Linux - Commands 

Page / - last modified by Julien Fleury on 2021/02/02 19:01 

Commands 
last modified by Julien Fleury
on 2021/02/02 19:01

Table of Contents
Useful Linux commands
Telnet like
Test disk speed

Contents
•	Useful Linux commands
•	Telnet like
•	Test disk speed
Useful Linux commands
Here is a list of useful commands to be executed on a Linux server (debian). Feel free to contribute by feeding this page with your own tricks and tips.
Telnet like
It is often required to test if a host[:port] is reachable and access is granted from a server. Best way to execute a telnet like command on a Linux console is to work with special files used to communcate with peripherals. Thus, in order to test tcp port 8000 on server 10.100.100.100, simply try to write in file /dev/tcp/10.100.100.100/8000 and add a return value depending on success or failure
echo > /dev/tcp/10.100.100.100/8000 && echo 'up' || echo 'down'
-bash: connect: Connection refused
-bash: /dev/tcp/10.100.100.100/8000: Connection refused
down
Test disk speed
dd command allows to copy all or parts of a disk by bytes block without impact from content structure of the disk.
Use dd command with caution as it can cause severe dammage to the system
Do not use dd to duplicate a disk. Prefer ddrescue command
Command structure
dd if=<source> of=<target> bs=<block size> count=<number of blocks> oflag=<flag>
oflag: 'dsync' to use synchronized I/O for data
dd if=/dev/zero of=/tmp/test2.img bs=512 count=1000 oflag=dsync
1000+0 records in
1000+0 records out
512000 bytes (512 kB, 500 KiB) copied, 1.22846 s, 417 kB/s