[System Security Reinforcement]

System security reinforcement
**1.**Password policy Modify the password policy of the system
1) Change the password frequently
2) Use some special characters and the length of the password to increase the difficulty of the password
3) Don’t tell others the password casually
**2.** Permission ugo locks unnecessary system users and groups in the system. Lock the following users. Before locking, back up the /etc/passwd and /etc/shadow files. Disable irrelevant groups. Prohibit root users from remote login
. 3. Prevent flood attacks . Prevent SYN flood in Linux. Add net.ipv4.tcp_syncookies=1 to the /sysctl.conf file
**4.**Reinforce TCP/IP protocol settings /etc/sysctl.conf file corresponding permissions
**5.**Default permissions and umask Do not modify the correct umask Value 022
**6.** Do any file modification action, first back up and then do the operation