Linux root password recovery in RHEL 6 and other non-systemd systems

• Introduction
• Four options of recovering root password in Linux
• Using init=/bin/bash trick in grub (classic method for RHEL6)
• Switching to a single user mode it it is not password protected (works for SUSE)
• Booting from the rescue disk, mounting and chrooting root filesystem
• Creating a new account and adding it to wheel group instead of resetting root password

Introduction

NOTE: This is a procedure for RHEL6. For RHEL7 see Recover the Root Password in RHEL 7

Generally it is highly recommended to configure  Sudo so the wheel group does not require password to get to root. Wheel group should be limited to users who are system administrators of the server. That increases the resilience of the system against lost root password problem without negatively affecting the security of the machine (you need an inside information to know which user belongs to wheel group and the password of the user to get to the root via privileged account).

If you have many servers with different root passwords, using Casio Databank watches is good protection against losing root passwords. The battery last 10 years, so you should not worry about finding that when you need the data the washes have no battery life left, as can happen with smartwatches. Please note that storing  passwords on a cell phone or smart watches or any device connected to the Net is not a good idea.

Paper works OK too (contrary to opinion in the popular security literature). They key issue here is store if in a safe place (envelope in protected box or safe are OK). Efforts to open the safe and get the password are minor then efforts of the recovery of password for a remote server.  See Password Policy for more information.

Four options of recovering root password in RHEL 6 and similar systems with old grub and no systemd

If the root password is lost, there are four main options:

1. Adding init=/bin/bash trick in grub.  This is a classic method for Red Hat.  This method has an important advantage over booting from rescue dist or CD distribution: if you root partition is an LVM partition it will be mounted correctly.
2. Booting into single user mode by adding 1 to the grub kernel option command line  and hoping that it is not password protected. Various distribution configure single user mode differently. SLES and RHEL require password, but SLES accepts Enter as a password in single user mode (unless you set empty password in /etc/shadow in your previous attempt; then you are screwed and need to use CD-based distro).
   • While you system is starting up, hold down the Ctrl key or Esc to see the boot loader menu. After you see the menu. After that:
   • Use the arrows to select the boot entry you want to modify.
   • Press e to edit the entry.
   • Use the arrows to go to rescue system kernel line.
   • Press a or e to append this entry.
   • At the end of the line add the word single or the number 1.
   • Press Enter to accept the changes.
   • Press b to boot this kernel.
3. Booting into recovery mode from the rescue disk and mount the disk with root filesystem. This is the only method is you have other problems along with lost root password. It is more difficult if you use LVM for root filesystem and that's why generally it is better to use regular partition for root.
4. You can add another account and enroll it in wheel group setting for wheel group members the ability to execute any command as root without password. This way it you forget root password you still can get to it from you user account.  

Adding init=/bin/bash trick in grub (Classic method for RHEL6)

In case single user mode is password protected you need to add  init=/bin/bash to the grub kernel command line.  It is very similar to previous, but instead of appending 1 you append  init=/bin/bash  Alternatively and less intuitively can all add 1 to the line:

First, try single user. If you don't see either a LILO or GRUB boot screen, try hitting CTRL-X to get one. If it's LILO, just type "linux single" and that should do it (assuming that "linux" is the lilo label). If GRUB, hit 'e", then select the "kernel" line, hit "e" again, and add " single" (or just " 1") to the end of the line. Press ENTER, and then "b" to boot. (Newer version of grub uses "a" to append to the boot line)

If you do get the prompt, the root filesystem may not be mounted rw (although "mount" may say it is). You need to remount it with the command:

mount -o remount,rw /

If that doesn't work (it might not), just type "mount" to find out where "/" is mounted. Let's say it is on /dev/sda2. You'd then type:

mount -o remount,rw /dev/sda2

Type 'e' to edit the boot entry, select the kernel line and press 'e' again, then type "init=/bin/bash", enter, press 'b' to boot it. You end up at a root prompt with root filesystem mounted read-only. (depending on the distro, you might need /bin/sh instead)

# mount / -o remount,rw 
	# passwd 
	<change your root password here> 	

Remount the filesystem back to read/only (to flash buffers):

# mount -o remount,ro /

Try to reboot.  Generally it is better to do it from DRAC or ILO as the command reboot does not always work as you are not in init. If reboot does not work you can try ctrl-alt-del.  Do not type exit: that leads to kernel  panic -- bash is init and it is interpreted as an attempt to kill init.

Switching to a single user mode it it is not password protected (works for SUSE)

The first thing to try is to boot to single user mode and check if your system was configured to ask for a root password to get to single user mode.

When presented with the grub boot menu, select your choice, then hit 'e' to edit instead of Enter.

Then scroll down to the line it displays with 'kernel /boot/kernel-X.Y.Z ....' and enter  'e' to edit it.

Scroll to the end of the line and append a 1 ( put a space after the last symbol on the line, no quotes). Then put Enter. This tells the kernel to boot into runlevel 1, the single user level.

If you are just having problems with X (can't login to via X11) you can append 3. That will get you to the command line mode.

Enter 'b' to boot using this new configuration. Note that this is a temporary change to your grub configuration. Upon next reboot the 1 will not be there and the system will be booted with default options.

You should get a fairly normal looking boot sequence except that it terminates a little early at a bash prompt. If you get a "Give root password for system maintenance", this isn't going to work. If you are lucky you will be presented with a root prompt (/bin/bash). Even if it asks password (SLES does) it might accept zero length password. Hit Enter to try.

On many distros the 'single' or 'rescue' boot will still ask for a password. You can get around this by starting linux without starting init, just launch a shell instead (this is classic way to reset root password for RHEL6  above).

Booting from the rescue disk, mounting and chrooting root filesystem

The strategies for setting a new root password also can vary.

• Reset password using passwd command. This is possible even if you booted from rescue disk. The idea is to use chroot command. Once you're at a command prompt, mount the system's root directory if it's not already mounted:

  mount -o rw /dev/sda1 /mnt

  Now, execute chroot command. After that you can reset the password:

  chroot /mnt/
  passwd

Creating a new account and adding it to wheel group instead of resetting root password

• Popular of the Internet recommendation to delete root password from /etc/shadow file does not work on all distributions. For example SLES controls if the root password is null and blocks login in this case. Fedora generally prohibit login for root via GUI.
   
• The simplest way is to modify sudoers file providing wheel group with root access and adding one existing account to the wheel group. .  
   
• Also if you have one existing account you can set it temporary to UID 0 which makes it equivalent of root.

NOTE: If nonroot account have a known password you can copy it to root account in /etc/shadow.

NEWS CONTENTS

• 201228 : Recover Root Password ( openSUSE )
• 201228 : Howtos Reset A Forgotten Root Password - 5dollarwhitebox.org Media Wiki ( Howtos Reset A Forgotten Root Password - 5dollarwhitebox.org Media Wiki, )
• 201228 : Lost Root Password Linux ( Lost Root Password Linux, )
• 201228 : FedoraProject ( FedoraProject, )
• 201228 : Howtos Reset A Forgotten Root Password ( 5dollarwhitebox.org Media Wiki )
• 201228 : Lost Root Password Linux ( Lost Root Password Linux, )
• 201228 : Resetting the Root Password ( Linux Journal )
• 201228 : lostlinuxpassword.html ( lostlinuxpassword.html, )
• 201228 : Using Grub To Change RedHat Linuxs Root Password ( 08/06/2008 , The Linux and Unix Menagerie )
• 201228 : shutting down after init=-bin-bash - LinuxQuestions.org ( shutting down after init=-bin-bash - LinuxQuestions.org, )

Old News ;-)

Recover Root Password

openSUSE

Set Root Password

If you've lost your root password, you might be able to recover it using the steps below. However, some systems are protected with boot loader passwords that will not let you do that without THAT password. If the boot loader is password protected, you need to boot from other media Like the OpenSUSE CD/DVD/mini-boot. OpenSUSE install CD is probably the best one to use.

CD/DVD Recovery Mode

If using CD/DVD boot media, You need to choose Rescue System. You enter root and then mount the disk manually. For example, a Compaq raid controller will probably be /dev/ida/c0d0 or an IDE drive will be /dev/hda1. Find the partitions by using fdisk /dev/ida/c0d0 or fdisk /dev/hda (just "p" and quit) and then mount what you need.

mount -o remount,rw /dev/sda2 /mnt

# cd /mnt
# chroot /mnt
# passwd

For 10.3, you need somemore steps:

Start the rescue system. Find the disk root partition, then, assuming its hdxy (or probably sdxy):

mount /dev/hdxy /mnt
mount -o bind /proc /mnt/proc
mount -o bind /sys /mnt/sys
mount -o bind /dev /mnt/dev
chroot /mnt

you are root in the installed sytem, with all at hand: passwd, but also YaST...

"bind" allow using two mount points for system virtual folders.

If all fails, consider that you can pull this drive (or install another drive in this machine) and mount it from another running Linux. Then recover the root password as explained above.

Single User Mode

The first thing to try is to boot to single user mode. This MIGHT not work for you, because your system might be configured to still ask for a root password to get to single user mode. If that's the case, we'll use another trick that replaces init with /bin/bash.

First, try single user. If you don't see either a LILO or GRUB boot screen, try hitting CTRL-X to get one. If it's LILO, just type "linux single" and that should do it (assuming that "linux" is the lilo label). If GRUB, hit 'e", then select the "kernel" line, hit "e" again, and add " single" (or just " 1") to the end of the line. Press ENTER, and then "b" to boot. (Newer version of grub uses "a" to append to the boot line)

You should get a fairly normal looking boot sequence except that it terminates a little early at a bash prompt. If you get a "Give root password for system maintenance", this isn't going to work, so see the "init or /bin/bash" version below.

If you do get the prompt, the / filesystem may not be mounted rw (although "mount" may say it is). Do

mount -o remount,rw /

If that doesn't work (it might not), just type "mount" to find out where "/" is mounted. Let's say it is on /dev/sda2. You'd then type:

mount -o remount,rw /dev/sda2

If you can do this, just type "passwd" once you are in and change it to whatever you like. Or just edit /etc/shadow to remove the password field: move to just beyond the first ":" and remove everything up to the next ":". With vi, that would be "/:" to move to the first ":", space bar once, then "d/:" and ENTER. You'll get a warning about changing a read-only file; that's normal. Before you do this, /etc/shadow might look like:

root:$1$8NFmV6tr$rT.INHxDBWn1VvU5gjGzi/:12209:0:99999:7:-1:-1:1074970543
bin:*:12187:0:99999:7:::
daemon:*:12187:0:99999:7:::
adm:*:12187:0:99999:7:::

and after, the first few lines should be:

root::12209:0:99999:7:-1:-1:1074970543
bin:*:12187:0:99999:7:::
daemon:*:12187:0:99999:7:::
adm:*:12187:0:99999:7:::

You'll need to force the write: with vi, ":wq!". (If that still doesn't work, you needed to do the -o remount,rw, above).

INIT or /bin/bash Mode

Another trick is to add "init=/bin/bash" (LILO "linux init=/bin/bash" or add it to the Grub "kernel" line). This will dump you to a bash prompt much earlier than single user mode, and a lot less has been initialised, mounted, etc. You'll definitely need the "-o remount,rw" here. Also note that other filesystems aren't mounted at all, so you may need to mount them manually if you need them. Look in /etc/fstab for the device names.

Keep this in mind if you have a Linux machine in a publically accessible place : without more protection, it's not usually hard to recover a lost root password, which means it's just as easy for someone to CHANGE it, or access root without your knowledge.

Another way to do this is to remove the password from /etc/shadow. Just in case you screw up, I'd copy it somewhere safe first. You want to end up with the root line looking something like this:

Original line:

root:$1$EYBTVZHP$QtjkCG768giXzPvW4HqB5/:12832:0:99999:7:::

After editing:

root::12832:0:99999:7:::

If you are having trouble with editing (you really do have to learn vi one of these days), you could just (after making a copy, of course) just

 echo  "root::12832:0:::::" > /mnt/etc/shadow 

or, if you were in single user mode

 echo  "root::12832:0:::::" > /etc/shadow 

and then fix things up when rebooted.

Howtos Reset A Forgotten Root Password - 5dollarwhitebox.org Media Wiki

In Grub :

• Type 'e' to edit the default kernel line
• Then 'e' again on the line that starts with 'kernel'
• Add 'init=/bin/bash' to the end of the 'kernel' line
• Press <ENTER>
• Type 'b' to boot it

Once you're at a /bin/bash prompt...

Remount the filesystem read/write (will be ro when bin/bash'ing):

# mount -o remount,rw /

Then change the passwd: # passwd root

Remount the filesystem back to read/only (keep things clean):

# mount -o remount,ro /

Then CTR-ALT-DELETE (though this will result in a kernel panic most likely). After rebooting the system and you should be good to go.

Lost Root Password Linux

First, try single user. If you don't see either a LILO or GRUB boot screen, try hitting CTRL-X to get one. If it's LILO, just type "linux single" and that should do it (assuming that "linux" is the lilo label). If GRUB, hit 'e", then select the "kernel" line, hit "e" again, and add " single" (or just " 1") to the end of the line. Press ENTER, and then "b" to boot.

You should get a fairly normal looking boot sequence except that it terminates a little early at a bash prompt. If you get a "Give root password for system maintenance", this isn't going to work, so see the "init" version below.

If you do get the prompt, the / filesystem may not be mounted rw (although "mount" may say it is). Do

mount -o remount,rw /

If that doesn't work (it might not), just type "mount" to find out where "/" is mounted. Let's say it is on /dev/sda2. You'd then type:

mount -o remount,rw /dev/sda2

If you can do this, just type "passwd" once you are in and change it to whatever you like. Or just edit /etc/shadow to remove the password field: move to just beyond the first ":" and remove everything up to the next ":". With vi, that would be "/:" to move to the first ":", space bar once, then "d/:" and ENTER. You'll get a warning about changing a read-only file; that's normal. Before you do this, /etc/shadow might look like:

root:$1$8NFmV6tr$rT.INHxDBWn1VvU5gjGzi/:12209:0:99999:7:-1:-1:1074970543
bin:*:12187:0:99999:7:::
daemon:*:12187:0:99999:7:::
adm:*:12187:0:99999:7:::

and after, the first few lines should be:

root::12209:0:99999:7:-1:-1:1074970543
bin:*:12187:0:99999:7:::
daemon:*:12187:0:99999:7:::
adm:*:12187:0:99999:7:::

You'll need to force the write: with vi, ":wq!". (If that still doesn't work, you needed to do the -o remount,rw, see above).

Another trick is to add "init=/bin/bash" (LILO "linux init=/bin/bash" or add it to the Grub "kernel" line). This will dump you to a bash prompt much earlier than single user mode, and a lot less has been initialized, mounted, etc. You'll definitely need the "-o remount,rw" here. Also note that other filesystems aren't mounted at all, so you may need to mount them manually if you need them. Look in /etc/fstab for the device names.

See also
http://aplawrence.com/Bofcusm/861.html
http://aplawrence.com/Bofcusm/872.html
http://aplawrence.com/Bofcusm/873.html

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