Permissions in Linux

Each file, when created, has an owner and a group.

The permissions displayed of a file (or a directory) refer to the owner (whoever created the file), the group (to whom the file belongs) and others (the rest of users).

If the current user is not the owner and does not belong to the group of the file, then "others" apply.

list commands

permissions for a file or folder

ls -l name

list of files of a directory with permissions

ls -l

list of groups for current user

groups // users sales

list of groups for a certain user

groups peter // users manager

Symbols

There are two kinds of symbols:

Symbol type:

- ==> Regular file

d ==> Directory

l ==> Symbolic link

Symbol Permission

r ==> read

w ==> write

x ==> execute

There are three categories that these permissions can be applied to, which are user, group and other

Numeric Permission (octal mode)

r // w // x

0 // 0 // 0 ==>Base 10 (decimal) value for off

4 // 2 // 1 ==> Base 10 (decimal) value for on

some examples:

700 ==> -rwx------

664 ==> -rw-rw-r--

Symbol category

u ==> User

g ==> Group

o ==> Other

a ==> All (user, group and other)

Permission string

-rw-r--r--

The first character is a symbol type

From then on, there is three groups of three characters, that display the permissions for user, group and others, respectively.

Change permissions command

Permissions are also known as nodes, that is why the command to use is called chmod (change mode).

chmod mode file                  

chmod ==> The change mode command.

ugoa ==> The user category. One or more of u for user, g for group, o for other, a for all.

+ - = ==> One of +, -, or =. Use + to add permissions, - to subtract them, or = to explicitly set them.

rwx ==> The permissions. One or more of r for read, w for write, and x for execute.

examples:

chmod u+x script.sh

chmod g-w report.txt

chmod a+rw document.txt

chmod 755 my_program

chmod 644 file.txt