Posts in category “Linux”

Using crontab to backup your mysql data

  1. on a server with huge disk space, run crontab -e and put the following code in it (you may need to change the directory names to fit your situation)
30 3 * * * mysqldump --databases DB1 DB2 DB3 DB4 | gzip > /data/backups/mysql/db_`date '+\%Y\%m\%d-\%H\%M\%S'`.sql.gz
30 4 * * * find /data/backups/mysql/db_* -mtime -1 -exec scp {} anotherserver:/data/backups/mysql \;
30 5 * * * find /data/backups/mysql/db_* -mtime +30 -exec rm {} \;
  1. on another server, run crontab -e and put the following line into it:
30 5 * * * find /data/backups/mysql/db_* -mtime +7 -exec rm {} \;

summary & explanation:

  1. at 3:30 backup MySQL data in a local directory and keep latest 30 days backup in that directory
  2. at 4:30 transfer the latest backup to another server in case the first backup may be destroyed by an accident.
  3. at 5:30 remove the oldest backup on the local backup server (the code shows that the latest 30 days backups are kept on the server).
  4. at 5:30 remove the oldest backup on the remote server (the code shows that only the latest 7 days backups are kept on that server).

Using sed to insert a line after several lines after the match line

最近一直在写 .net core，它有诸多优点我且不提，我实在头痛于手写注入服务时的模式化代码，因此动了心思要写个小脚本帮我自动化一些事情。我的想法是告诉我要加入的 ServiceName， 指定一个 Controller然后脚本自动在这个 Controller 里声明一个 private readonly 属性，自动修改类的construction 函数，自动注入这个服务，并在construction 函数体写上 _serviceName = serviceName;

在第一步，注入 private readonly 属性那里，我就绊了个跟头。用 sed 匹配到某行，在它之前，或者之后插入数据是简单的。但我匹配到 public class xxxController 这行之后是单独一行 {，而我要加的变量要放到 {这行之后。网上一通搜索，试图找到定位到某行之后N行的命令，然而并没有这样的命令。然而功夫不负有心人，我最后还是找到了一个解决方案，那就是

sed '/pattern/!b;n;n;i\something'

具体解释见 Reference

ubuntu 20.04 手工生成通配符ssl证书

其实很简单，但因为网上有流传很广的教程并不适用于最新的 ubuntu 20.04，造成我也走了一点弯路。 certbot-auto 官方已停止维护，但网上广为流传的教程仍然推荐使用 certbot-auto 来生成证书。这是问题的根源。正确的姿势是这样的

sudo apt install certbot
sudo certbot certonly --manual -d *.yourdomain.com -d youdomain.com --preferred-challenges dns-01 --server https://acme-v02.api.letsencrypt.org/directory

照提示一步一步来就好了。是不是超级简单？

switch case in bash script

, change the first letter of the value of the variable to lowercase, ,, change the value of the whole variable to lower case.

$ test='HELLO'
$ echo $test
HELLO
$ echo ${test,}
hELLO
$ echo ${test,,}
hello
$ test=${test,,}
$ echo ${test^}
Hello
$ echo ${test^^}
HELLO

A bash script to keep two git branch identical. 

#!/bin/bash

git push
currentbranch=`git branch --show-current`
if [ "${currentbranch}" == "local" ]; then
   git checkout develop
   git merge local
   git push
elif [ "${currentbranch}" == "develop" ]; then
   git checkout local
   git merge develop
   git push
fi
git checkout $currentbranch

Don't ask why I wrote this foolish script. I have to do it 😀