Resource Monitoring Tools

There are programs available to watch various aspects of your system.

iftop

See active internet connections. e.g.

# iftop -i eth1

Will show you websites that don't close a connection, when the tab is left open. A privacy and security nightmare. This is a reason why Javascript is bad.

vmstat

See RAM usage. Can be watched, to monitor swapping. e.g.

$ vmstat 3

Leave it running. It will update every 3 seconds.

iotop

See HDD accesses. e.g.

# iotop --only
# iotop -o

only flag will show active processes only

# iotop -d 0.01  or -d 0.1

delay flag can be set to be faster than 1 second. Some writes are missed otherwise.

Monitor Library Reads from PID

$ ltrace -p -pidhere-

See what a program is doing. (Note: not available on ARM deb repos)

Monitor IP address up/down via ping

#!/bin/bash

SERVERIP=$1
LOGFILE=$1_$(date +%A)_LOG
HISTORYFILE=$1_$(date +%A)_LOCKFILE
NOTIFYEMAIL=myemail@address.com

#setup this script in cron each minute, and also
#crontab requires historyfile / lockfile to be blanked (echo "" > file) each day or each hour, whatever you prefer.
#mkdir /var/log/networkalerts
#e.g. $ script.sh <ipaddress>
# in /etc/crontab
#*/3 * * * *   root /root/email_alerts/test_up.sh 192.168.1.1 #tune this frequency based on your priority
#0 */2 * * * root rm /var/log/networkalerts/*LOCKFILE
#0 0 * * *   root rm /var/log/networkalerts/*$(date +%A)*LOG

#keep track of time
  date >> /var/log/networkalerts/$LOGFILE
  ping -c 6 $SERVERIP >> /var/log/networkalerts/$LOGFILE
#nothing after ping, as we need return value
#if return val is error (see man on ping regarding count and deadline)
# == or -eq can be used. == is intuitive, therefore better
  if test $? == 1
  then
#if file empty
#[ -s FILE ] True if FILE exists and has a size greater than zero. Thus, you get "empty.txt" if "diff.txt" is not e>
#https://stackoverflow.com/questions/9964823/how-to-check-if-a-file-is-empty-in-bash
#https://mywiki.wooledge.org/BashGuide/TestsAndConditionals    for all the other tests like -s
#   [! -s file] to invert didn't work because of missing spaces (i think)
# must be space between [ and -s and also last bracket. test brackets are unintuitive so don't use them.
#  if [ -s /var/log/networkalerts/$HISTORYFILE ]
  if test -s /var/log/networkalerts/$HISTORYFILE
   then
    exit 5
   else
    # Use your favorite mailer here:
    # wiki.zoneminder.com/Email explains how to configure email for devuan
    echo "alert" | mutt  -s "Network Down" -- $NOTIFYEMAIL
    #lock file / history file
    echo "alertsent" > /var/log/networkalerts/$HISTORYFILE
   fi
  fi