Analyzing disk usage is an important task for Linux admin. Disk I/O bottlenecks can bring down applications. Hope this post can give you more ideas on how to troubleshoot disk problems.
Check Disk Space Usage with df
Check Disk Utilization In Linux
Check Disk IOPS and Bandwidth In Linux
Check IO usage by Process
What does actimeo mean in nfs mount
The "actimeo=0" option means turn attribute caching off. The actimeo option actually makes the time duration the nfs client holds the various cache attributes like "acregmin","acregmax","acdirmin" and "acdirmax" to zero seconds, which means that the nfs client will need to look for the attributes everytime from the server.
tcpdump -v -s 1500 -c 1 '(ether[12:2]=0x88cc or ether[20:2]=0x2000)'
This will often show you the uplink Cisco chassis switch info like the native vlan, port info, device name, serial name etc.
tcpdump -v -s 1500 -c 1 'ether[20:2] == 0x2000'
DHCP v4 traffic operates on port 67 (Server) and port 68 (Client). So we can capture the appropriate traffic with the following expression. (v4)
tcpdump -i eth0 udp port 67 or port 68 -vvv
source: Why Tcp Window Scaling Improves Network Performance?
Tcp window scaling is a key design in tcp protocol to improve network performance. Today we will dive into this topic to see how tcp window scale works in Linux.
This type of for loop is characterized by counting. The range is specified by a beginning (#1) and ending number (#5). The for loop executes a sequence of commands for each member in a list of items. A representative example in BASH is as follows to display welcome message 5 times with for loop:
#!/bin/bash
for i in 1 2 3 4 5
do
Each TCP flag corresponds to 1 bit in size. The list below describes each flag in greater detail. Additionally, check out the corresponding RFC section attributed to certain flags for a more comprehensive explanation.
| In networking, a port is a virtual place on a machine that is open to connections from other machines. Every networked computer has a standard number of ports, and each port is reserved for certain types of communication. | |
| Think of ports for ships in a harbor: each shipping port is numbered, and different kinds of ships are supposed to go to specific shipping ports to unload cargo or passengers. Networking is the same way: certain types of communications are supposed to go to certain network ports. The difference is that the network ports are virtual; they are places for digital connections rather than physical connections. | |
| ## DNS Port | |
| Most of the time, DNS happens over UDP port 53. It's lightweight and faster than TCP. This is to reduce performance overhead on the DNS server due to the number of requests it is likely to receive. | |
| But DNS servers still need to be available on TCP. Zone transfers happen over TCP port 53. This happens on the DNS server side which is not related to the end-user. |