Linux Cheatsheet

Linux Architecture

Shell - interface
Kernel - A core component of OS that manages communication between HW & SW.
OS = Kernel Space + User Space
User Space = GUI, file system, text editor, compiler, sys admin cmds.
Microkernel Architecture: Bare minimum code to run in kernel space and the rest in user space.
Some key characteristics of kernel include Basic IPC, Virtual Memory Mgmt., Scheduling.

Linux distros and packages

600+ distros
Package management -> apt-get: Debian, apt: Ubuntu, yum: RHEL, dnf: Fedora

Useful Linux commands

NOTE: No command in caps.

pwd is print working directory.

grep

grep is general regular expression pattern.

grep -inc RAM user.txt

i - case insensitive, n - line #, c - # of times matched.

( ) | grep "Star Wars"

awk

awk used for text data extraction, like from a .csv file.

awk -F: '{print $1, "-->" $NF}' /etc/passwd

ssh

ssh is replacement for telnet. telnet is not secure.

ssh <ip-addr>

On server, to check if sshd is running

systemctl status sshd

From client,

ssh -p 2201 <server-ip-addr>

If not root, user "ram" can with password (by default) access remote server

ssh -p 2201 ram@<server-ip-addr>

netcat

Network swiss-army-knife netcat

netcat -l 8080
netcat <server-ip-addr> 2201

o/p will inform if port 2201 is open.

tar

To Compress ----> tar -cvf <tar-file> <source-folder>
To Decompress --> tar -xvf <tar-file>

How to Set Static IP Address and Configure Network in Linux [Click Here]

Print out contents of multiple files with filenames:

Approach 1:

$ for i in *
> do
> echo $i
> cat $i
> done

Output:
board_fp_subtype
XENONboard_subtype
XENONboard_type

Approach 2:

$ find ./ -type f |  xargs tail -n +1

Output:
==> ./sfp3_config <==
BADACCE5

Save debugs messages from mem_table.txt onto a log file:

echo "Contents of mem_table.txt: " >> debug_script.log
var1="$(cat /etc/mem_table.txt)"
echo "$var1" >> debug_script.log

Script not executing the piece of code you added in it?

Let set_config be the function of interest and config be the flag inside that function.

In your linux shell, run:

source /etc/init_common.sh
set_config
echo $config