To log in into a computer, we need a username. Username is an identity to recognized by a computer. Based on it, computer will apply a set of rules to a someone that log in with that username. On Linux system we can use id command.
What is id command
id command is command which can print real and effective User ID (UID) and Group ID (GID). An UID is a single identity for a user. While Group ID (GID) can consist more than one UID.
How to use it
By default, id command is installed on most of Linux system. To use it, just type id on your console. Typing id without no options will result as below. The result will use the active user.
Here’s how to read the output :
pungki with GID = 1000
adm with GID = 4
cdrom with GID = 24
sudo with GID = 27
dip with GID = 30
plugdev with GID = 46
lpadmin with GID = 108
sambashare with GID = 124
Using id with options
There are some options that can applied to id command. Here’s some options that may useful on day-to-day basis.
Print user name, UID an all the group to which the user belongs
To do this, we can use -a option
$ id -a
Output all different group IDs (effective, real and supplementary)
We can use -G option to do fulfill this.
$ id -G
The result will only show the GID numbers. You can compare it with /etc/group file. Here’s a sample of /etc/group content :
Output only the effective group ID
Use -g option to output only the effective group ID
$ id -g
Print the specific user information
We can output a specific user information related UID and GID. Just put the user name after id command.
$ id leni
Above command will print UID and GID of user named leni.
This id command is useful for us when we want to know about UID and GID of a user. Some applications may need UID / GID to be run. id make us easier to find UID and GID of a user without seeing and searching it inside /etc/group file. As usual you can go to id manual page by typing man id from your console to explore more detail.