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.
Linux. For additional features switch to the generic flavour.
linux-secure- Security hardened variant of the generic kernel.
linux-rt- This is a Photon Real Time kernel.
linux-aws- Optimized for AWS hypervisor kernel.
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.
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
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
# 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
To view message buffer of the kernel run the
To view a list of all active units run the
systemctl list-units command.
The kernel statistics can be found by running the following commands:
To view the kernel log buffer run the
journalctl -k command.
To view a list of available kernel modules run the
To view detailed information about all connected PCI buses run the