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Chapter 7 Section 1: Linux boot process

  • Explain RHEL7 boot process and replacing init/upstart with systemd
  • Explain each phase: Firmware phase > grub phase > kernel phase (ramdisk) > initialization phase
  • Explain system startup 0

Kernel version and file structure

  • using uname and determining version
  • upgrading kernel

[root@ie ~]# cat /proc/cmdline BOOT_IMAGE=/vmlinuz-3.10.0-327.28.3.el7.x86_64 root=/dev/mapper/vg00-root ro rd.lvm.lv=vg00/swap crashkernel=auto rd.lvm.lv=vg00/usr rd.lvm.lv=vg00/root rhgb quiet LANG=en_GB.UTF-8 [root@ie ~]# cat /proc/version Linux version 3.10.0-327.28.3.el7.x86_64 (mockbuild@x86-037.build.eng.bos.redhat.com) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-4) (GCC) ) #1 SMP Fri Aug 12 13:21:05 EDT 2016

Kernel modules

  • lsmod, modprobe, cat /proc/modules
  • modinfo, depmod

Grub

  • Give introduction to grub
  • modifying grub at boot time for password reset, other issues (grub2-mkconfig /boot/grub2/grub.cfg and /boot/efi/EFI/redhat/grub.cfg)
  • grub2-set-default 1

Resetting root password example

  • chroot /sysroot
  • mount -o remount,rw /
  • passwd
  • touch /.autorelabel
  • exit
  • reboot

fstab

chroot /sysroot mount -o remount,rw / modify fstab touch ./autorelabel exit reboot

System D Units

  • example of pstree (pstree -p and pstree -u)
  • example of pkg-config (display systemdsystem unit directory and userconf directory)
  • make note of special units created and destroyed at run time in /etc/rc.d/init.d
  • describe some unit types
  • systemd-analyze
  • systemd-analyze blame (work out how long processes took to start)

Control groups

  • explain and give examples of control groups (cgroups)
  • systemd-cgls, systemctl-cgtop
  • systemctl show -p BlockIOWeight -p CPUShares atd
  • systemctl set-property atd BlockIOWeight=200 CPUShares=256

Systemctl command

  • explain systemctl commands and give examples
  • systemctl get-default
  • systemctl set-default graphical.target
  • systemctl set-default multi-user.target
  • systemctl halt (shutdown to halt state)
  • systemctl poweroff (shutdown system)
  • systemctl reboot (reboot the system)
  • systemctl hybrid-sleep (put machine in sleep.)

Shutdown command

  • examples of shutdown shutdown -P 20 etc

System logging

  • starting and enabling rsyslog service
  • rsyslog conf examples
  • rsyslogd -N 1 (to check for errors)

Logrotate

  • explain log rotate and cron job, log rotation config
  • custom log rules example

Boot log file

  • explain /var/log/boot.log

Journalctl

  • explain the journal and Journalctl
  • show examples of using journactl (journalctl -f, journalctl -o verobose, journalctl -b etc)