lid Command in Linux
The lid command in Linux is a versatile tool used for displaying user and group information. It's a part of the libuser package and is available on many Linux distributions. This command is particularly useful for system administrators who need to manage user permissions and group memberships.
The lid command in Linux is a versatile tool used to display user groups or groups of users. It is a part of the libuser package and provides a quick way for system administrators to query group memberships.
Table of Contents
Here's a comprehensive guide to using the lid command with various options and their explanations.
Understanding lid Command
The ld command in Linux is a linker, which is a program that combines object files and libraries into a single executable program. It resolves external references and relocates code and data.
On some systems, the lid might not be installed by default. You can install it using the package manager of your distribution.
To use lid, you must have superuser privileges, otherwise, you will encounter an error message. If lid is not installed on your system, you can install it using the package manager, for example, on Debian-based systems −
sudo apt-get install libuser
When executed, lid displays the groups containing the specified user name, or if a group name is provided, it lists the users contained in that group. If no name is specified, the lid will show information about the groups containing the invoking user.
lid --version
How to Use lid Command in Linux?
The lid command can also be used in scripts and combined with other commands for more complex tasks. For example, you can pipe the output of lid to grep to search for a specific user within a group.
The basic syntax of the lid command is as follows −
lid [options] [name]
| Options | Descriptions |
|---|---|
| -T script: | Specifies a linker script to control the layout of the output file. |
| -e entry_point: | Specifies the entry point of the program. |
| -l library: | Links the specified library. |
| -o output_file: | Specifies the output file name. |
| -m architecture: | Specifies the target architecture. |
| -static: | Creates a statically linked executable. |
| -shared: | Creates a shared object library. |
| -r: | Creates a relocatable object file. |
Examples of lid Command in Linux
Here are some practical examples of how to use the lid command −
Listing a User's Groups
To list all the groups a user belongs to, you can use the following command −
sudo lid ubuntu
Replace the username with the actual user name to get their group memberships.
Listing Users in a Group
If you want to see all the users that belong to a specific group, you can do so with −
sudo lid -g ubuntu
Here, ubuntu is the name of the group whose members you wish to view.
Hiding User/Group IDs
By default, the lid shows the user IDs (UIDs) or group IDs (GIDs). To hide these IDs, use the -n option −
sudo lid -n username sudo lid -n -g groupname
This will display only the names without the corresponding IDs.
List members of a named group
This -g or --group option allows you to list members of a named group instead of the group memberships for the named user. For example −
lid -g webmaster
This will display all users belonging to the 'webmaster' group.
Hide the User IDs (UID)
Use this -n option if you want to hide the User IDs (UID) or Group IDs (GID) that are displayed by default. For instance −
lid -n -g webmaster
This will list the members of the 'webmaster' group without showing their UIDs.
Linking two object files into an executable
ld -o myprogram object1.o object2.o
Linking an object file with a library
ld -o myprogram object1.o -lmylibrary
Creating a statically linked executable
The -lc option links the standard C library.
ld -o myprogram -static object1.o object2.o -lc
Creating a shared object library
ld -shared -o mylibrary.so object1.o object2.o
Linking a program with a shared object library
The -L option specifies the directory where the library can be found.
ld -o myprogram object1.o -L/path/to/library -mylibrary
Specifying the entry point of the program
ld -o myprogram -e main object1.o object2.o
Using a linker script
The linker script can be used to customize the layout of the output file.
ld -T mylinker.script -o myprogram object1.o object2.o
Linking for a specific architecture
This example links to the 32-bit x86 architecture.
ld -m elf32-i386 -o myprogram object1.o object2.o
Advanced Options
The lid command also offers several options for more advanced usage −
- - -i or --interactive − Prompts for all information.
- - -g or --group − Lists members of a named group instead of the group memberships for the named user.
The ld command is usually used implicitly by the compiler when you compile a program. There are other linkers available for Linux, such as gold and lld. The ld command can be used to create various types of output files, including executables, shared object libraries, and relocatable object files.
Conclusion
The lid command is a simple yet powerful tool for managing user groups and memberships in Linux. It provides clear and concise information that can be crucial for system administration tasks. With the examples provided, you should be able to utilize the lid effectively in your day-to-day operations.
Remember, managing user permissions and groups is a critical aspect of system security, and tools like lid make it easier to handle these responsibilities.