linux filesystem structure - politecnico di milano · federico reghenzani 4/19 dipartimento di...

Titolo presentazionesottotitolo

Milano, XX mese 20XX

Piattaforme Software per la Rete

Linux and BASH Introduction

A.A. 2016/17Federico Reghenzani

Federico Reghenzani 2/19

Dipartimento di Elettronica, Informazione e Bioingegneria

Outline

1) Linux filesystem structure

2) The Linux Prompt

3) Basic commands

4) Permissions

Linux filesystem structure



Linux Filesystem Layout

● Files and directories are structured as a tree

● Unlike Windows, the tree structure is not dependent on disk partitioning

● The root of the tree is identified by / character

● Directories are preceded by a slash and they compose the path:

– /directory1/directory2/file.txt



Linux Filesystem Layout

/

bin boot dev etc home lib lost+found mnt

opt proc root sbin tmp usr var

william federico lara

bin include ...



Everything in Linux is a file

● Files are files

● Directories are files containing a list of files

● I/O devices are special files (usually located under /dev)

● Sockets are files (/proc/net)

● Named pipes are files

The Linux prompt



The Linux Prompt

In order to modify the prompt, you have to change the PS1 environment variable



How to execute a command?

● Using an absolute path:

– Example:

● Using a relative path:

– Example:

● Using directly its name if the executable directory is in the PATH environmental variable

– Example:

●

/path/to/somewhere/$ /usr/bin/df

/usr/bin $ ./df

/path/to/somewhere/$ df



The PATH environmental variable

● The PATH variable specifies where executables are located

● When you type a command that is not a built-in command of the shell, it searches in the directories specifies in the PATH variable the executable

● tells you where is the binary

which command

Basic commands



Help

● If you don’t know what a command is:

–

–

– Search engines are your friends!

command --help

man command



Basic commands

●

– Write parameters to standard output

●

– List files in the current directory or in [directory] if specified

●

– Change the current working directory to path (it may be realtive or absolute)

●

– Print the working directory

echo [param1 param2 ...]

ls [directory]

cd path

pwd



Basic commands

●

– Concatenate files and print to standard output

●

– Copy the file source to destination (if copying a directory you have to add -r option)

●

– Move or rename a file or a directory

●

– Remove a file (if removing a directory, you have to add -r option)

cat [file1 file2 ...]

cp source destination

rm file

mv source destination



Basic commands

●

– Create a link named link_name that points to destination. If -s is specified, the link is symbolic.

●

– Create a new directory

●

– Remove an empty directory

ln [-s] destination link_name

mkdir directory

rmdir directory

Permissions



Permission classes and modes

● Every file is identified by three classes of permission:

– User

– Group

– Other

● Every permission class has three permission mode:

– Read 22=4

– Write 21=2

– Execute 20=1



Permissions

● They are common reported as

– Examples:● rwxr-xr-x: Owner R,W,X; Group R,X; Other R,X● r-x-w----: Owner R,X; Group W; Other -● rw-------: Owner R,W; Group -; Other -

● Or using the three-digits numerical values XXX

– Examples:● 755: Owner R,W,X; Group R,X; Other R,X● 520: Owner R,X; Group W; Other -;● 600: Owner R,W; Group -; Other -;

rwxrwxrwx



Change permissions

●

– Assign the permission mode to file_name. mode can be expressed as:

Numerical value, e.g. 755 Symbolic name, e.g. +x, +r, -r, etc. u,g,o can be used to select classes, e.g. u=rwx, g=rx

●

– Change the owner of the file

chmod mode file_name

chown user[:group] file_name

linux filesystem structure - politecnico di milano · federico reghenzani 4/19 dipartimento di...

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