Hi, I'm Jeff!
Working With Linux Files And Permissions
Linux is an ultra efficient, powerful, and secure operating system. There are many distributions of Linux, but once you learn the command syntax, it's pretty much the same accross all the varients. Here are some of the basics to get you started working with directories, files, and users.
List File/Directory Permissions
ls -l -h
(-)(---)(---)(---)
(1st - file or directory - = file d = directory)
(2nd (---) Owner permissions)
(3rd (---) Group permissions)
(4th (---) Other (the world) permissions)
r = read permission
w = write permission
x = execute permission
- = no permission
Change File/Directory Permissions
sudo chmod 777 filename
Number / Permission / Symbol
0 / No Permission / ---
1 / Execute / --x
2 / Write / -w-
3 / Execute + Write / -wx
4 / Read / r--
5 / Read + Execute / r-x
6 / Read + Write / rw-
7 / Read + Write +Execute / rwx
Change File/Directory Ownership
sudo chmod jeff filename
sudo chown user:group filename
sudo chgrp groupname filename
List all users
cat /etc/passwd
List all groups and members
cat /etc/group
List what users are members of a spcific group
grep groupnamehere /etc/group
List what users are members of a spcific group
grep groupnamehere /etc/group
Add new user with home directory, ability to log in, and password
sudo useradd -m testuser -p NewUserPassword
sudo useradd -m jeff -p userpasswordgoeshere
Add a new group
sudo groupadd testgroup
Add a user to a group
sudo usermod -a -G testgroup testuser
sudo usermod -a -G adm, dialout, cdrom, floppy, sudo, audio, dip, video, plugdev, netdev, lxd jeff
Give A User SUDO Access
sudo visudo
%sudo ALL=(ALL:ALL) ALL
allow the user to run sudo commands without being asked for a password.
username ALL=(ALL) NOPASSWD:ALL
Another typical example is to allow the user to run only specific commands via sudo. For example, to allow only the mkdir and rmdir commands you would use:
username ALL=(ALL) NOPASSWD:/bin/mkdir,/bin/rmdir
Instead of editing the sudoers file, you can accomplish the same by creating a new file with the authorization rules in the /etc/sudoers.d directory. Add the same rule as you would add to the sudoers file:
echo "username ALL=(ALL) NOPASSWD:ALL" | sudo tee /etc/sudoers.d/username
Listing ACLs
sudo usermod -a -G testgroup testuser
getfacl testfile.foo
getfacl testdirectory
Add A Group/User/Other to File/Directory ACL
sudo setfacl -R -m g:groupname:rwx testfile.foo
sudo setfacl -R -m g:groupname:rwx testfile.foo
sudo setfacl -R -m u:username:rwx testfile.foo
sudo setfacl -R -m u:username:rwx testfile.foo
sudo setfacl -R -m o:rwx testfile.foo
sudo setfacl -R -m o:rwx testfile.foo
Removing a Group from an ACL
setfacl -x g:groupname testfile.foo
Set ACL Mask
setfacl -m m:--- testfile.foo