel

I work in an environment where we are slowly transitioning machines from Red Hat Enterprise Linux 5 to RHEL 6.

I need some of my scripts to do something subtly different on RHEL6 machines to what is currently being done on RHEL5 machines.

The pragmatic solution is to check at runtime and run some commands on RHEL5, others on RHEL6 and some on both.

A practical example of this is that we are using environment modules and my .bashrc includes a module load git line, but on RHEL6 machines this command errors:

RHEL6 system, git should be installed - not loading module

Looking in the modulefile I find the following code:

set redhatrelease [eval exec "cat /etc/redhat-release"]
if { [regexp -nocase {release 6} $redhatrelease] } {
  puts stderr "\n\t RHEL6 system, git should be installed - not loading module\n"
} else {
  ...
}

This seems to do what I want, but I was hoping for something shorter.

So, what is the easiest way to tell RHEL5 from RHEL6 in a bash script?

Ideally it should be robust across different major versions, but be tolerant of variations in minor release numbers.

Best Answer

You can also use the lsb_release command. If you're already certain it's RHEL, getting the major version number is:

majversion=$(lsb_release -rs | cut -f1 -d.)

Related Solutions

Bash – How to stop Fork Bomb out of memory error – RHEL 6

Is there anyway to stop this without rebooting the machine?

It's not quite impossible, and you can do it via luck -- i.e., you manage to kill all the processes before another one is spawned.¹ But you have to get very very lucky, so it is not a reliable or worthwhile effort [maybe slm is luckier than me here, lol -- TBH I haven't tried that hard]. If you play around with priorities, your chances could improve (see man nice), although I suspect this will also mess with the efficacy of the fork bomb.

A better idea might be to use one that times out. For an example in C, see footnote number 5 to my answer here.² You can do the same thing with a shell script, albeit would not be as short as :(){ :|:& };::

#!/bin/bash

export fbomb_duration=$1
export fbomb_start=$(date +%s)

go () {
    now=$(date +%s)
    if [[ $(($now-$fbomb_start)) -gt $fbomb_duration ]]
        then exit 0;
    fi
    go &
}

while ((1)); do
    go
done

Execute that with one argument, a number of seconds. All forks will die after that time.

¹ In fact, it can happen all on its own, eventually, if the kernel OOM killer gets lucky. But don't hold your breath.

² The method used there to hamstring that particular bomb (by setting vm.overcommit_memory=2) will almost certainly not work in general, but you could try. I'm not since I'd like to leave my system running for now ;)

How to find out the version number of an installed library

If you want to know what version is installed, just run:

rpm -q libxcb-devel

If you want to prevent upgrades to this package, you can add the package to the yum exclude configuration. Add the following to the main section in /etc/yum.conf:

exclude=libxcb-devel

The library version (e.g., in libxcb.so.1.1.0) very seldom tracks the package version, and is meant to track API changes.

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