check os version in linux

$uname -a

Linux ip-10–0–0–224 5.4.0–1045-aws

#47-Ubuntu SMP Tue Apr 13 07:02:25 UTC

2021 x86_64 x86_64 x86_64 GNU/Linux

more /proc/version

$ more /proc/version
Linux version 5.4.0–1045-aws

(buildd@lcy01-amd64–026)

(gcc version 9.3.0

(Ubuntu 9.3.0–17ubuntu1~20.04))

more /etc/os-release

$ more /etc/os-release
NAME=”Ubuntu”
VERSION=”20.04.2 LTS (Focal Fossa)”
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME=”Ubuntu 20.04.2 LTS”
VERSION_ID=”20.04″

lsb_release -a$lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 20.04.2 LTS
Release: 20.04
Codename: focal

how to check os version