You have probably heard the term “mount-point” and wondered, or maybe not. You know it’s there, and files are in it, but you don’t know what it is? If this is the case then read this article…
I am assuming that you know what a file and/or a directory is, a directory is also called a folder. Well, a mount-point is simply the directory or file for which e device, normally a disk, either local or remote, is exposed to the system for interaction. Let’s take a common Linux system for example, this particular system is a CentOS, but it should not matter which system or UNIX type it is.
At the root “/” of your system we have the following files and directories:
lrwxrwxrwx 1 root root 7 Oct 6 09:26 bin -> usr/bin dr-xr-xr-x. 6 root root 3072 Oct 6 09:37 boot drwxr-xr-x 19 root root 3140 Oct 6 09:36 dev drwxr-xr-x. 82 root root 4096 Oct 6 09:47 etc drwxr-xr-x. 3 root root 4096 Nov 5 2016 home lrwxrwxrwx 1 root root 7 Oct 6 09:26 lib -> usr/lib lrwxrwxrwx 1 root root 9 Oct 6 09:26 lib64 -> usr/lib64 drwx------. 2 root root 16384 Apr 13 2015 lost+found drwxr-xr-x. 3 root root 4096 Nov 5 2016 media drwxr-xr-x. 2 root root 4096 Nov 5 2016 mnt drwxr-xr-x. 3 root root 4096 Nov 5 2016 opt dr-xr-xr-x 100 root root 0 Oct 6 09:36 proc dr-xr-x---. 4 root root 4096 Oct 6 10:18 root drwxr-xr-x 27 root root 780 Oct 6 10:18 run lrwxrwxrwx 1 root root 8 Oct 6 09:26 sbin -> usr/sbin drwxr-xr-x. 2 root root 4096 Nov 5 2016 srv dr-xr-xr-x 13 root root 0 Oct 6 09:36 sys drwxrwxrwt. 12 root root 4096 Oct 6 11:33 tmp drwxr-xr-x. 13 root root 4096 Oct 6 09:26 usr drwxr-xr-x. 21 root root 4096 Oct 6 09:45 var
If you wonder what I used to retrieve the list, simply type “ls -l /”. Now let’s type a different command, the “df -h” command, you should see something similar to the following:
Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg-lv_root 18G 2.5G 14G 15% / devtmpfs 486M 0 486M 0% /dev tmpfs 497M 0 497M 0% /dev/shm tmpfs 497M 6.8M 490M 2% /run tmpfs 497M 0 497M 0% /sys/fs/cgroup /dev/sda1 477M 136M 313M 31% /boot tmpfs 100M 0 100M 0% /run/user/1000 /dev/mapper/vg-lv_opt 20G 1G 19G 5% /opt
Now, for simplicity, let’s concentrate on the first line “/” and the last line “/opt”. I have highlighted the 2 lines.
So, this tells us that device “/dev/mapper/vg-lv_root” is mounted on “/” (the root of the filesystem) and that device “/dev/mapper/vg-lv_opt” is mounted on “/opt”, this is a very common setup for a UNIX system.
“/” is 18G and “/opt” is 20G. So, all files residing in “/” and sub-directories with the exception on “/opt” will reside on device “/dev/mapper/vg-lv_root” and all the files residing in “/opt” and sub-directories will reside on device “/dev/mapper/vg-lv_opt“.
This system is mainly used to segregate parts of systems so that they can be controlled and not interfere with each other. For example: if /opt fills up to 100% the system will continue to function because “/” is independent.
I hope this clears up mount-points and what/how/why they are used.
Always thanks for reading…