Oracle linux

Oracle linux boot sequence:

The computer performs a power-on-self-test and invokes firmware code.
Firmware (Bios or UEFI) code locate the boot instructions on the disk.
The boot instructions start the grub 2 bootloader.
Grub 2 boot loader loads the vmlinuz kernel image.
Vmlinuz is a compressed kernel image and initrd provides a temporary root file system to facilitate the kernel in loading necessary modules to access the root file system.
Grub 2 extract the contents of the initramfs image.
The kernel loads driver modules from initramfs.
Kernel starts the system process. Systemd

Basic input/output system (BIOS)

Only support booting from legacy MS-DOS labelled disk upto 2tb.

Unified Extensible firmware interface (UEFI)

Boots from GPT labelled disk
Include a secure boot mode which validates against the boot.

efibootmgr utility:

Efibootmgr is manage the boot order.
Secure boot is option feature with UEFI. Boot proces must be signed and authenticate in order to loaded and excited if not enabled the secure boot.
grub2-mkconfig command created the configuration file using template scripts in the /etc/grub.d/ directory and configuration variables in the /etc/default/grub

Boot loader specification (BLS) is a new way to define each kernel available to boot. Blscfg command in grub.cfg process the boot loader entry. Each boot loader entry file contains details of one kernel.
Setting a default kernel through command:

grub2-set+default or grubby —set-default

The value of Grub_default should be set to saved in /etc/default/grub. The commands update thr saved entry in the grubenv file.

The initial ram dial image preloads the block device modules so that root file system can be mounted.

Oracle announced the unbreakable enterprise kernel (UEK) in September 2010.

It is used by Exadata and Exalogic for extreme performance.
Btrfs file system : no volume manager needed with built-in RAID support

Systemd:

Speed up the booting ny loading services concurrently.
Provide a backward compatibility for the applications still using init script.
Forking service have a main process that forks another to do the work and exits.

#systemctl list-units —type mount

Cheony

chrony provides a client and server implementation of NTP.
Oracle linux can run tasks automatically, and comes with automated task utilities such as cron, anacron and systemd timers.
Anacron can run a job once a day. Scheduled a job are remembered and run the next time the system is up.
The main configuration file is /etc/anacrontab.
Chronyc tracking
Chronyc waitsync (synchronized the time)
chronyc -n sourcestats -v

Kernel module:

Kernel modules are dynamically loaded and unloaded. Kernel modules are store under /lib/modules/kernel_version

Modinfo module_name

Sysctl utility:

The sysctl utility is used to assign values to writable files in /proc/sys.
Added a change in /etc/sysctl.d and use sysctl -p filename to make a change immediately.

Device link:

Create a rule fils - /etc/udev/rules.d/20-local.rules

Run a udevadm trigger to proces the rule files.

Sysctl -w net. Ipv4.ip_forward=0

Package management:

Errata - bug fixing , security fix and enhancement
Rpm -qc package name (file associated with package)

Cves - common vulnerable and explicit

DNF automatic tool :

Providing a automatic notification, download and install of upgrades
Systemctl enable —now dnf-automatic.timer

Network security:

Linux kernel has builtin packet filtering function. Netfilter provide a framework inside the linux kernel.
Zone defines a set of firewalld configuration that should be applied. A zone can be associated with any number and combination of interfaces and source addresses.

The firewalld software package includes a set of predefined network zones on the following directory - /usr/lib/firewalld/zones
The default firewalld configuration file - /etc/firewalld/firewalld.conf
Change the default zone through command line:

#firewall-cmd —set-default-zone=work

Ksplice:

Updates the kernel and select space libraries on a running system.
Rollback updates without any reboot.
Patches going into new kernel or user space releases are tested by Oracle. They are then applied as Ksplice updates from Oracle Linux packages.
Install available user space updates:

#ksplice -y user upgrade

Linux shared memory:

#ls /proc/sys/kernel/sh*

Set a shared memory kernel parameters in /etc/sysctl.d/97-oracle-database-sysctl.conf.

Network Tuning : ip ports is assigned to a server process when it starts.

TCPDUMP:

To display for a network device on port 80.

#tcpdump -i eth1 port 80

To display packets without resolving host names.

#tcpdump -i eth1 —nnn port 80

For saving captured packets.

#tcpdump -i eth1 —nn port 80 -w caturefile.pcap

#tshark -D (To view a list of available network interfaces)

Partition devices are listed in the /proc/paritions.

To have the kernel re-read the partition

#partprobe device_name

Sd - scsi disk, hd-IDE disk, xvd- virtual disk, vd - Virtual disk

File system type:

ext2 - High performance for fixed disk and removable media.
ext3 - Journaling version of ext2
ext4 - supports larger files and file system sizes.
vfat - Ms-Dos file system useful when sharing a files between Windows and Linux.
Xfs - High performance journaling file system.
Btrfs - Addresses scalability requirements of large storage system.

Add a user into secondary group.

#usermod -aG groupID user name