9 Essential Linux Shell Scripts for System Administration and Automation

Below are nine useful shell script examples that operations engineers can adapt to their environments.

1. DDoS attack prevention (auto‑block IP)

<code>#!/bin/bash
DATE=$(date +%d/%b/%Y:%H:%M)
LOG_FILE=/usr/local/nginx/logs/demo2.access.log
ABNORMAL_IP=$(tail -n5000 $LOG_FILE | grep $DATE | awk '{a[$1]++} END {for(i in a) if(a[i]>10) print i}')
for IP in $ABNORMAL_IP; do
    if [ $(iptables -vnL | grep -c "$IP") -eq 0 ]; then
        iptables -I INPUT -s $IP -j DROP
        echo "$(date +'%F_%T') $IP" >> /tmp/drop_ip.log
    fi
done
</code>

2. Linux system alert script (mailx configuration)

<code># yum install mailx
# vi /etc/mail.rc
set [email protected] smtp=smtp.163.com
set [email protected] smtp-auth-password=******
set smtp-auth=login
</code>

3. MySQL single‑loop backup

<code>#!/bin/bash
DATE=$(date +%F_%H-%M-%S)
HOST=localhost
USER=backup
PASS=123.com
BACKUP_DIR=/data/db_backup
DB_LIST=$(mysql -h$HOST -u$USER -p$PASS -s -e "show databases;" 2>/dev/null | egrep -v "Database|information_schema|mysql|performance_schema|sys")
for DB in $DB_LIST; do
    BACKUP_NAME=$BACKUP_DIR/${DB}_${DATE}.sql
    if ! mysqldump -h$HOST -u$USER -p$PASS -B $DB > $BACKUP_NAME 2>/dev/null; then
        echo "$BACKUP_NAME 备份失败!"
    fi
done
</code>

4. MySQL multi‑loop backup

<code>#!/bin/bash
DATE=$(date +%F_%H-%M-%S)
HOST=localhost
USER=backup
PASS=123.com
BACKUP_DIR=/data/db_backup
DB_LIST=$(mysql -h$HOST -u$USER -p$PASS -s -e "show databases;" 2>/dev/null | egrep -v "Database|information_schema|mysql|performance_schema|sys")
for DB in $DB_LIST; do
    BACKUP_DB_DIR=$BACKUP_DIR/${DB}_${DATE}
    [ ! -d $BACKUP_DB_DIR ] && mkdir -p $BACKUP_DB_DIR >/dev/null
    TABLE_LIST=$(mysql -h$HOST -u$USER -p$PASS -s -e "use $DB;show tables;" 2>/dev/null)
    for TABLE in $TABLE_LIST; do
        BACKUP_NAME=$BACKUP_DB_DIR/${TABLE}.sql
        if ! mysqldump -h$HOST -u$USER -p$PASS $DB $TABLE > $BACKUP_NAME 2>/dev/null; then
            echo "$BACKUP_NAME 备份失败!"
        fi
    done
done
</code>

5. Nginx access log daily rotation

<code>#!/bin/bash
LOG_DIR=/usr/local/nginx/logs
YESTERDAY_TIME=$(date -d "yesterday" +%F)
LOG_MONTH_DIR=$LOG_DIR/$(date +"%Y-%m")
LOG_FILE_LIST="default.access.log"
for LOG_FILE in $LOG_FILE_LIST; do
    [ ! -d $LOG_MONTH_DIR ] && mkdir -p $LOG_MONTH_DIR
    mv $LOG_DIR/$LOG_FILE $LOG_MONTH_DIR/${LOG_FILE}_${YESTERDAY_TIME}
done
kill -USR1 $(cat /var/run/nginx.pid)
</code>

6. Nginx access log analysis script

<code>#!/bin/bash
# Log format: $remote_addr - $remote_user [$time_local] "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent" "$http_x_forwarded_for"
LOG_FILE=$1
echo "Top 10 IPs by requests"
awk '{a[$1]++} END {print "UV:",length(a); for(v in a) print v,a[v]}' $LOG_FILE | sort -k2 -nr | head -10
echo "----------------------"

echo "Top IPs in specific time range"
awk '$4>="[01/Dec/2018:13:20:25" && $4<="[27/Nov/2018:16:20:49" {a[$1]++} END {for(v in a) print v,a[v]}' $LOG_FILE | sort -k2 -nr | head -10
echo "----------------------"

echo "Top 10 pages by requests"
awk '{a[$7]++} END {print "PV:",length(a); for(v in a) if(a[v]>10) print v,a[v]}' $LOG_FILE | sort -k2 -nr
echo "----------------------"

echo "Request count per status code"
awk '{a[$7" "$9]++} END {for(v in a) if(a[v]>5) print v,a[v]}' $LOG_FILE
</code>

7. Real‑time network interface traffic script

<code>#!/bin/bash
NIC=$1
echo -e " In ------ Out"
while true; do
    OLD_IN=$(awk '$0~"'$NIC'"{print $2}' /proc/net/dev)
    OLD_OUT=$(awk '$0~"'$NIC'"{print $10}' /proc/net/dev)
    sleep 1
    NEW_IN=$(awk '$0~"'$NIC'"{print $2}' /proc/net/dev)
    NEW_OUT=$(awk '$0~"'$NIC'"{print $10}' /proc/net/dev)
    IN=$(printf "%.1fKB/s" $((($NEW_IN-$OLD_IN)/1024)))
    OUT=$(printf "%.1fKB/s" $((($NEW_OUT-$OLD_OUT)/1024)))
    echo "$IN $OUT"
    sleep 1
done
</code>

8. Server system initialization script

<code>#/bin/bash
# Set timezone and sync time
ln -s /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
if ! crontab -l | grep ntpdate >/dev/null; then
    (echo "* 1 * * * ntpdate time.windows.com >/dev/null 2>&1"; crontab -l) | crontab
fi

# Disable SELinux
sed -i '/SELINUX/{s/permissive/disabled/}' /etc/selinux/config

# Stop firewall
if egrep "7.[0-9]" /etc/redhat-release >/dev/null; then
    systemctl stop firewalld
    systemctl disable firewalld
elif egrep "6.[0-9]" /etc/redhat-release >/dev/null; then
    service iptables stop
    chkconfig iptables off
fi

# Show command execution time in history
if ! grep HISTTIMEFORMAT /etc/bashrc; then
    echo 'export HISTTIMEFORMAT="%F %T `whoami` "' >> /etc/bashrc
fi

# SSH timeout
if ! grep "TMOUT=600" /etc/profile >/dev/null; then
    echo "export TMOUT=600" >> /etc/profile
fi

# Disallow root remote login
sed -i 's/#PermitRootLogin yes/PermitRootLogin no/' /etc/ssh/sshd_config

# Disable email notifications for cron jobs
sed -i 's/^MAILTO=root/MAILTO=""/' /etc/crontab

# Increase max open files
if ! grep "* soft nofile 65535" /etc/security/limits.conf >/dev/null; then
    cat >> /etc/security/limits.conf <<EOF
* soft nofile 65535
* hard nofile 65535
EOF
fi

# Kernel optimizations
cat >> /etc/sysctl.conf <<EOF
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_max_tw_buckets = 20480
net.ipv4.tcp_max_syn_backlog = 20480
net.core.netdev_max_backlog = 262144
net.ipv4.tcp_fin_timeout = 20
EOF

# Reduce swap usage
echo "0" > /proc/sys/vm/swappiness

# Install performance tools
yum install -y gcc make autoconf vim sysstat net-tools iostat
</code>

9. Monitor disk usage on 100 servers

<code>#!/bin/bash
HOST_INFO=host.info
for IP in $(awk '/^[^#]/{print $1}' $HOST_INFO); do
    USER=$(awk -v ip=$IP 'ip==$1{print $2}' $HOST_INFO)
    PORT=$(awk -v ip=$IP 'ip==$1{print $3}' $HOST_INFO)
    TMP_FILE=/tmp/disk.tmp
    ssh -p $PORT $USER@$IP 'df -h' > $TMP_FILE
    USE_RATE_LIST=$(awk 'BEGIN{OFS="="}/^\/dev/{print $NF,int($5)}' $TMP_FILE)
    for USE_RATE in $USE_RATE_LIST; do
        PART_NAME=${USE_RATE%=*}
        USE_RATE=${USE_RATE#*=}
        if [ $USE_RATE -ge 80 ]; then
            echo "Warning: $PART_NAME Partition usage $USE_RATE%!"
        fi
    done
done
</code>

These scripts can be customized to fit specific operational requirements and help automate routine system administration tasks.