diff --git a/cmd/zed/zed.d/zed-functions.sh b/cmd/zed/zed.d/zed-functions.sh
index c4ed5aa8ac7a..9f8531d737a6 100644
--- a/cmd/zed/zed.d/zed-functions.sh
+++ b/cmd/zed/zed.d/zed-functions.sh
@@ -1,614 +1,614 @@
 #!/bin/sh
 # shellcheck disable=SC2039
 # zed-functions.sh
 #
 # ZED helper functions for use in ZEDLETs
 
 
 # Variable Defaults
 #
 : "${ZED_LOCKDIR:="/var/lock"}"
 : "${ZED_NOTIFY_INTERVAL_SECS:=3600}"
 : "${ZED_NOTIFY_VERBOSE:=0}"
 : "${ZED_RUNDIR:="/var/run"}"
 : "${ZED_SYSLOG_PRIORITY:="daemon.notice"}"
 : "${ZED_SYSLOG_TAG:="zed"}"
 
 ZED_FLOCK_FD=8
 
 
 # zed_check_cmd (cmd, ...)
 #
 # For each argument given, search PATH for the executable command [cmd].
 # Log a message if [cmd] is not found.
 #
 # Arguments
 #   cmd: name of executable command for which to search
 #
 # Return
 #   0 if all commands are found in PATH and are executable
 #   n for a count of the command executables that are not found
 #
 zed_check_cmd()
 {
     local cmd
     local rv=0
 
     for cmd; do
         if ! command -v "${cmd}" >/dev/null 2>&1; then
             zed_log_err "\"${cmd}\" not installed"
             rv=$((rv + 1))
         fi
     done
     return "${rv}"
 }
 
 
 # zed_log_msg (msg, ...)
 #
 # Write all argument strings to the system log.
 #
 # Globals
 #   ZED_SYSLOG_PRIORITY
 #   ZED_SYSLOG_TAG
 #
 # Return
 #   nothing
 #
 zed_log_msg()
 {
     logger -p "${ZED_SYSLOG_PRIORITY}" -t "${ZED_SYSLOG_TAG}" -- "$@"
 }
 
 
 # zed_log_err (msg, ...)
 #
 # Write an error message to the system log.  This message will contain the
 # script name, EID, and all argument strings.
 #
 # Globals
 #   ZED_SYSLOG_PRIORITY
 #   ZED_SYSLOG_TAG
 #   ZEVENT_EID
 #
 # Return
 #   nothing
 #
 zed_log_err()
 {
     logger -p "${ZED_SYSLOG_PRIORITY}" -t "${ZED_SYSLOG_TAG}" -- "error:" \
         "$(basename -- "$0"):""${ZEVENT_EID:+" eid=${ZEVENT_EID}:"}" "$@"
 }
 
 
 # zed_lock (lockfile, [fd])
 #
 # Obtain an exclusive (write) lock on [lockfile].  If the lock cannot be
 # immediately acquired, wait until it becomes available.
 #
 # Every zed_lock() must be paired with a corresponding zed_unlock().
 #
 # By default, flock-style locks associate the lockfile with file descriptor 8.
 # The bash manpage warns that file descriptors >9 should be used with care as
 # they may conflict with file descriptors used internally by the shell.  File
 # descriptor 9 is reserved for zed_rate_limit().  If concurrent locks are held
 # within the same process, they must use different file descriptors (preferably
 # decrementing from 8); otherwise, obtaining a new lock with a given file
 # descriptor will release the previous lock associated with that descriptor.
 #
 # Arguments
 #   lockfile: pathname of the lock file; the lock will be stored in
 #     ZED_LOCKDIR unless the pathname contains a "/".
 #   fd: integer for the file descriptor used by flock (OPTIONAL unless holding
 #     concurrent locks)
 #
 # Globals
 #   ZED_FLOCK_FD
 #   ZED_LOCKDIR
 #
 # Return
 #   nothing
 #
 zed_lock()
 {
     local lockfile="$1"
     local fd="${2:-${ZED_FLOCK_FD}}"
     local umask_bak
     local err
 
     [ -n "${lockfile}" ] || return
     if ! expr "${lockfile}" : '.*/' >/dev/null 2>&1; then
         lockfile="${ZED_LOCKDIR}/${lockfile}"
     fi
 
     umask_bak="$(umask)"
     umask 077
 
     # Obtain a lock on the file bound to the given file descriptor.
     #
-    eval "exec ${fd}> '${lockfile}'"
+    eval "exec ${fd}>> '${lockfile}'"
     if ! err="$(flock --exclusive "${fd}" 2>&1)"; then
         zed_log_err "failed to lock \"${lockfile}\": ${err}"
     fi
 
     umask "${umask_bak}"
 }
 
 
 # zed_unlock (lockfile, [fd])
 #
 # Release the lock on [lockfile].
 #
 # Arguments
 #   lockfile: pathname of the lock file
 #   fd: integer for the file descriptor used by flock (must match the file
 #     descriptor passed to the zed_lock function call)
 #
 # Globals
 #   ZED_FLOCK_FD
 #   ZED_LOCKDIR
 #
 # Return
 #   nothing
 #
 zed_unlock()
 {
     local lockfile="$1"
     local fd="${2:-${ZED_FLOCK_FD}}"
     local err
 
     [ -n "${lockfile}" ] || return
     if ! expr "${lockfile}" : '.*/' >/dev/null 2>&1; then
         lockfile="${ZED_LOCKDIR}/${lockfile}"
     fi
 
     # Release the lock and close the file descriptor.
     if ! err="$(flock --unlock "${fd}" 2>&1)"; then
         zed_log_err "failed to unlock \"${lockfile}\": ${err}"
     fi
     eval "exec ${fd}>&-"
 }
 
 
 # zed_notify (subject, pathname)
 #
 # Send a notification via all available methods.
 #
 # Arguments
 #   subject: notification subject
 #   pathname: pathname containing the notification message (OPTIONAL)
 #
 # Return
 #   0: notification succeeded via at least one method
 #   1: notification failed
 #   2: no notification methods configured
 #
 zed_notify()
 {
     local subject="$1"
     local pathname="$2"
     local num_success=0
     local num_failure=0
 
     zed_notify_email "${subject}" "${pathname}"; rv=$?
     [ "${rv}" -eq 0 ] && num_success=$((num_success + 1))
     [ "${rv}" -eq 1 ] && num_failure=$((num_failure + 1))
 
     zed_notify_pushbullet "${subject}" "${pathname}"; rv=$?
     [ "${rv}" -eq 0 ] && num_success=$((num_success + 1))
     [ "${rv}" -eq 1 ] && num_failure=$((num_failure + 1))
 
     zed_notify_slack_webhook "${subject}" "${pathname}"; rv=$?
     [ "${rv}" -eq 0 ] && num_success=$((num_success + 1))
     [ "${rv}" -eq 1 ] && num_failure=$((num_failure + 1))
 
     zed_notify_pushover "${subject}" "${pathname}"; rv=$?
     [ "${rv}" -eq 0 ] && num_success=$((num_success + 1))
     [ "${rv}" -eq 1 ] && num_failure=$((num_failure + 1))
 
     [ "${num_success}" -gt 0 ] && return 0
     [ "${num_failure}" -gt 0 ] && return 1
     return 2
 }
 
 
 # zed_notify_email (subject, pathname)
 #
 # Send a notification via email to the address specified by ZED_EMAIL_ADDR.
 #
 # Requires the mail executable to be installed in the standard PATH, or
 # ZED_EMAIL_PROG to be defined with the pathname of an executable capable of
 # reading a message body from stdin.
 #
 # Command-line options to the mail executable can be specified in
 # ZED_EMAIL_OPTS.  This undergoes the following keyword substitutions:
 # - @ADDRESS@ is replaced with the space-delimited recipient email address(es)
 # - @SUBJECT@ is replaced with the notification subject
 #
 # Arguments
 #   subject: notification subject
 #   pathname: pathname containing the notification message (OPTIONAL)
 #
 # Globals
 #   ZED_EMAIL_PROG
 #   ZED_EMAIL_OPTS
 #   ZED_EMAIL_ADDR
 #
 # Return
 #   0: notification sent
 #   1: notification failed
 #   2: not configured
 #
 zed_notify_email()
 {
     local subject="$1"
     local pathname="${2:-"/dev/null"}"
 
     : "${ZED_EMAIL_PROG:="mail"}"
     : "${ZED_EMAIL_OPTS:="-s '@SUBJECT@' @ADDRESS@"}"
 
     # For backward compatibility with ZED_EMAIL.
     if [ -n "${ZED_EMAIL}" ] && [ -z "${ZED_EMAIL_ADDR}" ]; then
         ZED_EMAIL_ADDR="${ZED_EMAIL}"
     fi
     [ -n "${ZED_EMAIL_ADDR}" ] || return 2
 
     zed_check_cmd "${ZED_EMAIL_PROG}" || return 1
 
     [ -n "${subject}" ] || return 1
     if [ ! -r "${pathname}" ]; then
         zed_log_err \
                 "$(basename "${ZED_EMAIL_PROG}") cannot read \"${pathname}\""
         return 1
     fi
 
     ZED_EMAIL_OPTS="$(echo "${ZED_EMAIL_OPTS}" \
         | sed   -e "s/@ADDRESS@/${ZED_EMAIL_ADDR}/g" \
                 -e "s/@SUBJECT@/${subject}/g")"
 
     # shellcheck disable=SC2086
     ${ZED_EMAIL_PROG} ${ZED_EMAIL_OPTS} < "${pathname}" >/dev/null 2>&1
     rv=$?
     if [ "${rv}" -ne 0 ]; then
         zed_log_err "$(basename "${ZED_EMAIL_PROG}") exit=${rv}"
         return 1
     fi
     return 0
 }
 
 
 # zed_notify_pushbullet (subject, pathname)
 #
 # Send a notification via Pushbullet <https://www.pushbullet.com/>.
 # The access token (ZED_PUSHBULLET_ACCESS_TOKEN) identifies this client to the
 # Pushbullet server.  The optional channel tag (ZED_PUSHBULLET_CHANNEL_TAG) is
 # for pushing to notification feeds that can be subscribed to; if a channel is
 # not defined, push notifications will instead be sent to all devices
 # associated with the account specified by the access token.
 #
 # Requires awk, curl, and sed executables to be installed in the standard PATH.
 #
 # References
 #   https://docs.pushbullet.com/
 #   https://www.pushbullet.com/security
 #
 # Arguments
 #   subject: notification subject
 #   pathname: pathname containing the notification message (OPTIONAL)
 #
 # Globals
 #   ZED_PUSHBULLET_ACCESS_TOKEN
 #   ZED_PUSHBULLET_CHANNEL_TAG
 #
 # Return
 #   0: notification sent
 #   1: notification failed
 #   2: not configured
 #
 zed_notify_pushbullet()
 {
     local subject="$1"
     local pathname="${2:-"/dev/null"}"
     local msg_body
     local msg_tag
     local msg_json
     local msg_out
     local msg_err
     local url="https://api.pushbullet.com/v2/pushes"
 
     [ -n "${ZED_PUSHBULLET_ACCESS_TOKEN}" ] || return 2
 
     [ -n "${subject}" ] || return 1
     if [ ! -r "${pathname}" ]; then
         zed_log_err "pushbullet cannot read \"${pathname}\""
         return 1
     fi
 
     zed_check_cmd "awk" "curl" "sed" || return 1
 
     # Escape the following characters in the message body for JSON:
     # newline, backslash, double quote, horizontal tab, vertical tab,
     # and carriage return.
     #
     msg_body="$(awk '{ ORS="\\n" } { gsub(/\\/, "\\\\"); gsub(/"/, "\\\"");
         gsub(/\t/, "\\t"); gsub(/\f/, "\\f"); gsub(/\r/, "\\r"); print }' \
         "${pathname}")"
 
     # Push to a channel if one is configured.
     #
     [ -n "${ZED_PUSHBULLET_CHANNEL_TAG}" ] && msg_tag="$(printf \
         '"channel_tag": "%s", ' "${ZED_PUSHBULLET_CHANNEL_TAG}")"
 
     # Construct the JSON message for pushing a note.
     #
     msg_json="$(printf '{%s"type": "note", "title": "%s", "body": "%s"}' \
         "${msg_tag}" "${subject}" "${msg_body}")"
 
     # Send the POST request and check for errors.
     #
     msg_out="$(curl -u "${ZED_PUSHBULLET_ACCESS_TOKEN}:" -X POST "${url}" \
         --header "Content-Type: application/json" --data-binary "${msg_json}" \
         2>/dev/null)"; rv=$?
     if [ "${rv}" -ne 0 ]; then
         zed_log_err "curl exit=${rv}"
         return 1
     fi
     msg_err="$(echo "${msg_out}" \
         | sed -n -e 's/.*"error" *:.*"message" *: *"\([^"]*\)".*/\1/p')"
     if [ -n "${msg_err}" ]; then
         zed_log_err "pushbullet \"${msg_err}"\"
         return 1
     fi
     return 0
 }
 
 
 # zed_notify_slack_webhook (subject, pathname)
 #
 # Notification via Slack Webhook <https://api.slack.com/incoming-webhooks>.
 # The Webhook URL (ZED_SLACK_WEBHOOK_URL) identifies this client to the
 # Slack channel.
 #
 # Requires awk, curl, and sed executables to be installed in the standard PATH.
 #
 # References
 #   https://api.slack.com/incoming-webhooks
 #
 # Arguments
 #   subject: notification subject
 #   pathname: pathname containing the notification message (OPTIONAL)
 #
 # Globals
 #   ZED_SLACK_WEBHOOK_URL
 #
 # Return
 #   0: notification sent
 #   1: notification failed
 #   2: not configured
 #
 zed_notify_slack_webhook()
 {
     [ -n "${ZED_SLACK_WEBHOOK_URL}" ] || return 2
 
     local subject="$1"
     local pathname="${2:-"/dev/null"}"
     local msg_body
     local msg_tag
     local msg_json
     local msg_out
     local msg_err
     local url="${ZED_SLACK_WEBHOOK_URL}"
 
     [ -n "${subject}" ] || return 1
     if [ ! -r "${pathname}" ]; then
         zed_log_err "slack webhook cannot read \"${pathname}\""
         return 1
     fi
 
     zed_check_cmd "awk" "curl" "sed" || return 1
 
     # Escape the following characters in the message body for JSON:
     # newline, backslash, double quote, horizontal tab, vertical tab,
     # and carriage return.
     #
     msg_body="$(awk '{ ORS="\\n" } { gsub(/\\/, "\\\\"); gsub(/"/, "\\\"");
         gsub(/\t/, "\\t"); gsub(/\f/, "\\f"); gsub(/\r/, "\\r"); print }' \
         "${pathname}")"
 
     # Construct the JSON message for posting.
     #
     msg_json="$(printf '{"text": "*%s*\n%s"}' "${subject}" "${msg_body}" )"
 
     # Send the POST request and check for errors.
     #
     msg_out="$(curl -X POST "${url}" \
         --header "Content-Type: application/json" --data-binary "${msg_json}" \
         2>/dev/null)"; rv=$?
     if [ "${rv}" -ne 0 ]; then
         zed_log_err "curl exit=${rv}"
         return 1
     fi
     msg_err="$(echo "${msg_out}" \
         | sed -n -e 's/.*"error" *:.*"message" *: *"\([^"]*\)".*/\1/p')"
     if [ -n "${msg_err}" ]; then
         zed_log_err "slack webhook \"${msg_err}"\"
         return 1
     fi
     return 0
 }
 
 # zed_notify_pushover (subject, pathname)
 #
 # Send a notification via Pushover <https://pushover.net/>.
 # The access token (ZED_PUSHOVER_TOKEN) identifies this client to the
 # Pushover server. The user token (ZED_PUSHOVER_USER) defines the user or
 # group to which the notification will be sent.
 #
 # Requires curl and sed executables to be installed in the standard PATH.
 #
 # References
 #   https://pushover.net/api
 #
 # Arguments
 #   subject: notification subject
 #   pathname: pathname containing the notification message (OPTIONAL)
 #
 # Globals
 #   ZED_PUSHOVER_TOKEN
 #   ZED_PUSHOVER_USER
 #
 # Return
 #   0: notification sent
 #   1: notification failed
 #   2: not configured
 #
 zed_notify_pushover()
 {
     local subject="$1"
     local pathname="${2:-"/dev/null"}"
     local msg_body
     local msg_out
     local msg_err
     local url="https://api.pushover.net/1/messages.json"
 
     [ -n "${ZED_PUSHOVER_TOKEN}" ] && [ -n "${ZED_PUSHOVER_USER}" ] || return 2
 
     if [ ! -r "${pathname}" ]; then
         zed_log_err "pushover cannot read \"${pathname}\""
         return 1
     fi
 
     zed_check_cmd "curl" "sed" || return 1
 
     # Read the message body in.
     #
     msg_body="$(cat "${pathname}")"
 
     if [ -z "${msg_body}" ]
     then
         msg_body=$subject
         subject=""
     fi
 
     # Send the POST request and check for errors.
     #
     msg_out="$( \
         curl \
         --form-string "token=${ZED_PUSHOVER_TOKEN}" \
         --form-string "user=${ZED_PUSHOVER_USER}" \
         --form-string "message=${msg_body}" \
         --form-string "title=${subject}" \
         "${url}" \
         2>/dev/null \
         )"; rv=$?
     if [ "${rv}" -ne 0 ]; then
         zed_log_err "curl exit=${rv}"
         return 1
     fi
     msg_err="$(echo "${msg_out}" \
         | sed -n -e 's/.*"errors" *:.*\[\(.*\)\].*/\1/p')"
     if [ -n "${msg_err}" ]; then
         zed_log_err "pushover \"${msg_err}"\"
         return 1
     fi
     return 0
 }
 
 
 # zed_rate_limit (tag, [interval])
 #
 # Check whether an event of a given type [tag] has already occurred within the
 # last [interval] seconds.
 #
 # This function obtains a lock on the statefile using file descriptor 9.
 #
 # Arguments
 #   tag: arbitrary string for grouping related events to rate-limit
 #   interval: time interval in seconds (OPTIONAL)
 #
 # Globals
 #   ZED_NOTIFY_INTERVAL_SECS
 #   ZED_RUNDIR
 #
 # Return
 #   0 if the event should be processed
 #   1 if the event should be dropped
 #
 # State File Format
 #   time;tag
 #
 zed_rate_limit()
 {
     local tag="$1"
     local interval="${2:-${ZED_NOTIFY_INTERVAL_SECS}}"
     local lockfile="zed.zedlet.state.lock"
     local lockfile_fd=9
     local statefile="${ZED_RUNDIR}/zed.zedlet.state"
     local time_now
     local time_prev
     local umask_bak
     local rv=0
 
     [ -n "${tag}" ] || return 0
 
     zed_lock "${lockfile}" "${lockfile_fd}"
     time_now="$(date +%s)"
     time_prev="$(grep -E "^[0-9]+;${tag}\$" "${statefile}" 2>/dev/null \
         | tail -1 | cut -d\; -f1)"
 
     if [ -n "${time_prev}" ] \
             && [ "$((time_now - time_prev))" -lt "${interval}" ]; then
         rv=1
     else
         umask_bak="$(umask)"
         umask 077
         grep -E -v "^[0-9]+;${tag}\$" "${statefile}" 2>/dev/null \
             > "${statefile}.$$"
         echo "${time_now};${tag}" >> "${statefile}.$$"
         mv -f "${statefile}.$$" "${statefile}"
         umask "${umask_bak}"
     fi
 
     zed_unlock "${lockfile}" "${lockfile_fd}"
     return "${rv}"
 }
 
 
 # zed_guid_to_pool (guid)
 #
 # Convert a pool GUID into its pool name (like "tank")
 # Arguments
 #   guid: pool GUID (decimal or hex)
 #
 # Return
 #   Pool name
 #
 zed_guid_to_pool()
 {
 	if [ -z "$1" ] ; then
 		return
 	fi
 
 	guid="$(printf "%u" "$1")"
 	$ZPOOL get -H -ovalue,name guid | awk '$1 == '"$guid"' {print $2; exit}'
 }
 
 # zed_exit_if_ignoring_this_event
 #
 # Exit the script if we should ignore this event, as determined by
 # $ZED_SYSLOG_SUBCLASS_INCLUDE and $ZED_SYSLOG_SUBCLASS_EXCLUDE in zed.rc.
 # This function assumes you've imported the normal zed variables.
 zed_exit_if_ignoring_this_event()
 {
 	if [ -n "${ZED_SYSLOG_SUBCLASS_INCLUDE}" ]; then
 	    eval "case ${ZEVENT_SUBCLASS} in
 	    ${ZED_SYSLOG_SUBCLASS_INCLUDE});;
 	    *) exit 0;;
 	    esac"
 	elif [ -n "${ZED_SYSLOG_SUBCLASS_EXCLUDE}" ]; then
 	    eval "case ${ZEVENT_SUBCLASS} in
 	    ${ZED_SYSLOG_SUBCLASS_EXCLUDE}) exit 0;;
 	    *);;
 	    esac"
 	fi
 }