[Unit]
Description=Purge old kernels
After=local-fs.target
ConditionPathExists=/boot/do_purge_kernels

[Service]
Type=oneshot
Nice=19
IOSchedulingClass=idle
ExecStartPre=/bin/rm -f /boot/do_purge_kernels
ExecStart=/sbin/purge-kernels

[Install]
WantedBy=multi-user.target