Install/update Node Exporter on OpenWRT

node_exporter-router.sh

#!/bin/sh
# Install, start and enable Prometheus Node Exporter
# on a OpenWRT system. Does not check for space!
# Overwrites any existing versions. Changing release before running should 
# be enough to update node_exporter version.
set -e

# node_exporter release version
release="1.5.0"

# get harware architecture
#arch=$(uname -m)
arch=armv7 # uname reports armv7l

# get node_exporter binary
url="https://github.com/prometheus/node_exporter/releases/download/v${release}/node_exporter-${release}.linux-${arch}.tar.gz"
wget -O node_exporter.tar.gz --continue $url

# check for space
required=$(tar -zvtf node_exporter.tar.gz node_exporter-${release}.linux-armv7/node_exporter | \
awk '{print $3/1024}')
available=$(df -Pk / | awk '/\/$/{print $4}')
if [ $available -lt $required ]
then
    echo "insufficient space for node_exporter $release"
    exit 1
fi

# extract archive
mkdir -p staging
tar zxf node_exporter.tar.gz -C staging
chmod 755 staging/node_exporter-${release}.linux-${arch}/node_exporter

# place it in /usr/bin/node_exporter
mv staging/node_exporter-${release}.linux-${arch}/node_exporter /usr/bin/

# cleanup
rm -r *.gz staging

# set up init.d config
# Adapted from https://github.com/prometheus/node_exporter/blob/master/examples/openwrt-init.d/node_exporter
cat <<'EOF' > /etc/init.d/node_exporter
#!/bin/sh /etc/rc.common

START=99

USE_PROCD=1
PROG="/usr/bin/node_exporter"
OPTIONS="--no-collector.bonding \
--no-collector.fibrechannel \
--no-collector.infiniband \
--no-collector.ipvs \
--no-collector.mdadm \
--no-collector.nfs \
--no-collector.nfsd \
--no-collector.nvme \
--no-collector.pressure \
--no-collector.rapl \
--no-collector.schedstat \
--no-collector.tapestats \
--no-collector.zfs \
--web.listen-address=:9100"

start_service() {
        procd_open_instance
        procd_set_param command "$PROG" ${OPTIONS}
        procd_close_instance
}
EOF
chmod 755 /etc/init.d/node_exporter

# ensure service is started
if [ "$(/etc/init.d/node_exporter status)" != "running" ]
then
    /etc/init.d/node_exporter start
else
    /etc/init.d/node_exporter restart
fi

# enable service on boot
/etc/init.d/node_exporter enable