I have root ssh/terminal access to a linux server. How do I determine which version of centos I have?

Some people suggested I run the command cat /etc/redhat-release but I got an error saying file not found.

In fact, i'm not entirely sure i'm even using CentOS. That's what some suggested it might be.

Here's a list of commands I tried that gave me no file or directory error:

cat /etc/*release*
cat /etc/*version*
cat /proc/*version*
cat /proc/*release*

Here's a list of linux commands that do not exist:

lsb_release: command not found
wget: command not found
yum: command not found