Essential Bash Scripts for Linux Server Automation and Monitoring

This article provides a collection of Bash scripts for common Linux server administration tasks, ranging from file consistency verification to automated firewall blocking.

1. Detect file consistency between two servers

#!/bin/bash
######################################
# 检测两台服务器指定目录下的文件一致性
#####################################
# 通过对比两台服务器上文件的md5值，达到检测一致性的目的
dir=/data/web
b_ip=192.168.88.10
# 将指定目录下的文件全部遍历出来并作为md5sum命令的参数，进而得到所有文件的md5值，并写入到指定文件中
find $dir -type f | xargs md5sum > /tmp/md5_a.txt
ssh $b_ip "find $dir -type f | xargs md5sum > /tmp/md5_b.txt"
scp $b_ip:/tmp/md5_b.txt /tmp
# 将文件名作为遍历对象进行一一比对
for f in `awk '{print $2}' /tmp/md5_a.txt`; do
    if grep -qw "$f" /tmp/md5_b.txt; then
        md5_a=`grep -w "$f" /tmp/md5_a.txt | awk '{print $1}'`
        md5_b=`grep -w "$f" /tmp/md5_b.txt | awk '{print $1}'`
        if [ $md5_a != $md5_b ]; then
            echo "$f changed."
        fi
    else
        echo "$f deleted."
    fi
done

2. Hourly log cleanup and size recording

#!/bin/bash
#################################################################
# 每小时执行一次脚本（任务计划），当时间为0点或12点时，将目标目录下的所有文件内容清空，但不删除文件，其他时间则只统计各个文件的大小，一个文件一行，输出到以时间和日期命名的文件中，需要考虑目标目录下二级、三级等子目录的文件
################################################################
logfile=/tmp/$(date +%H-%F).log
n=$(date +%H)
if [ $n -eq 00 ] || [ $n -eq 12 ]; then
    for i in `find /data/log -type f`; do
        true > $i
    done
else
    for i in `find /data/log -type f`; do
        du -sh $i >> $logfile
    done
fi

3. Record network interface traffic every minute

#!/bin/bash
#######################################################
# 检测网卡流量，并按规定格式记录在日志中
# 规定一分钟记录一次
# 日志格式如下所示:
# 2019-08-12 20:40
# ens33 input: 1234bps
# ens33 output: 1235bps
#######################################################
while :
do
    LANG=en
    logfile=/tmp/$(date +%d).log
    exec >> $logfile
    date +"%F %H:%M"
    sar -n DEV 1 59 | grep Average | grep ens33 | awk '{print $2,"\t","input:","\t",$5*1000*8,"bps","
",$2,"\t","output:","\t",$6*1000*8,"bps"}'
    echo "####################"
    # sar runs ~59 seconds, no extra sleep needed
 done

4. Count numbers per line and total in a file

#!/bin/bash
#########################################################
# 计算文档每行出现的数字个数，并计算整个文档的数字总数
#########################################################
n=$(wc -l a.txt | awk '{print $1}')
sum=0
for i in $(seq 1 $n); do
    line=$(sed -n "${i}p" a.txt)
    n_n=$(echo $line | sed 's/[^0-9]//g' | wc -L)
    sum=$((sum + n_n))
done
echo "sum:$sum"

5. Kill all scripts that may overload the system

#!/bin/bash
################################################################
# 有一些脚本加入到了cron之中，存在脚本尚未运行完毕又有新任务需要执行的情况，导致系统负载升高，因此可通过编写脚本，筛选出影响负载的进程一次性全部杀死。
################################################################
ps aux | grep 指定进程名 | grep -v grep | awk '{print $2}' | xargs kill -9

6. Download a file from an FTP server

#!/bin/bash
if [ $# -ne 1 ]; then
    echo "Usage: $0 filename"
fi
dir=$(dirname $1)
file=$(basename $1)
ftp -n -v <<EOF
open 192.168.1.10
user admin password
binary
cd $dir
get "$file"
EOF

7. Input five numbers and compute sum, min, max

#!/bin/bash
COUNT=1
SUM=0
MIN=0
MAX=100
while [ $COUNT -le 5 ]; do
    read -p "请输入1-10个整数：" INT
    if [[ ! $INT =~ ^[0-9]+$ ]]; then
        echo "输入必须是整数！"
        exit 1
    elif [ $INT -gt 100 ]; then
        echo "输入必须是100以内！"
        exit 1
    fi
    SUM=$((SUM + INT))
    [ $MIN -lt $INT ] && MIN=$INT
    [ $MAX -gt $INT ] && MAX=$INT
    let COUNT++
done
echo "SUM: $SUM"
echo "MIN: $MIN"
echo "MAX: $MAX"

8. User guesses a random number

#!/bin/bash
num=$[RANDOM%100+1]
while :
do
    read -p "计算机生成了一个 1-100 的随机数,你猜: " cai
    if [ $cai -eq $num ]; then
        echo "恭喜,猜对了"
        exit
    elif [ $cai -gt $num ]; then
        echo "Oops,猜大了"
    else
        echo "Oops,猜小了"
    fi
done

9. Monitor Nginx 502 errors and restart php‑fpm

#!/bin/bash
###########################################################
# 监测Nginx访问日志502情况，并做相应动作
###########################################################
log=/data/log/access.log
N=30  # 阈值：每300条日志中出现30条502即触发
while :
do
    err=$(tail -n 300 $log | grep -c '502"')
    if [ $err -ge $N ]; then
        /etc/init.d/php-fpm restart 2>/dev/null
        sleep 60  # 防止频繁重启
    fi
    sleep 10
done

10. Assign command results to variables

#!/bin/bash
# 方法1
for i in $(echo "4 5 6"); do
    eval a$i=$idone
    echo $a4 $a5 $a6
done
# 方法2：拆分位置参数
num=0
for i in $(eval echo $*); do
    let num+=1
    eval node${num}="$i"
done
echo $node1 $node2 $node3
# 方法3：数组示例
arr=(4 5 6)
INDEX1=$(echo ${arr[0]})
INDEX2=$(echo ${arr[1]})
INDEX3=$(echo ${arr[2]})

11. Batch rename HTML files

#!/bin/bash
# 将 article_*.html 重命名为 bbs_*.html
for file in $(ls *html); do
    mv $file bbs_${file#*_}
done

12. Delete lines containing letters in a text file

#!/bin/bash
# 删除前5行中含字母的行，随后删除6-10行中的所有字母
sed -n '1,5'p 2.txt | sed '/[a-zA-Z]/d'
sed -n '6,10'p 2.txt | sed 's/[a-zA-Z]//g'
sed -n '11,$'p 2.txt

13. Calculate total size of .html files in current directory

#!/bin/bash
# 方法1
find . -name "*.html" -exec du -k {} \; | awk '{sum+=$1} END {print sum}'
# 方法2
sum=0
for size in $(ls -l *.html | awk '{print $5}'); do
    sum=$((sum + size))
done
echo $sum

14. Scan host ports

#!/bin/bash
HOST=$1
PORTS="22 25 80 8080"
for p in $PORTS; do
    if echo >/dev/null > /dev/tcp/$HOST/$p; then
        echo "$p open"
    else
        echo "$p close"
    fi
done

15. Print words with fewer than six letters

#!/bin/bash
# 示例句子
for w in Bash also interprets a number of multi-character options.; do
    n=$(echo $w | wc -c)
    if [ $n -lt 6 ]; then
        echo $w
    fi
done

16. Menu‑driven command execution

#!/bin/bash
echo "*cmd menu* 1-date 2-ls 3-who 4-pwd 0-exit "
while :; do
    read -p "please input number :" n
    n1=$(echo $n | sed 's/[0-9]//g')
    if [ -z "$n" ]; then
        continue
    fi
    if [ -n "$n1" ]; then
        exit 0
    fi
    break
done
case $n in
    1) date ;;
    2) ls ;;
    3) who ;;
    4) pwd ;;
    0) break ;;
    *) echo "please input number is [1-4]" ;;
esac

17. Expect script for non‑interactive SSH

#!/bin/bash
USER=root
PASS=123.com
IP=192.168.1.120
expect <<EOF
set timeout 30
spawn ssh $USER@$IP
expect {
    "(yes/no)" {send "yes\r"; exp_continue}
    "password:" {send "$PASS\r"}
}
expect "$USER@*" {send "$1\r"}
expect "$USER@*" {send "exit\r"}
expect eof
EOF

18. Automatic iptables blocking of abusive IPs

#!/bin/bash
# Block IPs that exceed 200 requests per minute (example for Nginx access log)
DATE=$(date +"%d/%b/%Y:%H:%M")
ABNORMAL_IP=$(tail -n5000 access.log | grep $DATE | awk '{a[$1]++} END {for(i in a) if(a[i]>200) print i}')
for IP in $ABNORMAL_IP; do
    if ! iptables -vnL | grep -q "$IP"; then
        iptables -I INPUT -s $IP -j DROP
    fi
done
# Block SSH brute‑force attempts (more than 10 failures per minute)
DATE=$(date +"%a %b %e %H:%M")
ABNORMAL_SSH=$(lastb | grep "$DATE" | awk '{a[$3]++} END {for(i in a) if(a[i]>10) print i}')
for IP in $ABNORMAL_SSH; do
    if ! iptables -vnL | grep -q "$IP"; then
        iptables -I INPUT -s $IP -j DROP
    fi
done