/lib/dhcpcd/dhcpcd-hooks/30-hostname is in dhcpcd5 6.11.5-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 | # Set the hostname from DHCP data if required
# A hostname can either be a short hostname or a FQDN.
# hostname_fqdn=true
# hostname_fqdn=false
# hostname_fqdn=server
# A value of server means just what the server says, don't manipulate it.
# This could lead to an inconsistent hostname on a DHCPv4 and DHCPv6 network
# where the DHCPv4 hostname is short and the DHCPv6 has an FQDN.
# DHCPv6 has no hostname option.
# RFC4702 section 3.1 says FQDN should be prefered over hostname.
#
# As such, the default is hostname_fqdn=true so that a consistent hostname
# is always assigned.
: ${hostname_fqdn:=true}
# Some systems don't have hostname(1)
_hostname()
{
local name=
if [ -z "$1" ]; then
if type hostname >/dev/null 2>&1; then
hostname
elif [ -r /proc/sys/kernel/hostname ]; then
read name </proc/sys/kernel/hostname && echo "$name"
elif sysctl kern.hostname >/dev/null 2>&1; then
sysctl -n kern.hostname
elif sysctl kernel.hostname >/dev/null 2>&1; then
sysctl -n kernel.hostname
else
return 1
fi
return $?
fi
# Always prefer hostname(1) if we have it
if type hostname >/dev/null 2>&1; then
hostname "$1"
elif [ -w /proc/sys/kernel/hostname ]; then
echo "$1" >/proc/sys/kernel/hostname
elif sysctl kern.hostname >/dev/null 2>&1; then
sysctl -w "kern.hostname=$1"
elif sysctl kernel.hostname >/dev/null 2>&1; then
sysctl -w "kernel.hostname=$1"
else
# We know this will fail, but it will now fail
# with an error to stdout
hostname "$1"
fi
}
need_hostname()
{
local hostname hfqdn=false hshort=false
case "$force_hostname" in
[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|1) return 0;;
esac
hostname="$(_hostname)"
case "$hostname" in
""|"(none)"|localhost|localhost.localdomain) return 0;;
esac
case "$hostname_fqdn" in
[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|1) hfqdn=true;;
""|[Ss][Ee][Rr][Vv][Ee][Rr]) ;;
*) hshort=true;;
esac
if [ -n "$old_fqdn" ]; then
if ${hfqdn} || ! ${hsort}; then
[ "$hostname" = "$old_fqdn" ]
else
[ "$hostname" = "${old_fqdn%%.*}" ]
fi
elif [ -n "$old_host_name" ]; then
if ${hfqdn}; then
if [ -n "$old_domain_name" -a \
"$old_host_name" = "${old_host_name#*.}" ]
then
[ "$hostname" = \
"$old_host_name.$old_domain_name" ]
else
[ "$hostname" = "$old_host_name" ]
fi
elif ${hshort}; then
[ "$hostname" = "${old_host_name%%.*}" ]
else
[ "$hostname" = "$old_host_name" ]
fi
else
# No old hostname
false
fi
}
try_hostname()
{
if valid_domainname "$1"; then
_hostname "$1"
else
syslog err "Invalid hostname: $1"
fi
}
set_hostname()
{
local hfqdn=false hshort=false
need_hostname || return
case "$hostname_fqdn" in
[Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|1) hfqdn=true;;
""|[Ss][Ee][Rr][Vv][Ee][Rr]) ;;
*) hshort=true;;
esac
if [ -n "$new_fqdn" ]; then
if ${hfqdn} || ! ${hshort}; then
try_hostname "$new_fqdn"
else
try_hostname "${new_fqdn%%.*}"
fi
elif [ -n "$new_host_name" ]; then
if ${hfqdn}; then
if [ -n "$new_domain_name" -a \
"$new_host_name" = "${new_host_name#*.}" ]
then
try_hostname "$new_host_name.$new_domain_name"
else
try_hostname "$new_host_name"
fi
elif ${hshort}; then
try_hostname "${new_host_name%%.*}"
else
try_hostname "$new_host_name"
fi
fi
}
# For ease of use, map DHCP6 names onto our DHCP4 names
case "$reason" in
BOUND6|RENEW6|REBIND6|REBOOT6|INFORM6)
new_fqdn="$new_dhcp6_fqdn"
old_fqdn="$old_dhcp6_fqdn"
;;
esac
if $if_up; then
set_hostname
fi
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