Linux network security skills (2)

Linux network security tips-alias file aliases

Edit the alias file/etc/aliases or/etc/mail/aliases) and remove/comment the following line.

 
 

  
  
# Basic system aliases -- these MUST be present.  
  
  
 
  
  
MAILER-DAEMON: postmaster  
  
  
 
  
  
postmaster: root  
  
  
 
  
  
# General redirections for pseudo accounts.  
  
  
 
  
  
bin: root  
  
  
 
  
  
daemon: root  
  
  
 
  
  
#games: root ?remove or comment out.  
  
  
 
  
  
#ingres: root ?remove or comment out.  
  
  
 
  
  
nobody: root  
  
  
 
  
  
#system: root ?remove or comment out.  
  
  
 
  
  
#toor: root ?remove or comment out.  
  
  
 
  
  
#uucp: root ?remove or comment out.  
  
  
 
  
  
# Well-known aliases.  
  
  
 
  
  
#manager: root ?remove or comment out.  
  
  
 
  
  
#dumper: root ?remove or comment out.  
  
  
 
  
  
#operator: root ?remove or comment out.  
  
  
 
  
  
# trap decode to catch security attacks  
  
  
 
  
  
#decode: root  
  
  
 
  
  
# Person who should get roots mail  
  
  
 
  
  
#root: marc 
 
 

After the last update, do not forget to run/usr/bin/newaliases to make the change take effect.

Linux network security tips prevent your system from responding to any external/internal ping requests.

Since no one can ping your machine and receive a response, you can greatly enhance the security of your site. You can add the following command to/etc/rc. d/rc. local to run automatically after each startup.

Echo 1>/proc/sys/net/ipv4/icmp_echo_ignore_all

Linux network security tips do not show the operating system and version information.

If you want someone to remotely log on to your server without displaying the operating system and version information, you can change

The line in/etc/inetd. conf is as follows:

Telnet stream tcp nowait root/usr/sbin/tcpd in. telnetd-h

Add the-h sign to the end so that the telnet background does not display system information, but only login:

Linux network security tips: The/etc/host. conf file

Edit the host. conf file (vi/etc/host. conf) and add the following line:

 
 

  
  
# Lookup names via DNS first then fall back to /etc/hosts.  
  
  
 
  
  
order bind,hosts  
  
  
 
  
  
# We don have machines with multiple IP addresses on the same card  
  
  
 
  
  
(like virtual server,IP Aliasing).  
  
  
 
  
  
multi off  
  
  
 
  
  
# Check for IP address spoofing.  
  
  
 
  
  
nospoof on  
  
  
 
  
  
IP Spoofing: IP-Spoofing is a security exploit that works by tricking  
  
  
 
  
  
computers in a trust relationship that you are someone that you really aren . 
 
 

Linux network security tips: The/etc/securetty file

This file specifies the tty device that allows root login./etc/securetty is read by the/bin/login program. Its format is a list of allowed names in a row, for example, you can edit/etc/securetty and comment out the following rows.

 
 

  
  
tty1  
  
  
 
  
  
#tty2  
  
  
 
  
  
#tty3  
  
  
 
  
  
#tty4  
  
  
 
  
  
#tty5  
  
  
 
  
  
#tty6  
  
  
 
  
  
#tty7  
  
  
 
  
  
#tty8 
 
 

-This means that the root user is only allowed to log on to the tty1 terminal.

There are many other Linux network security skills that can effectively protect the security of Linux networks. We will introduce them in future articles. You can also learn more in the past articles.