Automate Linux Email Alerts and Memory Monitoring with msmtp, mutt, and Bash

1. Install msmtp

# tar jxvf msmtp-1.4.16.tar.bz2
# cd msmtp-1.4.16
# ./configure --prefix=/usr/local/msmtp
# make
# make install

Download the source from http://downloads.sourceforge.net/.../msmtp-1.4.16.tar.bz2 and compile it with the commands above.

2. Create msmtp configuration and log file

# vim ~/.msmtprc
account default
host 126.com
from [email protected]
auth login
user test
password 123456
logfile ~/.msmtp.log

# chmod 600 ~/.msmtprc
# touch ~/.msmtp.log

This file tells msmtp how to connect to the SMTP server and where to write logs.

3. Configure mutt to use msmtp

# vim ~/.muttrc
set sendmail="/usr/local/msmtp/bin/msmtp"
set use_from=yes
set realname="memory"
set [email protected]
set envelope_from=yes
set rfc2047_parameters=yes
set charset="utf-8"

Most Linux distributions already have mutt installed; the above settings make mutt invoke msmtp for sending mail.

4. Test email sending

# echo "邮件内容123456" | mutt -s "邮件标题测试邮件" -a /scripts/test.txt [email protected]

5. Monitor memory with the free command

# free -m
# free -m | grep Mem | awk '{print $4}'   # physical memory free (M)
# free -m | grep - | awk '{print $4}'    # buffer cache free (M)
# free -m | grep Swap | awk '{print $4}' # swap free (M)

6. Bash script to record memory statistics

# vim /scripts/free-mem.sh
#!/bin/bash
# Record current time
date >> /scripts/date-time.txt
# Record free values
echo "Mem-free: `free -m | grep Mem | awk '{print $4}'`M" >> /scripts/mem-free.txt
echo "buffers/cache-free: `free -m | grep - | awk '{print $4}'`M" >> /scripts/buffers-free.txt
echo "Swap-free: `free -m | grep Swap | awk '{print $4}'`M" >> /scripts/swap-free.txt
# Combine into one file
paste /scripts/date-time.txt /scripts/mem-free.txt /scripts/buffers-free.txt /scripts/swap-free.txt > /scripts/freemem.txt
chmod a+x /scripts/free-mem.sh

7. Script to email the memory report

# vim /scripts/sendmail-mem.sh
#!/bin/bash
# Get server IP
IP=`ifconfig eth0 | grep "inet addr" | cut -f2 -d":" | cut -f1 -d" "`
# Current date
today=`date -d "0 day" +%Y年%m月%d日`
# Send email with attachment
echo "这是${IP}服务器${today}的内存监控报告，请下载附件。" \
| mutt -s "${IP}服务器${today}内存监控报告" -a /scripts/freemem.txt [email protected]
chmod a+x /scripts/sendmail-mem.sh

8. Swap usage warning script (alert when usage >80%)

# vim /scripts/swap-warning.sh
#!/bin/bash
IP=`ifconfig eth0 | grep "inet addr" | cut -f2 -d":" | cut -f1 -d" "`
swap_total=`free -m | grep Swap | awk '{print $2}'`
swap_free=`free -m | grep Swap | awk '{print $4}'`
swap_used=`free -m | grep Swap | awk '{print $3}'`
if ((swap_used != 0)); then
  swap_per=$(echo "scale=2; $swap_free/$swap_total" | bc)
  swap_warn=0.20
  swap_now=$(expr $swap_per ">" $swap_warn)
  if (( $swap_now == 0 )); then
    echo "${IP}服务器swap交换分区只剩下 ${swap_free} M 未使用，剩余不足20%，使用率已经超过80%，请及时处理。" \
    | mutt -s "${IP} 服务器内存告警" [email protected]
  fi
fi
chmod a+x /scripts/swap-warning.sh

9. Schedule tasks with cron

# crontab -e
*/10 * * * * /scripts/free-mem.sh
*/10 * * * * /scripts/swap-warning.sh
0 8 * * * /scripts/sendmail-mem.sh
# service crond restart

These entries run memory collection and swap warning every ten minutes and send a daily summary at 08:00.