Linux Kernel
The Linux kernel is the main component of Photon OS and is the core interface between a computer’s hardware and its processes. It communicates between the two, managing resources as efficiently as possible.
##Kernel Flavours and Versions The following list contains the different Linux kernel flavours available:
linux
- A generic kernel designed to run everywhere and support everything.linux-esx
- Optimized to run only on VMware hypervisor (ESXi, WS, Fusion). It has minimal set of device drivers to support VMware virtual devices.uname -r
displaysLinux
. For additional features switch to the generic flavour.linux-secure
- Security hardened variant of the generic kernel.uname -r
displays-secure
suffix.linux-rt
- This is a Photon Real Time kernel.uname -r
displays-rt
suffix.linux-aws
- Optimized for AWS hypervisor kernel.uname -r
displays-aws
suffix.
To see the version of kernel installed, run the following command:
# rpm -qa | grep -e "^linux\(\|-esx\|-secure\|rt\|aws\)-[[:digit:]]"
linux-4.9.111-1.ph2.x86_64
linux-esx-4.9.111-1.ph2.x86_64
To see the version of the Kernel that is running currently, run the following command:
# uname -r
4.9.107-1.ph2-esx
From the output, you can see that the kernel running currently doesn’t match the installer. This happens when linux-* rpms were updated but was not restarted. Restart is required.
##Configuration
To find the configurations of the installed Kernel, check the /boot directory by running the following command:
# ls /boot/config-*
config-4.9.111-1.ph2 config-4.9.111-1.ph2-esx
To get a copy of the kernel configuration (Not all flavours support this feature), run the zcat /proc/config.gz
command.
##Boot Parameters and initrd Several kernel flavors can be installed on the system, but only one is used during boot. /boot/photon.cfg symlink points to the kernel which is used for boot.
# ls -l /boot/photon.cfg
lrwxrwxrwx 1 root root 23 Jun 12 2018 /boot/photon.cfg -> linux-4.9.111-1.ph2.cfg
Its contents can be checked by running the following command:
# cat /boot/photon.cfg
# GRUB Environment Block
photon_cmdline=init=/lib/systemd/systemd ro loglevel=3 quiet no-vmw-sta
photon_linux=vmlinuz-4.9.111-1.ph2
photon_initrd=initrd.img-4.9.111-1.ph2
Where:
photon_cmdline
- Kernel parameters. This list will be extended by values from /boot/systemd.cfg file and the values are hardcoded to /boot/grub2/grub.cfg file (For example: root=).photon_linux
- Kernel image to boot.photon_initrd
- Initrd to use at boot.
Parameters of the kernel loading currently can be found by running the /proc/cmdline
command:
# cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.9.107-1.ph2-esx root=PARTUUID=29194d05-4a6e-4e0c-b1f4-5020e5e8472c net.ifnames=0 init=/lib/systemd/systemd ro loglevel=3 quiet no-vmw-sta
##Dmesg
To view message buffer of the kernel run the dmesg
command.
##Sysctl State
To view a list of all active units run the systemctl list-units
command.
##Kernel Statistics
The kernel statistics can be found by running the following commands:
procfs
sysfs
debugfs
##Kernel Modules
To view the kernel log buffer run the journalctl -k
command.
To view a list of available kernel modules run the lsmod
command.
To view detailed information about all connected PCI buses run the lspci
command.