Waits until a systemd system or user unit is active.

systemd-wait-unit-active.sh

#!/bin/bash
# systemd-wait-unit-active.sh
# Waits until a systemd system or user unit is active.
#
# Notice: When using this script with user units you must ensure that `sudo`
# can call `systemctl` proberly. This often fails due to `systemctl` not
# finding the user's D-Bus socket. Ensure that the user runs a D-Bus daemon
# and that the '$XDG_RUNTIME_DIR' environment variable is defined.
#
# Copyright (C) 2021 Daniel Rudolf (<https://www.daniel-rudolf.de>)
# License: The MIT License <http://opensource.org/licenses/MIT>
#
# SPDX-License-Identifier: MIT

set -eu -o pipefail

print_usage() {
    echo "Usage:"
    echo "  $(basename "$0") [--quiet] [--timeout SEC] [--user USER] SYSTEMD_UNIT"
}

UNIT=
QUIET=
TIMEOUT=30
USER=

while [ $# -gt 0 ]; do
    if [ "$1" == "--quiet" ] || [ "$1" == "-q" ]; then
        QUIET=1
        shift
    elif [ "$1" == "--timeout" ] || [ "$1" == "-t" ]; then
        if [ $# -lt 2 ]; then
            print_usage >&2
            exit 1
        elif ! [[ "$2" =~ ^[0-9]+$ ]]; then
            echo "Invalid timeout '$2'" >&2
            exit 1
        fi

        TIMEOUT="$2"
        shift 2
    elif [ "$1" == "--user" ] || [ "$1" == "-u" ]; then
        if [ $# -lt 2 ]; then
            print_usage >&2
            exit 1
        elif ! id -u "$2" > /dev/null 2>&1; then
            echo "Invalid user '$2'" >&2
            exit 1
        fi

        USER="$2"
        shift 2
    elif [ -z "$UNIT" ]; then
        UNIT="$1"
        shift
    else
        print_usage >&2
        exit 1
    fi
done

if [ -z "$UNIT" ]; then
    print_usage >&2
    exit 1
fi

if [ -z "$USER" ]; then
    UNIT_INFO="system unit '$UNIT'"

    __systemctl() {
        systemctl --full --no-legend --no-pager --plain --system "$@" 2> /dev/null
    }
else
    UNIT_INFO="user unit '$UNIT' of '$USER'"

    __systemctl() {
        sudo --non-interactive --login --user "$USER" -- \
            systemctl --full --no-legend --no-pager --plain --user "$@" 2> /dev/null
    }
fi

if [ -z "$(__systemctl list-unit-files "$UNIT" ; __systemctl list-units --all "$UNIT")" ]; then
    echo "Unknown $UNIT_INFO" >&2
    exit 1
fi

[ -n "$QUIET" ] || echo -n "Waiting for $UNIT_INFO to start"

for (( ; TIMEOUT > 0 ; TIMEOUT-- )); do
    if __systemctl is-active --quiet "$UNIT"; then
        [ -n "$QUIET" ] || echo " [success]"
        exit 0
    fi

    [ -n "$QUIET" ] || echo -n "."
    sleep 1
done

[ -n "$QUIET" ] || echo " [timeout]"
exit 1