Linux boot process

• When we start linux machine , the firmware which is stored on EPROM chip in the motherboard initializes the POST (Power-On self test) to check the state of system hardware
• After success, the firmware searches and loads 1st stage boot loader in the MBR or the EFI Partition and gives control
• From here the System startup manager gets called
  • Systemd
  • SysVinit

SysVinit

• This will have a concept or runlevels which specifies different ways to use a system by controlling which service is running.
• Now execute ls -l /etc | grep rc[0-6].d
• RunLevels
  • 0: Halt the system.
  • 1: aliased to s or S. this runlevel is called as maintenance mode.
  • 2: Multiuser, this is default runlevel
  • 3: This was default multiuser mode on Redhat systems, This runs everything apart from graphical environment
  • 4: Used for customization
  • 5: Used on RedHat systems for GUI login
  • 6: Reboot the system
• Now navigate to /etc/init.d and you should be seeing scripts, so these scripts will be executed when the start/stop/reload the service.

Lets switch back to systemd and look at Logging daemon

• Linux distributions traditionally used syslogd to provide the logging services.
• Now modern linux distributions have standardized on the rsyslog package as well as the logging component of systemd referred as journald
• rsyslogd provides standard means of performing logging.
• rsyslogd cand send its output to various destinations
  • straight text files in /var/log directory
  • SQL databases
  • Other hosts
• Each log entry consists of single line containing the date, time, hostname, process name, PID & the message.
• rsyslogd configuration file (/etc/rsyslog.conf)