OS

OS

Print the OS or Linux distribution name and version

Module type	os
Default order	3 (only used by --gen-config)
Module source	src/modules/os/os.c
Detection source	src/detection/os/

Prints one line: the distribution's pretty name, with the architecture appended when the pretty name does not already mention it.

The key defaults to the module name and is itself a format string when you override it; it may use {sysname}, {name}, {icon} and {module-name}.

OS: Ubuntu 24.04.1 LTS (Noble Numbat) x86_64
OS: macOS Sequoia 15.3 (24D60) arm64
OS: Windows 11 Pro (24H2) x86_64

Platform support

Platform	Implementation	Notes
Linux	os_linux.c	/etc/os-release, with distribution-specific fixups
Android	os_android.c	Android system properties (ro.build.version.*)
FreeBSD / MidnightBSD / DragonFly	os_linux.c	Same os-release reader as Linux
NetBSD	os_nbsd.c	Name is hard-coded, version from uname -r
OpenBSD	os_obsd.c	Name is hard-coded, version from uname -r
Solaris / illumos	os_sunos.c	First line of /etc/release
Haiku	os_haiku.c	Parses the API version of the loaded libroot image
GNU/Hurd	os_linux.c	Same os-release reader as Linux
macOS	os_apple.m	SystemVersion.plist, plus a hard-coded codename table
Windows	os_windows.c	winbrand.dll BrandingFormatString

Configuration

Key	Type	Default	Description
key	string	module name	Module key. A single space hides the key and the separator.
keyColor	color	–	Overrides display.color.keys.
keyWidth	integer	–	Overrides display.key.width.
keyIcon	string	built-in glyph	Printed when display.key.type includes the icon bit. Any glyph works; "" prints none.
outputColor	color	–	Overrides display.color.output.
format	string	–	Custom output format (see below).
condition	object	–	Show the module only if the conditions match.

There are no module-specific keys — everything the module can print is reachable through format.

Format string

Run fastfetch -h os-format for the authoritative list.

Variable	Description
{sysname}	Kernel name, e.g. Linux, Darwin
{name}	OS name as recorded by the distribution
{pretty-name}	Distribution's preferred display name
{id}	Lower-case distribution ID, e.g. ubuntu, macos
{id-like}	Parent distribution, e.g. debian
{variant}	Variant string
{variant-id}	Variant ID
{version}	Version string (may contain the codename)
{version-id}	Version ID
{codename}	Version codename
{build-id}	Build ID
{arch}	Machine architecture
{kernel-release}	Release of the kernel, e.g. 27.0.0

JSON output

{
    "type": "os",
    "result": {
        "buildID": "24D60",
        "codename": "Sequoia",
        "id": "macos",
        "idLike": "",
        "name": "macOS",
        "prettyName": "macOS Sequoia 15.3 (24D60)",
        "variant": "",
        "variantID": "",
        "version": "15.3",
        "versionID": "15.3"
    }
}

Examples

{ "type": "os", "key": "{icon} {name}", "format": "{pretty-name} ({id})" }

{ "type": "os", "format": "{name} {kernel-release} {arch}" }

Pitfalls

• {kernel-release} is the raw kernel release, not a distribution version. It is the uname -r value (27.0.0, 6.12.9-arch1-1), which is what makes it useful for a distro-agnostic format — it says nothing about the distribution, unlike {version}.
• The printed architecture is not in the JSON output. The console line appends {arch}, but ffGenerateOSJsonResult writes only the ten distribution fields — a config that reads --format json gets a different field set than the console shows.
• The architecture suffix is a substring test. It is appended only when the built line does not already contain the architecture string, case-insensitively. A pretty name that happens to embed it (for example an OS whose name contains aarch64) suppresses the suffix.
• On Ubuntu the distribution's own pretty name is discarded. fastfetch rebuilds it as NAME + VERSION from os-release (which contains the codename, so it reads Ubuntu 24.04.1 LTS (Noble Numbat)). Editing PRETTY_NAME in /etc/os-release has no effect on the Ubuntu family.
• id-like is empty on macOS and Android. Neither implementation fills it; only the Linux (and Solaris) readers do.
• Some values only exist on one platform. {build-id} is empty on Linux, {codename} is empty on Windows unless the registry provides DisplayVersion, and {id-like} is empty on macOS.
• The module fails loudly when nothing was found — Could not detect OS means all of name, pretty-name and id were empty.
• Detection has no runtime override. FASTFETCH_TARGET_DIR_ETC is a build-time CMake value, not a command-line option; there is no --target.

Implementation

Linux, FreeBSD, DragonFly, GNU/Hurd

detectOS() runs a fallback chain, stopping as soon as enough fields are filled:

1. /bedrock/strata/bedrock/etc/os-release (Bedrock Linux only, skipped when BEDROCK_RESTRICT=1).
2. <ETC>/os-release — 11 keys, one ffParsePropFileValues pass: PRETTY_NAME, NAME, ID, ID_LIKE, VARIANT, VARIANT_ID, VERSION, VERSION_ID, VERSION_CODENAME, CODENAME, BUILD_ID. PRETTY_NAME is matched with a trailing space so PRETTY_NAME cannot accidentally match a longer key.
3. <ETC>/lsb-release — only when os-release left one of id/version/prettyName/codename empty; reads DISTRIB_ID, DISTRIB_DESCRIPTION, DISTRIB_RELEASE, DISTRIB_CODENAME.
4. <USR>/lib/os-release — only when id/name/prettyName are all still empty.
5. HarmonyOS, which ships no os-release file at all.

Because os-release keys are matched by prefix, a file that stores DISTRIB_ID-style keys without the documented spacing still parses; the query strings include the = and the surrounding space exactly as the file format specifies.

Distribution-specific post-processing then runs, keyed off ID:

• ubuntu — getUbuntuFlavour(). Armbian is recognised from its PRETTY_NAME prefix (and its ID is rewritten to armbian with ID_LIKE set to the original ID). Then Linux Lite, Rhino Linux and VanillaOS are matched by pretty-name prefix, LliureX by the presence of /usr/bin/lliurex-version (which it executes to get the version), and the official flavours — Ubuntu Studio, Kubuntu, Xubuntu, Lubuntu, Budgie, Cinnamon, MATE, Kylin, Sway, Touch, Unity — by comparing $XDG_CONFIG_DIRS against flavour keywords. This one is environment dependent: a KDE install whose XDG_CONFIG_DIRS does not mention kde/plasma/kubuntu is reported as plain Ubuntu.
• debian — detectDebianDerived(), matching Armbian, Loc-OS, Parrot Security, Lilidog, Proxmox VE (/usr/bin/pveversion), Proxmox Backup Server, Raspberry Pi OS (/etc/rpi-issue), DietPi (/boot/dietpi/.version, whose three components are appended to the pretty name), TrueNAS Scale (kernel release ends with +truenas), Emmabuntüs, and MX Linux (an /etc/lsb-release containing DISTRIB_ID=MX). Anything not matched falls through to getDebianVersion(), which replaces the version ID with /etc/debian_version and rebuilds the pretty name.
• fedora — CoreOS/Kinoite/Sericea/Silverblue append their variant ID to ID.
• linuxmint — LMDE is re-labelled as lmde / id-like: linuxmint.
• deepin — /etc/os-version supplies MinorVersion and EditionName.
• astra — the version is peeled off VERSION_ID (which looks like 2.12_x86-64).

macOS

SystemVersion.plist is parsed with NSDictionary for ProductName, ProductUserVisibleVersion and ProductBuildVersion, falling back to the kern.osproductversion / kern.osversion sysctls. The codename comes from a hard-coded major → codename table (including a nested one for the 10.x releases) and is matched by the first component of the version string. prettyName is assembled as name codename version (buildID) and id is fixed to macos.

Two deliberate quirks:

• A version starting with 16. has its first character rewritten to 2 — macOS 26 reported itself as 16.x during development, and the codename table also accepts both 16 and 26.
• id-like is never set, so it is always empty on macOS.

Windows

BrandingFormatString(L"%WINDOWS_LONG%") from winbrand.dll supplies the raw product string, for example Windows 11 Pro Insider Preview. It is split into name / version / edition:

• Windows and optional Server / Embedded prefixes become name.
• The first space-delimited token becomes version; a trailing Rx on a Server name is folded into the version.
• A leading (TM) is stripped, and the Microsoft prefix that WMI adds is removed so both sources agree.
• If the string does not start with Windows , the whole value is treated as the name.
• getCodeName() reads DisplayVersion, then CSDVersion (Windows 7/8), then ReleaseId (early Windows 10) from SOFTWARE\Microsoft\Windows NT\CurrentVersion and appends it to the pretty name in parentheses.
• id becomes "<name> <version>" (lower-cased later) and id-like is fixed to Windows.

BrandingFormatString allocates with GlobalAlloc, so the returned pointer is released with GlobalFree after being copied into a FFstrbuf. There is deliberately no branding field for the bare release number: basebrd.dll keeps it inside the same per-edition resource as %WINDOWS_LONG%, so it can only be peeled off that string.

Android, Haiku, Solaris, NetBSD, OpenBSD

• Android reads the ro.build.version.release, ro.build.version.codename and ro.build.id system properties. The codename has a built-in version→name table (the same desert names as the Android version history); the property is only consulted when the major version is not in the table.
• Haiku walks get_next_image_info(B_SYSTEM_TEAM, …) and decodes the api_version of libroot — the high 16 bits are the release, the remainder encodes alpha/beta/pre-release states (odd last bit means "pre"). Very old images map to BEOS / BONE / DANO. If no image carries a version, get_system_info().kernel_version is printed as a hex release.
• Solaris takes the first line of /etc/release, drops anything from the first ( onward, and uses the first word as id with id-like: sunos.
• NetBSD / OpenBSD hard-code the name and copy uname -r into version; there is no codename, id or pretty name, so the fallback builder in os.c assembles the line.