This is one of the best part of linux, we can grant access for all services, directories, files, and even commands that can be executed for a specific user or group.
User management
- Check who am i
$ whoami
- Check the user id
$ id USERNAME
- Check the group of user
$ groups USERNAME
- Check who is currently logged in
$ w
- Check the last logged in
$ last
- Change user
$ su
- Add a new user
$ useradd USERNAME
- Set password for a user
$ passwd PASSWORD
- Change user name
$ usermod -l USERNAME NEW_USERNAME
- Add a user to a group
$ usermod -a -G GROUPNAME USERNAME
- Change user primary group
$ usermod -g GROUPNAME USERNAME
- Remove user from a group
$ gpasswd -d USERNAME GROUPNAME
- Delete a user
$ userdel -r USERNAME
- Lock a user
$ passwd -l USERNAME
- Unlock a user
$ passwd -u USERNAME
Group management
- Add a new group
$ groupadd GROUPNAME
- Change group name
$ groupmod -n GROUPNAME NEW_GROUPNAME
- Delete a user
$ groupdel GROUPNAME
Permission
After create a user or group, we can grant access for specific user or group.
Permission format :
rwxrwxrwx
First 3 characters are the user permission, next 3 characters are the group permission, and the last 3 are other permission.
-
r
is forread
with value4
-
w
is forwrite
with value2
-
x
is forexecute
with value1
-
-
is forno permission
with value0
We can also use the value of the characters to define the permission. Simply sum the values of the permissions for each role, and use only 3 numbers to define the permission.
# rwxrwxrwx
777
# rwxr-x-rx
755
# rwx------
700
We can see the files or directories permission by run ls -l
.
$ ls -la
drwxrwxrwx 1 root root 96 Jun 11 07:58 directory
-rwxr-xr-x 1 zaki zaki 96 Jun 11 07:58 file.txt
The first column is the permission, the third column is the user, the fourth column is the group name.
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