sendmail/files/check-hostname.sh

#!/bin/sh --
#
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#

# Check hostname configuration as per the sendmail code.
#
# See http://www.sendmail.org/sun-specific/migration.html#FQHN for details.
#
# Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
# Use is subject to license terms.
#

PATH=/bin:/usr/sbin

# If $1 has a ".", accept it and exit.

accept_if_fully_qualified() {
    case $1 in
    *.*)
        echo "Hostname $myhostname OK: fully qualified as $1"
        exit 0
        ;;
    esac
}

# Check the `getent hosts $1` output, skipping the 1st entry (IP address).

check_gethostbyname() {
    for host in `getent hosts $1 | awk '{for (f=2; f <= NF; f++) print $f}'`
    do
        accept_if_fully_qualified $host
    done
}

# Parse /etc/hosts, looking for $1 as an entry by itself, and try to find
# a long name on the same line.  First kill all comments, then check for
# $1 as a word by itself, then take just the first such line, then skip
# its first entry (IP address).

check_hosts_file() {
    for entry in `sed -e 's/#.*$//' /etc/hosts | \
        awk '/[     ]'$1'([     ]|$)/ \
            {for (f=2; f <= NF; f++) print $f; exit}'`
    do
        accept_if_fully_qualified $entry
    done
}

# Parse the output of `nslookup $1`, checking the Name and Aliases.

check_dns() {
    for host in `nslookup $1 2>/dev/null | \
        awk '$1 == "Name:" || $1 == "Aliases:"{print $2}'`
    do
        accept_if_fully_qualified $host
    done
}

# Check the `ypmatch $1 hosts` output, skipping the 1st entry (IP address).

check_nis() {
    for hst in `ypmatch $1 hosts | awk '{for (f=2; f <= NF; f++) print $f}'`
    do
        accept_if_fully_qualified $hst
    done
}

# Recommend how to reconfigure to get $1.$2 as the FQHN.
# $3 is the first entry for hosts in /etc/nsswitch.conf .

suggest_fix_and_exit() {
    myhost=$1
    suggested_domain=$2
    fhe=$3
    myipaddr=`getent hosts $myhost | head -1 | awk '{print $1}'`

    # aliases: skip the 1st & 2nd entries: IP address & canonical name

    set -- '' '' '[ aliases ... ]'
    set -- `grep "^$myipaddr[    ]" /etc/hosts 2>/dev/null`
    result=$?
    shift 2
    echo "We recommend \c"
    if [ "x$fhe" != "xfiles" ] ; then
        echo "listing files first for hosts in /etc/nsswitch.conf"
        echo "and then \c"
    fi
    if [ $result = 0 ] ; then
        echo "changing the /etc/hosts entry:\n"
        echo "$myipaddr $myhost $*\n"
        echo "to:\n"
    else
        echo "adding the /etc/hosts entry:\n"
    fi
    echo "$myipaddr $myhost $myhost.$suggested_domain $*"
    exit 0
}

# Fall back to the NIS domain, minus the first label.  If it is non-null,
# use it but recommend against it.  $2 is just informative, indicating whether
# we're checking the NIS domain.  $3 is to pass on.

check_nis_domain() {
    nisdomain=`domainname`
    realdomain=`echo $nisdomain | sed 's/[^.]*\.//'`
    if [ "x$realdomain" != "x" ] ; then
        echo "Hostname $1 can be fully qualified using NIS$2 domain"
        echo "  $nisdomain"
        echo "resulting in the name"
        echo "  $1.$realdomain"
        echo "but this is bad practice.\n"
        suggest_fix_and_exit $1 $realdomain $3
    fi
}

# Goal: try to fully qualify `hostname` as sendmail would.
# Algorithm (stop as soon as a name with a dot is found):
#    1. gethostbyname (simulate with getent hosts)
#    2. fall back to individual hosts: methods in nsswitch.conf, using
#       only those that are configured, in their configured order
#       * files (parse /etc/hosts directly)
#       * dns (parse nslookup output)
#       * nis (parse ypmatch output)
#    3. fall back to the NIS domain name.
# If none of the above succeed, give up.  Recommend:
#    a. the domain entry in /etc/resolv.conf, if one exists
#    b. "pick.some.domain"

myhostname=`hostname`

check_gethostbyname $myhostname

hosts_line=`sed -n -e 's/^hosts:\([^#]*\).*/\1/p' /etc/nsswitch.conf`
first_hosts_entry=`echo $hosts_line | awk '{print $1}'`
nis_domains=""

for entry in $hosts_line
do
    case $entry in
    files)
        check_hosts_file $myhostname
        ;;
    dns)
        check_dns $myhostname
        ;;
    nis)
        check_nis $myhostname
        nis_domains="$nis_domains nis"
        ;;
    esac
done

for entry in $nis_domains
do
    case $entry in
    nis)
        check_nis_domain $myhostname "" $first_hosts_entry
        ;;
    esac
done

realdomain=`awk '$1 ~ /^domain/ {print $2}' 2>/dev/null < /etc/resolv.conf`
case $realdomain in
*.*)
    # OK
    ;;
*)
    realdomain="pick.some.domain"
    ;;
esac

echo "Hostname $myhostname could not be fully qualified."
suggest_fix_and_exit $myhostname $realdomain $first_hosts_entry