Waking up a destination machine using WOL

The most transparent way to wake up a target MacOS system for znapzend transfers, is to edit the ~/.ssh/config file on the host. The rationale is to inject a WOL command whenever ssh (i.e. the znapzend daemon) tries to access the destination system.

Here's an excerpt

user@host-iMac ~ % cat ~/.ssh/config
Match host destination.local exec "/usr/local/bin/wakeonlan ax:ax:5x:bx:7x:bx &"

Obviously, the wakeonlan command must be installed as outlined previously.

Running a script on the destination, to check (and return) a control condition

This is relevant to the skipOnPreSendCmdFail optional daemon feature, allowing the znapzend backup plan to check for a condition and, depending on the result, proceed or abort the transfer.

Here's a sample excerpt, checking for hung zfs recv processes

dst_b=username@destinationserver:zpoolname/dataset
dst_b_mbuffer=off
dst_b_mbuffer_size=1G
dst_b_plan=1weeks=>1days,1months=>1days
dst_b_precmd=/usr/bin/ssh -A username@destinationserver "/Users/username/DontZEND.sh"
dst_b_pstcmd=off

And here's the control script

❯ cat DontZEND.sh
#!/bin/bash
# check to see if there is a pending zfs recv process
#

check_zfs_recv()
{
/usr/bin/pgrep -fl 'zfs recv'
myvar=$?
let myvar+=-1

echo -n "[" $myvar "]  " >> dont.log
date >> dont.log
echo "------------------------------------------------------------------------------------" >> dont.log
arcstat >> dont.log
pgrep -fl 'zfs recv' >>  dont.log
echo "------------------------------------------------------------------------------------" >> dont.log

# May 18, 2024 - set to readony, will only log and return suxess
#
#  exit $myvar
exit 0

# 0 = no zfs recv running
# any other = block znapzend at host
}

check_zfs_recv


echo “This line will not be printed”