Automatically truncate docker logs on a coreos machine

docker-log-truncate

cat > /var/tmp/log-truncate <<EOF
#!/bin/sh
set -eux
cd /var/lib/docker/containers
for id in *
do
  logfile="\${id}/\${id}-json.log"
  [ -e "\${logfile}" ] && truncate -s 0 "\${logfile}"
done
btrfs balance start -v -dusage=20 /var/lib/docker/btrfs
EOF
chmod 0755 /var/tmp/log-truncate
cat > /etc/systemd/system/log-truncate.service <<EOF
[Unit]
Description=Log truncator

[Service]
ExecStart=/var/tmp/log-truncate

[Install]
WantedBy=log-truncator.timer
EOF
cat > /etc/systemd/system/log-truncate.timer<<EOF
[Unit]
Description=Run truncator every two days

[Timer]
OnUnitActiveSec=2d
[Install]
WantedBy=multi-user.target
EOF
systemctl start log-truncate.timer
systemctl enable log-truncate.timer