How does one identify the linux distro in use?

It depends on the distro.

Debian and relatives use

     lsb_release -a
     cat /etc/lsb-release

either one should be fine. But, despite this being related to LSB (Linux Standard Base), not all distros have it. If you get no reply from the above commands, you should try

      ls /etc/*release

and then look inside whichever file you found. You must be careful to this: while RedHat does have /etc/redhat-release, others, like Arch Linux, have an empty /etc/arch-release file, and the one that does contain the info you are looking for is /etc/os-release.

So, YMMV.

It may not be foolproof, but /proc/version should at least give you a ballpark:

Redhat derivative:

# cat /proc/version 
Linux version 2.6.18-92cp (builder@Lnx30BccCmp5) (gcc version 4.1.1 20061011 (Red Hat 4.1.1-30)) #1 SMP Wed Apr 8 17:12:19 IDT 2015

Ubuntu:

$ cat /proc/version
Linux version 3.13.0-24-generic (buildd@panlong) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #46-Ubuntu SMP Thu Apr 10 19:11:08 UTC 2014

Debian:

$ cat /proc/version 
Linux version 3.2.0-4-amd64 ([email protected]) (gcc version 4.6.3 (Debian 4.6.3-14) ) #1 SMP Debian 3.2.65-1+deb7u1      

Centos:

# cat /proc/version 
Linux version 2.6.18-400.el5xen ([email protected]) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-55)) #1 SMP Thu Dec 4 13:29:23 EST 2014