Boot
-
systemd
The init system and service manager (PID 1): units, targets, dependencies, journals.
8 minsystemctl statussystemctl startsystemctl stop -
System boot and GRUB
How Linux boots: firmware, the GRUB bootloader, the kernel, systemd targets and emergency mode.
5 minupdate-grubgrub-installsystemctl get-default -
Mounting and fstab
Mounting filesystems: the mount command, persistent mounts in /etc/fstab, UUIDs and options.
7 minlsblk -ffindmntblkid -
The kernel
What the Linux kernel is, what it does, and how to check its version and parameters.
4 minuname -runame -acat -
Persistent networking with netplan
Persistent network configuration on Ubuntu — netplan YAML files, static addresses and DHCP, applying safely.
6 minnetplan generatenetplan trynetplan apply -
Boot targets: default, multi-user, rescue and emergency
A target is a group of units systemd brings the boot up to; rescue and emergency are the targets for repairs.
11 minsystemctl get-defaultsystemctl set-defaultsystemctl list-units -
systemd-analyze: what slows the boot and what is wrong in a unit
Breaks the boot down by time and by the chain of unit dependencies, and checks a unit file before the service runs.
11 minsystemd-analyzesystemd-analyze blamesystemd-analyze critical-chain -
Kernel modules
Kernel modules: loading and unloading with modprobe, kernel messages in dmesg, module parameters.
4 minuname -rlsmodmodprobe -
sysctl — kernel parameters at runtime
sysctl reads and changes kernel parameters; -w lasts until reboot, a file in /etc/sysctl.d/ makes it permanent.
9 minsysctlsysctl -nsysctl -w -
cloud-init — first-boot VM setup
Automatic setup of cloud/virtual machines on first boot — user-data, debugging.
4 mincloud-init statuscloud-init schemaless