Users and groups
Users and groups are used on GNU/Linux for access control—that is, to control access to the system’s files, directories, and peripherals. Linux offers relatively simple/coarse access control mechanisms by default. For more advanced options, see ACL, Capabilities and PAM#Configuration How-Tos.
Overview
A user is anyone who uses a computer. In this case, we are describing the names which represent those users. It may be Mary or Bill, and they may use the names Dragonlady or Pirate in place of their real name. All that matters is that the computer has a name for each account it creates, and it is this name by which a person gains access to use the computer. Some system services also run using restricted or privileged user accounts.
Managing users is done for the purpose of security by limiting access in certain specific ways. The superuser (root) has complete access to the operating system and its configuration; it is intended for administrative use only. Unprivileged users can use several programs for controlled privilege elevation.
Any individual may have more than one account as long as they use a different name for each account they create. Further, there are some reserved names which may not be used such as «root».
Users may be grouped together into a «group», and users may be added to an existing group to utilize the privileged access it grants.
Note: The beginner should use these tools carefully and stay away from having anything to do with any other existing user account, other than their own.
Permissions and ownership
The UNIX operating system crystallizes a couple of unifying ideas and concepts that shaped its design, user interface, culture and evolution. One of the most important of these is probably the mantra: «everything is a file,» widely regarded as one of the defining points of UNIX. This key design principle consists of providing a unified paradigm for accessing a wide range of input/output resources: documents, directories, hard-drives, CD-ROMs, modems, keyboards, printers, monitors, terminals and even some inter-process and network communications. The trick is to provide a common abstraction for all of these resources, each of which the UNIX fathers called a «file.» Since every «file» is exposed through the same API, you can use the same set of basic commands to read/write to a disk, keyboard, document or network device.
A fundamental and very powerful, consistent abstraction provided in UNIX and compatible operating systems is the file abstraction. Many OS services and device interfaces are implemented to provide a file or file system metaphor to applications. This enables new uses for, and greatly increases the power of, existing applications — simple tools designed with specific uses in mind can, with UNIX file abstractions, be used in novel ways. A simple tool, such as cat, designed to read one or more files and output the contents to standard output, can be used to read from I/O devices through special device files, typically found under the /dev directory. On many systems, audio recording and playback can be done simply with the commands, » cat /dev/audio > myfile » and » cat myfile > /dev/audio ,» respectively.
Every file on a GNU/Linux system is owned by a user and a group. In addition, there are three types of access permissions: read, write, and execute. Different access permissions can be applied to a file’s owning user, owning group, and others (those without ownership). One can determine a file’s owners and permissions by viewing the long listing format of the ls command:
total 13740 drwxr-xr-x 2 root root 4096 Jan 12 00:33 grub -rw-r--r-- 1 root root 8570335 Jan 12 00:33 initramfs-linux-fallback.img -rw-r--r-- 1 root root 1821573 Jan 12 00:31 initramfs-linux.img -rw-r--r-- 1 root root 1457315 Jan 8 08:19 System.map26 -rw-r--r-- 1 root root 2209920 Jan 8 08:19 vmlinuz-linux
The first column displays the file’s permissions (for example, the file initramfs-linux.img has permissions -rw-r—r— ). The third and fourth columns display the file’s owning user and group, respectively. In this example, all files are owned by the root user and the root group.
total 16 drwxrwx--- 1 root vboxsf 16384 Jan 29 11:02 sf_Shared
In this example, the sf_Shared directory is owned by the root user and the vboxsf group. It is also possible to determine a file’s owners and permissions using the stat command:
Add a new user account
You can add multiple user accounts to your computer. Give one account to each person in your household or company. Every user has their own home folder, documents, and settings.
You need administrator privileges to add user accounts.
- Open the Activities overview and start typing Users .
- Click on Users to open the panel.
- Press Unlock in the top right corner and type in your password when prompted.
- Press the + Add User. button under Other Users to add a new user account.
- If you want the new user to have administrative access to the computer, select Administrator for the account type. Administrators can do things like add and delete users, install software and drivers, and change the date and time.
- Enter the new user’s full name. The username will be filled in automatically based on the full name. If you do not like the proposed username, you can change it.
- You can choose to set a password for the new user, or let them set it themselves on their first login. If you choose to set the password now, you can press the icon to automatically generate a random password. To connect the user to a network domain, click Enterprise Login .
- Click Add . When the user has been added, Parental Controls and Language settings can be adjusted.
If you want to change the password after creating the account, select the account, Unlock the panel and press the current password status.
In the Users panel, you can click the image next to the user’s name to the right to set an image for the account. This image will be shown in the login window. The system provides some stock photos you can use, or you can select your own or take a picture with your webcam.