lsblk

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lsblk lists the block devices on the system and their relationships — disks, their partitions, and the device-mapper and loop devices layered on top. It is the device-oriented companion to mount: where mount with no arguments shows what is mounted, lsblk shows what is available to mount and what filesystem sits on each device.

lsblk [options] [DEVICE...]

By default it prints a tree, one row per device with children indented beneath their parent. Given one or more DEVICE operands (a name like sda, a full path like /dev/sda, or anything resolving to a device node), it re-roots the output at those devices.

Where the data comes from #

Each column is sourced from one of four places, and any that cannot be read degrades to an empty cell rather than aborting the run:

sysfs (/sys/block) — the device tree, sizes, and the topology/hardware columns. Peios leaves /sys/block unpatched, so this is the standard no-udev path.
libblkid — filesystem identity: FSTYPE, FSVER, UUID, LABEL, and the partition-table columns. libblkid is opened at runtime.
The device node's security descriptor — OWNER and MODE, read the same way ls -l reads them.
The /dev/disk/by-* symlink farm — ID-LINK. Populated by the device manager once it has run; there is deliberately no /run/udev/data parser, so the column reads the links themselves and is empty in the initramfs, where no device manager runs.

Output modes #

The mode selects how the rows are formatted; it does not change which columns are shown.

Flag	Mode
(default)	Indented tree.
`-l`, `--list`	Flat list — the same columns, no tree glyphs.
`-J`, `--json`	JSON. Flag columns render as bare booleans and `MOUNTPOINTS` as an array; children nest under a `children` key.
`-P`, `--pairs`	`KEY="value"` pairs, one device per line.
`-r`, `--raw`	Raw, space-separated. Values that could contain a space or control character are hex-escaped (`\xNN`) so fields stay parseable.
`-T`, `--tree[=COLUMN]`	Force tree output even alongside `-l`, optionally attaching the tree glyphs to `COLUMN` instead of `NAME`.

Columns #

With no column flag, lsblk prints the default set: NAME, MAJ:MIN, RM, SIZE, RO, TYPE, MOUNTPOINTS. Three flags swap in a preset, and -o names an explicit list (which wins over all of them):

Flag	Column set
`-o`, `--output LIST`	Exactly the comma-separated columns named (case-insensitive; an unknown name is a usage error).
`-O`, `--output-all`	Every available column.
`-f`, `--fs`	Filesystem view: `NAME`, `FSTYPE`, `FSVER`, `LABEL`, `UUID`, `MOUNTPOINTS`.
`-m`, `--perms`	Permissions view: `NAME`, `SIZE`, `OWNER`, `MODE`.

The available columns are NAME, KNAME, PATH, MAJ:MIN, FSTYPE, FSVER, LABEL, UUID, PTUUID, PTTYPE, PARTTYPE, PARTLABEL, PARTUUID, MOUNTPOINT, MOUNTPOINTS, SIZE, RO, RM, HOTPLUG, TYPE, OWNER, MODE, MODEL, VENDOR, REV, SERIAL, TRAN, HCTL, ALIGNMENT, MIN-IO, OPT-IO, PHY-SEC, LOG-SEC, STATE, ROTA, SCHED, PKNAME, and ID-LINK.

The `OWNER` and `MODE` columns #

OWNER and MODE describe the device node, not the filesystem on it, and they mirror ls -l exactly — there is no GROUP column and no POSIX permission bits, because access to a device node is governed by its security descriptor, not by a mode. OWNER is the owner SID (S-1-…); MODE is a three-character [type][x][+]: the device-type character (b for a block device, c for a character device), an x slot (never set for a block device), and a + when the DACL is inheritance-protected. When the SD cannot be read — for instance on a non-Peios host with no KACS syscalls — OWNER shows ? and MODE degrades honestly.

Filtering, sorting and shaping #

Flag	Effect
`-a`, `--all`	Include empty (zero-size) devices, which are hidden by default.
`-d`, `--nodeps`	Do not print a device's holders or slaves (drop the children).
`-I`, `--include LIST`	Show only devices with these major numbers (comma-separated).
`-e`, `--exclude LIST`	Exclude devices by major number. The default is `1` (RAM disks); an explicit `-e` replaces that default, and `-a` clears exclusions entirely.
`-s`, `--inverse`	Print dependencies in inverse order (holders above the devices they depend on).
`-M`, `--merge`	Collapse a subtree shared by several parents (a multipath device) to a single occurrence.
`-E`, `--dedup COLUMN`	Drop rows whose `COLUMN` value duplicates an earlier one.
`-x`, `--sort COLUMN`	Sort siblings by `COLUMN` (numeric columns sort by value, not text).

Formatting #

Flag	Effect
`-b`, `--bytes`	Print `SIZE` as an exact byte count instead of a human-readable value.
`-p`, `--paths`	Print full `/dev` paths in the `NAME` column.
`-n`, `--noheadings`	Omit the header row.
`-i`, `--ascii`	Draw the tree with ASCII characters instead of box-drawing glyphs.
`-y`, `--shell`	Render column keys shell-safe (`MAJ:MIN` becomes `MAJ_MIN`).
`-w`, `--width NUM`	Truncate each table row to `NUM` columns wide.
`--sysroot DIR`	Read sysfs, the mount table and `/dev` from `DIR` instead of `/` (chiefly for testing against a fixture).
`-h`, `--help` / `-V`, `--version`	Standard.

Exit status #

Code	Meaning
`0`	Success.
`1`	Incorrect invocation (an unknown column, a malformed major-number or width value) or a failed run (for example, `/sys/block` is unreadable).

lsblk uses this single non-zero code, matching util-linux. A per-device read failure is not fatal: it degrades the affected columns to empty or ? and the run continues. A broken output pipe (piping into head, for instance) is treated as success.

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