awk

xargs

xargs -I {} rm {}

-I {} 指定{}为需要替换的位置

sed

df -h

df -hi

check inodes place

du --inodes -xS

Clear system logs

cat /dev/null > /path/to/logfile

host files

environment variable

crob

create service

生成任意大小的文件

dd if=/dev/zero of=junk.data bs=1M count=1

Concepts

inodes
probes

Tools

ncdu: https://dev.yorhel.nl/ncdu

analysis disk usage

Trouble Shot

disk analysis:

df -h 显示整个磁盘空间使用状况

df -hi显示整个磁盘inodes使用状况

network analysis

dig [domain name]

分为question和answer section

answer section返回DNS records

http://www.ruanyifeng.com/blog/2016/06/dns.html

Network

check for open prots

sudo netstat -pltn

查看占用端口信息

lsof -i :8080

关闭占用端口

sudo lsof -i :5000 | grep "python" | cut -d " " -f3 | xargs kill -9

Web Server

Apache不适合处理大流量高并发，Nginx没有Built-in动态内容处理，两者可以联合使用。

nginx reverse proxy: https://www.nginx.com/resources/admin-guide/reverse-proxy/

nginx load balancer: layer 7 HTTP traffic, layer 4 database traffic https://www.nginx.com/resources/admin-guide/load-balancer/

常见配置

http {
    upstream backend {
        server backend1.example.com weight=5;
        server backend2.example.com;
        server 192.0.0.1 backup;
    }
}

Load balancing method, server weights, health check, limit number of connections, persistence session

HTTPS

数据同步

scp

sftp

rsync

Remote disk usage health monitor

#!/bin/bash
#Filename: disklog.sh
#Description: Monitor disk usage health for remote systems


logfile="diskusage.log"

if [[ -n $1 ]]
then
  logfile=$1
fi

if [ ! -e $logfile ]
then

  printf "%-8s %-14s %-9s %-8s %-6s %-6s %-6s %s\n" "Date" "IP address" "Device" "Capacity" "Used" "Free" "Percent" "Status" > $logfile
fi

IP_LIST="127.0.0.1 0.0.0.0"
#provide the list of remote machine IP addresses 

(
for ip in $IP_LIST;
do

  ssh slynux@$ip 'df -H' | grep ^/dev/ > /tmp/$$.df

  while read line;
  do
    cur_date=$(date +%D)
    printf "%-8s %-14s " $cur_date $ip
    echo $line | awk '{ printf("%-9s %-8s %-6s %-6s %-8s",$1,$2,$3,$4,$5); }'

  pusg=$(echo $line | egrep -o "[0-9]+%")
  pusg=${pusg/\%/};
  if [ $pusg -lt 80 ];
  then
    echo SAFE
  else
    echo ALERT
  fi

  done< /tmp/$$.df    
done

) >> $logfile

logrotate

It helps to restrict the size of logfile to the given SIZE

config file

/etc/logrotate.d/

example

$ cat /etc/logrotate.d/nginx
/var/log/nginx/*.log {
    daily
    missingok
    rotate 14
    compress
    delaycompress
    notifempty
    create 0640 www-data adm
    sharedscripts
    prerotate
        if [ -d /etc/logrotate.d/httpd-prerotate ]; then \
            run-parts /etc/logrotate.d/httpd-prerotate; \
        fi \
    endscript
    postrotate
        invoke-rc.d nginx rotate >/dev/null 2>&1
    endscript
}

useful config

/var/log/program.log {
missingok
notifempty
size 30k
  compress
weekly
  rotate 5
create 0600 root root
}

Linux Command