uid/gid tool

idtool.sh

#!/bin/bash

# Change user uids and group gids, preserving file permissions on all mounted
# volumes.

change_user_uid() {
    if (( $# != 2 )); then
        echo "${0}: usage: ${0} USERNAME NEW_UID" >&2
        return 1
    fi

    local username="$1"
    local new_uid="$2"

    if ! [[ "$new_uid" =~ ^[0-9]+$ ]]; then
        echo "${0}: new_uid must be numeric" >&2
        return 1
    fi
    if [[ "$(getent passwd "$new_uid" | cut -d: -f1)" == "$username" ]]; then
        echo "${0}: user's uid already matches" >&2
    elif getent passwd "$new_uid" >/dev/null; then
        echo "${0}: new_uid ${new_uid} already taken; choose another" >&2
        return 1
    fi

    if (( $(ps --no-headers -u "$username" | wc -l) > 0 )); then
        echo "${0}: user ${username} has processes open; stop them first" >&2
        return 1
    fi

    chown --changes --from "$username" --recursive "$new_uid" / || true
    usermod --uid "$new_uid" "$username"
}

change_group_gid() {
    if (( $# != 2 )); then
        echo "${0}: usage: ${0} GROUP_NAME NEW_GID" >&2
        return 1
    fi

    local group_name="$1"
    local new_gid="$2"

    if ! [[ "$new_gid" =~ ^[0-9]+$ ]]; then
        echo "${0}: new_gid must be numeric" >&2
        return 1
    fi
    if getent group "$new_gid" >/dev/null; then
        echo "${0}: new_gid ${new_gid} already taken; choose another" >&2
        return 1
    fi

    find / -group "$group_name" -exec chgrp --changes --recursive "$new_gid" {} \; || true
    groupmod --gid "$new_gid" "$group_name"
}