postinst is in spl 0.6.5.6-0ubuntu2.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
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 | #!/bin/sh -e
# The hostname and hostid of the last system to access a ZFS pool are stored in
# the ZFS pool itself. A pool is foreign if, during `zpool import`, the
# current hostname and hostid are different than the stored values thereof.
#
# The hostname and hostid on Solaris are intrinsic, but they are not on Linux,
# so the spl kernel module invokes /bin/hostname and /usr/bin/hostid from the
# userland in its initialization routine.
#
# However, these two indentifiers are usually undefined in the Linux initramfs
# environment, so the /etc/hostname and /etc/hostid files must be added to the
# initrd. Things like a DHCP lease change can affect the hostid too.
#
# ZFS requires stable values for hostname and hostid, but basic Linux systems
# do not. The hostid is therefore stabilized by creating the /etc/hostid file
# in the regular environment if it does not already exist. An undefined
# hostname is usuallly stable.
#
# Neither /etc/hostname nor /etc/hostid are controlled configuration files in
# Debian distributions, but the spl package nevertheless installs a dummy
# /etc/hostid file that contains the HW_INVALID_HOSTID sentinal value so that
# the package manager will track it.
# This result is always an eight-character hexadecimal number sans the 0x
# prefix. Remember that /usr/bin/hostid generates a value if the /etc/hostid
# file doesn't exist or is malformed.
HOSTID=$(hostid)
if [ -f /etc/hostid -a "0x$HOSTID" != "0xffffffff" ]
then
# This system already has a stable hostid.
exit 0
fi
# Truncate the dummy file and generate the actual system hostid.
: >/etc/hostid
HOSTID=$(hostid)
# @TODO: Check whether this method is appropriate for gethostid(2) on big
# endian systems. (Update: It isn't.)
#
# The /etc/hostname file on i386 and amd64 systems must be a little endian
# integer of exacly four bytes. Regardless, a consistent hostid is more
# important than a correct byte order here.
# Conveniences like a ${HOSTID:$ii:2} substring range or a `sed` one-liner
# are prohibited here because this file must be dash-compatible by policy.
AA=$(echo $HOSTID | cut -b 1,2)
BB=$(echo $HOSTID | cut -b 3,4)
CC=$(echo $HOSTID | cut -b 5,6)
DD=$(echo $HOSTID | cut -b 7,8)
# Invoke the external printf because the dash builtin lacks the byte format.
"$(which printf)" "\x$DD\x$CC\x$BB\x$AA" >"/etc/hostid"
# @ASSERT: [ "$HOSTID" = "$(hostid)" ]
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