Automate Linux Memory & Swap Monitoring with Email Alerts

来自网络旧文，原作者不详

1. Install and configure msmtp

Download the msmtp source package, extract it, compile and install it to /usr/local/msmtp using the typical ./configure --prefix=/usr/local/msmtp, make and make install steps.

Create the configuration file ~/.msmtprc with the SMTP server, user name, password and log file, then protect it with chmod 600 and create the log file.

Configure ~/.muttrc to use msmtp as the sendmail program, set the sender address, enable envelope‑from and UTF‑8 charset.

Test the setup with a mutt command that pipes a message body and attaches a file, e.g.

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

.

2. Monitor memory with the free command

Run free -m to display memory usage in megabytes. Extract the free values for physical memory, buffers/cache and swap using awk pipelines.

Example commands:

# free -m | grep Mem | awk '{print $4}'   # physical free

# free -m | grep - | awk '{print $4}'   # buffers/cache free

# free -m | grep Swap | awk '{print $4}' # swap free

3. Script to log memory statistics

Create /scripts/free-mem.sh that records the current timestamp, the three free values, and concatenates them into /scripts/freemem.txt using paste. Make the script executable.

#!/bin/bash
date >> /scripts/date-time.txt
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
paste /scripts/date-time.txt /scripts/mem-free.txt /scripts/buffers-free.txt /scripts/swap-free.txt > /scripts/freemem.txt

4. Script to email the memory report

The script /scripts/sendmail-mem.sh extracts the server’s IP address and the current date, then sends freemem.txt as an attachment with a descriptive subject line.

#!/bin/bash
IP=`ifconfig eth0 | grep "inet addr" | cut -f2 -d":" | cut -f1 -d" "`
today=`date -d "0 day" +%Y年%m月%d日`
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]

5. Swap usage warning script

The script /scripts/swap-warning.sh calculates the percentage of free swap space, compares it with a 20 % threshold (meaning usage >80 %), and sends an alert email when the threshold is exceeded.

#!/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=$(echo "$swap_per > $swap_warn" | bc)
    if ((swap_now == 0)); then
        echo "$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

6. Schedule the tasks with cron

Add the following entries to crontab -e so that memory and swap checks run every ten minutes, and the daily summary is sent at 08:00.

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