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