RHEL5/6 Interview Questions : System Initialization

1. GRUB has three stages. Can you name them?
Ans:

• Stage 1: During this stage, the primary bootloader is read into memory by the BIOS from the MBR.
• Stage 1.5: During this stage, the bootloader is read into memory by the stage 1 bootloader (only if necessary).
• Stage 2: During this stage, the bootloader reads the operating system or kernel.

2. What option at the GRUB boot menu can you use to append something to a kernel?

2A. By entering the GRUB boot menu, you can choose the a option to append something to the kernel command-line options.

3. The old SysInit scripts have been replaced in Red Hat Enterprise Linux 6 for what new boot utility?

3A. Upstart. The Upstart utility is now used in the boot process for Red Hat Enterprise Linux 6.

4. Runlevel 0 reboots the system. True or False?

4A. False. Runlevel 0 halts the system. Runlevel 6 reboots the system.

5. If your system crashes and becomes unbootable, you have to reinstall the whole operating system. True or False?

5A. False. Most boot issues can be resolved by entering rescue mode and repairing the problem.

6. What command can you use to manage system services?

6A. The service command is used to start, stop, and manage system services.

7. What command disables the SSH service from running when the system boots?

7A. chkconfig sshd off

8. How can you list all services on the system to tell whether they will boot during startup?

8A. chkconfig —list

9. What does S12rsyslog in the /etc/rc.d/rc2.d directory mean?

9A. When the system enters into runlevel 2, the rsyslog service has a priority of 12 when starting. Anything with a lower number (or the same number and lower first letter) starts before the rsyslog service.

10. How can you verify the status of the SSH service after the system has booted? 

10A. service sshd statuts

11. What command and option can you use to enable a service to start on boot? 

11A. Use the chkconfig command to enable or disable services during the boot process. The on option enables the service and off disables it.