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I am running a small vServer with Debian 9 (stretch) and 2GB RAM.

For a few months I am somehow missing about 500MB RAM and which I cannot find out how they are used.

When I run free -h

              total     used      free    shared  buff/cache     available
Mem:           2.0G     1.0G      482M       66M        511M     764M
Swap:          1.0G       0B      1.0G

I can see that half of the memory is used, about a quarter is used for caches that can be freed if it is needed and the rest is free.

But when I now check my running processes I can only find about 500MB are used by my processes. 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                   
 1458 mysql     20   0  927516 359260      0 S   0.0 17.5 108:31.26 mysqld                                                                                                    
  877 seafile   20   0  258032  94644   4876 S   0.0  4.6   0:22.92 python2.7                                                                                                 
  460 seafile   20   0  237156  85504   8036 S   0.0  4.2   0:13.14 python2.7                                                                                                 
  463 seafile   20   0  233096  82236   8956 S   0.0  4.0   0:05.79 python2.7                                                                                                 
  875 seafile   20   0  244356  81644   5408 S   0.0  4.0   0:19.50 python2.7                                                                                                 
  461 seafile   20   0  232464  81032   8232 S   0.0  3.9   0:03.58 python2.7                                                                                                 
 4054 www-data  20   0  374264  54976  45128 S   0.0  2.7   0:07.58 php-fpm7.0                                                                                                
 4026 www-data  20   0  372652  54840  44408 S   0.0  2.7   0:10.36 php-fpm7.0                                                                                                
 1865 seafile   20   0 1704520  52828     16 S   0.0  2.6   3:45.10 seaf-server                                                                                               
 4021 www-data  20   0  370836  48880  40468 S   0.0  2.4   0:10.83 php-fpm7.0                                                                                                
 1975 seafile   20   0  129128  47156   1944 S   0.0  2.3   0:02.06 python2.7                                                                                                 
21106 netdata   20   0  189412  36600   2660 S   0.3  1.8  16:07.50 netdata                                                                                                   
 1604 lukas     20   0  107132  34860   2736 S   0.0  1.7   2:07.91 gunicorn

I have no clue where the remaining 500MB Memory are.

I suspected the kernel but running slabtop shows it uses only about 80MB.

 Active / Total Size (% used)       : 76599.41K / 79594.40K (96.2%)

I am running netdata on my server, which shows a nice overview of the memory usage per category and indeed it shows my missing 530MB. I played around with the grouping and created a new group called testing with the following config and it includes my missing memory (in /etc/netdata/apps_groups.conf)

testing: systemd*

Netdata

Why does systemd (or something netdata categorizes as systemd) use about a quarter of my memory? After a reboot it uses only 50MB but after some time it always uses about 500MB.

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systemd is the process with pid 1. All the other processes are children of systemd.

In netdata, all processes not matched by the groups given are assigned to category other.

Since netdata assigns processes to groups respecting their hierarchy, the match systemd* just moved most processes from other to testing. So systemd* is not a really useful match.

If I were you, I would attempt to understand which applications the server runs and add groups for these specific applications.

Additionally you can enable the systemd charts in netdata. This will allow you see the Services section in netdata. Depending on the debian version, a reboot may be required to enable memory reporting for them (you may need to add a kernel boot parameter - check the wiki).

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  • That really makes sense. In the meantime I noticed by chance that stoping Seafile solves it. Maybe it uses a lot of processes with little memory usage each. I’ll investigate further tomorrow. – lw1.at Aug 6 '17 at 19:39
  • You were right. I enabled the systemd charts and indeed seahub is at fault. I didn't notice it in htop as it is running many processes using about 80MB each. – lw1.at Aug 7 '17 at 17:58
  • nice! I am glad netdata helped. – Costa Tsaousis Aug 7 '17 at 23:03

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