Command Line

mkdir

To create sub directories even if the parent directories dont exist:

$ mkdir -p /tmp/foo/bar/this/dir

To create multiple directories with one command, to achieve:

/disk1/ebooks/category-tech
/disk1/ebooks/category-motivation
/disk2/ebooks/category-tech
/disk2/ebooks/category-motivation
/disk3/ebooks/category-tech
/disk3/ebooks/category-motivation

You can do:

mkdir -p /disk{1..5}/ebooks/category-{tech,motivation}

Disk

To check disk space:

$ df -h

To see the size of consumption per directory:

$ du -sh /path/to/dirs/*

To view disk and sata input mappings: (0 is port 1)

$ lsblk -o NAME,MODEL,SERIAL,WWN,HCTL
NAME   MODEL              SERIAL   WWN                HCTL
sda    ST4000D0000-000000 XXXXXXXX 0x5000c50000000000 0:0:0:0
sdb    ST4000D0000-000000 XXXXXXXX 0x5000c50000000000 1:0:0:0
└─sdb1                             0x5000c50000000000
sdc    ST4000D0000-000000 XXXXXXXX 0x5000c50000000000 2:0:0:0
└─sdc1                             0x5000c50000000000

Unable to unmount

This scenario is when a disk cannot be unmounted, usually this is because the disk is still in use with another application:

umount /data
umount: /data: target is busy.

Use the lsof (list open files) command to find out which processes are using the /data directory. Run sudo lsof /data. This will list all processes accessing files in /data.

sudo lsof /data
COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF     NODE NAME
sudo    21204 root  cwd    DIR  259,3     4096 27525121 /data/tmp
bash    28594 root  cwd    DIR  259,3     4096 27525121 /data/tmp

In this scenario there was a shell session that was changed to that directory, we can either kill the pid (kill 28594) or jump to that session and exit the directory.

Memory

Memory Stats

Difference between vsz and rss:

The Virtual Set Size is a memory size assigned to a process ( program ) during the initial execution. The Virtual Set Size memory is simply a number of how much memory a process has available for its execution. 

As oppose to VSZ ( Virtual Set Size ), RSS is a memory currently used by a process. This is a actual number in kilobytes of how much RAM the current process is using.

Using ps to sort by memory usage:

$ ps aux --sort -rss
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root      2124  0.1 11.4 422028 232864 ?       Ssl  Mar19   0:35 /bin/thanos

Using /proc/meminfo:

$ cat /proc/meminfo
MemTotal:       16424260 kB
MemFree:          173988 kB
MemAvailable:   13493104 kB
Buffers:          253116 kB
Cached:         12950152 kB

Using vmstat:

$ vmstat -s
16424260 K total memory
 2598624 K used memory
 3701676 K active memory
11821540 K inactive memory
  328008 K free memory
  253208 K buffer memory
  13244420 K swap cache

Using top:

$ top -n 1 -b
top - 07:50:06 up 13 days, 22:22,  1 user,  load average: 0.06, 0.07, 0.02
Tasks: 124 total,   1 running,  73 sleeping,   0 stopped,   0 zombie
%Cpu(s):  2.0 us,  0.4 sy,  0.0 ni, 97.3 id,  0.0 wa,  0.0 hi,  0.2 si,  0.0 st
KiB Mem : 16424260 total,   249368 free,  2597924 used, 13576968 buff/cache
KiB Swap:        0 total,        0 free,        0 used. 13490404 avail Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
15482 user      20   0 7949520 2.150g  24408 S  37.5 13.7  40:35.70 java

More info on above:

%MEM is directly related to RES, it’s the percentage use of total physical memory by the process.
VIRT is the total memory that this process has access to shared memory, mapped pages, swapped out pages, etc.
RES is the total physical memory used shared or private that the process has access to.
SHR is the total physical shared memory that the process has access to.

Get memory stats:

$ wget https://raw.githubusercontent.com/pixelb/ps_mem/master/ps_mem.py
$ sudo python ps_mem.py

Permissions

Permissions for Directories and Files

$ sudo chmod 755 /disk
$ sudo chown -R ubuntu:ubuntu /disk
$ sudo find /disk/2/htpc -type f -print -exec chmod 644 {} \;
$ sudo find /disk/2/htpc -type d -print -exec chmod 755 {} \;

External Resources