Authentication failure (Clock skew too great)

I’ve faced a ACCESS DENIED issue when trying to login  after vmware tools update. While checking on /var/log/secure I found (Clock skew too great) error.

To overcome this I re-synchronized ntp and authentication worked successfully.

Jul 25 06:34:13 RHEL7 sshd[16099]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=domain.platforms.com  user=Ranjith_P04

Jul 25 06:34:13 RHEL7 sshd[16099]: pam_krb5[16099]: authentication fails for 'Ranjith_P04' (Ranjith_P04@PLATFORMS.COM): Authentication failure (Clock skew too great)

Jul 25 06:34:13 RHEL7 sshd[16099]: pam_krb5[16099]: authentication fails for 'Ranjith_P04' (Ranjith_P04@PLATFORMS.COM): Authentication failure (Clock skew too great)

Jul 25 06:34:15 RHEL7 sshd[16099]: Failed password for Ranjith_P04 from 10.81.11.250 port 50457 ssh2

Jul 25 06:34:20 RHEL7 sshd[16099]: pam_krb5[16099]: authentication fails for 'Ranjith_P04' (Ranjith_P04@PLATFORMS.COM): Authentication failure (Clock skew too great)

Jul 25 06:34:20 RHEL7 sshd[16099]: pam_krb5[16099]: authentication fails for 'Ranjith_P04' (Ranjith_P04@PLATFORMS.COM): Authentication failure (Clock skew too great)

How to set grub password in rhel 7

 Set grub password in rhel 7

GRUB 2 supports both plain-text and encrypted passwords in the GRUB 2 template files. To enable the use of passwords, specify a superuser who can reach the protected entries. Other users can be specified to access these entries as well. Menu entries can be password-protected for booting by adding one or more users to the menu entry as described below

Use grub2-mkpasswd-pbkdf2 command as superuser and generate hash of your password

[root@RHEL7 ~]# grub2-mkpasswd-pbkdf2

Enter password:

Reenter password:

PBKDF2 hash of your password is grub.pbkdf2.sha512.10000.94B202970DD3C124AF25AC9F05B504C6CAFBDEB976821E5D8247A938D3DBC0D9678B62E9519EEBC8A01DA479666578DC87B8CD0A8AF45A2D27285E76A1810F27.C8C6F75E5B6F9063271FEBB8294CA1276F4E87848632D30A95E29471F9AD43D845903B98CFE547C08B272E37E441768786BDC9899239CAC6599A8522D845F3A6

When the users and passwords are set up, specify the menu entries that should be password-protected in the /etc/grub.d/40_custom file in a similar fashion to the following:

[root@RHEL7 ~]# cat /etc/grub.d/40_custom

#!/bin/sh

exec tail -n +3 $0

set superusers="root"

password_pbkdf2 root grub.pbkdf2.sha512.10000.94B202970DD3C124AF25AC9F05B504C6CAFBDEB976821E5D8247A938D3DBC0D9678B62E9519EEBC8A01DA479666578DC87B8CD0A8AF45A2D27285E76A1810F27.C8C6F75E5B6F9063271FEBB8294CA1276F4E87848632D30A95E29471F9AD43D845903B98CFE547C08B272E37E441768786BDC9899239CAC6599A8522D845F3A6

# This file provides an easy way to add custom menu entries.  Simply type the

# menu entries you want to add after this comment.  Be careful not to change

# the 'exec tail' line above.

NOTE: the line below "set superusers" is a single line it should be password_pbkdf2 root followed by the encrypted password.

[root@RHEL7 ~]#

Run grub2-mkconfig -o /boot/grub2/grub.cfg to import the changes into the main configuration file.

[root@RHEL7 ~]# grub2-mkconfig -o /boot/grub2/grub.cfg

Generating grub configuration file ...

Found linux image: /boot/vmlinuz-3.10.0-327.3.1.el7.x86_64

Found initrd image: /boot/initramfs-3.10.0-327.3.1.el7.x86_64.img

Found linux image: /boot/vmlinuz-3.10.0-229.el7.x86_64

Found initrd image: /boot/initramfs-3.10.0-229.el7.x86_64.img

Found linux image: /boot/vmlinuz-0-rescue-aed9495c9fa84bfbb71646105626f6c3

Found initrd image: /boot/initramfs-0-rescue-aed9495c9fa84bfbb71646105626f6c3.img

done