Sometimes you want the root user or other trusted users to be able to run cronjobs or timed scripts with at. In order to lock these down, you will need to create a cron.deny and at.deny file inside /etc with the names of all blocked users. An easy way to do this is to parse /etc/passwd. The script below will do this for you.
echo “Locking down Cron”
touch /etc/cron.allow
chmod 600 /etc/cron.allow
awk -F: ‘{print $1}’ /etc/passwd | grep -v root > /etc/cron.deny
echo …

If you have repaired your system from a backup tape (by dump or tar), for example, you will need to repair the bootstrap area.You need to re-install the bootstrap code that is grub.
Please perform the following steps:

Boot from OS(Redhat,Fedora,CentOS) installation disc (for example, CD #1 or DVD).
Type “linux rescue” at the “boot:” prompt.
Mount all filesystems in read-write mode.
Change root to real root (‘/’) on your hard disk:
# chroot /mnt/sysimage

Re-install bootstrap code (GRUB).

If you wish to re-install GRUB to the MBR …

Centos is BAck, seems all centos users are happy to see this message.
CentOS is not dead or going away. The signers of the Open Letter are fully committed to continue the CentOS Project. Updates and new releases will continue.
The CentOS Development team had a routine meeting  with Lance Davis in attendance. During the meeting a majority of issues were resolved immediately and a working agreement was reached with deadlines for remaining unresolved issues. There should be no impact to any …