CentOS and Ubuntu both are Linux distros. Below are some major differences between them.
1. CentOS is based on RHEL (Red Hat Enterprise Linux), while Ubuntu has its roots in Debian.
2. On an Ubuntu system the root password is randomly generated which is not known to the administrator. You will have to use ‘sudo command’ to get root-privileges.
3. Repositories of Ubuntu contain fresher packages than CentOS, it tends to be less conservative than CentOS, whereas CentOS packages focuses only on security patches.
4. CentOS uses YUM package manager with RPM packages whereas Ubuntu uses apt with DEB packages.
5. Ubuntu cleanly upgrades between major versions, CentOS is not so good to do that (needs a reinstall often). [via: Liz Quilty]
Know some more differences? Please put them in the comment box, I will add them in the post.
Recommended reading: “CentOS vs Ubuntu“