What is sudo?

Sudo stands for SuperUser DO and is used to access restricted files and operations.
sudo (/ˈsuːduː/ or /ˈsuːdoʊ/) is a program for Unix-like computer operating systems that allows users to run programs with the security privileges of another user, by default the superuser.
The sudo command temporarily elevates privileges allowing users to complete sensitive tasks without logging in as the root user.

Root

Root, often referred to as “Superuser” is a special directory represented by a forward slash (/). Root has access to all files and commands in any Unix-like operating system.

Sudo

The Sudo command can help you get around the annoying “Access Denied” prompt that you may have run into when attempting to run something in the command terminal.

Syntax

To start using sudo, use the following syntax:

sudo [command]

When the sudo command is used, a timestamp is entered in the system logs. The user can run commands with elevated privileges for a short time (default 15 minutes). If a non-sudo user tries to use the sudo command, it is logged as a security event.

Why is Sudo A Better Alternative to Root

Using sudo is far safer for your system than going into root and attempting commands. You run a greater risk of messing something up while you’re in root, that to be able to perform elevated commands without the risk is a no brainer.
Sudo is also a better alternative to the switch user (Su) command. Su will request the root password and provide a superuser prompt in the form of a #. This # is to let you know that you are currently inside the root directory.

 

Visudo

Visudo is an escalated permission version of vi that allows you to safely edit the sudoers file /etc/sudoers which contains the users that have access to the sudo command.Visudo will allow you to edit the sudoers file and save the changes. It will also lock the file, preventing anyone else from making changes to it. Once you’ve finished editing the file, errors will be parsed from the file prior to saving.

The sudoers file contains many different parameters where you can specify which users of which groups can perform specific commands. To provide a user with sudo command capabilities, enter the username followed by a space and the word ALL in all caps.

username ALL

The same thing can be done for groups by adding a % in front of the group name, followed by ALL in all caps.

%groupname ALL

Now the user(s) and group(s) you’ve granted sudo permissions to will have full root permissions.

 

sudo accepts the following command line options:

TagDescription
-bThe -b (background) option tells sudo to run the given command in the background. Note that if you use the -b option you cannot use shell job control to manipulate the process.
-EThe -E (preserve environment) option will override the env_reset option in sudoers(5)). It is only available when either the matching command has the SETENV tag or the setenv option is set in sudoers(5).
-eThe -e (edit) option indicates that, instead of running a command, the user wishes to edit one or more files. In lieu of a command, the string sudoedit is used when consulting the sudoers file. If the user is authorized by sudoers the following steps are taken:
TagDescription
1.Temporary copies are made of the files to be edited with the owner set to the invoking user.
2.The editor specified by the VISUAL or EDITOR environment variables is run to edit the temporary files. If neither VISUAL nor EDITOR are set, the program listed in the editor sudoers variable is used.
3.If they have been modified, the temporary files are copied back to their original location and the temporary versions are removed.

If the specified file does not exist, it will be created. Note that unlike most commands run by sudo, the editor is run with the invoking user’s environment unmodified. If, for some reason, sudo is unable to update a file with its edited version, the user will receive a warning and the edited copy will remain in a temporary file.

-HThe -H (HOME) option sets the HOME environment variable to the homedir of the target user (root by default) as specified in passwd(5). By default, sudo does not modify HOME (see set_home and always_set_home in sudoers(5)).
-hThe -h (help) option causes sudo to print a usage message and exit.
-iThe -i (simulate initial login) option runs the shell specified in the passwd(5) entry of the user that the command is being run as. The command name argument given to the shell begins with a ‘-’ to tell the shell to run as a login shell. sudo attempts to change to that user’s home directory before running the shell. It also initializes the environment, leaving TERM unchanged, setting HOME, SHELL, USER, LOGNAME, and PATH, and unsetting all other environment variables. Note that because the shell to use is determined before the sudoers file is parsed, a runas_default setting in sudoers will specify the user to run the shell as but will not affect which shell is actually run.
-KThe -K (sure kill) option is like -k except that it removes the user’s timestamp entirely. Like -k, this option does not require a password.
-kThe -k (kill) option to sudo invalidates the user’s timestamp by setting the time on it to the Epoch. The next time sudo is run a password will be required. This option does not require a password and was added to allow a user to revoke sudo permissions from a .logout file.
-LThe -L (list defaults) option will list out the parameters that may be set in a Defaults line along with a short description for each. This option is useful in conjunction with grep(1).
-lThe -l (list) option will list out the allowed (and forbidden) commands for the invoking user on the current host.
-PThe -P (preserve group vector) option causes sudo to preserve the invoking user’s group vector unaltered. By default, sudo will initialize the group vector to the list of groups the target user is in. The real and effective group IDs, however, are still set to match the target user.
-pThe -p (prompt) option allows you to override the default password prompt and use a custom one. The following percent (‘%’) escapes are supported:
TagDescription
%Hexpanded to the local hostname including the domain name (on if the machine’s hostname is fully qualified or the fqdn sudoers option is set)
%hexpanded to the local hostname without the domain name
%pexpanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags in sudoers)
%Uexpanded to the login name of the user the command will be run as (defaults to root)
%uexpanded to the invoking user’s login name
%%two consecutive % characters are collapsed into a single % character
-SThe -S (stdin) option causes sudo to read the password from the standard input instead of the terminal device.
-sThe -s (shell) option runs the shell specified by the SHELL environment variable if it is set or the shell as specified in passwd(5).
-uThe -u (user) option causes sudo to run the specified command as a user other than root. To specify a uid instead of a username, use #uid. When running commands as a uid, many shells require that the ’#’ be escaped with a backslash (’\’). Note that if the targetpw Defaults option is set (see sudoers(5)) it is not possible to run commands with a uid not listed in the password database.
-VThe -V (version) option causes sudo to print the version number and exit. If the invoking user is already root the -V option will print out a list of the defaults sudo was compiled with as well as the machine’s local network addresses.
-vIf given the -v (validate) option, sudo will update the user’s timestamp, prompting for the user’s password if necessary. This extends the sudo timeout for another 5 minutes (or whatever the timeout is set to in sudoers) but does not run a command.
The flag indicates that sudo should stop processing command line arguments. It is most useful in conjunction with the -s flag.

 

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