Added info about version pinning (#2131)

* Update linux.md

Added version pinning

Signed-off-by: spacemanspiff2007 <10754716+spacemanspiff2007@users.noreply.github.com>

* Update linux.md
---------

Signed-off-by: spacemanspiff2007 <10754716+spacemanspiff2007@users.noreply.github.com>

installation/linux.md

@@ -115,6 +115,8 @@ Next, resynchronize the package index:
 sudo apt-get update
 ```
 
+##### Installing the latest version
+
 Now install openHAB with the following command:
 
 ```shell
@@ -128,6 +130,44 @@ If you plan on disconnecting your machine from the internet, then you will want
 sudo apt-get install openhab-addons
 ```
 
+##### Prevent automatic upgrade of openHAB
+
+To prevent unexpected breakage by accidentally updating openHAB it's recommended to only manually upgrade to the newest version.
+This can be achieved by putting the openHAB package on "hold".
+
+```shell
+sudo apt-mark hold openhab
+sudo apt-mark hold openhab-addons
+```
+
+To enable automatic upgrades again run
+
+```shell
+sudo apt-mark unhold openhab
+sudo apt-mark unhold openhab-addons
+```
+
+To show the packages on hold run
+
+```shell
+sudo apt-mark showhold
+```
+
+##### Installing a specific version
+
+Installing a specific version is possible by specifing the version that should be installed.
+
+```shell
+sudo apt install openhab=4.0.1
+sudo apt install openhab-addons=4.0.1
+```
+
+To get a list of all available versions you can use
+
+```shell
+apt list -a openhab
+```
+
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