Step 1 . add --collector.textfile.directory to file 

[Unit]
Description=Node Exporter
Wants=network-online.target
After=network-online.target

[Service]
User=node_exporter
Group=node_exporter
Type=simple
ExecStart=/usr/local/bin/node_exporter --collector.systemd --collector.textfile.directory /var/lib/node_exporter/textfile_collector/
[Install]
WantedBy=default.target

Step 2: Create mkdir -p /var/lib/node_exporter/textfile_collector/ 

Step 3 : Create file process.sh

$ vi /opt/directory_size.sh

#!/bin/bash

du -sb /var/log /var/cache/apt /var/lib | sed -ne 's/^\([0-9]\+\)\t\(.*\)$/ {directory="\2"} \1/p' >

/var/lib/node_exporter/textfile_collector/directory_size.prom.$$ && mv

/var/lib/node_exporter/textfile_collector/directory_size.prom.$$

/var/lib/node_exporter/textfile_collector/directory_size.prom

Step 4 : chmod +x /opt/directory_size.sh

Step 5 : useradd -r -M -s /bin/false prometheus

Step 6: chown -R prometheus:prometheus /var/lib/node_exportersystemctl daemon-reload 

Step 7: Create file timer 10s 

# vim /etc/systemd/system/directory.timer

[Unit]

Description=Timer for write cpu to file

[Timer]

OnCalendar=*:*:0/10

[Install]

WantedBy=timers.target

Step 8 :

systemctl start directory.timer

systemctl enable directory.timer

systemctl daemon-reload

systemctl restart node_exporterrestart prometheus

Step 9: Monitor

watch -n 1 cat /var/lib/node_exporter/textfile_collector/directory_size.prom