Posts published in “Linux”

It might not make sense to use RDP to remote linux machines. The speed and performance all are not that good from my point to view. But in certain situation, you might need to use desktop on your remote Linux, then here comes this post.

1. CentOS 7

Commands to check system version:

uname -r
cat /proc/version
cat /etc/os-release
lsb_release -a
Note: lsb_release command sometimes does not work on CentOS

The Linux kernel includes the Netfilter subsystem, which is used to manipulate or decide the fate of network traffic headed into or through your server. All modern Linux firewall solutions use this system for packet filtering.


Security-Enhanced Linux (SELinux) is a Linux kernel security module that provides a mechanism for supporting access control security policies, including mandatory access controls (MAC). SELinux is a set of kernel modifications and user-space tools that have been added to various Linux distributions.

This post summarizes how to configure a basic usage for Firewall and SElinux on two most popular linux distribution : CentOS and Ubuntu.

This post is going to use an java code example to show the process how to analysis linux system performance issue using all kinds of Linux internal commands without other third party tools.

public class JavaDemo2 {
    public static void main(String[] args) {
        while (true){
            System.out.println(new java.util.Random().nextInt(77778888));
        }
    }
}

[[email protected] ~]# top
top - 11:28:50 up 7 min, 2 users, load average: 0.73, 0.39, 0.18
Tasks: 230 total, 1 running, 229 sleeping, 0 stopped, 0 zombie
Cpu(s): 1.0%us, 2.3%sy, 0.0%ni, 96.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 1906280k total, 649948k used, 1256332k free, 21164k buffers
Swap: 2097148k total, 0k used, 2097148k free, 203820k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3672 root 20 0 3158m 94m 11m S 15.6 5.1 0:13.67 java
3397 root 20 0 100m 5388 3396 S 9.3 0.3 0:09.00 sshd
39 root 20 0 0 0 0 S 1.7 0.0 0:00.25 events/4
37 root 20 0 0 0 0 S 1.0 0.0 0:00.39 events/2
35 root 20 0 0 0 0 S 0.3 0.0 0:01.27 events/0
36 root 20 0 0 0 0 S 0.3 0.0 0:00.34 events/1
41 root 20 0 0 0 0 S 0.3 0.0 0:00.24 events/6
[[email protected] ~]# uptime
11:29:09 up 7 min, 2 users, load average: 0.52, 0.36, 0.18

I am having a couple of low memory vm in the cloud to run some basic testing lab. It always gets me a notification for the performance , especially on memory since they are only have 587M memory.

Performance Issue on Low Memory Cloud VM