Add overview.md to namespace

container-101/.gitignore

@@ -0,0 +1,4 @@
+######################
+.DS_Store
+.DS_Store?
+._*

container-101/namespaces/index.json

@@ -11,6 +11,10 @@
       {
         "title": "unshare",
         "text": "unshare.md"
+      },
+      {
+        "title": "overview",
+        "text": "overview.md"
       }
     ]
   },

container-101/namespaces/overview.md

@@ -0,0 +1,28 @@
+"If host is a house, namespace is the room within the house assigned to each children providing privacy. Each child can only see inside their own room but not anything outside their room." -- KodeKloud (Youtuber)
+
+What is namespace?
+Namespace are used by container to implement network isolation.
+
+Process ID(PID) namespace:
+PID helps system tracks a specific task on the computer.
+Ex. When you have safari and chrome searching on google for things, PID is used to identify where to direct the package sent back from google.
+PID == 1 means it is the common ancestor to all the processes below.
+
+Net namespace:
+Network namespaces allow processes inside each namespace instance to have access to a new IP address along with the full range of ports.
+Ex. Allowing us to run multiple versions of an email server listening on port 25 without any software conflicts.
+
+UTS namespace:
+Allows a single system to have different host and domain name to different processes.
+
+User namespace:
+Allows system to restrict access to sensitive files.
+Ex. Not letting people using the same computer to access files that should not be seen by them.
+
+Mount(mnt) namespace:
+The mount namespace is used to isolate mount points such that processes in different namespaces cannot view each others' files.(just like chroot cmd)
+
+
+RESOURCES:
+1. https://www.youtube.com/watch?v=j_UUnlVC2Ss (Network Namespaces Basics Explained in 15 Minutes)(Youtube)
+2. https://www.redhat.com/sysadmin/7-linux-namespaces (The 7 most used Linux namespaces)(Web)

container-101/namespaces/unshare.md

@@ -1,7 +1,7 @@
 
 input by normal user
 ```
-unshare --user --map-root-user --pid --mount --fork 
+unshare --user --map-root-user --pid --mount --fork
 ```
 
 ```
@@ -35,4 +35,52 @@ lrwxrwxrwx 1 shawn111 shawn111 0 Oct  3 17:50 time -> 'time:[4026531834]'
 lrwxrwxrwx 1 shawn111 shawn111 0 Oct  3 17:51 time_for_children -> 'time:[4026531834]'
 lrwxrwxrwx 1 shawn111 shawn111 0 Oct  3 17:50 user -> 'user:[4026532478]'
 lrwxrwxrwx 1 shawn111 shawn111 0 Oct  3 17:50 uts -> 'uts:[4026532304]'
-```
+```
+
+
+
+Unshare is used to create new namespace
+```
+#sudo unshare -u
+```
+
+Shows your current hostname
+```
+#hostname
+ubuntu
+```
+
+Change your current hostname
+```
+#hostname hello
+#hostname
+hello
+```
+
+But when you open a new tab, and check the host name
+```
+#hostname
+ubuntu
+```
+
+To see the namespace of the current terminal
+```
+#ls /proc/$$/ns
+cgroup  ipc  mnt  net  pid  pid_for_children  user  uts
+#readlink /proc/$$/ns/uts
+uts:[4026532341]
+```
+
+But at the other terminal you opened
+```
+#readlink /proc/$$/ns/uts
+uts:[4026531838]
+```
+The uts is different!
+Meaning it is at different UTS namespace.
+However, if we check the mount namespace, it is the same.
+```
+#readlink /proc/$$/ns/mnt
+mnt:[4026531840]
+```
+This is because it is mounted on the same mount point. It is just separated under the point.