diff --git a/_sidebar.md b/_sidebar.md
index 5d271e6..ed6f698 100644
--- a/_sidebar.md
+++ b/_sidebar.md
@@ -15,6 +15,7 @@
 - [Devops](categories/devops.md)
     - [Docker](categories/devops/docker.md)
     - [Incident Management](categories/devops/incident.md)
+    - [Linux](categories/devops/linux.md)
 - [Web](categories/web.md)
 - [Success Team Work](categories/team-work.md)
 - [Uncategorised](categories/uncategorised.md)
diff --git a/categories/devops.md b/categories/devops.md
index 216f9c6..6fc8a6a 100644
--- a/categories/devops.md
+++ b/categories/devops.md
@@ -10,26 +10,6 @@
 - Gitlab CI
 - Travis
 
-# Linux
-- ssh
-- IP table
-- Cron job
-- ps aux
-- tail
-- nohup
-- df -h
-- free
-- Tips
-	- Change timezone
-		- TZ=Asia/Shanghai;ln -snf /usr/share/zoneinfo/$TZ /etc/localtime
-	- Check release
-		- cat /etc/*-release
-- Packages
-	- htop
-		- like top, but more
-	- mosh
-		- auto reconnect ssh
-
 # Everything is code
 - Infrastructure as code
 - CI config as code
@@ -98,4 +78,4 @@ terraform apply # Apply changes to cluster
 - oh-my-zsh
 - IDE/tools
 	- Intellij
-	- vscode
\ No newline at end of file
+	- vscode
diff --git a/categories/devops/linux.md b/categories/devops/linux.md
new file mode 100644
index 0000000..0116e0b
--- /dev/null
+++ b/categories/devops/linux.md
@@ -0,0 +1,83 @@
+# Linux
+
+## Useful commands and tips
+
+### ssh
+Do not use default `22` port
+```bash
+ssh user@ip -p 22222
+```
+### IP table
+### Cron job
+
+### PS
+```bash
+ps aux | grep 'ruby'
+```
+List process, using `grep` to filter processes
+### tail
+Tailing texts from file in realtime
+
+```bash
+tail -f a.log
+```
+`f` means following, auto append texts to console
+### nohup
+Simply running application in background
+
+
+### df
+```bash
+df -h
+```
+Show disk usage and left, `h` means show in human readable way. Normally by MB/GB.
+### free
+```bash
+              total        used        free      shared  buff/cache   available
+Mem:        3960624      416720      270024       22252     3273880     3264060
+Swap:       4104188      109688     3994500
+```
+Show memory usage and
+
+### Watch
+```
+watch kubectl get pods
+```
+Continuous running the commands, watching the changes. By default it refresh the result every `2s`.
+
+### Change timezone
+```bash
+TZ=Asia/Shanghai;
+ln -snf /usr/share/zoneinfo/$TZ /etc/localtime
+```
+
+### Check release
+```bash
+cat /etc/*-release
+```
+
+### Debian check system version
+```bash
+cat /etc/issue
+
+cat /etc/debian_version
+```
+
+### htop
+  like top, but more
+
+#### mosh
+  auto reconnect ssh
+
+### show last something time
+
+```bash
+last shutdown
+last reboot
+```
+
+### Count files in current folder
+
+```bash
+find . -type f | wc -l
+```