As we all know, network security is a very important topic, and servers are the most critical link in network security. Linux is considered to be a safer Internet server. As an open-source operating system, once a security vulnerability is found in Linux, volunteers from around the world on the Internet will actively fix it. However, system administrators often cannot obtain and correct information in a timely manner, which gives hackers an opportunity. However, compared with the security vulnerabilities of these systems, more security problems are caused by improper configuration and can be prevented by appropriate configuration. The more services run on the server, the more opportunities for improper configuration, and the greater the possibility of security problems. This article introduces how to enhance the security of Linux/Unix servers.
System security record file
Recording files in the operating system are important clues for detecting network intrusion. If your system is directly connected to the Internet, you find that many people try to Telnet/FTP login to your system, you can run "# more/var/log/secure grep refused" to check the system for attacks, so as to take corresponding countermeasures, such as replacing Telnet/rlogin with SSH.
Startup and login security
1. BIOS Security
Set the BIOS password and modify the boot sequence to disable system startup from a floppy disk.
2. User Password
The user password is a basic starting point for Linux security. The user password used by many people is too simple, which opens the door to the intruders, although theoretically speaking, as long as you have enough time and resources to use, there is no user password that cannot be cracked. However, selecting a proper password is difficult to crack. A good user password is a string of characters that only he can easily remember and understand, and should never be written anywhere.
3. Default Account
All default accounts that are started by the operating system and are not necessary should be prohibited. This should be done when you install the system for the first time. Linux provides many default accounts, and the more accounts, the more vulnerable the system is.
You can use the following command to delete an account.
Or use the following command to delete the group user account.
4. Password File
The chattr command adds unchangeable attributes to the following files to prevent unauthorized users from obtaining permissions.
# chattr +i /etc/passwd# chattr +i /etc/shadow# chattr +i /etc/group# chattr +i /etc/gshadow |
5. Disable Ctrl + Alt + Delete to restart the machine command.
Modify the/etc/inittab file and comment out the line "ca: ctrlaltdel:/sbin/shutdown-t3-r now. Then reset the permission for all files in the/etc/rc. d/init. d/directory and run the following command:
# chmod -R 700 /etc/rc.d/init.d/* |
In this way, only the root user can read, write, or execute all the above script files.
6. Restrict su commands
If you don't want anyone to use su as root, you can edit the/etc/pam. d/su file and add the following two lines:
auth sufficient /lib/security/pam_rootok.so debugauth required /lib/security/pam_wheel.so group=isd |
In this case, only users in the isd group can use su as root. Then, if you want the user admin to use su as root, run the following command:
7. Delete logon information
By default, the logon prompt includes the Linux release, kernel version, and server host name. For a machine with high security requirements, too much information is leaked. You can edit/etc/rc. d/rc. local to comment out the following lines of output system information.
# This will overwrite /etc/issue at every boot. So，make any changes you# want to make to /etc/issue here or you will lose them when you reboot# echo ""＞/etc/issue# echo ""＞＞/etc/issue# echo "Kernel 100 100uname -r） on 100 100uname -m）"＞＞/etc/issue# cp -f /etc/issue /etc/issue.net# echo＞＞/etc/issue |
Then, perform the following operations:
# rm -f /etc/issue# rm -f /etc/issue.net# touch /etc/issue# touch /etc/issue.net |
