I have 4GB RAM. When I open Firefox, IntelliJ IDEA or VS Code and some other application my memory is about used up thus my machine hangs and I can't do anything. I can't even close any applications.

Date and time are shown in the top bar so that I can view it any time without any thing typing.

If I would view memory status in this way without typing anything then I can make a decision whether to open an application or whether this application may put my machine in hanging state or not.

Is it possible in Ubuntu 18.04 LTS?

I use my computer for scientific programming. It has a healthy 8GB of RAM and 12GB of swap space. Often, as my problems have gotten larger, I exceed all of the available RAM. Rather than crashing (which would be preferred), it seems Ubuntu starts loading everything into swap, including Unity and any open terminals. If I don't catch a run-away program in time, there is nothing I can do but wait - it takes 4-5 minutes to switch to a command prompt eg. Ctrl-Alt-F2 where I can kill the offending process.

Since my own stupidity is out of scope of this forum, how can I prevent Ubuntu from crashing via thrashing when I use up all of the available memory from a single offending program?

At-home experiment*!

Open a terminal, launch python and if you have numpy installed try this:

>>> import numpy
>>> [numpy.zeros((10**4, 10**4)) for _ in xrange(50)]

* Warning: may have adverse effects, monitor the process via iotop or top to kill it in time. If not, I'll see you after your reboot.

I need a step-by-step, simple and easy way to configure swappiness.

Ubuntu has been crashing on me recently. I think its because it runs out of memory so I ran the free -m command and found that my memory usage was really high. So then, i ran top to find the culprit, but the displayed processes were using less than 1.5% of memory. How do I know which program is making ubuntu crash/run out of memory? Below is the output:

shafee@shafee-pc:~$ free -m
             total       used       free     shared    buffers     cached
Mem:          3824       3714        110          0        978       1954
-/+ buffers/cache:        780       3044
Swap:           99          0         99

shafee@shafee-pc:~$ top
top - 02:12:14 up  1:24,  2 users,  load average: 0.16, 0.42, 1.49
Tasks: 182 total,   1 running, 181 sleeping,   0 stopped,   0 zombie
Cpu(s):  2.9%us,  1.9%sy,  0.3%ni, 79.3%id, 15.5%wa,  0.0%hi,  0.2%si,  0.0%st
Mem:   3916708k total,  3803848k used,   112860k free,  1002308k buffers
Swap:   102396k total,        0k used,   102396k free,  2001852k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND            
 4200 root      20   0  289m  53m  38m S    2  1.4   1:06.45 Xorg               
 5590 shafee    20   0 19348 1368  956 R    2  0.0   0:00.01 top                
    1 root      20   0 24124 2136 1264 S    0  0.1   0:02.05 init               
    2 root      20   0     0    0    0 S    0  0.0   0:00.00 kthreadd           
    3 root      20   0     0    0    0 S    0  0.0   0:24.23 ksoftirqd/0        
    6 root      RT   0     0    0    0 S    0  0.0   0:00.00 migration/0        
    7 root      RT   0     0    0    0 S    0  0.0   0:00.00 migration/1        
    9 root      20   0     0    0    0 S    0  0.0   0:00.11 ksoftirqd/1        
   11 root      RT   0     0    0    0 S    0  0.0   0:00.00 migration/2        
   13 root      20   0     0    0    0 S    0  0.0   0:03.89 ksoftirqd/2        
   14 root      RT   0     0    0    0 S    0  0.0   0:00.00 migration/3        
   16 root      20   0     0    0    0 S    0  0.0   0:00.16 ksoftirqd/3        
   17 root       0 -20     0    0    0 S    0  0.0   0:00.00 cpuset             
   18 root       0 -20     0    0    0 S    0  0.0   0:00.00 khelper            
   19 root       0 -20     0    0    0 S    0  0.0   0:00.00 netns              
   21 root      20   0     0    0    0 S    0  0.0   0:00.01 sync_supers        
shafee@shafee-pc:~$

Or is it normal to have 110mb of free memory and is my issue related to something else?

I have used top to see the memory usage at the moment. But I would like to monitor the memory usage over a period of time. E.g start monitoring and then execute a few commands, and final stop the monitoring and see how much memory that have been used during the period.

How can I do this on Ubuntu Server?

I guess I could start a cronjob every 5th second or so, and invoke a command that log the current memory usage in a textfile. But what command should I use to get the current memory usage in a format that is easy to log to a text file?