all can root/sudo

sudo su
passwd to set pw=1

sshd

• add ports in /etc/ssh/sshd_config:
  ListenAddress 0.0.0.0:22
  ListenAddress 0.0.0.0:5022
  then service sshd restart (won't break connected ssh).

• if "key exchange algorithm" not found:
  append "diffie-hellman-group1-sha1" to "KexAlgorithms" in /etc/ssh/sshd_config

vnc for X

vnc4server(by realvnc) --> tightvnc -2009->tigervnc
tigervnc allow 1 char password.

ip, ports, connections

curl cip.cc
netstat -atpn
nmap IP -Pn -pNNN or telnet IP NNN

PS1

item format \e[XXXm, with XXX=0 to clear format.
PS1='\e[1;33m\W \e[31m\# \e[0m'
ref https://misc.flogisoft.com/bash/tip_colors_and_formatting
from https://wiki.archlinux.org/title/Bash/Prompt_customization

repo for centos:

• base repo, may use vault
  https://mirrors.cloud.tencent.com/help/centos.html
  https://developer.aliyun.com/mirror/centos

• epel repo
  https://mirrors.cloud.tencent.com/help/epel.html
  https://developer.aliyun.com/mirror/epel

• forge repo, ~5k pkgs for centos6
  https://mirrors.cloud.tencent.com/help/repoforge.html
  https://developer.aliyun.com/mirror/repoforge
  releasever=$(rpm -E %centos)
basearch=$(rpm -E %_arch)
  then copy-paste "cat > .repo" code,
  ali: sed -i s:el7:el$releasever:g /etc/yum.repos.d/rpmforge.repo

• fusion repo, ~300 pkgs for centos6
  here yum may create two files: epel.repo.rpmnew, epel-testing.repo
  yum install --nogpgcheck http://mirrors.tencentyun.com/rpmfusion/free/el/rpmfusion-free-release-$(rpm -E %centos).noarch.rpm http://mirrors.tencentyun.com/rpmfusion/nonfree/el/rpmfusion-nonfree-release-$(rpm -E %centos).noarch.rpm
sed -i s#download1.rpmfusion.org#mirrors.tencentyun.com/rpmfusion#g /etc/yum.repos.d/rpmfusion-*.repo
yum install --nogpgcheck http://mirrors.cloud.aliyuncs.com/rpmfusion/free/el/rpmfusion-free-release-$(rpm -E %centos).noarch.rpm http://mirrors.cloud.aliyuncs.com/rpmfusion/nonfree/el/rpmfusion-nonfree-release-$(rpm -E %centos).noarch.rpm
sed -i s#download1.rpmfusion.org#mirrors.cloud.aliyuncs.com/rpmfusion#g /etc/yum.repos.d/rpmfusion-*.repo

• sum for following
  sed -i '/^\W*http/d; /^\W*mirrorlist/d; s/^\W*#\W*baseurl/baseurl/; s/https/http/g;' /etc/yum.repos.d/*.repo
  this cmd can run multiple times without repeated replace.

• • remove alt baseurl
    sed -i '/^\W*http/d' /etc/yum.repos.d/*.repo
• • remove mirrorlist, use baseurl
    sed -i '/^\W*mirrorlist/d' /etc/yum.repos.d/*.repo
sed -i 's/^\W*#\W*baseurl/baseurl/' /etc/yum.repos.d/*.repo
• • https -> http
    sed -i s/https/http/g /etc/yum.repos.d/*.repo

• use private network:
  mirrors.tencentyun.com
  mirrors.cloud.aliyuncs.com
  sed -i 's/cloud\.tencent/tencentyun/g' /etc/yum.repos.d/*.repo
sed -i 's/aliyun\./cloud.aliyuncs./g' /etc/yum.repos.d/*.repo
  this cmd can run multiple times without repeated replace.