Basic Kernel Management

10. How do you install a new version of the kernel?

# yum update kernel

Command to upgrade the kernel.

# yum upgrade kernel or # yum install kernel

An alternative method of loading kernel modules is through what directory.

/etc/modules-load.d this directory has a counterpart in /usr/lib/modules-load.d

2. Where do you find current version information about your RHEL 7 installation?

/etc/redhat-release

What directory does systemd-udevd look in for custom rules?

/etc/udev/rules.d

To decide how the devices are initialized, systemd-udevd reads rules files in what directory?

/usr/lib/udev/rules.d

1. What causes a tainted kernel?

A tainted kernel is caused by drivers that are not available as open source drivers. Using these may have impact on the stability of the Linux operating system, which is why it is good to have an option to recognize them easily.

8. Where do you specify kernel module parameters that should be used persistently?

Create a file in /etc/modprobe.d and include the parameters using an "options" statement.

6. Where does your system find the default rules that are used for initializing new hardware devices?

Default rules for hardware initialization are in the directory /usr/lib/udev/rules.d; custom rules should be stored in /etc/udev/rules.d.

10. Which statements about updating the kernel are true?

Kernels are not updated, they are installed, and you can use either yum update kernel or yum install kernel to do so.

9. Where do you specify a kernel module parameter to make it persistent?

On RHEL 7, kernel module parameters are passed through /usr/lib/modprobe.d if it is for operating system managed permanent parameters. The /etc/modprobe.d directory is used for files that create custom configuration

5. What is the name of the process that helps the kernel initializing hardware devices properly?

On a systemd-based operating system such as RHEL 7, the systemd-udevd process takes care of initializing new hardware devices.

4. Which command shows the current version of RHEL you are using?

The /etc/redhat-release version contains information about the current version of RHEL you are using, including the update level.

2. What is the name of the command that shows kernel events since booting?

The dmesg utility shows the contents of the kernel ring buffer. This is the area of memory where the Linux kernel logs information to and gives a clear overview of recent kernel events.

8. Which command enables you to see whether the appropriate kernel modules have been loaded for hardware in your server?

The lspci -k command lists devices that are detected on the PCI bus and supporting kernel modules that have been loaded for those devices. Alternatively, lspci -v shows more verbose information about modules that are currently loaded.

7. Which command should you use to unload a kernel module, including all of its dependencies?

The modprobe command is the only command that should be used for managing kernel modules, as it considers kernel module dependencies as well. Use modprobe to load a kernel module and modprobe -r to unload it from memory.

3. Which command enables you to find the actual version of the kernel that is used?

The uname -r command shows the current kernel version. The uname -v command gives information about the hardware in your computer.

How do you recognize kernel thread in the ps aux command?

They will have square brackets in the last column.

6. What can you do if you get an error message while trying to unload a kernel module?

Use lsmod to find out which other kernel modules currently need this kernel module and unload these kernel modules first. Notice that this will not always work, especially not if the considered hardware currently is in use.

7. How do you find which kernel module parameters are supported?

Use modinfo.

What is a tainted kernel?

a kernel that contains closed source drivers

Command which gives detailed information about each memory segment and what exactly is happening in these memory segments.

cat /proc/meminfo

What are 3 tools to help analyze what the kernel is doing?

dmesg, the /proc file system, and uname

Another command to show kernel version.

hostnamectl status

Command to show clock time with dmesg info instead of time relative to the kernel starting

journalctl -k / --dmesg

3. Which command shows a list of kernel modules that currently are loaded?

lsmod

Command to list currently loaded kernel modules.

lsmod

Command to display info about the kernel modules.

modinfo

4. Which command enables you to discover kernel module parameters?

modinfo modulename

Command to load kernel modules and all of their dependencies.

modprobe

5. How do you unload a kernel module?

modprobe -r

Command to unload kernel modules considering dependencies.

modprobe -r

9. Assuming that the cdrom module has a parameter "debug", which must be set to 1 to enable debug mode, which line would you include in the file that will automatically load that module?

options cdrom debug=1

Required kernel modules are loaded automatically and status about the kernel modules and associated hardware is written to the what file system.

sysfs, which is mounted on the /sys directory

What process takes care of loading the appropriate driver and making the hardware device available

systemd-udevd

1. Which command shows the current version of the kernel that is used on your computer?

uname -r