Writing a systemd service to be executed at resume

I know this is an old question, but the following unit file worked for me to run a script upon resume from sleep:

[Unit]
Description=<your description>
After=suspend.target

[Service]
User=root
Type=oneshot
ExecStart=<your script here>
TimeoutSec=0
StandardOutput=syslog

[Install]
WantedBy=suspend.target

I believe it is the After=suspend.target that makes it run on resume, rather than when the computer goes to sleep.

As an alternative to writing and enabling a unit file, you can also put a shell script (or a symlink to your script) into /lib/systemd/system-sleep/.

It will be called before sleep/hibernate, and at resume time.

From man systemd-suspend.service :

Immediately before entering system suspend and/or hibernation systemd-suspend.service (and the other mentioned units, respectively) will run all executables in /usr/lib/systemd/system-sleep/ and pass two arguments to them. The first argument will be "pre", the second either "suspend", "hibernate", or "hybrid-sleep" depending on the chosen action. Immediately after leaving system suspend and/or hibernation the same executables are run, but the first argument is now "post". All executables in this directory are executed in parallel, and execution of the action is not continued until all executables have finished.

Test it with this:

#!/bin/sh
## This file (or a link to it) must be in /lib/systemd/system-sleep/

logger -t "test" "\$0=$0, \$1=$1, \$2=$2"

Followup to mivk's answer, in which I avoid mucking with a new unit file (see my question here How to react to laptop lid events?). Here's my solution; it's not 100% straightforward (sigh) because the system is not stable when it's coming out of sleep:

On my Fedora 26 box I put a symlink here: /usr/lib/systemd/system-sleep/sleepyhead which points here: /root/bin/sleepyhead, which contains:

#!/bin/sh
## This file (or a link to it) must be in /lib/systemd/system-sleep/

# This is called when the lid is closed, as follows:
# $0=/usr/lib/systemd/system-sleep/sleepyhead, $1=pre, $2=suspend
# ...and when the lid is opened, as follows:
# $0=/usr/lib/systemd/system-sleep/sleepyhead, $1=post, $2=suspend


touch /tmp/sleepyrun
logger -t "sleepyhead" "Start: \$1=$1, \$2=$2"
if [ "$1" = "post" ] ; then
    action="RUN trackpoint"
    bash /root/bin/trackpoint >/tmp/trackpoint-run 2>&1
else
    action="NO ACTION"
fi
logger -t "sleepyhead" "${action}: " "\$1=$1, \$2=$2"

The /root/bin/trackpoint script follows. Note that the first sleep is critical. The device is set up every time the lid is opened, so it doesn't exist at first. If I try to do anything but sleep, the "sleepyhead" script takes a really long time to exit and my pointer will be frozen for at least 60 seconds. Furthermore, note that you cannot put the /root/bin/trackpoint script in the background in sleepyhead, above. If you do, the process will be killed when sleepyhead exits.

#!/bin/bash
# This is /root/bin/trackpoint

echo "Start $0"
date

found=false
dir=""
# dirlist can look like:
# /sys/devices/platform/i8042/serio1/serio25/speed
# /sys/devices/platform/i8042/serio1/serio24/speed
# ...the older one appears to get cleaned a little later.

sleep 1 # If I don't put this in here, my pointer locks up for a really long time...
for i in 1 2 3 4; do
    speedfiles=$(find /sys/devices/platform/i8042 -name speed) # There may be multiple speed files at this point.
    [ -z "$speedfiles" ] && { sleep 1; continue; }
    dirlist=$(dirname $speedfiles)
    printf "Speed file(s) at $(find /sys/devices/platform/i8042 -name speed | tail -1) \n"
    # All this remaking of the path is here because the filenames change with
    # every resume, and what's bigger: 9 or 10? ...Depends if you're
    # lexicographical or numerical. We need to always be numerical.
    largest_number="$(echo $dirlist | tr ' ' '\n' | sed -e 's/.*serio//' | sort -n | tail -1)"
    dir="$(echo $dirlist | tr ' ' '\n' | egrep serio${largest_number}\$ )"
    echo "Dir is $dir number is $largest_number" 
    [ -n "$dir" ] && found=true && break
done
$found || exit 1


date
echo -n 4 > $dir/inertia
echo -n 220 > $dir/sensitivity
echo -n 128 > $dir/speed
date
echo "Done $0"