How to enhance the security of Linux and UNIX server systems

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.

1. system security record files

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 or FTP 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.

Ii. 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, but it is difficult to choose a proper password. A good user password is a string of characters that can only be easily remembered and understood by him, and should never be written anywhere.

3. Default Account

All default accounts that are started by the operating system itself 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.

# Userdel Username

Or use the following command to delete the group user account.

# Groupdel Username

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 do not want anyone to use Su as the root user, you can edit the/etc/PAM. d/su file and add the following two lines:

Auth sufficient/lib/security/pam_rootok.so debug

Auth required/lib/security/pam_wheel.so group = ISD

In this case, only users in the ISD group can use Su as the root user. After that, if you want the user admin to Su as the root user, you can run the following command:

# Usermod-G10 Admin

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 "$ R">/etc/issue

# Echo "kernel $ (uname-R) on $ A $ (uname-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