How to check the current username in linux

How to check the current user name in Linux: 1. Use the id command to display the current user name, user ID, and the ID of the group to which it belongs. The syntax is "id -un"; 2. Use the whoami command. You can print the user name currently performing the operation; 3. Use the who command with the syntax "who am i" to print the user name logged in to the current Linux system.

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

Two ways to view the current user name in Linux

Method 2: Use the id command

The Linux id command is used to display the user's ID and the ID of the group to which it belongs.

id will display the actual and effective ID of the user and the group to which they belong. If the two IDs are the same, only the actual ID is displayed. If only the user name is specified, the current user's ID will be displayed.

Print the information of the current user name. The fields of the output results are as follows:

• uid: Display the user ID and user name

• gid: Display the user group ID and group name

• groups: Display the user's additional group ID and group name

id
 
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uid=0(root) gid=0(root) groups=0(root)

Want to exploit the id Command to find the current user name, execute id -un

[root@localhost ~]# id -un
root

Method 2: Use the whoami command

The whoami command in Linux is used to print the user name of the current operation. This command is equivalent to executing the "id -un" command.

whoami

Method 3: Use the who am i command

Linux who command is used to display the system Which users are on it? The displayed information includes user ID, terminal used, where they are connected from, online time, latency, CPU usage, actions, etc.

who am i

--------------------------------------------------------------------------------
Cyuyan    pts/0    2017-10-09 15:30 (:0.0)

Explanation: whoami command vs who am icommand

whoami command and who am i command are different 2 commands, the former is used to print the user name currently performing the operation, and the latter is used to print the user name logged in to the current Linux system.

In order to better distinguish the functions of these two commands, let me give you an example. We first log in to the Linux system using the user name "Cyuyan", and then execute the following command:

[Cyuyan@localhost ~]$ whoami
Cyuyan
[Cyuyan@localhost ~]$ who am i
Cyuyan    pts/0    2017-10-09 15:30 (:0.0)

On this basis, use the su command to switch to the root user and execute the above command again:

[Cyuyan@localhost ~] su - root
[root@localhost ~]$ whoami
root
[root@localhost ~]$ who am i
Cyuyan    pts/0    2017-10-09 15:30 (:0.0)

See it? Before switching the user identity, the output of the whoami and who am i commands are the same. However, after using the su command to switch the user identity, the whoami command prints the user name after the switch, while the who am i command still prints the login. The username used by the system.

Executing the whoami command is equivalent to executing the id -un command; executing the who am i command is equivalent to executing the who -m command.

In other words, using the su or sudo command to switch user identities can fool whoami, but not who am i. To explain the operating mechanism behind this, we need to understand what an actual user (UID) and an effective user (EUID, that is, Effective UID) are.

The so-called actual user refers to the user used when logging in to the Linux system. Therefore, the actual user will not change during the entire login session; and the effective user refers to the user currently performing the operation. Users, that is to say, users who really determine the level of permissions, can use the su or sudo command to switch at will.

Generally, the actual user and the effective user are the same. If there is a user identity switch, they will be different. It should be noted that there is a difference between actual users and effective users, and switching users is not the only trigger mechanism. As for other trigger conditions, subsequent chapters will introduce them in detail.

So, in what scenarios are whoami and who am i usually used? Usually, for system administrators who often need to switch users, they often need to know what identity they are currently using; in addition, for some shell scripts that require a special user to execute, you need to use the whoami command. Know who is the user who executes it; there are even some shell scripts that must be executed by a special user, even if you use the su or sudo command to switch to this identity, you need to use who am i to confirm.

Related recommendations: "Linux Video Tutorial"

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