On Sat, Jul 20, 2019 at 1:38 PM Elio Fabri <[log in to unmask]> wrote:
>
> Hi all, I had a bad surprise: the root password I know is no longer
> accepted. Neither bu su, nor by yum.
> I've been using Linux for many years (now SL 6.2) and it never happened
> before, so I'm stuck.
> What can I do?
> --
> Elio Fabri

Reboot your system with a recovery disk. The Scientific Linux
installation disk images support typing "linux rescue" at the disc
boot prompt.

Other methods are covered pretty well here:

https://urldefense.proofpoint.com/v2/url?u=https-3A__www.tecmint.com_reset-2Dforgotten-2Droot-2Dpassword-2Din-2Drhel-2Dcentos-2Dand-2Dfedora_&d=DwIBaQ&c=gRgGjJ3BkIsb5y6s49QqsA&r=gd8BzeSQcySVxr0gDWSEbN-P-pgDXkdyCtaMqdCgPPdW1cyL5RIpaIYrCn8C5x2A&m=VIAIdZdbjUx2Ruwrj-sIpKTgnGkocdW8SKqEX6ii_Ig&s=aYTQVfqPD_oclWJIXcwEm1FCqO7WM4eKX6tMNqsUCqI&e=