Boot Process Flashcards
Boot process
1) boot device
2) boot loader (grub2)
3) kernel / initramfs -> systemd -> initrd.target mount to /sysroot -> switch
4) systemd -> default target
What is RHEL boot loader?
grub2: Grand Unified Boot Loader
What is a systemd target?
A set of related systemd units
Determine default systemd target
systemctl get-default
Find all targets available on your system
systemctl list-units -t target
What are dependecies of a given target
systemctl list-dependencies graphical.target
what does it mean to isolate a target
Make that target the top most target
isolate target multi-user.target
systemctl isolate multi-user.target
set a target as default
systemctl set-default multi-user.target
How do I access the grub config?
Type letter e during boot process
How do I look at the kernel params of my last boot
cat /proc/cmdline
Inside my grub config, how do I set a systemd target?
at the end of the line starting with linux, add: systemd.unit=graphical.target
How do you exit the grub config so that it considers your changes
Ctrl X
In maintenance mode, how do you exit and continue the boot process?
Ctrl D
What is the maintenance mode systemd target
rescue.target
What is kernel param to pause the boot process?
rd.break
Change the grub timeout to 20s
sed -i 's/TIMEOUT=5/TIMEOUT=20/g' /etc/default/grub
grub2-mkconfig -o /boot/grub2/grub.cfg
Change the root passwd while not logged in
1) Boot into grub
2) add kernel param rd.break and exit with Ctr X
3) Type end to get the prompt
4) mount -o remout,rw /sysroot
5) chroot /sysroot
6) passwd
7) loadpolicy -i
8) restorecon -FvR /etc/shadow
Command to repair file system
fsck.ext4
fsck.xfs
Fix fstab issue
1) Add kernel param to boot in emergency.target
2) mount -o remount,rw /
3) Troubleshoot with lsblk and edit /etc/fstab
4) mount -av
5) reboot
