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Monday, May 23, 2022

 In this post we are going to go over the steps to install the Ssysstat tool in Linux. Log in as root or su then run the command yum install -y sysstat, you might already have it installed so you might get this message

[root@cent7 jhuynh]# yum install -y sysstat
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
 * base:
 * epel:
 * extras:
 * updates:
base                                                                                                                                                                                        | 3.6 kB  00:00:00     
extras                                                                                                                                                                                      | 2.9 kB  00:00:00     
updates                                                                                                                                                                                     | 2.9 kB  00:00:00     
updates/7/x86_64/primary_db                                                                                                                                                                 | 8.8 MB  00:00:01     
Package sysstat-10.1.5-19.el7.x86_64 already installed and latest version
Nothing to do

Now that we know sysstat is installed we can start the service with the command systemctl start sysstat then enable it with the command systemctl enable sysstat and finally we can check to see the that service is running by checking the status with this command systemctl status sysstat

Monday, May 16, 2022

 vmstat is used to report virtual memory stats on your Linux system.  It is helpful to see how much free memory you have left on your system.

As with top you can run the command by typing vmstat, it defaults to kilobytes

You can change the default measure unit by specifying the unit like this vmstat -S m, this will run the command in millibytes, we can see that we have 372 MB of memory free and 1 MB of buffer

You can also run vmstat in intervals by typing the following command vmstat 3 5, the command tells vmstat to run every 3 seconds for five times

Monday, May 9, 2022

 The top command is an essential tool in any Linux administrator's toolbelt.  Let's take a deeper look at the command.

First thing you can do is get the version of top we are using

[root@cent7 jhuynh]# top -v
  procps-ng version 3.3.10
  top -hv | -bcHiOSs -d secs -n max -u|U user -p pid(s) -o field -w [cols]

If you just type top with no options you will get the following information, the information will update every 3 seconds by default.  The top area is a summary of resources and CPU usage while the bottom portion are information about the processes.  The information is sort by CPU utilization by default.

Press q to quit, you can also run the top command in batch mode by specifying how many times you want it to run by typing the command like this top -b -n1 the command uses the -b option for batch and -n for the number of iterations, in this case it's one

As you can see it only runs once and you get your prompt back, you use your mouse to scroll back up. You can also write the results to a file like this top -b -n1 > top-stats

Monday, May 2, 2022

Instead of testing to see if a property exists in the object you could just use the for/in loop to iterate through all the enumerable properties in the object.  Enumerable properties are the properties that owned by the object.  In JavaScript there are always two objects that are created with each object, one hidden object that's always there is the prototype object.  It's like the blueprint for the object you just created.  The owned properties are the properties that explicitly created with your object. The prototype properties are what's called inherited properties. So if we use the for/in loop we  will get the owned properties and the prototype properties.

So to use the for/in loop to iterate through the object let's use our product object again.

        var product = new Object(); = "Chai";
        product.category = "Tea"; = "India";
        product.supplier = {
            name: "ACME Tea Of India",
            location: "New Delhi"

Now type in the following to loop through the object with the for/in loop and outputs the property name and property value to the console

Monday, April 25, 2022

An ASP.NET MVC can get big, and it could be overwhelming.  Areas are a way to break up the application into smaller segments,  A perfect candidate for an Area is the Administrative features of the site because it has multiple pages, and functionalities.  So it is a good idea to segment off the Administration area to its own area (no pun intended).

Monday, April 18, 2022

 In the previous post we created an EC2 instance in AWS in this post we are going to connect to that instance on a Linux workstation or server with SSH.

Here are the steps to connect to the EC2 instance using SSH on Linux, this will also work on a Mac as well:

1. Navigate to the folder that contains the key pair file that you've downloaded in the previous post, I store it in the folder /aws/EC2/KeyPair/ folder , so I would type cd /aws/EC2/KeyPair then type ls to see the file in the folder

Monday, April 11, 2022

 In this post we are going to look at another performance related command, which is the uptime command.

First let's look at the uptime command, as the name implies the uptime command shows you what the uptime is for the system:

[root@cent7 jhuynh]# uptime
 12:41:20 up  1:29,  2 users,  load average: 0.05, 0.04, 0.06

The command shows you the uptime for the system, the number of users who are using the system, and the system load average (Number of CPU used) in intervals of 5 minutes.

If you type w, you can see which users are using the system

[root@cent7 jhuynh]# w
 12:41:29 up  1:29,  2 users,  load average: 0.04, 0.04, 0.06
USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
jhuynh   :0       :0               11:15   ?xdm?   3:02   0.49s /usr/libexec/gnome-session-binary --session gnome-classic
jhuynh   pts/0    :0               11:21    1.00s  0.42s 11.27s /usr/libexec/gnome-terminal-server

The load average is the most important stat in the uptime command however, it is currently static, and to get updates you need to run the uptime every 5 minutes.  There's a better way to monitor your Linux system.  But you have to call now, and for a limited time only for just $19.99 you can have the answer.  Since I am such a nice guy I am going to give you the answer for free.

What you can do is type the command tload and it will monitor the load average time in real-time. Before we run the tload command a good command to run is the lscpu command to see how many CPU you have.  For instance you have just one CPU and your load average is 1+ then you have got a problem.

[root@cent7 jhuynh]# lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                1
On-line CPU(s) list:   0
Thread(s) per core:    1
Core(s) per socket:    1
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel

Now let's run the tload command

There are two parts to the tload utility, at the top you will see the average load time in real time instead of the 1, 5, 15 minute interval like before.  But it will be dynamic and updates automatically based on the load.

On the bottom you will see a graphical representation of the load average, it's probably not going to win any awards for best graphics 


Everything looks fine right now, but if you open another terminal and run the dnf update -y command you will see the load changing accordingly. Or some tasks that would put stress on the system.

Monday, April 4, 2022

 In this post we are going to look at the procps-ng package commands to get some performance related information on our Linux system.

The first command we are going to look at is the free command, which shows the free memory available

[root@cent7 jhuynh]# free
              total        used        free      shared  buff/cache   available
Mem:        1882072      754028      404848       33544      723196      942276
Swap:        978940           0      978940

We can use the free command with the -m option to show the free memory in megabytes

[root@cent7 jhuynh]# free -m
              total        used        free      shared  buff/cache   available
Mem:           1837         734         397          32         706         922
Swap:           955           0         955

Or free -g for gigabytes

[root@cent7 jhuynh]# free -g
              total        used        free      shared  buff/cache   available
Mem:              1           0           0           0           0           0
Swap:             0           0           0

The next command we are going to look at is the pmap command, let's grab a process id for this one with the ps -l  command

[root@cent7 jhuynh]# ps -l
4 S     0  3358  3315  0  80   0 - 68658 poll_s pts/0    00:00:00 sudo
4 S     0  3365  3358  0  80   0 - 58056 do_wai pts/0    00:00:00 su
4 S     0  3368  3365  0  80   0 - 29107 do_wai pts/0    00:00:00 bash
0 R     0  4238  3368  0  80   0 - 38332 -      pts/0    00:00:00 ps

Let's run the pmap command on the bash process, the pmap command displays the memory map of a process, besides the memory usage it's nice to see the shared libraries used for the process

[root@cent7 jhuynh]# pmap 3368
3368:   bash
0000000000400000    888K r-x-- bash
00000000006dd000      4K r---- bash
00000000006de000     36K rw--- bash
00000000006e7000     24K rw---   [ anon ]
00000000021b3000   1144K rw---   [ anon ]
00007f53b0616000     48K r-x--
00007f53b0622000   2044K -----
00007f53b0821000      4K r----
00007f53b0822000      4K rw---

Another useful command is the pwdx command, this command finds the home working directory of a process.  So if we run the command pwdx 3368 we will find out what the home working directory of the bash shell is

[root@cent7 jhuynh]# pwdx 3368
3368: /home/jhuynh
[root@cent7 jhuynh]# ps -l
4 S     0  3358  3315  0  80   0 - 68658 poll_s pts/0    00:00:00 sudo
4 S     0  3365  3358  0  80   0 - 58056 do_wai pts/0    00:00:00 su
4 S     0  3368  3365  0  80   0 - 29107 do_wai pts/0    00:00:00 bash
0 R     0  4345  3368  0  80   0 - 38332 -      pts/0    00:00:00 ps

Monday, March 28, 2022

 In Linux you can control the priority of a process with the commands nice and renice.  There are limitations if you are a non-root user. The nice and renice commands have the values in the range of -20 to +19. The higher the numbers the higher the priority, or the nicer the process is meaning the less CPU it would use, so it's kind of the opposite of what you are thinking.  So it's like nice guys finished last?

So if we run the sleep process again let's see what happens by default

sleep 1500&

[root@cent7 jhuynh]# sleep 1500&
[1] 3401
[root@cent7 jhuynh]# ps -l
4 S     0  3358  3315  0  80   0 - 68658 poll_s pts/0    00:00:00 sudo
4 S     0  3365  3358  0  80   0 - 58056 do_wai pts/0    00:00:00 su
4 S     0  3368  3365  0  80   0 - 29107 do_wai pts/0    00:00:00 bash
4 S     0  3401  3368  0  80   0 - 27014 hrtime pts/0    00:00:00 sleep
0 R     0  3402  3368  0  80   0 - 38332 -      pts/0    00:00:00 ps

As you can see the priority(PRI) is set to 80 percent by default

Now let's be a nice guy and assign the sleep process to the nicest value -19

[root@cent7 jhuynh]# nice -n 19 sleep 1500&
[2] 3438
[root@cent7 jhuynh]# ps -l
4 S     0  3358  3315  0  80   0 - 68658 poll_s pts/0    00:00:00 sudo
4 S     0  3365  3358  0  80   0 - 58056 do_wai pts/0    00:00:00 su
4 S     0  3368  3365  0  80   0 - 29107 do_wai pts/0    00:00:00 bash
4 S     0  3401  3368  0  80   0 - 27014 hrtime pts/0    00:00:00 sleep
4 S     0  3438  3368  0  99  19 - 27014 hrtime pts/0    00:00:00 sleep
0 R     0  3439  3368  0  80   0 - 38332 -      pts/0    00:00:00 ps

As you can see the new sleep process is set to priority 99 meaning only run the process if processes with the a lower number is ran first.  It's like being the 99th person in line.

If you run it at the highest nice value, not so nice. Let's see what happens

[root@cent7 jhuynh]# nice -n -20 sleep 1500&
[2] 3546
[root@cent7 jhuynh]# ps -l
4 S     0  3358  3315  0  80   0 - 68658 poll_s pts/0    00:00:00 sudo
4 S     0  3365  3358  0  80   0 - 58056 do_wai pts/0    00:00:00 su
4 S     0  3368  3365  0  80   0 - 29107 do_wai pts/0    00:00:00 bash
4 S     0  3543  3368  0  99  19 - 27014 hrtime pts/0    00:00:00 sleep
4 S     0  3546  3368  0  60 -20 - 27014 hrtime pts/0    00:00:00 sleep
0 R     0  3547  3368  0  80   0 - 38332 -      pts/0    00:00:00 ps

You can also reassign the priority of an existing process with renice command, with the renice command you have to specify the process id

[root@cent7 jhuynh]# renice -n 5 -p 3543
3543 (process ID) old priority 19, new priority 5
[root@cent7 jhuynh]# ps -l
4 S     0  3358  3315  0  80   0 - 68658 poll_s pts/0    00:00:00 sudo
4 S     0  3365  3358  0  80   0 - 58056 do_wai pts/0    00:00:00 su
4 S     0  3368  3365  0  80   0 - 29107 do_wai pts/0    00:00:00 bash
4 S     0  3543  3368  0  85   5 - 27014 hrtime pts/0    00:00:00 sleep
4 S     0  3546  3368  0  60 -20 - 27014 hrtime pts/0    00:00:00 sleep
0 R     0  3589  3368  0  80   0 - 38332 -      pts/0    00:00:00 ps

Linux was nice enough to tell you that the process has been changed from priority of 19 to 5, so now the process is assigned a priority value of 85.  Still the nicest priority!

The caveat on the renice command is that if you are not a user with root privileges, you cannot set a higher priority than the original priority of a process. 

If you are root you can also control other user's priority settings by editing the /etc/security/limits.conf. Priority is the last item or settings that you can set limits on, so move to the end of the line and type in the following for user limit, if you want group limits you just prefix it with the @ sign

#*               soft    core            0
#*               hard    rss             10000
#@student        hard    nproc           20
#@faculty        soft    nproc           20
#@faculty        hard    nproc           50
#ftp             hard    nproc           0
#@student        -       maxlogins       4

# End of file
techjunkie - priority 5

Now the next time techjunkie sets a priority he will be limited to priority number 5 nice value.  Since he is not a root user he cannot renice the process to be anything higher than 5.  Therefore he is a pretty nice guy.

Monday, March 21, 2022

 Linux allows you to run jobs in the background and in the foreground.  It accomplish this by identifying the processes as jobs and assigning the state to the jobs by numbers.

First let's create a process, we are just create a sleep job in the background, with the command sleep 1500& the & automatically put the process in the background.  If you observe the behavior you will noticed that the prompt is in your control right away because it's running in the background.

If you run the jobs command you see the process is running but it's running in the background.  However if you forgot to put the & at the end the job will have to be finished before you get your prompt back, the only way to get your prompt back before then is to type CTRL+Z , but that would also stop the process or job from running.  That's probably not what you wanted

You've gotten your prompt back but you've also stopped the process, that's probably not what you wanted to do.  You want to get your prompt and keep the job running at the same time.  So the solution is to use the bg command to run the job in the background

To bring the job into the foreground you just type fg

As you can see you lose the prompt once the job is put in the foreground because it has to finish running the job before you can get the prompt back. Press CTRL+Z again to interrupt the process

Now there's another way to put a process in the background, that is to specify the job number.  So if we want to put the second job that was stopped in the background again we can type bg 2 

You can do the same thing with the fg command.  Kill the sleep process with the command pkill sleep for cleanup

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