umount

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umount detaches a filesystem from the Peios mount tree. It is the counterpart of mount and, like it, reads live mount state from the kernel (/proc/self/mountinfo) rather than any /etc/mtab — Peios has none. Each operand is resolved against that live state and unmounted with umount2(2).

umount [-lfRA] [-dr] TARGET|SOURCE...

Operands and how they are resolved #

Each operand is either a mount point or a source:

If the (canonicalised) operand is itself a mount point in the current mount table, it is unmounted directly. This is always unambiguous.
Otherwise the operand is treated as a source and matched against the sources in the mount table. If it is mounted in exactly one place, that place is unmounted. If it is mounted in several places, umount refuses with an error naming the candidates — resolve it by naming a specific mount point, or use -A to unmount all of them.

If an operand matches nothing, it is "not mounted": normally an error (exit 32), but -g makes that a success and -q suppresses the message.

Several operands may be given in one invocation, and options may be interspersed with them (umount /a -f /b). Paths are handled as opaque bytes; an embedded NUL is a usage error. By default each operand is canonicalised; -c disables that and additionally selects UMOUNT_NOFOLLOW so the kernel does not follow a symlink in the final component.

Recursive and all-targets unmounts #

Two flags expand a single operand into multiple unmounts. Within one operand the expansion stops on the first failure.

-R / --recursive unmounts the target and everything mounted underneath it, including any over-mount stack at a single point, ordered deepest-first.
-A / --all-targets unmounts every mount point of the given source in the current mount namespace. This is the live-mountinfo "unmount everywhere" complement to source resolution; it is not an fstab feature.
-A -R together compose: for each mount point of the source, recurse underneath it.

-R and -r are mutually exclusive (combining them is a usage error, exit 1).

Flags #

Flag	Effect
`-l`, `--lazy`	Detach the filesystem now and clean up references later (`MNT_DETACH`).
`-f`, `--force`	Force the unmount (`MNT_FORCE`), e.g. for an unreachable server.
`-R`, `--recursive`	Unmount the target and everything under it (see above).
`-A`, `--all-targets`	Unmount every mount point of the given source (see above).
`-d`, `--detach-loop`	After unmounting, free the backing loop device. Best-effort and verified: it clears the device only if it still backs the mount just removed, so a recycled loop number is never clobbered. Usually redundant, since `mount`-created loops auto-clear on unmount.
`-r`, `--read-only`	If the unmount fails, remount the filesystem read-only instead (via `mount_setattr`). Mutually exclusive with `-R`.
`-g`, `--graceful`	Exit `0` when the target is absent or not mounted (rather than failing). Applied unconditionally.
`-q`, `--quiet`	Suppress "not mounted" messages.
`-c`, `--no-canonicalize`	Do not canonicalise paths; selects `UMOUNT_NOFOLLOW`. Applied unconditionally.
`-v`, `--verbose`	Say what is being unmounted. Repeatable.
`-N`, `--namespace NS`	Enter mount namespace `NS` (a PID, an ns file path, or a named namespace) before reading its mount table and unmounting. All work happens inside that namespace.
`-n`, `--no-mtab`	Accepted and ignored (no mtab on Peios).
`-i`, `--internal-only`	Do not invoke a `umount.<type>` helper (none ship).
`--fake`	Dry run: resolve operands and report, but skip the unmount syscalls.
`-h`, `--help` / `-V`, `--version`	Standard.

The umount2 flag mapping is direct: -l → MNT_DETACH, -f → MNT_FORCE, -c (or a symlinked final component) → UMOUNT_NOFOLLOW. MNT_EXPIRE is deliberately not exposed, matching util-linux.

On privilege #

As with mount, there is no coarse uid==0 check: the applet is not set-user-ID and every unmount is authorised per-operation by KACS. Where util-linux silently suppresses an option for non-root users (-c, and -g's effectiveness), Peios applies it unconditionally.

Exit status #

Code	Meaning
`0`	Success (or a `-g` no-op on an absent target).
`1`	Incorrect invocation or a permission denial — including `-R` with `-r`, a missing operand, an ambiguous source, an embedded NUL, or an authorisation failure.
`2`	System error (e.g. cannot read the mount table).
`8`	Interrupted (SIGINT).
`32`	Unmount failed, or the target is not mounted (unless `-g`).
`64`	Several source/target arguments were given and at least one succeeded while another failed.
`126`	An external `umount.<type>` helper was found but failed to execute (moot until a helper ships).

A single -R / -A / -A -R invocation stops on the first failure and yields 32; the aggregate 64 only appears across multiple top-level arguments. To see what is currently mounted before unmounting, use mount with no arguments or lsblk.

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