net-15-hostname

#!/usr/bin/env bash

# -------------------------------------------------------------------------- #
# Copyright 2002-2021, OpenNebula Project, OpenNebula Systems                #
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# Licensed under the Apache License, Version 2.0 (the "License"); you may    #
# not use this file except in compliance with the License. You may obtain    #
# a copy of the License at                                                   #
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# http://www.apache.org/licenses/LICENSE-2.0                                 #
#                                                                            #
# Unless required by applicable law or agreed to in writing, software        #
# distributed under the License is distributed on an "AS IS" BASIS,          #
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# limitations under the License.                                             #
#--------------------------------------------------------------------------- #

_kernel="$(uname -s)"
if [ "${_kernel}" = 'FreeBSD' ]; then
    SED_I="sed -i ''"
else
    SED_I="sed -i''"
fi

# Detects suitable running syslog service and restarts it
# to propagate the changed hostname into the logs
# (otherwise old or default value remains until reboot)
function restart_syslog() {
    for _name in syslog syslogd rsyslog; do
        if LANG=C systemctl is-active "${_name}" >/dev/null 2>&1; then
            systemctl restart "${_name}" && return
        elif service "${_name}" status >/dev/null 2>&1; then
            service "${_name}" restart && return
        fi
    done
}

function set_hostname() {
    local _hostname=$1

    # remember currently set hostname to detect a change
    local _old_hostname
    _old_hostname=$(hostname)

    if [ -d /run/systemd/system/ ] && hostnamectl status >/dev/null 2>/dev/null; then
        hostnamectl set-hostname --static "${_hostname}"
    else
        if [ -f /etc/sysconfig/network ]; then
            eval "${SED_I} '/^HOSTNAME=.*$/d' /etc/sysconfig/network"
            echo "HOSTNAME=${_hostname}" >>/etc/sysconfig/network
        elif [ "${_kernel}" = 'FreeBSD' ]; then
            sysrc hostname="${_hostname}"
        else
            echo "${_hostname}" >/etc/hostname
        fi

        hostname "${_hostname}"
    fi

    # restart syslog if actual hostname changed
    if [ "${_old_hostname}" != "$(hostname)" ]; then
        restart_syslog
    fi
}

function set_domainname() {
    local _domain=$1

    touch /etc/resolv.conf
    eval "${SED_I} -e '/^domain .*/d' /etc/resolv.conf"
    echo "domain ${_domain}" >>/etc/resolv.conf
}

function get_first_ip() {
    local ip

    ip=${ip:-$(ip route get 1 2>/dev/null | grep 'src [0-9\.]\+' | head -1 | sed -e 's/^.*src \([0-9\.]*\).*$/\1/')}
    ip=${ip:-$(ip -4 address show scope global up 2>/dev/null | awk '/inet / { gsub(/\/[^\/]+$/, "", $2); print $2; exit}')}
    ip=${ip:-$(ifconfig 2>/dev/null | awk '/inet / { gsub(/\/[^\/]+$/, "", $2); print $2; exit}')}
    ip=${ip:-$(hostname -I 2>/dev/null | cut -d' ' -f1)}
    ip=${ip:-$(hostname -i 2>/dev/null)}

    echo "${ip}"
}

function get_dns_name() {
    text=$(LC_ALL=C host "$1" 2>/dev/null)
    [ $? = 0 ] || exit 0
    [[ $text == *"has no PTR record" ]] && exit 0
    name=$(echo "$text" | awk '/(has address|name pointer)/ {print $(NF)}' | sed 's/\.$//')
    echo $name
}

function update_hosts() {
    ip=$1
    name=$2
    hostname=$3

    if [ "x${hostname}" = "x${name}" ]; then
        hosts="${name}"
    else
        hosts="${name} ${hostname}"
    fi

    note='# one-contextd'
    entry="${ip} ${hosts}  ${note}"

    # update our old entry
    if grep -qi "${note}" /etc/hosts; then
        eval "${SED_I} -e \"s/^.*${note}\$/${entry}/\" /etc/hosts"
    # update entry with same IP (but not localhost)
    elif grep -E "^${ip}[[:space:]]" /etc/hosts | grep -qv localhost; then
        eval "${SED_I} -e \"/localhost/! s/^${ip}[[:space:]].*\$/${entry}/\" /etc/hosts"
    # update entry with same name
    elif grep -qE "[[:space:]]${name}([[:space:]]|#|\$)" /etc/hosts; then
        eval "${SED_I} -re \"s/^.*[[:space:]]${name}([[:space:]#].*|$)/${entry}/\" /etc/hosts"
    # create new entry
    elif [ -s /etc/hosts ]; then
        # In FreeBSD, sed doesn't interpret \n. We put a real newline.
        eval "${SED_I} -e \"1s/^/${entry}\"$'\\\\\n/' /etc/hosts"
    else
        echo "${entry}" >>/etc/hosts
    fi
}

#####

first_ip=$(get_first_ip)

if [ -n "$SET_HOSTNAME" ]; then
    name=$(echo "$SET_HOSTNAME" | \
        sed -e 's/[^-a-zA-Z0-9\.]/-/g' -e 's/^-*//g' -e 's/-*$//g')

elif [ -n "$DNS_HOSTNAME" ]; then
    name=$(get_dns_name "${first_ip}")

elif [ "${EC2_HOSTNAME}" = 'YES' ]; then
    # try to quickly get hostname from the EC2 metadata server or
    # create hostname based on the first IPv4 (format: "ip-1-2-3-4")
    name=$(curl -sf -m 5 'http://169.254.169.254/latest/meta-data/local-hostname' 2>/dev/null)
    if [ -z "${name}" ]; then
        name="$(echo "${first_ip}" | grep -x '[0-9\.]\+' | tr . -)"
        if [ -n "${name}" ]; then
            name="ip-${name}"
        fi
    fi
fi

if [ -n "${name}" ]; then
    # split host and domain names
    hostname=${name%%.*}
    domain=${name#*.}

    [ "$domain" = "$hostname" ] && domain=''
    [ -n "${domain}" ] && set_domainname "${domain}"

    if [ "${_kernel}" = 'FreeBSD' ]; then
        set_hostname "${name}"
    else
        set_hostname "${hostname}"
    fi

    if [ -n "${DNS_HOSTNAME}" ]; then
        host_ip=$first_ip
    else
        name_ip=$(get_dns_name "${name}")

        # If selected hostname resolves on first IP,
        # use first IP for local hostname in /etc/hosts.
        # Otherwise use loopback IP.
        if [ "$first_ip" = "$name_ip" ]; then
            host_ip=$first_ip
        else
            host_ip='127.0.0.1'
        fi
    fi

    [ -n "${host_ip}" ] && update_hosts "${host_ip}" "${name}" "${hostname}"
fi