Linux Classroom Series – 04/Aug/2020

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 Preview
  • 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)

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