Users and rights
Introduction
Files and directories on the Linux system belong to an owner and a group. You can set read, write and execute permissions on a file or directory for owner, group and others. Users can belong to one or more groups. The command chmod is used to set the permissions, the command chown to change the owner and the command chgrp to change the group.
- https://wiki.archlinux.org/index.php/Users_and_Groups
- https://help.ubuntu.com/lts/serverguide/user-management
- http://www.cyberciti.biz/tips/unix-or-linux-commands-for-changing-user-rights.html
- http://www.cyberciti.biz/faq/how-to-use-chmod-and-chown-command/
- http://www.thinkplexx.com/learn/article/unix/command/chmod-permissions-flags-explained-600-0600-700-777-100-etc
Show ownership and permissions
ls -l /path/to/files/*
Example output:
| Directory | User | Group | Other | Number of links | Owner | Group | Size | Modified date/time | Object name |
|---|---|---|---|---|---|---|---|---|---|
| - | rwx | rw- | r-- | 1 | wilbert | users | 464843 | Apr 6 16:09 | file1.txt |
| - | rwx | rwx | r-- | 1 | wilbert | users | 1398792 | Apr 6 16:09 | file2.sh |
| d | rwx | rw- | r-- | 2 | wilbert | users | 4096 | Apr 17 23:16 | directory |
| - | rwx | rw- | r-- | 2 | wilbert | users | 93 | Apr 17 23:16 | link_to_file1.txt |
Add, remove and modify users and groups
Disable (lock) the root account:
sudo passwd -l root
Enable the root account by specifying a password for it:
sudo passwd
Add a user account and home folder, delete user:
sudo adduser username
Delete user:
sudo deluser username
Lock (l) or unlock (u) a user account:
sudo passwd -l username sudo passwd -u username
Add or delete a personalized group:
sudo addgroup groupname sudo delgroup groupname
Add a user to a group:
sudo adduser username groupname
Change permissions on files and directories
Flag method
User/group:
- u user/owner
- g group
- o other
Permissions:
- r read
- w write
- x execute
Options:
- -R full recursive
- + add permission
- - remove permission
Examples:
sudo chmod -R u+rwx /path/to/files sudo chmod -R go-x /path/to/files
Octal method
There are four OCTAL (0..7) digits, which control permissions. Mostly only three are used, for more info on the first digit:
Permissions:
1 = execute (x) 2 = write (w) 4 = read (r)
The octal number is the sum of those free permissions, i.e.
1+2+4 = 7 : can execute, write and read 2+4 = 6 : can write and read
Permissions are set for owner, group and others, depending on the position of the digit:
| who: | owner | group | others | ||||||
|---|---|---|---|---|---|---|---|---|---|
| may: | x | w | r | x | w | r | x | w | r |
| add: | 1 | 2 | 4 | 1 | 2 | 4 | 1 | 2 | 4 |
Examples:
chmod 600 file – owner r,w chmod 700 file – owner r,w,x chmod 777 file – all can r,w,x
Change ownership of files and directories
Note: option -R applies the change recursively to matching files and directories
Owner:
sudo chown user /path/to/file_or_dir sudo chown -R user /path/to/dir
Group:
sudo chgrp -R group /path/to/file_or_dir sudo chgrp -R group /path/to/dir
