Boot
8 articles, grouped by kind; the order follows the tracks.
Concepts 5
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System boot and GRUB
How Linux boots: firmware, the GRUB bootloader, the kernel, systemd targets and emergency mode.
5 minupdate-grubgrub-installsystemctl get-default -
The kernel
What the Linux kernel is, what it does, and how to check its version and parameters.
4 minuname -runame -acat -
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 -
Kernel modules
Kernel modules: loading and unloading with modprobe, kernel messages in dmesg, module parameters.
4 minuname -rlsmodmodprobe -
cloud-init — first-boot VM setup
Automatic setup of cloud/virtual machines on first boot — user-data, debugging.
4 mincloud-init statuscloud-init schemaless
Commands 3
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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 -
dmesg — kernel messages: OOM, disk and filesystem errors, segfaults
dmesg prints the kernel ring buffer: messages about disks, filesystems, OOM, crashed programs and hardware.
9 mindmesg -Tdmesg -ldmesg -x -
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
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