direnv/direnv · error

this feature is not supported

Error message

this feature is not supported

What it means

Returned by the Hook method of systemdShell, a pseudo-shell that only renders direnv's environment diff as systemd EnvironmentFile KEY=value lines via Export/Dump. Because an EnvironmentFile is a static file consumed by systemd at unit start, there is no interactive shell session to install a prompt hook into, so Hook unconditionally returns this sentinel error. It signals an intentionally unimplemented capability of the target 'shell' format, not a runtime failure; any caller that asks systemdShell for hook code (e.g. `direnv hook systemd`) will always get it.

Source

Thrown at internal/cmd/shell_systemd.go:16

package cmd

import (
	"errors"
	"strings"
)

// systemdShell is not a real shell
type systemdShell struct{}

// Systemd is not really a shell but is useful to add support
// to systemd EnvironmentFile(https://0pointer.de/public/systemd-man/systemd.exec.html#EnvironmentFile=)
var Systemd Shell = systemdShell{}

func (sh systemdShell) Hook() (string, error) {
	return "", errors.New("this feature is not supported")
}

func (sh systemdShell) Export(e ShellExport) (string, error) {
	var out string
	for key, value := range e {
		if value != nil {
			out += sh.export(key, *value)
		}
	}
	return out, nil
}

func (sh systemdShell) Dump(env Env) (string, error) {
	var out string
	for key, value := range env {
		out += sh.export(key, value)
	}
	return out, nil

View on GitHub (pinned to b00e451f54)

Solutions

1. Use `direnv export systemd` to generate EnvironmentFile content; hooking is not supported
2. Hook only real shells (`direnv hook bash` etc.) inside a user shell, not under systemd
3. Filter pseudo-shells out before invoking Hook in tooling

Example fix

// before
eval "$(direnv hook systemd)"
// after
# generate EnvironmentFile:
direnv export systemd > /etc/environment.d/myapp.conf

if [ "$1" = "systemd" ]; then direnv export systemd; else eval "$(direnv hook "$1")"; fi

func supportsHook(s cmd.Shell) bool {
    switch s.(type) {
    case cmd.Systemd, cmd.GzEnv, cmd.JSON, cmd.Vim:
        return false
    }
    return true
}

When it happens

Trigger: Calling Hook() on direnv's Systemd shell, e.g. `direnv hook systemd` or code that resolves the systemd shell and calls Hook.

Common situations: Users writing systemd EnvironmentFiles use `direnv export systemd` but mistakenly try hook; automation iterates shells calling Hook on all.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• the gzenv shell doesn't support hooking
• this feature is not supported
• this feature is not supported. Install the direnv.vim plugin
• missing PATH argument
• invalid arguments

AI-assisted analysis of direnv/direnv@b00e451f54 (2026-09-05). Data as JSON: /api/errors/49ba6560a1483607. Report an issue: GitHub.