Ttgjyuk

This is a follow-up to Memory limiting solutions for greedy applications that can crash OS?: ulimit and cgroups are not user friendly, and besides, wouldn't work with applications that spawn separate processes, such as Chrome/Chromium for each new (group of) tabs.

The simple and effective solution, used by Windows 7 actually, is to warn the user that the OS is running low on memory. This simple warning pop-up has prevented me from having any low-memory-caused system freeze in Windows, while I kept running into them on Ubuntu distros that I was testing live (where the RAM-mounted disk would eat up 2GB alone).

So, is there some way to automatically warn the user that the available RAM is nearing zero, without the user having to keep an eye on some memory monitoring gadget? Surely Conky could be configured to do that?

Check these scripts:
Need application/script alerting when system memory is running out

#!/bin/bash

#Minimum available memory limit, MB
THRESHOLD=400

#Check time interval, sec
INTERVAL=30

while :
do

 free=$(free -m|awk '/^Mem:/print $4')
 buffers=$(free -m|awk '/^Mem:/print $6')
 cached=$(free -m|awk '/^Mem:/print $7')
 available=$(free -m | awk '/^-/+/print $4')

 message="Free $free""MB"", buffers $buffers""MB"", cached $cached""MB"", available $available""MB"""

 if [ $available -lt $THRESHOLD ]
 then
 notify-send "Memory is running out!" "$message"
 fi

 echo $message

 sleep $INTERVAL

done

PHP:

#!/usr/bin/php
<?php
$alert_percent=($argc>1)?(int)$argv[1]:90;
//$interval=($argc>2):(int)$argv[2]:25;



//while(true)
//
 exec("free",$free);

$free=implode(' ',$free);
preg_match_all("/(?<=s)d+/",$free,$match);

list($total_mem,$used_mem,$free_mem,$shared_mem,$buffered_mem,$cached_mem)=$match[0];

$used_mem-=($buffered_mem+$cached_mem);

$percent_used=(int)(($used_mem*100)/$total_mem);

if($percent_used>$alert_percent)
exec("notify-send 'Low Memory: $percent_used% used'");

//sleep($interval);
//
exit();
?>

Another script that I wrote for this purpose:

#!/bin/bash
# Copyright 2019, Mikko Rantalainen
# License: MIT X License

# Minimum available memory until warning, default to 10% of total RAM (MiB)
THRESHOLD=$(grep "MemTotal:" /proc/meminfo | awk ' printf "%d", 0.1*$2/1024')
INTERVAL=60s

echo "Emitting a warning if less than $THRESHOLD MiB of RAM is available..."

while true; do
 meminfo=$(cat /proc/meminfo)
 free=$(echo "$meminfo" | grep "MemFree:" | awk ' printf "%d", $2/1024')
 available=$(echo "$meminfo" | grep "MemAvailable:" | awk ' printf "%d", $2/1024')
 inactive=$(echo "$meminfo" | grep "Inactive:" | awk ' printf "%d", $2/1024')
 reclaimable=$(echo "$meminfo" | grep "SReclaimable:" | awk ' printf "%d", $2/1024')
 usable=$(echo "$free + $inactive / 2 + $reclaimable / 2" | bc)
 if test -z "$available"; then
 message="Current kernel does not support MemAvailable in /proc/meminfo, aborting"
 notify-send "Error while monitoring low memory" "$message"
 echo "$message" 1>&2
 exit 1
 fi

 message="Available: $available MiB
Free: $free MiB
Maybe usable: $usable MiB"

 if [ "$available" -lt "$THRESHOLD" ]
 then
 notify-send -u critical "Low memory warning" "$message"
 echo "Low memory warning:"
 echo "$message"
 fi

 #echo "DEBUG: $message"
 sleep $INTERVAL
done

Updated version of the script which works with free from procps-ng 3.3.10

#!/bin/bash

#Minimum available memory limit, MB
THRESHOLD=400

#Check time interval, sec
INTERVAL=30

while :
do
 free_out=$(free -w -m)
 available=$(awk '/^Mem:/print $8' <<<$free_out)

 if (( $available < $THRESHOLD ))
 then
 notify-send -u critical "Memory is running out!" "Available memory is $available MiB"
 echo "Warning - available memory is $available MiB" 
 fi

 cat <<<$free_out
 sleep $INTERVAL
done

Updated above script to also add details on top 3 memory-hungry processes.
See at https://github.com/romanmelko/ubuntu-low-mem-popup

Here is the script itself:

#!/usr/bin/env bash

set -o errexit
set -o pipefail
set -o nounset

# If the language is not English, free will output localized text and parsing fails
LANG=en_US.UTF-8

THRESHOLD=500
INTERVAL=300
POPUP_DELAY=999999

# sleep some time so the shell starts properly
sleep 60

while :
do
 available=$(free -mw | awk '/^Mem:/print $8')
 if [ $available -lt $THRESHOLD ]; then
 title="Low memory! $available MB available"
 message=$(top -bo %MEM -n 1 | grep -A 3 PID | awk 'print $(NF - 6) " t" $(NF)')
 # KDE Plasma notifier
 kdialog --title "$title" --passivepopup "$message" $POPUP_DELAY
 # use the following command if you are not using KDE Plasma, comment the line above and uncomment the line below
 # please note that timeout for notify-send is represented in milliseconds
 # notify-send -u critical "$title" "$message" -t $POPUP_DELAY
 fi
 sleep $INTERVAL
done

Variant using RAM available, percentages and displays desktop notifications when called by cron (i.e. loop script doesn't have to be started after reboot):

#!/usr/bin/env bash

# dbus env var required when called via cron:
eval "export $(egrep -z DBUS_SESSION_BUS_ADDRESS /proc/$(pgrep -u $LOGNAME gnome-session)/environ | tr '' 'n')";

AVAIL_THRESHOLD=5

free_output=$(free)
mem_total=$(awk '/^Mem:/print $2' <<< $free_output)
mem_avail=$(awk '/^Mem:/print $7' <<< $free_output)
mem_avail_m=$(bc <<< "scale=1; $mem_avail/1024")
percent_avail=$(bc <<< "scale=1; $mem_avail*100 /$mem_total")
should_warn=$(bc <<< "$percent_avail < $AVAIL_THRESHOLD")

if (( $should_warn )); then
 notify-send "Memory warning - only $percent_avail% ($mem_avail_m MB) available"
else
 echo "Memory OK - $percent_avail% ($mem_avail_m MB) available"
fi