My focus is on CALMS. I am building better understanding of DevOps as driver for the organization. I led the DevOps Academy at EPAM Systems Poland, where we were shaping new engineers to be professionals. Currently I am Cloud Solution Architect at Tameshi.

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1. Syntax

Linux command is composed of the command and the argument

ls -l

- : one letter argument ex. l

-- : more than one letter argument ⇒ commonly in English words

• each columns has different meanings

  1. permissions

  2. number of hard links

  3. owner

  4. group

  5. file size in the bytes

  6. date and time of last modification of the object

  7. file name

• every arguments can be multiplied

• In Linux filesystem, the root is the first point we can access. This root directory is represented by / symbol. On the top level of the filestytem is always / directory.

• absolute path / relative path

• root user is the most powerful entity in the whole Linux system

  • The home directory of the root user is /root

  • Other user’s home directories are under /home

• there’s a variable for the home path

  • cd $HOME / cd / cd ~

• ~ = home directory

• * wild card ⇒ any string

  • ex. ls my*file

• ? any single character

root@ubuntu:~$ touch try1 try2 try01
root@ubuntu:~$ ls try*
try01  try1  try2
root@ubuntu:~$ ls try?
try1  try2

• l (pipe) combine the commands

  • command1 | command2

  • command1 | command2 | command3

  • ⇒ The output of command1 is taken over as input to command2

• > redirects all output from the left side of the sign, to the file on the right side of the sign

  • ls -al > directorylist.txt

  • notice

    • if file doesn’t exist, create it

    • add content from redirected output

    • if file exists and it is not empty, clear the file and write the redirected output in empty file

• >> add the output of the command on the end of existing content (only if there is any content in the fill)

2. times in Linux

atime : the last time when file was accessed

mtime : last modification time

ctime : last metadata modification time

ex. permissions change, location of the file, etc

3. basic commands

ls : show lists

• ls -1 shows lists in one line

• ls -a for hidden files

• ls -l detailed list

• ls -F with / in the name of files

• ls -la for various informations about the lists

  • permissions, ownership, size, modification date

• ls -lh shows lists in order to the size

• ls -d * / show only the folders

clear : clear all window

• the same by running /bin/echo -e "\x1b\x5b\x48\x1b\x5b\x32\x4a\c"

man : show a document for the command

mkdir : create directories

• mkdir testdir{1..10} make directories from 1 to 10

• mkdir -p parentdir/childdir{01..100} create parent directory

cd : short for Change Directory

pwd : show current work directory

rmdir : remove the directory

• rmdir testdir{1..10} remove the directories from 1st to 19th

• can remove parent directory only when it is empty

• works for files

• -r go recursively through directories and treat everything as file

• -f force / do not ask ⇒ risky command

touch : create empty file

• or use vim

grep : search for given pattern in the output

⇒ ex. grep case .bashrc : search for pattern case in a file .bashrc

wc : a utility for counting words, newlines, bytes.

• wc -l .bashrc count how many lines are in .bashrc file

sort sort the output in alphabetical order

• uniq always works beest with sort ⇒ sort is first

• ⇒ ex. cat numbers.txt | sort | uniq | wc -l

man document