Meaning of different command prompts

Unix/Linux: $: can be run as normal user
Unix/Linux: #: must be run as root (or with sudo)
Windows: >: Command Prompt or PowerShell
Windows: PS>: PowerShell only
Unix/Linux and Windows: $/>,#/>: Works in Windows and Unix/Linux.

These commands are important-to-know Linux commands for changing file permissions and managing groups.

# groupadd sample: create a group called sample

# usermod -a -G sample test: add the user test to the group sample

# gpasswd -d test sample: remove the user test from the group sample

# chown test example.txt: change the owner of example.txt to test

# chown test:sample example.txt: change the owner of example.txt to test, and the group to sample

• test does not need to be a member of sample

$ chown :sample example.txt: change the group of example.txt to sample

• can be run by a normal user, as long as they are both the owner of example.txt, and a member of sample.

• root or the file's owner can also run $ chgrp sample example.txt for the same effect, with the same restrictions as $ chown :sample example.txt for the owner

• if run as root, the owner does not need to be a member of sample.

Every file has an owner and group, and three sets of permissions. One is for the owner, one is for members of the group, and one is for everyone else.

Each set of permissions has three values: r, w, and x.

r is permission to read, w is permission to write, and x is permission to execute.

The overall permissions can be written with nine characters: rwxrwxrwx is full permissions, --------- is no permissions, and they can be combined to create the appropriate permission scheme. The first three characters are the owning user's permissions, the next three are the group's permissions, and the last three are the permissions for anyone else.

It can also be shortened to a set of three octal numerals. 4 is read permissions, 2 is write permissions, and 1 is execute permissions, and add them to combine them (7 is all three, 5 is read+execute, 1 is execute, etc.)

permissions	numeric	user r	user w	user x	group r	group w	group x	other r	other w	other x
rwxr-x---	750	yes	yes	yes	yes	no	yes	no	no	no
rwxr-xr--	754	yes	yes	yes	yes	no	yes	yes	no	no
--x-w-rwx	127	yes	yes	no	no	yes	no	yes	yes	yes

$ chmod 754 example.sh: changes the permissions for example.sh to rwxr-xr-- (anyone can read, user+group can execute, user can write)

$ chmod u+x,g-w example.sh: grants execute permissions to the user, revokes write permissions from group.

$ chmod u=rwx,g=rx,o=r example.sh: changes the permissions for example.sh to rwxr-xr--

$ chmod a+x example.sh, $chmod +x example.sh: allow all to execute