计算机基础教程

user file-creation mode mask (umask)

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/configuring_basic_system_settings/assembly_managing-file-permissions_configuring-basic-system-settings#user-file-creation-mode-mask_assembly_managing-file-permissions

# firewall

define your own service name in /usr/lib/firewalld/services/

firewall-cmd --get-services
firewall-cmd --permanent --zone=public --add-service=postgresql
firewall-cmd --reload

# selinux

chcon 会被重新标记

使用semanage getenforce

# Linux-PAM

Linux-PAM (short for Pluggable Authentication Modules which evolved from the Unix-PAM architecture) is a powerful suite of shared libraries used to dynamically authenticate a user to applications (or services) in a Linux system.

/etc/pam.d/crond
/etc/cron.allow

# example

# troubleshoot passwordless ssh login

Machine A need to access B using pub key instead of password

  1. Setup

on A: ssh-keygen -t rsa 重命名生成id_rsa_B/id_rsa_B.pub ssh-copy-id -i .ssh/id_rsa_B.pub [email protected] ssh [email protected] still prompt password require, 仍然弹出密码要求

  1. Troubleshoot:
  • selinux
  • make sure correct permission for .ssh(700 at least) and .ssh/authorized_keys (400 at least) Both the host and the client should have the following permissions and owners:

~/.ssh permissions should be 700 ~/.ssh should be owned by your account ~/.ssh/authorized_keys permissions should be 600 ~/.ssh/authorized_keys should be owned by your account Client environments should additionally have the following permissions and owners:

~/.ssh/config permissions should be 600 ~/.ssh/id_* permissions should be 600

  • remote server firewall
  • /etc/ssh/sshd_config PubkeyAuthentication yes RSAAuthentication yes

[[email protected] apps]# tail -f /var/log/secure Apr 26 13:58:29 os-node3 su: pam_unix(su-l:session): session opened for user fundingrate by root(uid=0) Apr 26 13:58:59 os-node3 sshd[31048]: reprocess config line 44: Deprecated option RSAAuthentication systemctl status sshd 也可以看到这个日志

有意思，之前我手动在 开启了 RSAAuthentication yes 日志的意思是，rsa的选项已经是废弃的了，难道ssh升级了？ 果然查了下，最新的ssh Protocol=2，之前的1可能不支持了，测试： on A: ssh -1 [email protected] Protocol major versions differ: 1 vs. 2 说明B不支持 ssh Protocol 1了，only Protocol 2 is supported

不过最后发现原因竟然是因为我创建秘钥对的时候重命名了id_rsa/id_rsa.pub 为 id_rsa_B/id_rsa_B.pub ssh默认只会找id_rsa（之前已经生成了一对id_rsa/id_rsa.pub），所以跟copy到B上的id_rsa_B.pub对不上， 需要指定 ssh -i id_rsa_B [email protected] 即可！ 查看版本号：ssh -v localhost