Tips and tweaks for reducing Linux startup time

Ready Set Go

Article from Issue 246/2021
Author(s):

Today's Linux systems boot faster than ever, but many users still get impatient waiting for that first glimpse of desktop. These tweaks will help you get a faster start from the bootloader and kernel.

CPUs, RAM modules, and storage media keep getting faster, but today's Linux systems are still a little too slow at startup for many busy users. With a few useful tools and a little knowledge of the Linux environment, you can shave some seconds from the startup process. Read on for some insights.

systemd-analyze

The systemd-analyze tool supplied with systemd gives a first impression of where time is being wasted. The time option outputs the total startup time and shows what portion of that time is used for firmware, bootloader, kernel, and user space:

systemd-analyze time

Listing 1 shows the output, which will vary depending on you firmware, hardware, and software configuration.

Listing 1

Analyzing Start Time

$ systemd-analyze time
Startup finished in 3.393s (firmware) + 10.554s (loader) + 2.123s (kernel) +   4.789s (userspace) = 20.860s
graphical.target reached after 4.778s in userspace

Test Setup

The test system for this article was a four-year-old Tuxedo BU1406 with a "Kaby Lake" Intel i7-7500U CPU, 32GB DDR4 RAM, and a 512GB NVMe SSD; this machine cost around a thousand dollars when it was new. The operating system was a Debian "Bullseye" ("Testing") from November 19, 2020 with a 5.9.9 kernel and systemd 246.6 set up by the Debian installer. The standard system with Gnome 3.38.1, GDM 3.38.2, and an OpenSSH server provides the user interface. Our focus was primarily on systems with UEFI firmware, which is common now on most modern hardware.

Our goal was to minimize the startup time based on the readings for firmware, loader, and kernel in the systemd-analyze output. Older systems with significantly longer default boot times typically offer far more potential to improve the boot speed.

Firmware

Users typically have few options to optimize the firmware, because it is often proprietary and only the device manufacturer can change and distribute it. In the default Debian configuration used on the test system, the UEFI firmware starts the GRUB bootloader. Other distributions might use the alternative systemd-boot boot manager in place of GRUB.

UEFI firmware is now ubiquitous on x86 systems. The startup screen typically announces which key or key pattern you need to press to access firmware settings. In the graphical firmware menu, you can look for functions that slow down the system, like network boot, and turn them off if they are not needed. Some systems even offer option for a faster startup, like Quick Boot or Fast Boot.

Aside from the lack of source code – and thus, lack of freedom – the size of the UEFI firmware is also a major criticism. Alternatives include coreboot for x86 systems, as well as U-Boot and coreboot for ARM systems. Coreboot lets you initialize only enough hardware to boot the operating system. Coreboot firmware is used in Chromebooks and on devices by vendors such as System76 and Purism. The minimal approach results in firmware startup times of less than a second, or even as little as 500ms for some devices.

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