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how to change root passwd (if forgotten)

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abdelkader belahcene

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Aug 10, 2011, 11:50:02 AM8/10/11
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Hi,
I ve forgotten my root passwd on centos 6 (red hat based),

I tried to change it as I used in debian (in debian it works perfectly) ,  that is:

use a cd live (or installation cd1), to access the hd,
I mount  my root partition and mount proc and devices

I tried  the command passwd, no error reprorted, but after reboot the passwd had´t changed.
then I decided to remove passwd from /etc/shadow (delete the
second field).

OK,  now I can access my machine  without passwd,  BUT I CAN´T GIVE ANY PASSWORD!!!!  I RECEIVE THIS ERROR

# passwd
Changing password for user root.
New password:
Retype new password:
passwd: Authentication token manipulation error

any idea to fix the problem.
thanks a lot

Umarzuki Mochlis

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Aug 10, 2011, 12:00:01 PM8/10/11
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if i'm not mistaken you can just go to single user mode on centos by appending "1" or "single" (without quotes) on boot parameter, no need for any live cd

2011/8/10 abdelkader belahcene <abela...@gmail.com>



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Umarzuki Mochlis
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Thierry Chatelet

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Aug 10, 2011, 12:10:02 PM8/10/11
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On Wednesday 10 August 2011 17:53:26 Umarzuki Mochlis wrote:
> if i'm not mistaken you can just go to single user mode on centos by
> appending "1" or "single" (without quotes) on boot parameter, no need for
> any live cd
>

Not with debian, but lots of trail if you google it.
Thierry


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Aniruddha

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Aug 10, 2011, 1:50:02 PM8/10/11
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On Wed, Aug 10, 2011 at 5:25 PM, abdelkader belahcene
<abela...@gmail.com> wrote:
> Hi,
> I ve forgotten my root passwd on centos 6 (red hat based),
>
> I tried to change it as I used in debian (in debian it works perfectly) ,
> that is:
...

>
> any idea to fix the problem.
> thanks a lot
>
http://www.centos.org/docs/5/html/Installation_Guide-en-US/ch-rescuemode.html


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shawn wilson

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Aug 10, 2011, 2:20:02 PM8/10/11
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you forgot chroot. might also need to do ldconfig -v to make sure the path to shared libraries is correct (but i don't think so).

you used to be able to clear out the field in the shadow file or clear out the x (iirc) in passwd, but i think default pam will stop you from doing this :)

Ivan Shmakov

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Aug 10, 2011, 2:20:02 PM8/10/11
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>>>>> abdelkader belahcene <abela...@gmail.com> writes:

[…]

> then I decided to remove passwd from /etc/shadow (delete the
> second field).

> OK, now I can access my machine without passwd, BUT I CAN´T GIVE ANY
> PASSWORD!!!! I RECEIVE THIS ERROR

> # passwd*
> *Changing password for user root.


> New password:
> Retype new password:
> passwd: Authentication token manipulation error

> any idea to fix the problem.

Running pwck(8) may give one more information on the issue.

Then, I'd make a backup for shadow(5) and try to use pwconv(8)
to fix the inconsistencies reported by pwck(8).

> thanks a lot *

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abdelkader belahcene

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Aug 10, 2011, 8:00:01 PM8/10/11
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On 8/10/11, Lucas Lima <lcs.fre...@gmail.com> wrote:
> the passwords are stored in /etc/shadow and you deleted the file, you should
> restore it.
I just removed the second field , the password for th root. no more things

restore it ?? how??


starting with level 1, (single ) is not a solution, the password is required.

regards


> And to set a new root password read more, its quite easy
>
> 2011/8/10 abdelkader belahcene <abela...@gmail.com>
>
>> *Hi,


>> I ve forgotten my root passwd on centos 6 (red hat based),
>>
>> I tried to change it as I used in debian (in debian it works perfectly) ,
>> that is:
>>
>> use a cd live (or installation cd1), to access the hd,
>> I mount my root partition and mount proc and devices
>>
>> I tried the command passwd, no error reprorted, but after reboot the
>> passwd had´t changed.
>> then I decided to remove passwd from /etc/shadow (delete the
>> second field).
>>
>> OK, now I can access my machine without passwd, BUT I CAN´T GIVE ANY
>> PASSWORD!!!! I RECEIVE THIS ERROR
>>

>> # passwd*
>> *Changing password for user root.


>> New password:
>> Retype new password:
>> passwd: Authentication token manipulation error
>>
>> any idea to fix the problem.

>> thanks a lot *
>>
>


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Francois Cerbelle

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Aug 11, 2011, 3:40:01 AM8/11/11
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Le Wed, 10 Aug 2011 18:10:02 +0200, Thierry Chatelet a écrit :
> On Wednesday 10 August 2011 17:53:26 Umarzuki Mochlis wrote:
>> if i'm not mistaken you can just go to single user mode on centos by
>> appending "1" or "single" (without quotes) on boot parameter, no need
>> for any live cd
>>
> Not with debian, but lots of trail if you google it. Thierry

But "init=/sbin/bash" should work, then mount, modify, dont forget to
umount everything and reboot

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Ivan Shmakov

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Aug 11, 2011, 6:00:02 AM8/11/11
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>>>>> Francois Cerbelle <fran...@cerbelle.net> writes:
>>>>> Le Wed, 10 Aug 2011 18:10:02 +0200, Thierry Chatelet a écrit:
>>>>> On Wednesday 10 August 2011 17:53:26 Umarzuki Mochlis wrote:

>>> if i'm not mistaken you can just go to single user mode on centos
>>> by appending "1" or "single" (without quotes) on boot parameter, no
>>> need for any live cd

>> Not with debian, but lots of trail if you google it.

> But "init=/sbin/bash" should work, then mount, modify, dont forget to
> umount everything and reboot

Instead of rebooting, one may exec the proper init(8) here,
like:

# exec /sbin/init

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Wawrzek Niewodniczanski

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Aug 11, 2011, 8:40:02 AM8/11/11
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On 08/11/11 00:35, abdelkader belahcene wrote: 
On 8/10/11, Lucas Lima <lcs.fre...@gmail.com> wrote:

the passwords are stored in /etc/shadow and you deleted the file, you should
restore it.

I just removed the second field , the password for th root. no more things
You can copy a password from other user or even from other machine.

Wawrzek

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Nico Kadel-Garcia

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Aug 11, 2011, 10:30:03 AM8/11/11
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On Wed, Aug 10, 2011 at 11:25 AM, abdelkader belahcene
<abela...@gmail.com> wrote:
> Hi,
> I ve forgotten my root passwd on centos 6 (red hat based),
>
> I tried to change it as I used in debian (in debian it works perfectly) ,
> that is:
>
> use a cd live (or installation cd1), to access the hd,
> I mount  my root partition and mount proc and devices

Definitely the wrong newsgroup, but:

* boot with CentOS, RHEL, or Scientific Linux rescue CD
* Select "linux rescue" or rescue mode from the CD boot process.
* Allow it to mount your old system at /mnt/sysimage with all
the relevant /dev and /dev/sys utilities under it.
* Do "chroot /mnt/sysimage" to enter the environment of the
mounted directories, in a chroot cage.
* THEN do "passwd root"
* Exit the chroot. (Just type "exit").
* Sync the disk changes, just as a precaution. (Just type "sync")
* Reboot and eject CD.

I generally setup PXE to make these tools available without a CD in
large environments,. The "chroot" business is core to updating messed
up grub configurations, password files, kernels, fstab, or core system
libraries.

> I tried  the command passwd, no error reprorted, but after reboot the passwd
> had´t changed.
> then I decided to remove passwd from /etc/shadow (delete the
> second field).


>
> OK,  now I can access my machine  without passwd,  BUT I CAN´T GIVE ANY
> PASSWORD!!!!  I RECEIVE THIS ERROR
>
> # passwd
> Changing password for user root.
> New password:
> Retype new password:
> passwd: Authentication token manipulation error
>
> any idea to fix the problem.
> thanks a lot
>

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Robert Blair Mason Jr.

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Aug 11, 2011, 1:10:02 PM8/11/11
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On Thu, 11 Aug 2011 07:14:23 +0000 (GMT)
Francois Cerbelle <fran...@cerbelle.net> wrote:

> Le Wed, 10 Aug 2011 18:10:02 +0200, Thierry Chatelet a écrit :
> > On Wednesday 10 August 2011 17:53:26 Umarzuki Mochlis wrote:
> >> if i'm not mistaken you can just go to single user mode on centos
> >> by appending "1" or "single" (without quotes) on boot parameter,
> >> no need for any live cd
> >>
> > Not with debian, but lots of trail if you google it. Thierry
>
> But "init=/sbin/bash" should work, then mount, modify, dont forget to
> umount everything and reboot
>

You mean init=/bin/bash right?

and you'll probably have to mount -o remount,rw / before you passwd.

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Walter Hurry

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Aug 11, 2011, 2:50:02 PM8/11/11
to

All the responses (except one) have me mystified. Why can't OP just boot
into single user mode?

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Dom

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Aug 11, 2011, 3:30:02 PM8/11/11
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On 11/08/11 19:46, Walter Hurry wrote:
> On Thu, 11 Aug 2011 10:23:17 -0400, Nico Kadel-Garcia wrote:
>
>> On Wed, Aug 10, 2011 at 11:25 AM, abdelkader belahcene
>> <abela...@gmail.com> wrote:
>>> Hi,
>>> I ve forgotten my root passwd on centos 6 (red hat based),
>>>
>>> I tried to change it as I used in debian (in debian it works perfectly)
>>> , that is:
>>>
(snippage)

>
> All the responses (except one) have me mystified. Why can't OP just boot
> into single user mode?

Because you need the root password to enter single user mode?

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Walter Hurry

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Aug 11, 2011, 5:40:02 PM8/11/11
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On Thu, 11 Aug 2011 20:28:33 +0100, Dom wrote:

> On 11/08/11 19:46, Walter Hurry wrote:
>> On Thu, 11 Aug 2011 10:23:17 -0400, Nico Kadel-Garcia wrote:
>>
>>> On Wed, Aug 10, 2011 at 11:25 AM, abdelkader belahcene
>>> <abela...@gmail.com> wrote:
>>>> Hi,
>>>> I ve forgotten my root passwd on centos 6 (red hat based),
>>>>
>>>> I tried to change it as I used in debian (in debian it works
>>>> perfectly) , that is:
>>>>
> (snippage)
>>
>> All the responses (except one) have me mystified. Why can't OP just
>> boot into single user mode?
>
> Because you need the root password to enter single user mode?

Not in RHEL and clones.

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Aaron Toponce

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Aug 11, 2011, 5:50:02 PM8/11/11
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On Thu, Aug 11, 2011 at 08:28:33PM +0100, Dom wrote:
> On 11/08/11 19:46, Walter Hurry wrote:
> >On Thu, 11 Aug 2011 10:23:17 -0400, Nico Kadel-Garcia wrote:
> >
> >>On Wed, Aug 10, 2011 at 11:25 AM, abdelkader belahcene
> >><abela...@gmail.com> wrote:
> >>>Hi,
> >>>I ve forgotten my root passwd on centos 6 (red hat based),
> >>>
> >>>I tried to change it as I used in debian (in debian it works perfectly)
> >>>, that is:
> >>>
> (snippage)
> >
> >All the responses (except one) have me mystified. Why can't OP just boot
> >into single user mode?
>
> Because you need the root password to enter single user mode?

sulogin is easy enough to bypass.

* Boot Live CD
* Mount /
* Edit /etc/inittab
* Comment out si::sysinit:/etc/init.d/rcS
* Reboot into single user mode

Much easer than chroots, or any of the other previous suggestion, IMO.

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Aaron Toponce

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Aug 11, 2011, 6:00:01 PM8/11/11
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On Thu, Aug 11, 2011 at 03:48:02PM -0600, Aaron Toponce wrote:
> * Comment out si::sysinit:/etc/init.d/rcS

Meh. Wrong copy/paste. Comment out: ~~:S:wait:/sbin/sulogin

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Robert Blair Mason Jr.

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Aug 11, 2011, 11:50:01 PM8/11/11
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On Thu, 11 Aug 2011 15:48:02 -0600
Aaron Toponce <aaron....@gmail.com> wrote:
>
> sulogin is easy enough to bypass.
>
> * Boot Live CD
> * Mount /
> * Edit /etc/inittab
> * Comment out si::sysinit:/etc/init.d/rcS
> * Reboot into single user mode
>
> Much easer than chroots, or any of the other previous suggestion, IMO.
>

Easier than:

* Add init=/bin/bash to the end of kernel in grub
* mount -o remount,rw /
* passwd
* sync & reboot

? Most people I know would rather blindly type commands than edit a
file, and I for one lose my Live CDs a lot :D

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Ivan Shmakov

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Aug 12, 2011, 12:10:01 AM8/12/11
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>>>>> Robert Blair Mason <rb...@verizon.net> writes:
>>>>> On Thu, 11 Aug 2011 15:48:02 -0600

>> sulogin is easy enough to bypass.

>> * Boot Live CD
>> * Mount /
>> * Edit /etc/inittab
>> * Comment out si::sysinit:/etc/init.d/rcS
>> * Reboot into single user mode

>> Much easer than chroots, or any of the other previous suggestion, IMO.

> Easier than:

> * Add init=/bin/bash to the end of kernel in grub
> * mount -o remount,rw /
> * passwd
> * sync & reboot

I'd rather recommend # umount -a instead of # sync here.

Then, to my experience, # exec /sbin/init is by no way inferior
to # reboot.

> ? Most people I know would rather blindly type commands than edit a
> file, and I for one lose my Live CDs a lot :D

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