Add new Linux info commands

src/linux.md

@@ -31,6 +31,9 @@ uname -mrs
 
 # Get distribution-specific information.
 lsb_release -a
+
+# Get Debian version.
+cat /etc/debian_version
 ```
 
 ### Updates
@@ -156,6 +159,9 @@ free -m
 
 # IP address
 ip a
+
+# Server uptime.
+uptime
 ```
 
 ## Package management