How to find out what Linux distribution is

cat /etc/*release  

Most distributions put a release file in /etc/ (like /etc/redhat-release, /etc/gentoo-release, etc.) which usually has the version number of your distribution in it.

$ cat /etc/*release

Oracle Linux Server release 7.7

NAME="Oracle Linux Server"

VERSION="7.7"

ID="ol"

ID_LIKE="fedora"

VARIANT="Server"

VARIANT_ID="server"

VERSION_ID="7.7"

PRETTY_NAME="Oracle Linux Server 7.7"

ANSI_COLOR="0;31"

CPE_NAME="cpe:/o:oracle:linux:7:7:server"

HOME_URL="https://linux.oracle.com/"

BUG_REPORT_URL="https://bugzilla.oracle.com/"

ORACLE_BUGZILLA_PRODUCT="Oracle Linux 7"

ORACLE_BUGZILLA_PRODUCT_VERSION=7.7

ORACLE_SUPPORT_PRODUCT="Oracle Linux"

ORACLE_SUPPORT_PRODUCT_VERSION=7.7

Red Hat Enterprise Linux Server release 7.7 (Maipo)

Oracle Linux Server release 7.7