Managing Users in Ubuntu

add a user: sudo adduser [newuser]

sudo adduser john

then give password, and setup home folder,when prompted

edit the list of super users

visudo

list users

cat /etc/passwd

change password of a user – sudo passwd [username]

sudo passwd john

to change your password you can just use sudo passwd.

delete user

sudo deluser username

This will not delete the home folder (and subfolder) those must be dealt with separately. A new user created with the old user name would have access to those files.

temporarily lock a user account – Simply locking a user account will not prevent a user from logging into your server remotely if they have previously set up RSA public key authentication.

sudo passwd -l username

To unlock the account

sudo passwd -u username

Groups

Groups are used in to control permissions (see file permissions)
add user to a group
usermod -G [group-name] [username]

usermod -G basketball john

using the -G switch ads the group as a supplemental group. Using -g would make the group that users primary group.

see what groups a user is in

id john

add a new group: groupadd [new_group_name]

groupadd ruby_developers

Linux/Ubuntu File and Directory Permissions

Linux (and therefore Ubuntu) has file permissions on each file and directory for the owner, group and everyone else. Those permissions determine if the file can be viewed, executed or edited.

Only the owner of a file or directory (or a privileged user, root for example) may change its mode.

Ownership of a file

To change the ownership of the file or directory: chown new_owner_username directory

chown john public_html

to change the ownership of directory (and all the files and folders in the directory) and also the group: chown -R new_owner_username:new_groupname directory

chown -R john:developers public_html

to change the ownership of all the files in the current directory and also the group: chown -R new_owner_username:new_groupname *

chown john:developers *

File permissions

The easiest way to set Linux file permissions is using a 3 digit sequence. The first digit designates owner permission; the second, the group permission; and the third, everyone else’s permission.

Read = 4
Write = 2
Execute = 1

The digit is the sum of those. So if you want to grant only read permission you use 4; read and execute 5; read, write and execute = 7.

chmod 775 index.html

That will set the permissions on index.html so the owner, and a user in the group specified can read, write and execute the file and everyone else can read and execute.

chmod -R 755 public_html

That will set the permissions on files and directories (recursively through all subdirectories) so the owner can read, write and execute; members of the group and everyone else can read and execute (but not write).

ls - l

That will give you a list of files and directories, in a directory, with the owner and group settings and the permissions for all 3 (those 2 and everyone else), which will look something like:

-rw-r--r-- 1 root developers   397 2008-05-25 20:33 index.html
-rw-r--r-- 1 mary developers  9177 2010-05-02 22:18 unix_file_permissions.html
...

The lines start with the permissions for the owner, group and then everyone else. There are 9 total characters, 3 for each. Taking the top line above:

rw-r--r--
rw-  (means the owner has read and write permission but not execute)
r--  (means the group has only read permission)
r--  (means everyone else has only read permission)

The next column tells you the number of hard links to the file or directory. Then column tells you the owner, then the group. Then the byte size of the file, the date it was last change and then the file name.

root
means the username of this file is named root

developers
group (means those users in the group named developers have the group permissions indicated)

Related: Ubuntu command line interface syntax examples

Using the Host File in Ubuntu

You can use the host file to have your computer route to whatever addresses you desire (instead of using your nameserver). For example, by putting

sudo nano /etc/hosts

Then add a line to the file with the ip address and the name you will use.

204.11.50.136 wastetime

One useful way to use this is to test out a website on a new host prior to changing the nameserver to point to the new host. In this case, if you want to make sure your host file is being read you can ping wastetime and if it is working it will show the results for a ping to 204.11.50.136

Ubuntu/Linux cli syntax

Command line interface syntax for various actions

Make new directory, make [directory_name]

sudo mkdir new_directory

Remove (file or directory)

rm [name]

rm -i file_to_remove.txt

Using -i prompts you to confirm the deletion.
Remove directory and all of its contents without having to confirm. Obviously be careful.
[/bash]sudo rm -r directory_to_remove[/bash]

Move a file

mv [name] [new_location]

mv file.txt new_sub_directory/file.txt

Rename a file (similar to moving)
mv [name] [new_name]

mv file.txt new_file_name.txt

Copy a fold

cp -r [folder]/* [new_location]

cp -r folder/* /some_place/else/

Keep ssh sessions live

If you want to stop your SSH sessions from being shut down you can add the following line to /etc/ssh/ssh_config on your local machine.

sudo gedit /etc/ssh/ssh_config

Then add:

ServerAliveInterval 30

This does remove the security feature of closing your session in case you leave your computer, but you may decide to take that risk. This sends a SSH package every 30 seconds so your server doesn’t close the connection due to inactivity.

Edit DNS Name Server

Set the DNS name server to use for your machine.

sudo nano /etc/resolv.conf

Then you can use for example (8.8.8.8 is Google public DNS, 208.67.222.222 is OpenDNS):

nameserver 208.67.222.222
nameserver 8.8.8.8
sudo lshw

will provide infor on your system, CPU types, 32 v 64 bit…