labex

$ sudo groups jack
$ sudo usermod -G sudo jack
$ sudo groups jack

$ sudo deluser jack –remove-home

• To display all files except the . (current directory) and .. (parent directory):

$ ls -A

• To use both the -A and -l parameters together:

$ ls -Al

• To view the full properties of a directory:

$ ls -dl <directory>

• To show all the file sizes:

$ ls -AsSh

touch iphonex

The file owner is jack:

Then we switch the user to « labex » . We can use the following command to change the file owner for « labex »:

$ cd /home/jack
$ ls iphonex
$ sudo chown labex iphonex

Find the file owner modified successfully for labex:

• Method 1：Binary number representation

Each file has three groups of permissions (owner, user group, others) corresponding to a « rwx » triplet. The file « iphonex » permissions are changed to « only for owner to use »:

In order to demonstrate, we write some words into the file：

$ echo "echo \"hello labex\"" > iphonex

Then modify the permissions:

$ chmod 700 iphonex

Now, other users are unable to read this « iphonex » file.

• Method 2：Addition and subtraction assignments

You can use the following command to achieve the same result as by method 1:

$ chmod go-rw iphonex

u, g and o respectively represent user (file owner), group and others. + and - represent to add and remove the corresponding permissions.

What is the difference between useradd and adduser?

The command useradd can only create the user. After that, we need to use passwd to set up password for the new user. The command adduser not noly creates a user, but also creates a directory, and a password.