On Thu, Feb 3, 2011 at 3:14 PM, Rafa Grimán <rafagriman@xxxxxxxxx> wrote:
> On Thursday 03 February 2011 20:42 Robert Heller wrote
>> At Thu, 3 Feb 2011 20:12:17 +0100 CentOS mailing list <centos@xxxxxxxxxx>
> wrote:
>> > Hi :)
>> >
>> > On Thursday 03 February 2011 14:59 Giles Coochey wrote
>> >
>> > > On 03/02/2011 14:40, Rafa Griman wrote:
>> > > > Hi :)
>> > > >
>> > > > On Wed, Feb 2, 2011 at 3:44 PM, James Bensley<jwbensley@xxxxxxxxx>
> wrote:
>> > > >> So on a virtual server the root password was no longer working (as
>> > > >> in I couldn't ssh in anymore). Only I and one other know it and
>> > > >> neither of us have changed it. No other account had the correct
>> > > >> privileges to correct this so I'm wondering, if I had mounted that
>> > > >> vdi as a secondary device on another VM, browsed the file system
>> > > >> and delete /etc/shadow would this have wiped all users passwords
>> > > >> meaning I could regain access again?
>> > > >>
>> > > >> (This is past tense because its sorted now but I'm curious if this
>> > > >> would have worked? And if not, what could I have done?).
>> > > >
>> > > > As the other said: DON'T delete /etc/shadow.
>> > > >
>> > > > Someone also mentioned you could modify the hash in /etc/shadow. This
>> > > > will work if you are root or have the right permissions with sudo.
>> > > >
>> > > > If you can reboot the system, what really works great is passing the
>> > > > following option to the kernel on the lilo/grub screen when the
>> > > > system
>> > > >
>> > > > boots:
>> > > > init=/bin/bash
>> > > >
>> > > > This will give you a shell without being asked for a password (unless
>> > > > the sys admin has done his homework ;) Now that you have shell access
>> > > >
>> > > > ... you are in charge so you can:
>> > > > - mount the / partition and chroot
>> > > >
>> > > > - edit /etc/shadow and delete the password hash
>> > > >
>> > > > - whatever you can imagine ... you decide ;)
>> > >
>> > > That would do it... There is single-user-mode (runlevel 1), just add
>> > > the word single to the kernel parameters line before bootup
>> > >
>> > > It will give you the same result and mount stuff without the need to
>> > > chroot etc...
>> >
>> > Yes, but S|Single|1 asks for root password to login ... And he doesn't
>> > have the root password ;)
>>
>> RedHat / RHEL / CentOS does not do that!
>
>
> True, just tried it with RHEL 6 and CentOS 5.3. Well it should ask for a
> passwd ... at least IMHO.
>
> Then again ... an admin should configure grub/lilo to ask for a password if you
> pass parameters to the kernel during boot time :)
>
>
>> At least never on any of my
>> machines -- is there some config option for that? Yes, for manual fchk
>> it does, but not otherwise.
>
>
> I'll check, but no idea.
In CentOS 5, use "~~:S:wait:/sbin/sulogin" in "/etc/inittab" to enter
runlevel S with a password.
In CentOS 6, use "SINGLE=/sbin/sushell" in "/etc/sysconfig/init" to
enter runlevel S without a password (default) and
"SINGLE=/sbin/sulogin" in "/etc/sysconfig/init" to enter runlevel S
with a password.
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